Dilated Cardiomyopathy in Dogs

What is dilated cardiomyopathy?What is dilated cardiomyopathy?

Cardiomyopathy is defined as degeneration of the heart muscle. As a result of this degeneration, the muscle becomesthinner, particularly the thick muscle wall of the left ventricle. The pressure of the blood inside the heart causes these thinwalls to stretch resulting in a much larger heart. This condition is described as dilated cardiomyopathy (DCM)dilated cardiomyopathy (DCM).

How common is the condition?How common is the condition?

Dilated cardiomyopathy is the most common cause of heart failure incertain large breeds of dogs. These include Boxer Dogs, DobermanPinschers, Great Danes, Irish Wolfhounds, and Saint Bernards. Occasionally,German Shepherd Dogs and some medium-sized breeds such as CockerSpaniels, English Springer Spaniels, and Portuguese Water Dogs are alsoaffected. Small breeds rarely develop DCM. It is more often diagnosed inmales than females.

My dog suddenly seemed to develop dilatedMy dog suddenly seemed to develop dilatedcardiomyopathy. Can this disease develop that quickly?cardiomyopathy. Can this disease develop that quickly?

Dilated cardiomyopathy may have a sudden onset of clinical signs; however, the disease has actually been developing slowlyand subtly. Some dogs may develop severe congestive heart failure (CHF) in only a few hours. Rapid, heavy breathing, a bluetongue, excessive drooling, or collapse may be the first signs.

What are the signs of DCM?What are the signs of DCM?

Signs may be sudden or progressive in onset. Annual checkups with your veterinarian may lead to a diagnosis of heartproblems before clinical signs are present (this is the best time to diagnose a problem). Signs can include:

• rapid breathing when resting or sleeping (more than 30-35 breaths per minute)

• increased effort associated with breathing

• restless sleeping; moving around a lot and changing positions

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• coughing or gagging

• weakness

• reduced ability to exercise

• collapse or fainting

• decreased appetite

• weight loss

• distended belly

• depressed attitude or quiet and not interactive

• sudden death

How is DCM diagnosed?How is DCM diagnosed?

Before a diagnosis of dilated cardiomyopathy ismade, several tests are performed to assessdifferent aspects of heart function.

Auscultation.Auscultation. Listening to the chest with astethoscope allows your veterinarian to identifymurmurs due to the improper closure of heartvalves. The murmur's location and intensity helpdetermine its significance. Heart rhythm is alsoassessed during auscultation, and if there areconcerns, your veterinarian may simultaneously palpate or feel the pulse to determine its strength and rhythm. Auscultationis also used to evaluate the lungs.

Blood and urine tests.Blood and urine tests. Liver and kidney function can be a concern, because these organs are often impaired in heart disease.

ProBNP.ProBNP. This is a blood test that measures a specific protein level in the body that changes with structural changes of theheart and heart disease. It is not as reliable a test as some of the others outlined below to indicate the source or an accurateassessment of the severity of the condition.

Chest radiographs (X-rays).Chest radiographs (X-rays). Chest radiographs allow your veterinarian to examine the lungs and measure the size andshape of the heart. Dilated cardiomyopathy usually causes obvious enlargement of the heart, particularly the left side.

Electrocardiogram (ECG).Electrocardiogram (ECG). This is an assessment based onthe electrical activity of the heart. It allows yourveterinarian to accurately determine heart rate and todiagnose any abnormal rhythms.

Ultrasound examination (echocardiogram).Ultrasound examination (echocardiogram). This gives themost accurate determination of each heart chamber's sizeand thickness of the heart walls. Measurements of theheart contractions can be taken to evaluate the heart'spumping efficiency.

Holter monitor.Holter monitor. This is a portable, wearable device yourdog wears for 24 hours. A Holter monitor records the heartrhythm and see if there is a consistency to arrhythmias orabnormal heart beats.

Can my dog be treated without these tests?Can my dog be treated without these tests?

The combination of many of these tests gives your veterinarian the best evaluation of heart function. An accurate diagnosisprovides a much better guide to the severity of the disease and the extent of treatment that is necessary. Treatment of thecondition without proper diagnosis can potentially be fatal.

What is the treatment?What is the treatment?

There are several drugs used to treat the symptoms of dilated cardiomyopathy. Initial stabilization depends upon the useof:

Diuretics.Diuretics. These are drugs that stimulate the kidneys to remove excess fluid from the body. Furosemide and spironolactoneare two commonly used diuretics.

Angiotensin converting enzyme (ACE) inhibitors.Angiotensin converting enzyme (ACE) inhibitors. ACE-inhibitors work by lowering blood pressure and reducing the after-load or resistance to blood flowing out of the heart. ACE-inhibitors are the only drugs proven to extend life expectancy inboth people and dogs. Enalapril and benazepril are commonly used ACE-inhibitors in dogs, although new ACE-inhibitorscontinue to be developed and may prove useful for treating dogs.

Cardiac glycosides.Cardiac glycosides. These drugs improve heart function in several ways. They slow the heart rate and strengthen heartcontractions, so the blood is pumped more effectively. Digoxin is the most common digitalis glycoside used in veterinarymedicine. Because of the potential for toxic side-effects., the dose must be closely regulated and monitored throughroutine blood tests and ECG analyses.

Vasodilators.Vasodilators. These drugs dilate the arteries or veins of the body so that the heart does not have to work so hard to pumpblood to the body. ACE-inhibitors have vasodilator activity, and are the vasodilators used most widely in the therapy ofcongestive heart failure associated with DCM.

Bronchodilators.Bronchodilators. These drugs make breathing easier for dogs experiencing DCM. Bronchodilators include theophylline andaminophylline.

Pimobendan.Pimobendan. This drug lowers the pressure in the arteries and veins and improves the heart muscle strength, thereforeincreasing blood flow to the body. Pimobendan does not appear to induce arrhythmias.

Anti-arrhythmic drugsAnti-arrhythmic drugs. Many dogs with DCM have arrhythmias. If arrhythmias are not controlled with the abovemedications, antiarrhythmic drugs may be added in cautiously. Two main classes are beta-blockers (such as atenolol,sotalol, carvedilol) and calcium channel blockers (such as diltiazem). Other types of antiarrhythmic drugs used long termcan include procainamide, mexiletine, and amiodarone.

Based on your dog’s condition, your veterinarian will choose the appropriate medication(s) to treat your dog with.

As a result of all these tests and treatment, will my dog will live much longer?As a result of all these tests and treatment, will my dog will live much longer?

Unfortunately, there are no guarantees in medicine. DCM is a serious disease that must be accurately diagnosed andaggressively treated. Some dogs with DCM do well with treatment for a period of time; however, some dogs will neverresume a normal lifestyle. Doberman Pinschers have been shown to live as little as 3 months once diagnosed. Other dogshave been known to live between 6-24 months if they respond well to treatment.

"DCM is a serious disease that must be accurately diagnosed and aggressively treated."

Dogs that have developed clinical signs of heart failure have a worse prognosis than those that are put onto cardiacmedication in the early stages of the disease. Your veterinarian will guide you through the diagnostic and treatment processto ensure that your pet receives the highest standard of care.

Contributors: Ryan Llera, BSc, DVM; Ernest Ward, DVM© Copyright 2019 LifeLearn Inc. Used and/or modified with permission under license.