Hi, pet parents! It’s February, which serves as American Heart Month as well as Heart Awareness Month. So what better time to discuss one of the most common manifestations of cardiac disease in dogs and cats: Congestive Heart Failure? ❤️
Veterinary cardiologist Dr. Michael Aherne joins The Meowing Vet to inform pet owners about congestive heart failure (CHF) in dogs and cats.
Congestive heart failure (CHF) in dogs and cats is a serious concern for many pet owners. It can be a scary and overwhelming diagnosis. There’s so much information to learn about the functioning of the heart, your pet’s clinical signs and prognosis, cardiac diagnostic tests, and new prescription medications. Lucky for you, The Meowing Vet‘s got an insider in the world of veterinary cardiology: Dr. Michael Aherne, MVB (Hons 1), GradDipVetStud, MS, MANZCVS (Small Animal Surgery), DACVIM (Cardiology). This boarded veterinary cardiologist is a stellar specialist who has provided our readers with everything (and we mean EEEVVVERRRYTHING!!!!!) you need to know about CHF and your dog or cat’s heart disease. Vet students, this one’s for you, too!
Okay, okay… I may be a bit biased because Dr. Aherne is my very own personal heart doctor… my husband! #VeterinaryPowerCouple! But I trust mi amor wholeheartedly (see what I did there?! ❤) to provide the most comprehensive information that any pet owner could ever want to know about the heart’s normal functions as well as congestive heart failure. So let’s give Dr. Michael Aherne a warm welcome in his debut article on The Meowing Vet!
– Maranda Elswick, DVM
Keep reading below to learn more…
- A novice at canine & feline cardiology? Click HERE to learn the basics of normal heart anatomy and function.
- Consider yourself a semi-expert? Click HERE to skip ahead to the pathophysiology of heart disease and congestive heart failure.
The Basics of Heart Disease & Congestive Heart Failure
The heart is one of the most wonderful feats of engineering found in nature. It is a dual-circuit pump with its own electrical power source. The right side of the heart responsible for pumping deoxygenated blood to the lungs where it becomes oxygenated (this is known as the pulmonary circulation) and the left side of the heart responsible for subsequently pumping oxygenated 
blood it receives from the lungs to the rest of the body (this is known as the systemic circulation). In the body tissues, oxygen is removed from the blood in order to produce energy and the remaining deoxygenated blood returns to the right side of the heart once more where the whole cycle starts again.
Looking a little closer at the anatomy of the heart, it is a 4-chambered organ primarily made of specialized cardiac muscle known as myocardium. As we have already seen, the heart can be divided into a left and right side; within each side there is an upper chamber called an atrium and a lower chamber called a ventricle. Both atria are relatively thin-walled chambers that receive blood from the veins, act as a conduit for the blood to pass into the ventricles, and actively push blood into the ventricles to ensure they are adequate filled. The left and right atria are separated from each other by a common wall called the atrial (or interatrial) septum. The ventricles have a much thicker muscular wall compared to the atria as the right and left ventricles function to pump blood to the lungs and the rest of the body respectively. Since the right ventricle only has to pump to the lungs, which are relatively near to the heart, it does not need to generate as high a pressure as the left ventricle and so its muscular wall is thinner than that of the left ventricle, which has to generate a higher pressure to pump to the rest of the body. The left and right ventricles are also separated by a common wall called the ventricular (or interventricular) septum which, for the most part, is thicker than the septum between the atria.
Each atrium is separated from its corresponding ventricle by a thin fibrous heart valve known as an atrioventricular or AV valve: the left AV valve is known as the mitral valve, so-called as its 
structure somewhat resembles a bishop’s hat or mitre; the right AV valve is known as the tricuspid valve, so-called as it tends to have 3 leaflets or cusps (however the number of leaflets in this valve can vary widely between individuals). Just as the atria are separated from their corresponding ventricle by AV valves, so too are the ventricles divided from their corresponding arteries by valves known as semi-lunar valves, so-called as their leaflets look like half-moons: the left semi-lunar valve is known as the aortic valve as is separates the left ventricle from the aorta; the right semi-lunar valve is called the pulmonic valve as it separates the right ventricle from the pulmonary artery. All of these valves move similar to trapdoors and have a very important function to keep blood flowing forward within their corresponding side of the circulation and prevent backflow in the wrong direction.
As mentioned, the heart has its own electrical power grid so to speak, a fine network of specialized nodes and electrical conduction pathways spread throughout the muscle of the heart. These serve to generate and transmit a coordinated electrical impulse that first stimulates the atria and then stimulates the ventricles thus causing the muscle cells in these chambers to contract resulting in pumping of the chambers. The electrical impulse begins in a region of specialized “pacemaker” cells within the right atrium known as the sinus node (aka sinoatrial or SA node). From here, the impulse the spreads across the atria causing them to contract allowing the ventricles to be completely filled. From here, the impulse takes a brief pause at another node of specialized cells call the atrioventricular (or AV) node located at the junction where the atrial septum, ventricular septum, mitral valve, and tricuspid valve meet. This brief pause ensures there is enough time for the atria to completely fill the ventricles before they too begin pumping. From the AV node, the electrical impulse then travels through a common bundle of specialized fibers that then divides into branches to the left and right ventricles and then further branch into many tiny fibers embedded between the muscle cells. Once the impulse reaches these tiny fibers it stimulates the muscle cells around each fiber to contract allowing all the muscle cells in the ventricles to contract together at once and pump blood to the lungs or the rest of the body.
The coordinated contraction and relaxation of the heart chambers results in the cardiac cycle; one cardiac cycle is equal to one heartbeat. The sounds of the normal heartbeat (the typical ‘lub-dub’) are generated by closure of the AV valves at the onset of contraction (i.e. the ‘lub’ sound) and closure of the semi-lunar valves at the onset of relaxation (i.e. the ‘dub’ sound). Normal animals typically have a nice, regular heart rhythm when which indicates normal coordination of electrical activity and subsequent pumping of the atria and ventricles. This normal rhythm is called a sinus rhythm. Dogs may frequently have a gradual rhythmic speeding-up and slowing-down of their heart rate which is called a sinus arrhythmia. Sinus arrhythmia is a normal finding in healthy dogs when relaxed however it is rather uncommon to find this in healthy individuals of other species. The normal heart rate can vary widely between species and it most cases faster heart rate is related to smaller size. For example, normal dogs can have resting heart rates between 60-170 beats per minute depending on the individual. Cats, on the other hand, tend to have higher heart rates than dogs with normal rates of 160 – 200 beats during a typical visit to the vet however, it is likely to be a little slower when they are relaxed at home. Horses tend to have rather slow heart rates at rest with rates of 16-40 beats per minute considered normal however during strenuous exercise (e.g. during a race) their heart rate can reach up to 180 beats per minute. In contrast, the tiny hummingbird has a heart rate of approximately 600 beats per minute.
Now that you have an understanding of how the normal heart works, we can now look at the common causes, clinical signs and outcomes of heart disease in companion animals. In general terms, heart disease can be broadly broken down into two categories: congenital heart disease (meaning the disease is present at birth) and acquired heart disease (meaning the disease develops over time). Each category contains many different diseases, each of which may vary in severity, and in severe cases may lead to heart failure. As with humans, acquired heart diseases are far more common than congenital heart diseases in companion animals. For the most part, the common causes of acquired heart disease in cats and dogs are not the same common causes in humans. One notable difference is that dogs and cats almost never get coronary artery disease unlike us humans, in which it is one of the leading causes of acquired heart disease. The table below shows some of the more common cardiac conditions seen in dogs and cats however it is important to note that this is far from exhaustive and many other conditions have been identified in these species. In fact, some of the conditions listed below have several different underlying causes.
| Dogs | Cats | ||
| Acquired | Congenital | Acquired | Congenital |
| Degenerative valve disease (aka myxomatous valve disease/mitral valve disease/mitral valve degeneration) | Patent ductus arteriosus (PDA) | Hypertrophic cardiomyopathy (HCM) | Ventricular septal defect (VSD) |
| Dilated cardiomyopathy (DCM) | Sub-aortic stenosis (SAS) | Dilated cardiomyopathy (DCM) | Tricuspid valve dysplasia (TVD) |
| Pulmonary Hypertension (PH) | Pulmonic stenosis (PS) | Restrictive Cardiomyopathy (RCM) | Mitral valve dysplasia (MVD) |
| Arrhythmogenic right ventricular cardiomyopathy (ARVC) | Ventricular septal defect (VSD) | Unclassified cardiomyopathy (UCM) | Atrioventricular septal defect (AVSD) / AV canal defect |
| Cardiac neoplasia | Tricuspid valve dysplasia (TVD) | Cardiac neoplasia | |
| Constrictive pericarditis | Mitral valve dysplasia (MVD) | Arrhythmogenic right ventricular cardiomyopathy (ARVC) | |
| Valvular endocarditis | Atrial septal defect (ASD) | ||
Even though there are many various types of heart disease, the heart has a relatively small number of mechanisms with which to respond to the presence of heart disease, and so, many different diseases can have identical or very similar clinical signs.
Congestive Heart Failure (CHF)
Left-sided Congestive Heart Failure
Diseases that primarily affect the left side of the heart (e.g. degenerative valve disease, hypertrophic cardiomyopathy, dilated cardiomyopathy, patent ductus arteriosus) may, depending on severity, result in poor forward flow of blood into the systemic circulation and subsequently may lead to a build-up of blood volume and/or pressure within the left atrium, which may expand and enlarge over time to compensate. However, once the left atrium has exceeded its capacity to expand and compensate, the pressure within the pulmonary veins and pulmonary capillaries (small blood vessels connecting arteries to veins) will increase. Once, the pressure in these blood vessels is high enough it causes fluid to leak out of the vessels and into the lung tissue – this fluid is called pulmonary edema and leads to difficulty with breathing (this is called dyspnea). Once patients have evidence of the development of pulmonary edema as a result of heart disease it is termed left-sided congestive heart failure (CHF). This is one of the most serious consequences of heart disease and requires immediate veterinary attention as the fluid within the lungs seriously impairs adequate uptake of oxygen into the bloodstream.
Right-sided Congestive Heart Failure
In a similar fashion to the changes to the left atrium with certain left-sided heart diseases, diseases that primarily affect the right side of the heart (e.g. primary pulmonary hypertension, heartworm disease, tricuspid valve dysplasia, pulmonic stenosis) may reduce forward flow of blood into the pulmonary circulation and, again depending on severity, may lead to a build-up of volume and/or pressure within the right atrium which will also try to enlarge to compensate. Once its capacity for expansion is exceeded then pressures in the systemic veins and systemic capillaries will also increase and result in leakage of fluid (edema) into the tissues of the body and body cavities: build-up of fluid within the abdomen is called ascites and results in a pot-bellied appearance; build-up of fluid in the lining of the chest cavity surrounding the lungs is called pleural effusion and results in compression of the lungs leading to difficulty with breathing; if severe enough fluid can build-up in the lining surrounding the heart, which is called pericardial effusion and impairs adequate filling of the heart, and so, exacerbates; a build-up of fluid within the limbs, or less commonly, the head leads to a swollen, puffy appearance and is called peripheral edema. When patients have evidence of these fluid accumulations as a result of right-sided heart disease, the term right-sided congestive heart failure (CHF) is used. This too requires prompt veterinary attention particularly due to the effects of pleural and pericardial effusions on the lungs and heart respectively.
In some patients, both the left and right sides of the heart may be affected. When signs of left-sided CHF and right-sided CHF are present together it is termed biventricular congestive heart failure.
Arrhythmias
Certain diseases may cause abnormal or irregular heart rhythms which are called arrhythmias. Arrhythmias can be broadly broken down into two types: tachyarrhythmias (very fast heart rhythms) and bradyarrhythmias (very slow heart rhythms) and both groups can be further broken down into the various arrhythmias. The table below summarizes some of the common types of arrhythmia seen in companion animals.
| Tachyarrhythmias | Bradyarrhythmias |
| Ventricular tachycardia (VT or V-tach) | Sick Sinus Syndrome |
Supraventricular tachycardias (SVTs):
|
Atrioventricular (AV) Block aka Heart Blocks:
|
Tachyarrhythmias impair the heart’s ability to fill normally due to the increased heart rate thus reducing the forward bloodflow from the ventricles. Conversely, bradyarrhythmias do not impair filling of the heart but rather reduce forward flow from the ventricles since the heart is pumping much slower than usual. There can be various mechanisms as to why arrhythmias develop with certain diseases. In some diseases, such as dilated cardiomyopathy in Doberman Pinschers or ARVC in boxers, cardiac muscle cells are replaced by fibrous (scar) tissue, fat, or fibro-fatty tissue, which creates an ideal environment to disrupt the normal electrical stimulation of the heart and cause arrhythmias particularly ventricular tachycardia. In other diseases, such as 2nd and 3rd degree heart block, the heart muscle is normal however, microscopic regions of scar tissue develop in the normal electrical conduction pathways resulting in either slowing or complete 
prevention of normal conduction and the ventricles have to rely on additional ‘pacemaker’ sites which beat at a much slower rate than the heart’s normal pacemaker, the SA node. With orthodromic AV reciprocating tachycardia (OAVRT), a condition that is identified most frequently in Labrador retrievers, an additional band of muscle (sometimes called an accessory or bypass tract) connects the atrium and ventricle allowing electrical conduction to bypass the normal pathways and, in the right circumstances can cause a repeating uninterrupted circuit (like a vicious circle) of electrical stimulation of the atria and ventricles. In some animals, especially giant-breed dogs like Irish Wolfhounds or horses, the size of the atria is simply so big that it creates the right circumstances for chaotic circuits of electrical activity to develop, resulting in lone atrial fibrillation. Atrial fibrillation can also occur when the atria become enlarged secondary to existing heart disease. Some non-cardiac diseases can even disrupt the normal balance of electrolytes within the body, which can result in certain arrhythmias. Tachyarrhythmias, if sustained over a period of time (sometimes just a few weeks), can result in the heart muscle become dilated and weak essentially due to exhaustion. Certain arrhythmias can be sudden and unexpected and may rapidly worsen and, unfortunately, can result in sudden death. For this reason, immediate veterinary attention is always recommended when an arrhythmia is suspected.
Staging of Heart Disease
Based on guidelines from the American College of Veterinary Internal Medicine (ACVIM), degenerative valve disease, the most common acquired heart disease in dogs, can be categorized into several stages shown in the table below. Some veterinarians will sometimes use these stages to describe heart diseases other than degenerative valve disease also, though the guidelines apply specifically to canine degenerative valve disease.
| ACVIM Stage (for canine degenerative valve disease) | Description |
| Stage A | Patients at high risk of developing degenerative valve disease but currently have no evidence of structural heart disease e.g. A young Cavalier King Charles Spaniel without evidence of a heart murmur. |
| Stage B1 | Patients with evidence of structural heart disease (e.g. have the characteristic type of murmur associated with degenerative valve disease), have never developed clinical signs associated with heart failure, and do not have any radiographic or echocardiographic evidence of cardiac remodeling (i.e. atrial or ventricular enlargement) as a result of the disease |
| Stage B2 | Patients with evidence of structural heart disease (e.g. have the characteristic type of murmur associated with degenerative valve disease), have never developed clinical signs associated with heart failure, but do have any radiographic or echocardiographic evidence of cardiac remodeling (i.e. atrial or ventricular enlargement) as a result of the disease |
| Stage C | Patients with previous or current clinical signs of heart failure due to structural cardiac disease that are responsive to standard therapy. |
| Stage D | Patients with end-stage disease with clinical signs of heart failure due to structural cardiac disease that are no longer responsive to standard therapy. |
Accurate staging of heart disease typically requires diagnostic tests such as chest radiographs (x-rays) and/or echocardiography (cardiac ultrasound) and provides more information for your vet to determine an accurate prognosis and determine what treatments, if any, are required for your pet’s stage of their heart disease.
Now that you have an understanding of how heart disease may progress, let’s look at common signs you may observe in your pets that may indicate heart disease, what your vet may find on examination and what diagnostics may be required.
Signs of Heart Disease
Firstly, it is very important to note that most heart diseases progress over time and so some pets may live with heart disease for years before obvious signs of heart disease even develop. For this reason, routine annual visits (or every 6 months for geriatric pets 8 years or older) to your vet are recommended as they may identify subtle changes long before overt signs of heart disease develop. Signs of heart disease may vary depending on the type of heart disease present and the underlying mechanisms (e.g. left-sided heart disease, right-sided heart disease or arrhythmias). Signs may also vary in severity depending on the severity of the underlying disease. For some diseases, such as degenerative valve disease, signs typically develop later in life and slowly progress, whereas with most congenital diseases signs may be present at birth. Puppies and kittens with congenital heart disease may be smaller than their littermates and may fail to thrive (i.e. don’t grow as much or as quick). They may also have other congenital abnormalities e.g. umbilical hernias. In pets that have arrhythmias due to their heart disease, such as boxers with ARVC, signs may be very sudden and very severe, in some cases even being fatal. Signs your pet may have heart disease include increased respiratory rate (called tachypnea) and/or effort (called dyspnea) when at rest, collapse or fainting episodes, weakness and lethargy, reduced exercise tolerance, abdominal swelling, cough, blue discoloration of the gums or tongue (called cyanosis), swelling of the limbs or head, distension or pulsation of the jugular veins in the neck. If your notice any of these signs in your pet, then you should see your veterinarian, who can examine your pet and perform further diagnostics as required to confirm or rule out the presence of heart disease.
Some signs are more specific than others in indicating the presence of heart disease. An elevated respiratory rate when at rest is the most sensitive indicator of left-sided congestive heart failure in dogs and cats. The resting respiratory rate is best observed when your pet is in a nice, deep sleep (but not dreaming as their respiratory rate may be higher while they are dreaming of chasing rabbits). To count the resting respiratory rate, simply watch your pet’s chest and count the number of breaths over 1 minute (or alternatively count the number of breaths over 15 seconds and then multiply by 4). Each rise and fall of the chest wall counts as 1 breath. In healthy dogs and cats, the normal resting respiratory rate is less than 35 breaths per minute. Rates that are consistently higher than this may indicate the presence of heart or lung disease and a visit to your veterinarian is recommended. Coughing is a relatively insensitive indicator of the presence of heart failure and can also be caused by a wide range of diseases affected the airways or lungs. Nevertheless, presence of a persistent cough, particular one that continues to worsen should warrant investigation by your vet.
In cats, signs of heart disease may be very subtle as cats are very good at hiding just how sick they may be and they tend not to exercise in the conventional sense at least when compared to dogs, with most cats perfectly happy to spend their days lounging in a comfortable bed. One less-subtle sign that may be seen in cats with heart disease is if your kitty falls while jumping or fails to make a jump on to a desk or table top, for example. This can occur due to weakness as a result of heart disease or can also happen if arrhythmias are present secondary to heart disease. An additional sign that may occur secondary to heart disease in both dogs and cats can be reduced appetite, particularly in animals with right-sided heart failure as the free fluid in the abdomen may cause the intestines to be somewhat inflamed however, this sign is very non-specific and can be seen with a huge variety of diseases affecting other organ systems. A much more acute sign associated with heart disease in cats is paralysis of the hindlimbs (occasionally other limbs may be affected) due to aortic thromboembolism (ATE). This can occur when a blood clot becomes lodged in the branching of the main arteries to the hindlimbs and can be very painful. The original clot typically has developed with an enlarged left atrium that has become dilated secondary to left-sided heart disease. This a rare consequence of heart disease however it requires immediate veterinary attention. Often, it is an indicator of very advanced heart disease in cats however, in some cats it may occur spontaneously without existing heart disease. Other consequences of clot formation may occur depending on the site the clot becomes lodged in. For example, some cats may exhibit neurologic signs or seizures if a clot becomes lodged in blood vessels within the brain, while patients with blood clots in the right side of the heart may develop acute respiratory distress if the clot lodges in blood vessels within the lungs. Unfortunately, in some animals that have developed arrhythmias, there may be no existing signs prior to a sudden, unexpected and fatal arrhythmia. As discussed, if you notice any of the above signs in your pet, then you should have them examined by your veterinarian, who can examine them and perform further investigations to determine what the underlying cause is and what treatments are required.
Heart Sounds and Cardiac Auscultation
One of the most useful tools for screening for heart disease is auscultation, which is when your veterinarian listens to your pet’s heart and lungs using a stethoscope as part of their physical examination. During auscultation, your vet will listen to determine if your pet has normal heart sounds and a normal rhythm. They will also listen for additional heart sounds, namely murmurs, gallop sounds and clicks. Heart murmurs are ‘swooshing’ sounds created by turbulent blood flow and are most commonly associated with diseases that affect the heart valves such as degenerative valve disease, AV valve dysplasia, pulmonic stenosis however, disease that do not primarily affect the valves such as dilated cardiomyopathy may secondarily cause a murmur by stretching apart the valve leaflets causing them to leak as the heart enlarges. Other conditions such as ventricular septal defects (also known as a ‘hole in the heart’) can also cause murmurs that can be identified on auscultation. Heart murmurs are characterized based on their location over the chest, the type of sound they make (e.g. if the murmur rises and falls sharply it described as a crescendo-decrescendo or ejection murmur), the timing of the murmur within the cycle of the heartbeat, and the intensity of the murmur. Murmur intensity is typically graded on a scale from 1-6, however some vets use a scale of 1-5. For the majority of heart diseases in our pets, the severity of cardiac disease is usually directly related to the loudness (or intensity) of the murmur however, this is not the case for all heart diseases such as ventricular septal defects, 
where murmur intensity may be lower or there may not even be a murmur. Dilated cardiomyopathy may also have no murmur or only a very soft murmur. Occasionally animals may have soft murmurs that are not due to structural cardiac disease. These are called functional murmurs (no structural heart disease but due to a physiologic cause e.g. anemia) or ‘innocent’ murmurs (no structural heart disease or no physiologic cause). Innocent murmurs are sometimes found in young puppies but, in the majority of cases, will disappear by about 6 months of age. In cats, the significance of the presence of a murmur can be more difficult to determine. Out of cats that have murmurs, approximately 30% have heart disease and, in the remaining cats, the murmur is functional or ‘innocent’ and unrelated to disease. Similarly, out of cats that have heart muscle diseases (cardiomyopathies), only approximately 30% have murmurs. This results in a significant number of cats that have murmurs without any disease and also of cats with heart disease but no murmur.
Mid-systolic clicks are clicking sounds that may be heard between the ‘lub’ and the ‘dub’ of the heartbeat. They are most commonly identified in dogs and are usually associated with prolapse of the mitral valve during the early stages of degenerative valve disease. As this disease progresses, the click usually becomes inaudible due to the development of a heart murmur caused by leakage of blood through the degenerative valve. Gallop sounds are additional sounds heard during the resting phase of the heartbeat (called diastole) and so occur between the ‘dub’ and the following ‘lub’ of the next heartbeat. Gallop sounds are often indicative of diseases that affect the heart muscle called cardiomyopathies however diseases that cause thickening of the heart muscle such as pulmonic stenosis and aortic stenosis can also result in gallop sounds. Gallop sounds are more commonly found in cats since the majority of heart diseases in cats are cardiomyopathies, unlike in dogs where the majority of heart disease is due to problems with the heart valves. Gallop sounds are sometimes referred to as gallop rhythms though this term does cause confusion as the heart rhythm is not affected by the presence of a gallop sound. When a gallop sound is present, the sound of the normal heart beat and the extra sound together is similar to the sound of a horse’s hooves at gallop, hence the name.
In addition to auscultation, your vet will also perform a complete physical examination. (Click here for The Meowing Vet’s article on physical examination to help identify other signs of cardiac disease, as discussed previously, or any other disease that may be causing those clinical signs.) Based on the results of their examination, they may suggest further diagnostic tests such as thoracic radiographs (chest x-rays), echocardiogram (cardiac ultrasound), bloodwork or urine testing in order to reach a definite diagnosis or stage your pet’s heart disease, if present.
Click here to read The Meowing Vet’s previous article on the importance of the veterinary physical examination.
Radiographs
Thoracic radiographs, also called chest x-rays, are a safe, quick, painless, non-invasive diagnostic test that can provide a lot of useful information about the heart and lungs, determine if cardiac disease is present and if so what stage it is at or determine if heart failure is present. A minimum of two views (one taken with the patient laying on its belly, and one taken with them laying on their side) is required in almost all cases, although three views is considered ideal (one view with the patient laying on their opposite side) in order to completely assess both lungs individually. The vast majority of cats and dogs are very tolerant of having radiographs performed however, for some nervous pets, mild sedation may be necessary to help your pet relax in order to acquire good-quality images. In some countries such as Ireland, the United Kingdom and Australia, radiation safety laws prohibit manual restraint of animals for radiographs unless in exceptional circumstances and so in these countries gentle restraint using light sandbags and/or foam wedges, and very often sedation, are necessary in order to keep your pet from moving while the radiograph is being taken.
In their advanced stages, most cardiac diseases will result in enlargement of various cardiac chambers depending on the disease and depending on the chambers affected, in combination with physical examination findings, will enable your veterinarian to reach a diagnosis. When left-sided congestive heart failure develops, pulmonary edema will become evident on thoracic radiographs primarily in one of two patterns: an interstitial pattern, or an alveolar pattern (sometimes a mix of both may be present). The pulmonary veins also become enlarged on x-rays when left sided congestive heart failure is presents. Thoracic radiographs are also a very important way to monitor the response to treatment of left-sided CHF and are recommended to be repeated typically 1-2 weeks after starting treatment, which will be discussed later, in order to ensure the pulmonary edema has resolved and that your pet is no longer in congestive failure.
Thoracic radiographs can also identify signs of right-sided heart failure, in particular pleural effusion with will be seen as rim of fluid opacity surrounding the lungs and, if severe enough, will make the lungs and heart very difficult to see. Your veterinarian may also recommend performing abdominal radiographs instead of or in addition to thoracic radiographs to look for free abdominal fluid (ascites) if they suspect right-sided congestive heart failure. When significant pericardial effusion is present, which is most commonly due to cardiac neoplasia (cancer), the silhouette of the heart on chest x-rays will become enlarged and rounded in appearance. Thoracic radiographs also allow your veterinarian to assess your pet’s lungs and airways to look for other potential causes for respiratory signs your pet may be experiencing. Diseases that cause pulmonary hypertension (high blood pressure within the arteries of the lungs), such as heartworm disease or chronic lung diseases, may cause enlargement of the pulmonary arteries which may be apparent on thoracic x-rays.
Your veterinarian may recommend repeating thoracic radiographs at various time-points to monitor for progression of your pet’s heart disease. The main limitations of thoracic radiographs in patients with heart disease are that they do not give any information on the function of the heart muscle and are unable to give definitive information on the internal structure of the heart i.e. the heart valves. Radiographs are also less sensitive than echocardiography in detecting subtle changes in heart chamber sizes. Your veterinarian may then recommend an echocardiogram (cardiac ultrasound) in order to gain further information to reach a definite diagnosis, determine prognosis or guide what, if any, treatments are indicated.
Echocardiography (Echo)
Like thoracic radiography, echocardiography is a safe, painless, non-invasive diagnostic test. In basics terms an ultrasound probe send out echo signals that then bounce off the structures within the body and send a signal back to the probe. A computer then translates the signals that return to the probe into an image displayed on a screen. This allows the heart, including its internal structures, to be viewed in real-time so that the contraction of the heart muscle and the function of the valves can be closely assessed. Cardiac chamber dimensions can be accurately measured with echocardiography. It also allows for measurement of bloodflow velocities which can be used to estimate the pressures within the various chambers of the heart – specific changes to these velocities and thus pressures are associated with specific cardiac diseases. Computerized mapping of the ultrasound signals allows turbulent bloodflow to be displayed on the image of the heart and aid in diagnosis of murmurs.
Echocardiography is a somewhat advanced imaging technique that requires advanced training and expensive equipment. In the majority of cases, your veterinarian will refer you to a veterinary cardiologist to have this procedure performed however, some veterinarians will have the training and equipment to provide this service at their own facility. If you are referred to a veterinary cardiologist, they may also recommend other advanced imaging techniques (such as cardiac CT or cardiac MRI scans) for diagnosis of complex heart diseases or cardiac catheterization procedures to treat certain congenital heart diseases such as pulmonic stenosis and patent ductus arteriosus. Your veterinary cardiologist be able to recommend additional or alternative medications if your pet has heart failure which is unable to be well controlled with standard treatments. Depending on your pet’s cardiac disease, your veterinary cardiologist may recommend follow-up echocardiograms at various time-points to monitor for progression of the disease or determine response to treatment. The main limitation with echocardiography is that is does not give any reliable information on the present of pulmonary edema and so cannot replace radiographs for the definitive diagnosis of left-sided heart failure.
Electrocardiography (ECG, a.k.a. EKG)
Electrocardiography (ECG) is a diagnostic test where the electrical activity of the heart displayed as a graph. It is most commonly used to determine the presence and severity of arrhythmias however, in certain circumstances the measurements may help detect significant enlargement of certain cardiac chambers but is not at all as sensitive as radiography or echocardiography for detecting these structural changes. For certain diseases, such as dilated cardiomyopathy or ARVC, continuous ECG monitoring devices are available. Such devices include:
- Holter monitor, which is essentially a small ECG unit worn like a backpack by your pet for a 24-hour period that is later analyzed using a computer;
- Event recorders, which are essentially the same as Holter monitors but can be worn for much longer periods (i.e. weeks at a time) and usually have a button or remote control to allow the unit to highlight and save the ECG in the time surrounding a particular event e.g. collapse episodes for later computer analysis;
- Implantable loop recorders, which are small devices similar in size to a USB drive that can be implanted under the skin (with the patient under sedation) and have a similar function to event recorders except they can be triggered to record and the data can be analyzed wirelessly meaning they can essentially remain in place under the skin indefinitely. These are particularly useful in cats as they tend to just freeze in the spot like a statue when wearing one of the other two devices.
Continuous ECG monitoring with one if the above devices provides more information on the presence and severity of arrhythmias since a regular ECG recording is typically only performed over several minutes and may happen to miss an arrhythmia if no irregular beats happen to occur during the relatively brief recording. All of the above continuous ECG devices are particularly useful to determine if a pet is having episodes of collapse due to arrhythmias (both from very fast rhythms or very slow rhythms) and also to help differentiate between seizures and syncope (or fainting: loss of consciousness due to reduced output by the heart) as in some circumstances these can look very similar. Since Holter monitors only record for a 24-hour period, they may not identify the cause of a collapsing episode unless these episodes are happening on a daily basis. Diseases such as ARVC in boxers or dilated cardiomyopathy (DCM) in Doberman Pinschers may be specifically diagnosed based on the number of abnormal heartbeats over a 24-hour Holter monitor recording. Your veterinarian or veterinary cardiologist may recommend repeat Holter monitor recordings to determine the effectiveness of any medications used to treat and arrhythmia or determine if any changes to treatment are necessary.
Click here for the U.S. FDA’s latest investigative report on atypical / nutritionally-mediated dilated cardiomyopathy (DCM) in various dog breeds, thought to be related to a grain-free diet.
One important point to note with Holter monitor recordings is that dogs with ventricular arrhythmias can have up to 85% variation in the number of abnormal heartbeats simply on a day-to-day basis without any treatment. For this reason, a simple reduction in the number of abnormal beats does not necessarily signify that a particular antiarrhythmic medication is working – unless there has been a greater than 85% reduction in abnormal beats then your veterinarian or veterinary cardiologist may recommend further adjustments to your pet’s therapy. The converse is also true for increases in the total number of abnormal beats in a 24-hour period – an increase of less than 85% may simply be normal day-to-day variation and adjustment of medications may or may not be recommended by your veterinarian or veterinary cardiologist.
Bloodwork for cardiac patients
Depending on your pet’s history and physical examination findings your veterinarian or veterinary cardiologist may recommend one or more of the following blood tests:
Serum biochemistry profile – this profile assesses the main biochemical markers of organ dysfunction within the body. Of particular interest to your veterinarian will be: markers of renal function, i.e. blood urea nitrogen (BUN) and serum creatinine (Crea) which indicate kidney function and are particularly important if your pet is receiving diuretic therapy for their heart disease or if your veterinarian is prescribing diuretic therapy; markers of liver damage/dysfunction, i.e. serum alanine transaminase (ALT) and alkaline phosphatase (ALKP), which indicate damage to the liver cells or the cells of the bile ducts respectively and may be elevated secondary to liver congestion as a result of right-sided heart disease; serum electrolytes, particularly sodium (Na+), potassium (K+) and chloride (Cl–) as derangements in levels of these electrolytes may frequently occur with diuretic therapy as well as result in certain arrhythmias.
- Renal biochemical profile – this is an abbreviated version of the serum biochemical profile which concentrates markers of kidney function i.e. BUN, Crea, Na+, K+ and Cl–. It may also include a packed cell volume (PCV), which is typically performed as part of a complete blood count (CBC). This profile is more cost effective than a full serum biochemistry profile in patients in which long-term routine monitoring of renal function is necessary, i.e. patients on long-term diuretic therapy.
- Complete blood count (CBC) – this profile assesses the red blood cells/corpuscles (RBCs) and the various types of white blood cells (CBCs). It is of particular use if inflammatory or infectious causes of heart disease are suspected
- Heartworm antigen test – in regions where heartworm disease, caused by the parasite Dirofilia immitis, is endemic, such as the southern USA, the Caribbean, Central and South America and Australia, routine heartworm antigen testing is recommended for you pets even if they are up-to-date with an appropriate heartworm preventative medication. This test reacts to a protein released from adult female heartworm and, if positive, will require adulticide therapy (as per the American Heartworm Society guidelines) to be given. This test is highly recommended if your pet displays signs of right-sided heart disease and lives or has a history of travel to/from heartworm endemic areas. Heartworm antigen tests are less reliable in cats as only very low numbers (i.e. 1-2) of adult female heartworms are required to cause severe disease in cats however most tests usually require approximately 6 or more adult females to be present for the test to react.
Total thyroid hormone (T4) level – Changes in thyroid hormone levels can have an effect on your pet’s heart. This is most commonly observed in older cats with high circulating hormone (hyperthyroidism), which can increase the circulating blood volume and increase the metabolic activity of the heart muscle as well as increasing blood pressure and heart rate (this is termed a hyperdynamic state). These changes can result in the heart muscle becoming thickened with mildly dilated chamber sizes and, if severe enough, can lead to heart failure. It may also worsen the effects of existing heart disease. This is recommended in all cats older than 7 years of age with evidence of thickening of their muscle to determine of the changes are due to hyperthyroidism or due to primary hypertrophic cardiomyopathy (HCM). If the changes are solely due to hyperthyroidism, then appropriate management either with radioactive treatment, medications or surgery will result in the heart returning to normal. In dogs, low circulating thyroid hormone levels (hypothyroidism) may result in the heart becoming slow, enlarged and somewhat weakened. If dogs with hypothyroidism receive appropriate supplementation then these cardiac changes should resolve.- N-terminal pro-brain natriuretic peptide (NT-proBNP) assay – NT-proBNP is a small protein released in response to enlargement and stretching of the atria in the heart. High levels indicate atrial enlargement however, normal levels need to be interpreted with caution as not all animals with atrial enlargement will have increased NT-proBNP levels. This test has limited usefulness as it does not provide any additional information if chest x-rays and/or echocardiography have already shown evidence of atrial enlargement. It may be helpful to rule in heart disease in settings where chest x-rays or echocardiography are not available.
- Genetic testing – there are several different commercial genetic tests available for certain cardiac diseases in dogs and cats. These are often used to help determine suitability for breeding. It is important to note that having a negative genetic test does not rule out the possibility that your pet may develop a particular condition as many conditions may be multi-factorial and more than one gene may play a role. If you are considering breeding your pet, consult with your veterinarian or veterinary cardiologist for more information for breed-specific screening of cardiac disease.
Wanna learn more about your pet’s bloodwork results? Click here for The Meowing Vet’s article on routine blood test analysis.
Blood Pressure Measurement
As part of a complete cardiac investigation, your veterinarian or veterinary cardiologist may recommend blood pressure measurement. High blood pressure can cause secondary changes to the heart including thickening of the left ventricle, and if severe enough can lead to heart failure. High blood pressure (systemic hypertension) is most commonly a result of kidney disease however sometimes the cause is unknown. Functional tumors of the adrenal glands (these secrete catecholamines i.e. epinephrine/adrenaline) and high circulating thyroid hormone levels (hyperthyroidism) may also result in high blood pressure. Blood pressure measurement is particularly important in cats as they have a relatively higher incidence of kidney disease compared to other species and may have systemic hypertension as a result. Since systemic hypertension is also a cause for thickening of the left ventricle, blood pressure measurement is required to distinguish hypertension from primary hypertrophic cardiomyopathy (HCM) as a cause for ventricular hypertrophy (thickening) in cats.
Treatment of Heart Disease
Whether or not treatment is required, and if so what treatment is necessary is heavily dependent on the type, severity and stage of your pet’s heart disease. There are very few cardiac diseases that are truly curable however, the majority of cardiac diseases can be effectively managed in order to provide your pet with a good quality of life for as long a time as possible. We will now discuss the various therapeutic options available for management of various cardiac disease.
Emergency Treatment
If your pet is displaying any signs of respiratory distress then you should seek immediate veterinary attention either with your family veterinarian, your nearest veterinary emergency hospital, or your veterinary cardiologist. Your pet can then be stabilized with supplemental oxygen therapy, which is usually administered via an oxygen mask or via an oxygen cage. Some pets will require sedation to reduce their anxiety which may be exacerbating their respiratory distress. Your pet will be examined by the veterinarian and diuretic medications may be administered prior to further diagnostics to help stabilize your pet if congestive heart failure is suspected. Depending on the findings of physical examination, brief thoracic (T-FAST) or abdominal (A-FAST) ultrasonographic exams may be performed to determine if pericardial, pleural or abdominal effusions are present. If significant volumes of pericardial, pleural or abdominal effusion are present then your pet may need to be further stabilized with pericardiocentesis, thoracocentesis or abdominocentesis respectively. All of these are procedures are similar and involve removal of fluid from the respective body cavity using a needle or over-the-needle catheter system and suction with a syringe. Removal of excess fluid, particularly from the pleural or pericardial cavities, can result in rather dramatic improvement in clinical signs in most cases. Sedation and local anesthesia is often required for patients undergoing thoracocentesis or pericardiocentesis. Thoracocentesis is somewhat commonly required in cats with congestive, even left-sided congestive failure, as they have a higher incidence of developing pleural effusion secondary to heart failure when compared with dogs. Once stabilized, further investigations as discussed previously can be performed.
Medications
- Diuretics: Diuretics, sometimes referred to as ‘water pills’, are the mainstay for the treatment of congestive heart failure in companion animals. All work at the level of the kidneys to increase the excretion of water (and typically electrolytes) from the body into the urine, which reduces the volume overload placed on the heart and controls the various manifestation of congestive heart. There are several different families of diuretic medications. The most commonly used diuretics used for treating veterinary cardiac disease are listed below:
Furosemide – this is by far the most commonly used diuretic medication in companion animals. It is often referred to by one of its most common brand names, which is Lasix®. It is part of a family of diuretics known as loop diuretics and will cause your pet to urinate more and subsequently drink more so be prepared for accidents in the house. Once your pet has been prescribed this medication, they require free access to water at all times to avoid injury to the kidneys. Since this medication causes the kidneys to work harder, routine monitoring of kidney values on bloodwork is recommended to help adjust to the lowest effective dose and ensure that unnecessary side effects on the kidneys are avoided as much as possible. Some animals may develop a tolerance to furosemide over time meaning that higher and higher doses are required to successfully control congestive heart failure.- Torsemide – this medication is from the same family as furosemide and carries the same risks and side effects on the kidneys. It is much more potent than furosemide and is particularly useful in patients that have appear to have developed a tolerance to furosemide over time and does not appear to have any tolerance issues itself. Close monitoring of kidney markers on bloodwork is recommended due to its potency and risk for kidney injury.
- Spironolactone – this medication is a very weak diuretic and is not strong enough to control congestive heart failure by itself. It is, however, often added as an additional therapy to loop diuretics to limit the amount of potassium lost as a result of those medications. For this reason, it is known as a potassium-sparing diuretic. It primarily works by blocking a hormone called aldosterone and so blunts the body’s mechanisms to retain water in the face of heart failure and diuretic use. Studies in rodents also suggest it may reduce the amount of secondary remodeling of the heart due to certain cardiac diseases. In some countries spironolactone is available as combination pills either combined with hydrochlorthiazide or combined with benazepril.
- Hydrochlorthiazide – this is a member of the thiazide diuretic family. These are very potent diuretics that carry an increased risk of kidney injury unless a patient’s renal function is closely monitored. They work at a different site within the kidney to promote water excretion and so reduce the volume on the heart. It is very rare to combine thiazide diuretics with loop diuretics as doing so dramatically increases the risk of unwanted side effects on the kidneys.
Pimobendan (ex. Vetmedin®) – this is a relatively novel medication that is licensed for veterinary use only, except for Japan, where it is also licensed for human use. This drug is known as an inodilator, which means it increases the force of contraction of the heart (positive inotrope) and dilates the arteries the ventricles pump into (dilatory effect), and thus reduces the workload on the heart. The overall effect is to increase the efficiency of the heart and control congestive heart failure. Pimobendan has been shown to prolong survival in dogs with congestive heart failure due to degenerative valve disease and dilated cardiomyopathy. It has also recently been shown to delay the onset of developing heart failure in dogs with these two conditions also, being one of the first veterinary medications proven to delay the onset of clinical manifestations of a disease. Though there are few studies on using this drug with other heart conditions, it may be prescribed for conditions other than degenerative heart disease and dilated cardiomyopathy. There is little information on its use in cats however, current evidence suggests that it is well tolerated in cats and may improve survival in cats with heart failure. Pimobendan tablets are usually quite large and so may need to be broken down. Pimobendan is not stable in water-based solutions and so liquid compounding of this medication is not recommended. Generally, pimobendan is well-tolerated with few side effects. Potential side effects typically include inappetance or gastrointestinal upset, and so pimobendan is usually recommended to be given on an empty stomach usually one hour before food.- Angiotensin Converting Enzyme Inhibitors (ACEIs) – these are a family of medications that blunt the renin-angiotensin-aldosterone-system (RAAS), which is a cascade of hormonal pathways that becomes stimulated by the presence of heart disease and by the administration of diuretics. This cascade ultimately results in retention of water by the kidneys and reduction of the effectiveness of diuretics. Since this cascade is blunted by ACEIs, they are typically given in conjunction with diuretics to increase their effectiveness. ACEIs also have a weak effect on reducing systemic blood pressure but typically this effect is too weak for them to be useful for treating systemic hypertension. Potential side effects include inappetance and kidney injury and so provides another reason for routine monitoring of kidney function in patients receiving treatment for congestive heart failure. Due to these potential side effects and the fact that ACEIs are generally just an adjunctive therapy, it is usually recommended that these medications only be started once the patient has been on diuretics and pimobendan for several days and only once their appetite has returned to normal. The most commonly used ACEIs are listed below:
- Enalapril – typically given twice daily. Potential side effects include inappetance, gastrointestinal upset and weakness.
- Benazepril – may be given once or twice daily. Potential side effects include inappetance, gastrointestinal upset and weakness. Benazepril is also used to treat proteinuric (or protein-losing nephropathy: this means losing protein in the urine) renal disease in cats and dogs.
Antiarrhythmic Drugs – there are many different types of anti-arrhythmic drugs used to treat arrhythmias in veterinary patients. They can be broadly broken down into 4 main classes based on their mechanism of action: sodium channel blockers; beta blockers; potassium channel blockers; and calcium channel blockers. Other miscellaneous antiarrhythmic drugs exist that do not lend themselves to this type of classification. The most commonly used oral antiarrhythmic medications are listed below.
- Sodium channel blockers
- Mexiletine – this sodium channel blocker is an oral analog of the injectable medication, lidocaine (also known as lignocaine outside of the US). Mexiletine is most commonly used to treat ventricular arrhythmias particularly in boxers with ARVC and Doberman Pinschers with dilated cardiomyopathy. Mexiletine has been shown to have an increased effect at lower doses when combined with sotalol (see below) in boxers with ARVC. It is required to be given three times a day and potential side effects typically include gastrointestinal signs such as inappetance, vomiting and diarrhea.
- Beta-adrenergic receptor blockers (Beta blockers) – this family of antiarrhythmic drugs work to slow the heart rate and contractility by blocking specific receptors called beta adrenergic receptors in the heart. They are typically used for treating certain supraventricular tachyarrhythmias. As a result of their effects on reducing the heart’s ability to contract they are not usually recommended in pets that have developed congestive heart failure. Unlike in humans, where beta-blockers have been shown to have a positive effect on survival in patients with heart failure, there is no evidence that these medications prolong survival in cats and dogs with heart disease or heart failure. Potential side effects include weakness and lethargy.
- Potassium channel blockers – these are usually very effective anti-arrhythmic agents particularly for the treatment of ventricular arrhythmias particularly in Doberman Pinschers with dilated cardiomyopathy and boxers with ARVC.
- Sotalol – this is primarily a potassium channel blocker however, it does also have some beta-blocker activity. It has been shown to have an increased effect at lower doses when combined with mexiletine (see above) in boxers with ARVC. It is typically given twice a day and potential side effects include weakness, lethargy and inappetance.
- Amiodarone – this is a very effective antiarrhythmic typically used to treat ventricular arrhythmias and atrial fibrillation. It is typically administered as a once daily loading dose over 7-10 days and then reduced down to a once weekly dose. Potential side effects are unpredictable and include gastrointestinal upset, liver damage and thyroid dysfunction (patients can have too much or too little circulating thyroid hormone). In humans, it has also been shown to cause blue discoloration of the skin with prolonged use and occasionally has been associated with an irreversible lung condition called pulmonary fibrosis however, these have not been documented in dogs or cats as a result of this medication.
- Calcium channel blockers – this family of drugs slows electrical conduction in the heart and is typically used to treat supraventricular tachyarrhythmias and atrial fibrillation. They also cause a mild reduction in the effectiveness of the heart to contract. Side effects may include generalized muscle weakness and inappetance.
- Diltiazem – this is the most commonly used calcium channel blocker in veterinary medicine. It is typically given three times a day however extended-release versions that can be given once daily are also available.
Digoxin – digoxin is one of the oldest cardiac medications used in veterinary medication. It slows the conduction of electrical impulses in the heart and is used to treat atrial fibrillation. It also increases the hearts ability to contract (positive inotrope) and so is useful in dogs with dilated cardiomyopathy particularly those that already have atrial fibrillation. However, side-effects may frequently be seen with digoxin and these can include inappetance, vomiting, diarrhea, neurologic signs such as seizures and other cardiac arrhythmias. Due to the risk of side effects, serum digoxin levels in the blood should be routinely monitored once this therapy has been started to ensure that your pet dose is within the safe range.
- Sodium channel blockers
- Sildenafil – this medication is related to pimobendan and is probably better known by one of its more common brand names, Viagra®. This medication is used to specifically dilate the arteries within the lungs and so is used for the treatment of pulmonary hypertension (high blood pressure in the lungs). It may be given once or twice daily and potential side-effects include weakness and collapse.
- Anti-clotting agents – there are several different types of anti-clotting agents available. These are mainly used on cats with significant atrial enlargement due to their increased risk of clot formation and subsequent lodgment in a major vessel (thromboembolism). This risk is typically not seen in dogs with heart disease. Some of the commonly-used anti-clotting agents are listed below:
- Clopidogrel – this medication inhibits the action of platelets in the blood to reduce clotting. Possibly better known by its brand name, Plavix®, it has been shown to be associated with longer survival in cats that have experienced aortic thromboelbolism when compared to aspirin. It is given once daily and potential side effects may include bruising or excessive bleeding though this is rare. Clopidogrel is very bitter to cats and many will resent having to take this medication. For this reason, it is best given within products such as Greenies® Pill-Pockets® or within a gelatin capsule (these are the same coating as any capsule medication), which can be purchased over-the-counter at your local pharmacy. Gelatin capsules also have the added benefit of being able to contain most of your cat’s other cardiac medications since feline doses are usually quite small and so you only have to give you cat a single administration of all medications together rather than run the risk of making your cat angrier with each successive medication you try to give them.
- Aspirin – this medication also reduces the action of platelets through a different mechanism to clopidogrel. It has the benefit of only requiring to be administered once every 3 days. It does however, have an increased risk of kidney injury when given at high doses and so you should always follow your veterinarian’s prescription instruction when giving this medication. Potential side-effects include gastrointestinal upset, bruising, bleeding and kidney dysfunction.
- Anti-hypertensives
- Amlodipine – this is a calcium channel blocking drug used to treat systemic hypertension (high blood pressure) in cats, typically, but may also be prescribed for dogs. It is usually well tolerated however, potential side-effects include weakness, lethargy and inappetance.
Interventional procedures
Interventional procedures are minimally-invasive procedures that usually involve cardiac catheterization (placing long tubes into the heart), are usually guided by fluoroscopy (essentially watching x-ray images in real-time), and are most commonly used for the treatment of congenital heart diseases. In these procedures, entry to a peripheral vein or artery is gained either directly via a needle through the skin or through an incision through the skin and the blood vessel. A long tube, called a catheter is then advanced to the region of interest within the heart and vary types of procedures may be performed. There are many different types of catheters and equipment depending on the procedure to be performed. Interventional cardiac procedures are performed by veterinary cardiologists, who have extensive, advanced training in these types of procedures. Some of the commonly performed interventional procedures are:
- Balloon valvuloplasty – this procedure is typically used for treatment of severe pulmonic stenosis (and sometimes subaortic stenosis though its effectiveness may be less for this condition when compared to pulmonic stenosis). In this procedure, a catheter containing a balloon at its tip is advanced across the narrowed (stenotic) valve and then inflated to help separate the valve leaflets and stretch the narrowed region thus removing the obstruction to blood flow.
- Vascular shunt occlusion – this procedure is most commonly used for closure (occlusion) of patent ductus arteriosus however, in certain circumstances and with certain devices this procedure can be performed to close atrial defects and ventricular septal defects. In this procedure, a catheter is advanced to the level of shunt (e.g. ductus arteriosus) and a vascular plug device is placed across the hole. This device traps platelets from the bloodstream and eventually forms a clot that will seal the hole and will eventually be covered with fibrous tissue. Patients that undergo successful patent ductus arteriosus occlusion typically live a normal lifespan and are essentially cured of their condition once closure is performed before the onset of heart failure.
Permanent pacemaker implantation – just like humans, dogs and cats can have permanent pacemakers implanted for the treatment of 2nd and 3rd degree heart blocks and sick sinus syndrome. In most dogs, this procedure can be performed through a minimally invasive procedure where a pacemaker lead is passed via the jugular vein, into the right atrium and into the right ventricle where it is anchored into the muscle of the right ventricle. The pacemaker lead is then connected to a pacemaker generator that is surgically placed under the skin of the neck and then provides electrical stimulation to the heart to maintain a normal heart rate.- Heartworm extraction – in heartworm-endemic areas, patients with severe adult heartworm burdens may require to undergo this emergency procedure. In this procedure special grasping devices, snare catheters or basket catheters are used to pull adult heartworms out of the right side of the heart.
Brush up on your knowledge of canine and feline heartworm disease. Click here for The Meowing Vet’s article.
Surgery
Unlike in humans, cardiac surgery is not readily available for the majority of veterinary patients. This is primarily a result of the increased cost, equipment and expertise required for these types of procedures. One area for potential growth in this field is surgical repair of the mitral valve in dogs with advanced degenerative valve disease. In humans, this is essentially a surgical disease with surgery being a treatment of choice however due to the limitations in the veterinary field as mentioned above, medical management of congestive heart failure is still the mainstay of treating the condition in dogs. However, there a small very small number of facilities worldwide in which this procedure is successfully performed in dogs. Consult with your veterinary cardiologist if you wish to find out more information about mitral valve repair surgery for your dog.
Diet
Similar to human patients, ideal diets for animals with cardiac disease should be low in sodium as this promotes water retention. There are a small number of prescription cardiac diets available as well as recipes available for homemade low-sodium diets for your dog or cat. Unfortunately, restricting the sodium content significant reduces palatability of these diets and so pets will often not want to eat them. One of the biggest risks with inappetance in animals with heart disease is the loss of muscle mass over time, which include cardiac muscle mass and thus increases the workload on an already failing heart. For this reason, I suggest to stick with a healthy, balanced diet that your pet enjoys and eats readily and to avoid treats high in sodium, which unfortunately is most treats. Pieces of boiled or grilled chicken breast with no added salt is often a good option for treats in dogs or cats with heart disease.
Another important point to note with diet for dogs and cats with heart disease is the role of meat protein in the diet. Cats, specifically, are obligate carnivores. This means there are certain essential amino acids that cats require but are completely unable to produce within the body and can only obtain these amino acids from eating meat (sorry to all vegans reading this!). Taurine is one such essential amino acid and when absent from the diet results in changes to the heart that resemble dilated cardiomyopathy. Fortunately, this condition is completely reversible if the cat is fed an appropriate diet (i.e. one that contains adequate meat protein) and all commercial cat foods are supplemented with this amino acid. Certain breeds of dogs, such as American Cocker Spaniels and Newfoundlands, may develop taurine-responsive cardiomyopathy. It is not completely clear if this is related to diet since dogs are able to produce their own natural taurine. However, cardiac changes in dogs with this condition will usually completely resolve with the addition of taurine and/or carnitine supplements to their diet. For this reason, your veterinarian or veterinary cardiologist may recommend adding these supplements to your dog’s diet if they show changes consistent with dilated cardiomyopathy.
Omega-3 and omega-6 fatty acids may also have a positive role in cardiac health and so may be recommended by your veterinarian or veterinary cardiologist.
Click here for more nutrition information for pets with heart disease, courtesy of Tufts Cummings School of Veterinary Medicine.
Need more info about the beneficial health effects of omega fatty acids? Click here. Learn more about the nutritional requirements of dogs and cats with The Meowing Vet’s article on pet nutrition.
Prognosis
Overall, prognosis with cardiac disease is very variable and is heavily dependent on the type of cardiac disease, how severe it is, and what stage of the disease your pet is in. For these reasons, appropriate diagnosis and staging of your pet’s cardiac disease are paramount. Consult with your veterinarian or veterinary cardiologist if your pet displays any signs associated with cardiac disease as discussed above or if signs reappear after successful medical or interventional treatment.
As discussed previously, few cardiac conditions are completely curable. Cardiac conditions that are essentially curable and carry an excellent prognosis with appropriate treatment include patent ductus arteriosus and taurine-responsive/dietary responsive cardiomyopathies. Dogs with mild and moderate forms of pulmonic stenosis and subaortic stenosis tend to have a normal lifespan, on average. Those with severe forms of these diseases have a reduced life expectancy and an increased risk of sudden death however, life expectancy and quality of life is increased if successful balloon valvuloplasty can be performed, particularly for dogs with pulmonic stenosis.
Degenerative valve disease is typically a very slowly progressive disease and may take years for clinical of disease to develop. The majority of dogs with this condition will not develop congestive heart failure. Of those dogs that do go on to develop congestive heart failure due to degenerative valve disease, typical survival times of 1-2 years can be expected however, these times may be shorter or longer depending on various factors. Unfortunately, survival times in dogs with congestive heart failure due to dilated cardiomyopathy are somewhat reduced when compared to dogs with congestive heart failure due to degenerative valve disease. Survival times of 6-9 months are usually expected in dogs with heart failure due to dilated cardiomyopathy and may be shorter due to the increased risk of sudden death from arrhythmias.
In cats, left atrial size is the most important indicator of prognosis, regardless of the exact underlying heart disease. Typical survival times of approximately 6 months are expected in cats with heart failure due to any cause but as with dogs these times may vary widely depending on various factors.
It is important to realize that these anticipated survival times are derived from looking at the average times over large numbers of animals and so any one particular individual may have a survival time that is better or worse than average. Moreover, it is very important to remember than the vast majority of patients with cardiac disease will not develop heart failure.
One of the most important factors in long-term survival in patient with heart failure is the balance between maintaining adequate heart function and maintaining adequate kidney function. Unfortunately, some animals experience heart failure and renal failure together which is a very difficult situation to treat as to treat heart failure you need to reduce the body’s fluid levels whereas to treat renal failure you need to administer excess fluid to the body to help the kidneys perform their function to remove toxins from the body. This is not an uncommon occurrence in cats as they have a high incidence of chronic kidney disease. Ultimately, one of these conditions requires preferential treatment over the other and very often adequate kidney function is sacrificed for adequate heart function since pets will die much quicker from congestive heart failure than they will from chronic kidney failure and, in many cases, will cope rather well with their kidney disease. As previously discussed, routine monitoring of your pet’s kidney values with your veterinarian is of huge importance if they are receiving diuretic therapy for heart failure in order to adjust your pet’s diuretic dose to the lowest effective dose to avoid unnecessary kidney injury.
Congestive heart failure, even with successful management, is usually a terminal condition in most cases. If you own a pet that has been diagnosed with congestive heart failure, you will likely one day be in that unenviable position of having to determine when your pet’s quality of life is reduced and allow your faithful companion to have a dignified and peaceful passing via euthanasia. However, by working closely with your veterinarian and your veterinary cardiologist, you can give your four-legged friend the best quality of life for as long as possible.
– Michael Aherne, MVB (Hons 1), GradDipVetStud, MS, MANZCVS (Small Animal Surgery), DACVIM (Cardiology)
Meet our author: Michael Aherne, MVB (Hons 1), GradDipVetStud, MS, MANZCVS (Small Animal Surgery), DACVIM (Cardiology) – Dr. Michael Aherne is a boarded veterinary cardiologist with the American College of Veterinary Internal Medicine (ACVIM). Earning his Bachelor of Veterinary Medicine (MVB) at University College Dublin (UCD) in Dublin, Ireland, Dr. Aherne has garnered additional advanced veterinary training in Australia as well as in the United States. He currently holds a university position as clinical assistant professor in cardiology at the University of Florida (USA).
Click HERE to read along as Dr. Michael Aherne shares with us his expert knowledge on canine degenerative mitral valve disease.
You can also learn more about heart disease in pets with these articles, courtesy of Tufts Cummings School of Veterinary Medicine.
