Cardiac Diseases & Conditions

Cardiac Anatomy/Physiology

Cardiac disease and conditions can have many different causes. Some diseases are caused by structural abnormalities in chambers or valves that are congenital (present at birth) or acquired. Other conditions are diseases of the heart muscle itself. Arrhythmias, or irregularities in the force or rhythm of the heartbeat, can cause or be caused by other cardiac conditions. Finally, other conditions such as thyroid disease or cancer can cause cardiac problems.

Blood empties into the right atrium from the body via the vena cava. Passing through the tricuspid valve, it enters the right ventricle then out to the lungs through the pulmonic valve via the pulmonary artery. After being oxygenated in the tissues of the lungs, the blood returns to the heart via the pulmonary veins into the left atrium. It then passes through the mitral valve to the left ventricle where it is pumped out the aorta across the aortic valve to the rest of the body.

Heart Murmurs

Dogs and cats often do not show obvious clinical signs until they are in severe congestive heart failure. The survival rate for treatment of mild congestive heart failure is near 100% when managed appropriately. For animals with severe congestive heart failure, there may be up to 25% mortality even with aggressive treatment. Many forms of heart disease which cause a murmur are much more treatable in the early stages, before any other symptoms appear. Early detection allows for medical treatment and client education to occur before the patient is crisis, and greatly improves the outcome for the patient. In most cases, abnormalities detected on cardiac auscultation precede the development of clinical signs.

Puppies and Kittens:
Many puppies and kittens will have a soft murmur which resolves over time. These innocent murmurs are typically low grade murmurs (Gr I-II/VI) and are heard over the left base. If the murmur persists beyond 6 months or is louder than a 2/6, referral is the best option for the pet. Puppies or kittens with clinical signs of cardiac disease should be referred at the first detection of any murmur. Puppies or kittens with loud or continuous murmurs should be referred immediately. Some congenital defects such as pulmonic stenosis and PDA can cause death within the first year of life if not identified and treated promptly while these same pets can live normal lives with interventional therapy.

Adult Small-Breed Dogs:
The most common cause of heart murmurs in small dogs is degenerative valve disease. Murmur intensity does not always correlate with the severity of the valvular regurgitation. Referral is recommended at the first detection of a murmur to allow for a definitive diagnosis and obtain baseline measurement of cardiac size and function. In some cases, the heart disease is more advanced than suspected based on auscultation alone.

Adult Large-Breed Dogs:
The most common cause of a murmur in large breed dogs is dilated cardiomyopathy. Affected dogs typically have a soft systolic murmur heard over the mitral valve. A gallop sound or arrhythmia may also be detected. Dogs with dilated cardiomyopathy are at risk for congestive heart failure, serious arrhythmias, and sudden death. Referral is recommended at the first detection of an abnormality on cardiac auscultation.

Adult Cats:
The most common cause of heart murmurs in cats is hypertrophic cardiomyopathy. Other forms of cardiomyopathy that can occur in cats are dilated, ischemic, restrictive, thyrotoxic, and unclassified. In cats, murmur intensity and location do not correlate with disease severity and risk for clinical signs. Cats with cardiac disease are at risk for congestive heart failure, thromboembolic (blood clot) events and sudden death. All cats with murmurs, arrhythmias, or gallops detected on exam should be referred to a board certified cardiologist for an echocardiographic evaluation.

Cardiomyopathy in Dogs

Dilated Cardiomyopathy
Dilated cardiomyopathy (DCM) is a primary disease of the heart muscle which results in a progressive loss of muscle strength, dilation of the heart chambers, and ultimately a decreased ability to pump blood to the body. The disease primarily afflicts purebred large and giant breed dogs, with the Doberman Pinscher and Great Dane having a higher incidence within the breed. Occurrence of DCM increases with the age of the patient, however it can affect both young and old dogs. DCM is most likely caused by inheritable genetic mutations, however the exact genes and heritability patterns have not been fully defined and are still under active investigation.

DCM can affect both the left and right sides of the heart with either side being more severely affected. Typically both the ventricle (main pumping chamber) and the atria (upper chamber) enlarge resulting in the ventricle losing its ability to contract and pump blood out to the body and/or lungs. The consequences of the heart's failing ability to pump blood can be compared to a simple mechanical pump. If the sump pump in your basement fails, water backs up into the basement; if the left heart fails, fluid backs up into the lungs, and if the right heart fails, fluid backs up in the abdomen or the space surrounding the lungs.

Treatment of DCM is aimed at improving the heart's ability to pump and controlling the signs of congestive heart failure. Unfortunately, cardiac arrhythmias (abnormal electrical activity/irregular heart beat) can be a serious complication in this disease, and certain breeds are more predisposed to this concurrent problem. When an irregular heart rhythm is present, anti-arrhythmic therapy may be an additional part of the treatment plan in order to improve cardiac function and prevent dangerous arrhythmias and sudden death.

The gold standard for assessing the severity and treatment options for affected pets is an evaluation and echocardiogram performed by a board certified veterinary cardiologist such as those at CVCA. We use a tiered approach to therapy, which is tailored to each individual patient based on all of the information obtained from our diagnostic tools and our collective clinical experience. Long term prognosis for DCM varies considerably. Dogs with signs of congestive heart failure at the time of diagnosis typically survive six months to two years, although some breeds are subject to a more severe form of the disease and may survive only weeks. Our goal is an open collaboration with you and your family veterinarian in order to prevent and/or eliminate signs of congestive heart failure and provide optimal quality and quantity of life at home.

Cardiomyopathy in cats

Hypertrophic Cardiomyopathy
Hypertrophic cardiomyopathy (HCM) is a primary disease of heart muscle that causes progressive muscle thickening of the left ventricle, the main pumping chamber of the heart. This thickening, called hypertrophy, reduces the ability of the ventricle to fill and results in a backup of blood into the left atrium, the chamber above the left ventricle (See Figure). In some cats the thickened muscle can also obstruct the flow of blood out of the heart. Over time the atrium enlarges to compensate for the back up of blood, but ultimately the pressure in the left atrium can increase enough to cause a back up of fluid into or around the lungs. This is known as left sided congestive heart failure and produces symptoms of increased respiratory rate and effort, lethargy, and/or reclusive behavior.

HCM is the most common form of heart disease in cats and is known to have a genetic basis in some purebred cats. This disease has a wide variation in its degree of severity at diagnosis, time of onset, and responsiveness to treatment. Younger cats have a tendency to develop a more aggressive form of the disease than our adult or geriatric feline patients. Furthermore, older cats can develop thickened heart muscle as a natural response to underlying systemic disease. Diseases such as hyperthyroidism, kidney disease, and/or systemic hypertension increase the workload of the heart and cause secondary heart muscle thickening. Therefore, we always try to initially rule out these diseases and then work closely with your primary care veterinarian to carefully monitor for their development over time in our feline cardiac patient. The development of these diseases can cause deterioration in a previously stable cardiac patient.

The gold standard for assessing the severity and treatment options for affected cats is an evaluation and echocardiogram performed by a board certified veterinary cardiologist such as those of CVCA. An echocardiogram allows us to precisely measure the size and thickness of the heart muscle/chambers and map out the blood flow through the heart. Given the variable and unpredictable nature of HCM, we tailor our therapy to each individual patient. We also recommend regular follow-up echocardiograms for monitoring of progression of the disease so we can intervene in a timely manner if necessary. Initial treatment of HCM is directed at slowing the heart rate, improving the ventricles ability to relax, and relieving the obstruction of blood from the ventricle if present. Additional medications may be added as indicated by the severity or progression of disease. With appropriate medication and early intervention, we can often achieve stabilization of the disease, and sometimes reversal of the cardiac changes. Our goal is an open collaboration with you and your primary care veterinarian in order to prevent the development of congestive heart failure and improve the quantity and quality of your feline companion's life.

Feline Arterial Thromboembolism

Feline arterial thromboembolism (FATE) is one of the most devastating consequences of cardiac disease in the feline patient. In cats with cardiomyopathy (heart muscle disease) an enlarged left atrium is a common secondary change. This enlarged left atrium is prone to decreased movement of blood. Spontaneous clot formation can occur within this slow moving and pooling blood. Clots within the left atrium can remain attached to the surface of the atrium or they can enter the circulation and block the arteries they enter.

Most commonly the clot will exit the heart, travel down the aorta, and lodge in the femoral arteries, thus interrupting blood flow to the rear legs. This is seen clinically as a sudden onset of weakness and inability to use the rear legs, pain, vocalization, and frequently respiratory difficulties. This is a medical emergency and prompt veterinary care should be obtained. Sadly, the clot could enter into any artery of the body as it exits the heart, so clinical signs can vary and include front limb lameness, inappropriate mentation, or even sudden death.

If your cat has an enlarged left atrium we may prescribe anti-platelet medications to help prevent the occurrence of an inappropriate blood clot. The most commonly utilized medications are aspirin and Plavix®, which are well tolerated in cats at appropriate doses. Choice of medication is dependent on the individual patient's risk factors. Unfortunately, the development of a blood clot is unpredictable and can occur despite medication.

If the clot enters the circulation, the overall prognosis for the patient is guarded. However, with medical therapy and supportive care to help reduce further clot formation, control pain, treat heart failure if present, and promote collateral circulation, approximately 50% of our patients will survive the event. The road to recovery in these patients can be long and we cannot predict how quickly or completely an individual will regain function of the affected limb(s). Many of the cats that survive the initial episode will not have an additional event, however, some cats will have another clot event within 6 months despite anti-platelet therapy. Our goal is an open collaboration with you and your primary care veterinarian in order to optimize the quantity and quality of your feline companion's life.

Chronic Degenerative Valvular Disease

Chronic degenerative valvular disease is the most common form of heart disease in the canine patient. It is characterized by the slow progressive degeneration of the edges of the heart valves. This creates an imperfect closure of the valve permitting backward flow, or regurgitation, between heart chambers. The most commonly affected valve is the mitral valve which separates the left ventricle, the primary pump to the body, and the left atrium, which receives oxygenated blood from the lungs. With degeneration of the mitral valve there is backflow into the left atrium with every contraction of the ventricle. Over time this results in compensatory enlargement of the ventricle, as it tries to continue to pump enough blood forward to the body. Additionally, the left atrium can enlarge as it stretches to accept the backward flow of blood. As the size of the leak increases, the heart may reach a point in which it can no longer compensate, resulting in fluid backing up from the left atrium into the lungs. This is known as left sided congestive heart failure and produces symptoms of respiratory difficulty and coughing.

Chronic degenerative valve disease typically affects older small breed dogs. A heart murmur caused by the turbulent backward flow of blood is frequently detected on physical exam before clinical signs of congestive heart failure are noted. The gold standard for assessing the severity and treatment options for affected pets is an evaluation and echocardiogram performed by a board certified veterinary cardiologist such as those of CVCA. We utilize the echocardiogram to determine the severity of the leak and secondary heart enlargement which in turn allows us to make informed decisions on how to best treat your pet. As previously mentioned, this is a chronic progressive disease and we utilize a tiered approach to therapy, which is tailored to each individual patient.

Based on the severity of disease at initial evaluation, multiple medications may be needed, however, some patients with mild degree of backflow and heart enlargement may not require any therapy. Regardless, the valvular degeneration is progressive in nature and requires vigilant monitoring and consistent follow-up in order to optimize treatment and maintain an ideal quality of life for your family member. Our goal is open collaboration with you and your primary care veterinarian in order to prevent, delay, eliminate signs of congestive heart failure and provide optimal quality and quantity of life at home.

Pulmonic Stenosis

Pulmonic stenosis (PS) is the narrowing of the diameter of the pulmonary artery resulting in restriction of the blood flow leaving the right ventricle headed out to the lungs. PS is usually caused by a thickened and abnormal pulmonic valve, but can also be caused by obstructive lesions above (supravalvular) or below (subvalvular) the pulmonic valve. PS is the third most common congenital defect in the dog and is seen most frequently in English Bulldogs, Chihuahuas, Beagles, Miniature Schnauzers, Cocker Spaniels, and several breeds of terriers.

The consequences of PS are directly proportional to the severity of the obstruction. The more pressure that is required to pump blood across the narrowed opening, the more the heart muscle must work. Like any muscle, the heart muscle becomes thicker (hypertrophies) with increased work load. Ultimately, with severe PS the heart can fail to pump enough blood to the lungs and can result in exercise intolerance, lethargy, or collapse associated with exercise or excitement. Some patients can also develop right sided congestive heart failure with fluid accumulation in the abdomen and thorax, resulting in signs of abdominal distension and/or difficulty breathing. Furthermore, the overworked heart can be prone to developing significant arrhythmias and unfortunately, can increase the risk for sudden death when left untreated.

Suspicion of PS is raised when a murmur, loudest at the base of the heart, is noted in a young dog on physical examination. Accurate diagnosis and assessment of the severity of pulmonic stenosis is provided non-invasively by an echocardiogram performed by a board certified veterinary cardiologist such as those of CVCA. Base on the results of the echocardiogram we can provide treatment recommendations tailored to the individual patient.

Mildly affected patients may not require any cardiac medications and frequently remain stable and asymptomatic throughout their lifetime. Patients with a moderate degree of stenosis frequently benefit from treatment with medications to slow their heart rate, improve cardiac perfusion, and prevent dangerous arrhythmias. For those patients that are severely affected, most benefit and are amenable to balloon valvuloplasty, a minimally invasive surgical intervention.

Balloon valvuloplasty involves a small surgical incision on the neck of the patient from which the jugular vein is isolated. Long cardiovascular catheters are then placed in the jugular vein and advanced into the heart under fluoroscopic guidance. The narrowed region of the pulmonic valve is then identified with the injection of radiographic dye and flouroscopy. Subsequently, a catheter with a non-distended balloon is advanced into the identified region and then dilated. This opens up the previously restricted region allowing blood to flow across more efficiently and with less resistance. This procedure is generally very well tolerated, with high success rates, and low risk of serious complications. Regardless of the severity of disease, our goal is an open collaboration with you and your primary care veterinarian in order to optimize the quantity and quality of your canine companion's life.

Subaortic Stenosis

Subaortic stenosis may be suspected when there is a murmur over the aortic region. Subaortic stenosis refers to a narrowing of the left ventricular outflow tract just below the aortic valve, or a narrowing of the area where blood leaves the heart to flow to the rest of the body. This obstruction is a result of a structural or anatomic narrowing that is heritable in nature. This lesion can very from inconspicuous nodules or ridges to thick fibrous rings that encircle the entire left ventricular outflow tract, and can involve a portion of the mitral valve apparatus. When the obstruction is moderate or severe, the muscle of the left ventricle may thicken as a result of the extra work (left ventricular hypertrophy). The definitive diagnosis is made via echocardiographic study. During the echocardiogram care must be taken to accurately measure the velocity (speed) of the blood flow through the stenotic area. This allows the cardiologist to determine the severity of the disease. Treatment for subaortic stenosis ranges from oral medications (beta blocker therapy) to invasive procedures such as balloon valvuloplasty.

Subaortic stenosis is more common in dogs than cats. The breeds most commonly affected with suboartic stenosis are: Newfoundlands, Golden Retrievers, Rottweilers, Boxers, Samoyeds Bulldogs, and German Shepherds.

Pericardial Effusion

The heart is normally encased by a protective thin fibrous sheet of tissue called the pericardium. The pericardium functions to keep the heart in place within the chest cavity and provide lubrication and thus prevent friction between the moving heart and surrounding tissues. Pericardial effusion is defined by the abnormal accumulation of excessive/abnormal fluid within the pericardial sac. This results in increased pressures within the pericardial sac that can cause compression of the chambers of the heart, known as cardiac tamponade. The right side of the heart has much lower internal pressures than the left side. Therefore, pericardial effusion usually results in the development of fluid accumulation in the abdomen as the return of blood from the body back to the right side of the heart is impeded and the vessels leak into the abdomen. However, when a sudden accumulation of fluid occurs from the spontaneous hemorrhage of a tumor; clinical signs of weakness, respiratory difficulties, and collapse can occur due to acute changes in hemodynamic balance.

Initial management of clinically significant pericardial effusion requires removal of the fluid from the pericardial sac. This is done by inserting a catheter through the chest wall and into the pericardial sac and then aspirating the fluid that is present. There is some risk in performing this procedure, but this is minimized by utilizing ultrasound guidance and monitoring the patient's ECG. The fluid removed is frequently submitted for cytology and fluid analysis and even cultured for underlying organisms if indicated in an attempt to determine the underlying cause.

Pericardial effusion in the canine patient is most commonly the result of spontaneous hemorrhage from a cardiac tumor. However, it can develop from infections, secondary to heart failure, or for no known cause which is termed idiopathic pericardial effusion. The prognosis for pericardial effusion is dependent on the underlying cause and can be highly variable. The optimal non-invasive evaluation of pericardial effusion is the performance of an echocardiogram by a board-certified veterinary cardiologist which allows real time evaluation for mass lesions, the hemodynamic consequences of the effusion, and therapeutic and diagnostic recommendations based on the study's findings.

Unfortunately, as many as two thirds of patients do not have an identifiable cause on initial evaluation and follow-up rechecks are required. Currently, we are actively researching the utility of certain biomarkers as an aid in the determination of the underlying cause of pericardial effusion in these situations. However, if a tumor is noted during the echocardiogram, then based on its location and appearance a strong working diagnosis can generally be made.

In cases of recurrent pericardial effusion due to an unknown cause or secondary to an identified heart base tumor; surgical pericardiectomy (removal of the pericardium) is recommended. By removing a portion of the pericardium it allows the fluid to accumulate within the chest cavity and prevents excessive compression of the heart, thus alleviating symptoms. Pericardiectomy can be performed via a thoracotomy (surgical opening of chest) or via thoracoscopic guidance. Typically the decision of which procedure is the better choice for the patient is made in conjunction with the cardiologist and the attending surgeon. The procedure results in a significant improvement in quality of life and long-term survival in this patients who are good candidates. Ultimately, our goal is to provide diagnostic and therapeutic plans tailored to the individual patient and carried out through open collaboration with you and your primary care veterinarian in order to optimize your pet's quality and quantity of life at home.