Arrhythmogenic Right Ventricular/Cardiomyopathy in Boxers

Rebecca E. Gompf DVM, MS, DACVIM (Cardiology)

BASIC INFORMATION

TREATMENT AND FOLLOW-UP

Treatment Options

If fainting episodes, VT, or severe VPCs are present, hospitalization is often needed to treat the arrhythmias with injectable medications. The more severe the arrhythmia, the higher the possibility of sudden death.

Once the heart rhythm is stabilized, several different drugs or drug combinations can be used orally. Not every drug works in every dog, so changes may be needed in therapy to control the ventricular arrhythmia.

• Oral drugs that may be used for the arrhythmias caused by ARVC include sotalol, mexiletine, and a combination of mexiletine and atenolol.

• If these medications do not control the arrhythmia, then a combination of mexiletine and sotalol may be tried.

• Amiodarone may be used as a last resort and often requires referral to a veterinary specialist for its administration.

Side effects of antiarrhythmic drugs include lethargy, anorexia, vomiting, and diarrhea. The last three effects are more common with mexiletine. Occasionally these drugs can make the arrhythmia worse, so that the dog must be switched to another medication. Amiodarone has multiple side effects, including liver damage with elevated liver tests, decreased white blood cell counts, and damage to the thyroid gland.

Follow-up Care

Affected boxers require frequent ECGs until their VT or VPCs are controlled. Ideally, a Holter monitor is applied to dogs with non–life-threatening arrhythmias to document the frequency of the arrhythmias prior to treatment. Then another Holter recording is done after the drug has reached adequate blood levels to judge how effective it is in controlling the abnormal beats. Affected dogs require antiarrhythmic therapy for the rest of their lives.

Prognosis

Boxers whose arrhythmias are well controlled with medications can live a long time. No drug is 100% effective in preventing sudden death, however. Animals on medication can still die suddenly. The better the arrhythmia is controlled, the less likely it is for sudden death to occur. Holter monitors provide the best way to evaluate how well the medication is controlling the arrhythmias.

Because this problem has a genetic basis and runs in families, it is wise not to breed dogs that have ARVC.

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Arterial Thromboembolism, Peripheral

Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)

BASIC INFORMATION

Description

Arterial thromboembolism occurs when a blood clot lodges in an artery. The place where the blood clot comes to rest depends on the size of the clot and the size of the artery. Most blood clots are small and lodge in smaller arteries. The clots can cause strokes if they cut off blood to certain areas of the brain. Clots can cause damage and eventual failure of any organ in the body. In cats, the clots usually lodge in a front leg or at the termination of the aorta where it divides into arteries that supply the rear legs. This disease occurs most often in cats; it is uncommon in dogs.

Causes

Dogs can develop clots secondary to kidney diseases, Cushing’s disease (excessive levels of circulating steroid hormones), infections of the left heart valves (bacterial endocarditis), and other conditions that affect clotting. Cats usually develop clots in the left atrium, the small chamber on the left side of the heart, when it becomes dilated from hypertrophic (HCM) or dilated (DCM) cardiomyopathy or other diseases of the heart muscle. Cats have sticky platelets, and clots may form if there is decreased blood flow in the big left atrium. Pieces of the clot can break off and travel in the bloodstream to other areas, especially to the end of the aorta.

Clinical Signs

Signs of the underlying diseases are usually present but can be subtle in cats. The first sign of a problem may be sudden paralysis of a front leg or both rear legs. If the incident is recent, the animal may be crying in pain. The affected limbs are cold and limp, with blue nail beds. Muscles in the affected legs may feel hard.

Diagnostic Tests

Numerous tests are required to find the underlying cause of the problem and to assess the extent of damage from the clot. Laboratory tests, chest x-rays, and an echocardiogram (heart ultrasound) are commonly performed. Abdominal x-rays and a Doppler ultrasound study of the aorta may also be recommended to assess other organs and the extent of the clot. Additional tests may be needed based on the results of initial procedures.

TREATMENT AND FOLLOW-UP

Treatment Options

Hospitalization is usually required for initial testing and therapy. Supportive care is started, with pain medications, sedatives, and intravenous (IV) fluids. Manual expression of the bladder and physical therapy for paralyzed legs are often needed. Specific treatments are given for the underlying disease.

Medications to break down the clot are rarely used in dogs and cats; they are often ineffective, perhaps because they must be given within a few hours of the arterial obstruction, and the event is not often witnessed in animals. Streptokinase and tissue plasminogen activator (TPA) are used in people, and both drugs have been used in cats, but with varying impact on survival. They have been used only infrequently in dogs, and there is little information about their effects.

Medications are started to prevent the clot from getting bigger and to try to prevent future clots. Injectable heparin is commonly used during hospitalization. Clopidogrel (Plavix) may be given orally in cats.

After discharge from the hospital, home care may involve the following:

• Medications for the underlying problem that caused the initial clot

• Supportive care, including physical therapy and possible bladder expression

• Medications to prevent additional clot formation, such as warfarin and aspirin in cats and dogs, and clopidogrel in cats

Follow-up Care

Frequent, often weekly, monitoring of the underlying problem and effects of the clots (such as kidney dysfunction) are usually needed. Repeated blood clotting tests are needed if warfarin is used. After a few weeks, the frequency of rechecks may be modified, depending on the response to treatment.

Prognosis

Animals with blood clots in the legs have a guarded prognosis. If there is no return of blood flow to the rear legs within a couple of days, prognosis is very poor, and it is unlikely the animal will recover function of the legs. Future clots are likely to develop if the underlying problem cannot be controlled or the preventive medications do not work.

Overall prognosis also depends on the underlying heart disease. In cats, each form of cardiomyopathy has a different prognosis; however, the formation of clots always makes the prognosis much worse. In dogs, some underlying diseases are easier to treat than others, so prognosis depends on the disease that is causing the clots.

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Atrial Fibrillation

Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)

BASIC INFORMATION

Description

Atrial fibrillation (AF) is an abnormal heart rhythm caused by rapid, irregular contractions of the upper chambers (atria) of the heart. Because the heart is beating faster and more irregularly than normal, it does not fill or pump blood properly. Failure to pump blood normally can result in fluid accumulation in the lungs, chest, or abdomen and can lead to weakness and heart failure.

Causes

The most common cause of AF is advanced heart disease, with enlargement of one or both atria. Advanced heart diseases in dogs may include degeneration and leakage of heart valves, diseases of heart muscle (cardiomyopathy), and certain congenital heart deformities.

AF can occur spontaneously for unknown reasons (idiopathic) in giant-breed dogs such as the Great Dane and Irish wolfhound. Occasionally the administration of narcotics has caused AF in large dogs.

Clinical Signs

Clinical signs of both heart disease and AF are usually present. Weakness and inability to exercise are common. Fainting episodes may occur, especially with exertion. Cats are often less active than usual. Breathing may be faster and labored, and coughing may be noted.

Giant-breed dogs usually have no symptoms at first, and the AF may be detected only when an irregular rhythm is heard with a stethoscope and an electrocardiogram (ECG) is performed. Some of these dogs eventually develop signs of heart disease.

Diagnostic Tests

An ECG is needed to confirm the presence of AF. Additional tests, such as chest x-rays and an echocardiogram (heart ultrasound), are then done to search for the underlying cause. Any fluid removed from the chest or abdomen may be sent for analysis. Laboratory tests are usually recommended to rule out other diseases that cause similar signs.

TREATMENT AND FOLLOW-UP

Treatment Options

Treatment is initially directed at any underlying heart disease or heart failure and may include drugs to increase contractility (such as pimobendan) or decrease fluid retention (diuretics).

Then medications such as the following are started to bring the heart rate down to a more normal range.

• Digoxin (a form of digitalis) increases the heart’s ability to contract and helps to slow the heart rate. It may be used in combination with other drugs (diltiazem, beta-blockers) to achieve the best control of heart rate. Side effects such as decreased appetite, vomiting, diarrhea, and other arrhythmias often limit it use. Cats do not tolerate digoxin well.

• Diltiazem is a calcium channel blocker commonly used to decrease heart rate in animals with AF. It also decreases the heart’s ability to contract, so it is not started until heart failure is controlled in dogs. In cats it may be used right away, because their underlying heart disease usually does not affect contraction. Side effects include depression, decreased appetite, worsening of heart failure, constipation (cats), and very slow heart rates.

• Multiple beta-blockers (atenolol, metoprolol, propranolol, carvedilol) are used in dogs, but in cats atenolol is used most commonly. These drugs slow the heart rate and also decrease contractions. Side effects include very slow heart rates, weakness, depression, low blood pressure, and worsening of heart failure.

• Giant breeds of dogs with spontaneous AF are usually started on a beta-blocker to control their heart rate. In some cases, a procedure called electrical cardioversion may be performed with the animal under anesthesia to try and convert the AF back to a normal sinus rhythm. Although the rate of conversion is good, recurrences are common.

Follow-up Care

Once medications are started, ECGs are periodically repeated to monitor heart rate and make adjustments in medications. A Holter monitor, which is a 24-hour continuous monitor, may be recommended to ensure that the heart rate stays within an acceptable range during normal activities. Chest x-rays, echocardiograms, abdominal x-rays, and laboratory tests may be repeated until the animal is stable and then periodically, especially in giant-breed dogs, to monitor for any signs of significant heart disease or in any animal if signs of heart failure develop.

Prognosis

Dogs with advanced heart disease and AF may live 3-12 months, depending on the type and severity of their heart disease. Cats live an average of 3-6 months. Affected cats are prone to develop blood clots in their left atrium, so they are usually placed on blood thinners such as aspirin or clopidogrel (anticoagulation therapy). Giant-breed dogs with idiopathic AF can live for years; however, their AF can progress to serious heart disease (dilated cardiomyopathy).

SPECIAL INSTRUCTIONS:

Atrial Premature Contractions and Tachycardia

Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)

BASIC INFORMATION

Description

The normal heartbeat originates in the small upper chambers of the heart, the atria. When the atria become irritated, irregular, premature beats called atrial premature contractions (APCs) may be generated, and the heart may beat faster than usual (tachycardia). Atrial tachycardia (AT) is a sequence of four or more APCs, usually occurring at a fast rate. As the number of abnormal beats increases and the heart rate becomes higher, the heart may not fill and pump blood properly.

Causes

The most common cause is heart disease that results in enlargement of one or both atria. The stretching of the atria causes abnormal beats to occur. These arrhythmias can also arise with other problems in the body, such as bruising of heart muscle after blunt trauma (such as being hit by a car), or liver or kidney failure.

Clinical Signs

No clinical signs occur if only sporadic, infrequent APCs are present. Frequent APCs may lead to an inability to exercise, increased rate and effort of breathing, and coughing. AT can cause weakness and possibly fainting. Fainting due to AT can be hard to tell from seizures.

Diagnostic Tests

An electrocardiogram (ECG) is needed to confirm the presence of APCs or AT. If these abnormal rhythms are not present all the time, continuous ECG monitoring may be recommended. Such monitoring can be done in the hospital or with a 24-hour, continuous Holter monitor or an event monitor that the animal wears at home.

Because APCs and AT are usually associated with heart disease and other systemic problems, additional tests are often recommended. Such tests may include laboratory tests, chest x-rays, an echocardiogram (heart ultrasound), an abdominal ultrasound study, and other tests. Any fluid in the chest or abdomen may be removed and sent for analysis.

TREATMENT AND FOLLOW-UP

Treatment Options

Treatment is initially directed at any heart disease present. If the overall heart rate is close to normal and no signs are present, then the APCs or AT may not be treated. If the heart rate is too fast, medications (alone or in combinations) are used to slow it down and may include the following:

• Digoxin (a form of digitalis) increases the heart’s ability to contract and helps to slow the heart rate. It may be used in combination with other drugs (diltiazem, beta-blockers) to achieve the best control of heart rate. Side effects such as decreased appetite, vomiting, diarrhea, and other arrhythmias often limit it use. Cats do not tolerate digoxin well.

• Diltiazem is a calcium channel blocker commonly used to decrease heart rate in affected animals. It also decreases the heart’s ability to contract, so it is not started until heart failure is controlled in dogs. In cats it may be used right away, because their underlying heart disease usually does not affect contraction. Side effects include depression, decreased appetite, worsening of heart failure, constipation (cats), and very slow heart rates.

• Multiple beta-blockers (atenolol, metoprolol, propranolol, carvedilol) are used in dogs, but in cats atenolol is used most commonly. These drugs slow the heart rate and also decrease contractions. Side effects include very slow heart rates, weakness, depression, low blood pressure, and worsening of heart failure.

If other diseases are causing the APCs, then those diseases are usually treated first, and the arrhythmia is monitored with ECGs. If the APCs do not resolve and AT occurs, they are treated as outlined earlier.

Follow-up Care

Once medications are started, ECGs are periodically repeated to monitor heart rate and make adjustments in medications. A Holter monitor may be used to make sure the heart rate stays within an acceptable range during normal activity. If the patient is started on medications, periodic laboratory tests may be recommended to check kidney function and monitor resolution of other diseases. Chest x-rays and echocardiograms may be repeated if heart disease is present.

Prognosis

Prognosis depends on the underlying disease that is causing the APCs or AT. Each disease has its own prognosis, and some are better than others. The more severe atrial arrhythmias are usually indicators of advanced heart disease.

SPECIAL INSTRUCTIONS:

Atrioventricular Valve Degeneration in Dogs

Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)

BASIC INFORMATION

Description

The left atrioventricular (AV) or mitral valve lies between the left atrium and the left ventricle. The right AV or tricuspid valve lies between the right atrium and ventricle. These valves keep blood from flowing backward into the atria when the heart contracts.

As these valves age, deposits occur and they become scarred (myxomatous degeneration), which causes them to leak when the heart pumps. As a result, the heart is less efficient in pumping blood and slowly enlarges. If the leakage is minor, the heart usually compensates, but as the leakage worsens, heart failure can develop. The mitral valve is most commonly affected and mitral degeneration may eventually lead to left-sided heart failure.

Causes

The cause of the myxomatous degeneration is unknown. AV valvular disease is the most common heart disease in dogs. It most commonly affects small to medium-sized breeds, especially the papillon, poodle, Chihuahua, dachshund, and Cavalier King Charles spaniel.

AV valvular disease is common in older dogs. The disease tends to develop at a younger age and progresses more rapidly in male dogs than in females. Genetic factors play a role in this disease, but other conditions (level of exercise, obesity, diet) may influence the severity of the problem.

Clinical Signs

The leaking valve often causes a heart murmur that can be detected on a routine physical examination before signs occur. The first clinical sign is usually coughing that is triggered by excitement or exercise. As the left heart enlarges, signs of heart failure may develop, such as more severe coughing, restlessness and pacing at night, inability to exercise normally, and rapid, labored breathing.

Dogs that go into right heart failure may also cough, but more often they tire while exercising, lose weight and muscle mass, and develop fluid in their abdomen. Eventually fluid also builds up in the chest, and they have trouble breathing.

TREATMENT AND FOLLOW-UP

Treatment Options

Treatment is usually started after clinical signs develop, because no drugs have yet been found that stop progression of this disease. Dogs with mild signs may be treated on an outpatient basis, but more severely ill dogs require hospitalization. A number of drugs are available for stabilizing heart failure, including injectable diuretics (such as furosemide) to decrease fluid in the lungs, vasodilators (such as nitroglycerine ointment, nitroprusside, or hydralazine) that decrease the heart’s workload, and oxygen therapy. Some fluid may be drained from the chest cavity or abdomen.

After heart failure is stabilized, long-term oral medications are started. Some of these drugs may also be used in dogs with mild clinical signs.

• Furosemide may be continued indefinitely and may be combined with other diuretics, such as spironolactone.

• Angiotensin-converting enzyme (ACE) inhibitors, such as enalapril, benazepril, or ramipril, may be used to improve the quality of the dog’s life and help reduce fluid retention.

• Pimobendan is a newer drug that helps relieve the workload of the heart and improves the heart’s contractions. It is reserved for dogs in heart failure.

• Other drugs (digoxin, beta-blockers, calcium channel blockers) may be started for high heart rates associated with abnormal rhythms such as atrial fibrillation.

In addition to drug therapy, dogs with heart failure should not be fed salty foods, and low-salt diets may be used to limit salt intake. Although strenuous exercise is avoided, mild to moderate exercise may be done based on guidelines from your veterinarian.

Follow-up Care

Dogs with no clinical signs are commonly monitored with physical examinations every 6-12 months and yearly chest x-rays. If your dog develops problems breathing, notify your veterinarian immediately. Intensive monitoring is needed during hospitalization for heart failure. Following discharge, periodic recheck visits and testing are needed for the rest of the dog’s life.

Prognosis

Dogs with asymptomatic disease may live for years without developing clinical problems. The more severe the leak in the valve and the bigger the left atrium, the more likely it is that the dog will develop heart failure. The average survival time for dogs with heart failure is 8-10 months, but every dog varies in how it responds to treatment. Dogs with other diseases, such as kidney failure, tend to do poorly.

Cavalier King Charles spaniels and other small dogs that develop AV valve degeneration before 5 years of age should not be used for breeding.

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Cardiac Tumors

Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)

BASIC INFORMATION

Description

Cardiac tumors arise from heart tissues (primary tumors) or metastasize to the heart from another location (secondary tumors). These tumors can interfere with normal heart function or cause bleeding into the pericardial sac (the sac around the heart). Decreased heart function may result in poor circulation and heart failure.

Causes

Primary tumors of the heart include hemangiosarcoma, heart base tumors, mesothelioma, rhabdomyosarcoma, fibrosarcoma, and lymphosarcoma. These tumors can also originate from other areas and metastasize to the heart. The cause of these tumors is unknown.

Hemangiosarcomas are highly malignant tumors of blood vessels. They often invade the wall of the right atrium—the small, upper chamber of the right heart. The tumor destroys the wall of the atrium and may bleed into the pericardial sac, causing pericardial effusion. (See also the handout on Pericardial Effusion.) Golden retrievers and German shepherd dogs are prone to develop hemangiosarcoma. Primary cardiac hemangiosarcoma has been reported in only one cat.

Heart base tumors form from structures close to the heart. They are slow growing and may cause no problems until they interfere with the blood supply to the pericardial sac. Although they are the second most common cardiac tumor in dogs, they are 10 times less common than hemangiosarcomas. The English bulldog, boxer, and Boston terrier breeds develop these tumors most frequently, usually between 6 and 15 years of age. These tumors are occasionally found in cats.

Mesotheliomas are small tumors that spread over the pericardial sac and chest wall. They can cause pericardial effusion that is lethal to dogs, but they are rare in cats. Lymphosarcomas, rhabdomyosarcomas, and fibrosarcomas occur in both dogs and cats. They often invade the wall of the heart, which decreases its ability to contract. They can also cause the heart valves to leak, in which the end result is heart failure.

Clinical Signs

Most animals with significant effusion have a sudden onset of lethargy, weakness, and collapse. Trouble breathing occurs in about half of affected dogs, and 23% have abdominal swelling. Loss of appetite, vomiting, or coughing may be noted. Signs associated with cancer in other organs may be present.

Diagnostic Tests

X-rays of the chest and abdomen are usually recommended. If an enlarged heart is seen on the x-rays, an echocardiogram (heart ultrasound) and an electrocardiogram (ECG) are done to differentiate pericardial effusion from other cardiac diseases. The echocardiogram also helps identify the presence of a tumor and its effects on the heart.

Laboratory tests and an abdominal ultrasound are often done to look for tumors in other organs and to evaluate their systemic effects. Some of these tests may be delayed until fluid has been removed from the pericardial sac and the animal is stable. Fluid may be submitted for analysis. Additional tests may also be indicated.

TREATMENT AND FOLLOW-UP

Treatment Options

If pericardial effusion is causing symptoms, it is removed by pericardiocentesis, which involves insertion of a catheter into the pericardial sac to drain the fluid. Removal of fluid helps prevent sudden death from cardiac tamponade, which is caused by poor filling of the heart due to severe fluid pressure.

Dogs with right atrial hemangiosarcoma are difficult to treat. Pericardiocentesis provides temporary relief, but the effusion returns in a short time. Surgical removal of the tumor and chemotherapy may be attempted in some cases. Dogs with heart base tumors benefit from removal of the pericardial sac, because these tumors grow very slowly. Treatment of other tumors depends on the tumor type and may involve removal of the pericardial sac and chemotherapy.

Follow-up Care

The frequency of recheck visits and repeated testing is determined by the treatment protocols chosen. Dogs with heart base tumors whose pericardial sacs are removed may only need to be rechecked every 3-6 months.

Prognosis

Dogs with right atrial hemangiosarcoma have a median survival time of 56 days (range, 0-229 days). Pericardial mesothelioma also carries a grave prognosis. Prognosis is better for heart base tumors; average survival time is 730 days after removal of the pericardial sac or 42 days if no surgery is performed.

Dogs with cardiac lymphosarcoma that is stage III or higher have a poor prognosis for remission and survival. In a study of 12 dogs treated with removal of the pericardial sac and chemotherapy, the median survival time was 41 days. Three dogs did live 328 days or longer, so not all of them did poorly.

SPECIAL INSTRUCTIONS:

Cardiopulmonary Resuscitation

Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)

BASIC INFORMATION

Description

Cardiopulmonary resuscitation (CPR) is a group of procedures that are done to try to revive an animal whose heart has gone into ventricular fibrillation (heart is just vibrating, not beating) or has totally stopped (cardiac arrest). Once the heart stops beating normally, the animal also stops breathing (respiratory arrest); sometimes breathing stops first.

The first step in CPR is placement of a tube into the animal’s throat, so that artificial respiration (assisted breathing) can be done. At the same time, chest compressions are started in an attempt to circulate blood throughout the body, and an intravenous catheter is inserted so that drugs can be given to help stimulate the heart. An electrical shock (defibrillation) may be applied to stop the fibrillation and stimulate the heart to beat normally. In extreme cases, your veterinarian may decide to open the animal’s chest and squeeze the heart by hand so that blood begins to circulate. When the chest is open, drugs can be administered directly into the heart.

Causes

Many factors can cause the heart to stop or go into ventricular fibrillation, including serious diseases, certain drugs, drowning, electrocution, being struck by a car, certain toxins, and general anesthesia, among others.

Clinical Signs

An animal that has gone into cardiac arrest will suddenly collapse and stop breathing. The animal may also become rigid or have muscle twitching. A few gasps of breath may be seen, but there is no continuous breathing.

Diagnostic Tests

Listening to your animal’s heart with a stethoscope will identify that the heart is not beating. A lack of breathing may also be noted. CPR is started immediately, and an electrocardiogram (ECG) is performed to determine what heart rhythm is present.

Laboratory tests may be run throughout CPR to monitor the response to the procedures. If your animal is successfully resuscitated, then numerous laboratory tests, chest and abdominal x-rays, and other tests may be recommended to determine why your animal went into cardiac arrest and its effects on other organs.

TREATMENT AND FOLLOW-UP

Prognosis

Animals that experience only respiratory arrest have a better chance of being successfully resuscitated than if their heart also stops. Following cardiac arrest, the survival rate for dogs is only 4%, and for cats it is only 2%. These rates are low because most affected animals have serious underlying medical problems that cannot be easily corrected. In addition, most animals that have arrested once will have another cardiac arrest within a short time.

People who experience a cardiac arrest have about a 30% chance of being resuscitated successfully, but fewer than 20% of those individuals ever leave the hospital, because they also have serious underlying medical problems. The most successful CPR outcomes occur in people who have suffered drug overdoses, electrocution, or drowning.

Fictional television programs have given people the wrong expectations with respect to successful CPR. In most television shows, the person who has arrested is saved and leaves the hospital at the end of the show healthy and happy. This is not a realistic depiction of CPR in animals, because most do not survive a cardiac arrest.

Because the success rate of CPR is low in seriously ill animals, consider discussing with your veterinarian what you would like to have done if your animal arrests. You may elect not to have CPR performed on your animal if the underlying disease is extremely serious. This is always a difficult decision to make and a very personal one. Your veterinarian can give you the information that you need to make a wise, informed decision on whether you want CPR performed if your animal goes into cardiac arrest while hospitalized.

SPECIAL INSTRUCTIONS:

Congestive Heart Failure in Dogs, Left-Sided

Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)

BASIC INFORMATION

Description

Left heart failure occurs when the left side of the heart is no longer working properly and cannot pump blood effectively to the body. Blood accumulates in the lungs and interferes with the ability of oxygen to enter the bloodstream. If left heart failure is not treated or if your dog does not respond to treatment, then death may occur from this accumulation of blood.

Causes

A number of diseases can cause left heart failure in dogs (see also the handouts on each of these conditions):

• Atrioventricular valve degeneration of the left atrioventricular (mitral) valve

• Bacterial endocarditis, an infection of either the aortic or the mitral valve

• Dilated cardiomyopathy, a disease of heart muscle in large-breed dogs that results in a big, flabby heart

• Congenital heart defects, particularly a patent ductus arteriosus (PDA) and sometimes a ventricular septal defect or mitral valve dysplasia

• Systemic hypertension (high blood pressure), an uncommon cause

Clinical Signs

Dogs with left heart failure cannot exercise; they cough when lying down, and they may get up and pace after lying down. As signs worsen, they eventually start breathing faster (more than 50 times per minute) and with more effort. A loud heart murmur that can be heard with a stethoscope is a common finding on physical examination.

TREATMENT AND FOLLOW-UP

Treatment Options

If the dog has moderate to severe left heart failure, it may be hospitalized for stabilization with injectable diuretics (such as furosemide), vasodilator drugs (such as nitroglycerin ointment, hydralazine, or sodium nitroprusside), and oxygen therapy. If the dog has mild heart failure, it may be managed on an outpatient basis. Dogs with left heart failure are very fragile and need aggressive treatment, with as little stress as possible. Once the dog is stable and breathing is improved, long-term oral medications are started, such as the following:

• Furosemide (Lasix) diuretic is usually continued indefinitely and may be combined with other diuretics, such as spironolactone. Dosages are adjusted to the lowest ones that keep the dog out of heart failure.

• Angiotensin-converting enzyme (ACE) inhibitors, such as enalapril, benazepril, or ramipril, may be used to improve the quality of your dog’s life and help reduce fluid retention by the body. Their effects are not immediate, but they exert modest positive effects over weeks to months.

• Pimobendan is a newer drug that acts as a vasodilator to relieve the workload of the heart and to increase the force of contractions. Pimobendan is commonly used with other medications, such as diuretics and ACE inhibitors.

• Digoxin is used in some dogs that have moderate to severe heart failure and very fast heart rates secondary to abnormal rhythms, such as atrial fibrillation.

• Beta-blockers, such as carvedilol, are being investigated to determine whether they can improve the quality of life in dogs with atrioventricular valve degeneration. Beta-blockers are also used to slow the heart rate secondary to atrial fibrillation.

• Occasionally, other classes of drugs, such as calcium channel blockers, may be needed to control the high heart rate caused by atrial fibrillation.

In addition to drug therapy, dogs with heart failure should not be fed salty foods, and low-salt diets may be used to limit salt intake. Although strenuous exercise should be avoided, mild exercise may be done based on guidelines from your veterinarian.

Follow-up Care

Intensive monitoring is often needed during hospitalization. Laboratory tests, chest x-rays, and other tests are often repeated until the dog is stable. Follow-up visits are usually scheduled within 7-14 days after discharge. Recheck visits may include chest x-rays and laboratory tests. The interval between visits and further testing depends on the underlying disease and how your dog responds to medications. Periodic monitoring is needed for the life of your dog. Notify your veterinarian if any signs of heart failure return while the dog is on therapy.

Prognosis

Dogs with left-sided heart failure can live from days to years, with the prognosis depending on the cause and severity of the heart failure.

SPECIAL INSTRUCTIONS:

Congestive Heart Failure in Dogs, Right-Sided

Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)

BASIC INFORMATION

Description

Right heart failure occurs when the right side of the heart is no longer working properly and cannot pump blood effectively to the lungs and left heart. Fluid accumulates in the abdomen and the chest. Eventually, if right heart failure is not treated, breathing is affected and death may occur.

TREATMENT AND FOLLOW-UP

Treatment Options

If there is a significant amount of fluid in the chest, it is usually removed so that the dog can breathe easier. Fluid may also be removed from the abdomen and from the pericardial sac to make the dog more comfortable.

Dogs with moderate to severe right heart failure may be hospitalized for stabilization with injectable diuretics (such as furosemide) and oxygen therapy. Once the dog is stable, oral medications are started. Which medications are chosen depends on the disease causing the right heart failure. Choices include the following:

• Furosemide (Lasix) diuretic is usually continued indefinitely and may be combined with other diuretics, such as spironolactone (especially to keep fluid levels low). Dosages are adjusted to the lowest ones that keep the dog out of heart failure.

• Angiotensin-converting enzyme (ACE) inhibitors, such as enalapril, benazepril, or ramipril, may be used to improve the quality of your dog’s life and help reduce fluid retention by the body. Their effects are not immediate, but they exert modest positive effects over weeks to months.

• Pimobendan is a newer drug that acts as a vasodilator to relieve the workload of the heart and to increase the force of contractions of the heart. Pimobendan is commonly used with other medications, such as diuretics and ACE inhibitors.

• Digoxin is used in some dogs that have moderate to severe heart failure and very fast heart rates secondary to abnormal rhythms, such as atrial fibrillation.

• Beta-blockers, such as carvedilol, are being investigated to determine whether they can improve the quality of life in dogs with heart disease. Beta-blockers are also used to slow the heart rate secondary to atrial fibrillation.

• Occasionally, other classes of drugs, such as calcium channel blockers, may be needed to control high heart rates caused by atrial fibrillation.

In addition to drug therapy, dogs with heart failure should not be fed salty foods, and low-salt diets may be used to limit salt intake. Although strenuous exercise should be avoided, mild exercise may be done based on guidelines from your veterinarian. If heartworm disease is present, it will be treated once the right heart failure is stable.

Follow-up Care

Intensive monitoring is often needed during hospitalization. Follow-up visits are usually scheduled within 7-14 days after discharge. Recheck visits may include chest x-rays, laboratory tests, and ECGs. The interval between visits and further testing depends on the underlying disease and how your dog responds to medications. Periodic monitoring is needed for the life of your dog. Notify your veterinarian if any signs of heart failure return while the dog is on therapy.

Prognosis

Most dogs with right heart failure have an average life span of 6-12 months; however, survival time is dependent on the underlying cause.

SPECIAL INSTRUCTIONS:

Dilated Cardiomyopathy in Cats

Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)

BASIC INFORMATION

Description

Dilated cardiomyopathy (DCM) is a disease in which the heart muscle becomes flabby and weak and the heart chambers dilate. The heart cannot effectively pump blood to the body, so the cat lacks energy and fluid may accumulate in the lungs, chest cavity, or both. As the heart dilates, the valvular openings between the chambers of the heart enlarge and the valves begin to leak, which adds an additional burden on the heart. Abnormal heart rhythms (arrhythmias) are also common, especially atrial fibrillation and ventricular arrhythmias.

Causes

Taurine deficiency can cause a reversible type of DCM in cats. Taurine is an essential amino acid that must be supplied in the food of cats. Commercial cat foods are supplemented with taurine, so taurine-deficient DCM is uncommon unless the cat is on a vegetarian diet, is fed exclusively dog food or a single kind of canned cat food, or has a medical problem that interferes with absorption of taurine from the intestinal tract.

Idiopathic DCM occasionally occurs in cats, which means the cause is unknown.

Clinical Signs

Signs often develop suddenly in cats with DCM. Some of the early signs may be exercise intolerance, weakness, decreased appetite, and cold feet. Increased rate and effort of breathing (faster than 50 times per minute) may be the first sign noted by the owner. If a blood clot becomes lodged in one of the front legs or in both rear legs, those legs will be paralyzed and cold, with blue foot pads. Your cat also may also be in pain if the clot happened recently.

TREATMENT AND FOLLOW-UP

Treatment Options

If moderate to severe heart failure is present, the cat is often hospitalized for stabilization with injectable diuretics (such as furosemide), oxygen therapy, removal of fluid from the chest, and other measures. After the cat is stable, oral medications are started and may include the following:

• Furosemide (Lasix) diuretic is usually continued indefinitely and may be combined with other diuretics.

• Angiotensin-converting enzyme (ACE) inhibitors, such as enalapril, benazepril, or ramipril, may be used to improve the quality of your cat’s life and help reduce fluid retention in the body.

• Pimobendan is a newer drug that acts as a vasodilator to relieve the workload of the heart and to increase the force of contractions of the heart. It is not yet approved for use in cats but shows promise.

• Digoxin is used in some cats with moderate to severe heart failure and very fast heart rates secondary to abnormal rhythms, such as atrial fibrillation. Cats with DCM do not tolerate digoxin very well.

• Beta-blockers and calcium channel blockers are used to slow fast heart rates secondary to atrial fibrillation. They can cause weakness and worsen in heart failure, so they are used cautiously.

• Ventricular arrhythmias are often treated with atenolol and sometimes sotalol, which are beta-blockers.

Cats with heart failure should not be fed salty foods, and low-salt diets may be used to limit their salt intake. Some cats do not like to eat low-salt diets, however. All cats with DCM are started on taurine supplementation, because some cats with normal taurine blood levels respond to taurine supplementation. If the left atrium is enlarged, medications may be started to prevent blood clots from forming. Baby aspirin has been used for many years for this purpose, and clopidogrel (Plavix) may also be beneficial.

Follow-up Care

Cats with heart failure are usually re-evaluated 7-14 days after discharge from the hospital. Chest x-rays, laboratory tests, and an ECG are often repeated. Echocardiograms may be done every 2-3 months, and recheck visits are needed for the life of the cat.

Prognosis

Cats with taurine-deficiency cardiomyopathy have a good prognosis if they survive the first several weeks after being treated for heart failure. Cats with idiopathic DCM have a grave prognosis, with survival times of several weeks to months.

SPECIAL INSTRUCTIONS:

Dilated Cardiomyopathy in Dogs

Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology)

BASIC INFORMATION

Description

Dilated cardiomyopathy (DCM) is a disease in which the heart muscle becomes flabby and weak and the heart chambers dilate. The heart cannot effectively pump blood to the body, so the animal lacks energy and fluid accumulates in the lungs, abdomen, or both.

As the heart dilates, the valvular openings between the chambers of the heart enlarge, and the valves begin to leak, which adds an additional burden on the heart. Abnormal heart rhythms (arrhythmias) are also common, especially atrial fibrillation and ventricular arrhythmias.

Causes

DCM is more common in large and giant breeds of dogs and in the American cocker spaniel. In most cases, no exact cause is found (idiopathic), but the disease is inherited as an autosomal dominant characteristic in certain families of boxers and Doberman pinschers.

Nutritional deficiencies of taurine and L-carnitine may cause DCM in American cocker spaniels. Taurine deficiency may also cause DCM in the golden retriever and Newfoundland. Less common causes of secondary cardiomyopathy include myocarditis (an inflammation of heart muscle), hormonal problems (hypothyroidism, hypoadrenocorticism, hyperthyroidism), and high doses of the chemotherapeutic drug doxorubicin.

Clinical Signs

Signs often develop suddenly in dogs with DCM. Some of the first signs are exercise intolerance, weakness, and cold feet. Coughing, loss of appetite, and increased rate and effort of breathing may occur. Abdominal distention with fluid and loss of muscle mass may be noted.

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