Canine Cardiomyopathy - An Update for the MCOA
Authors: Taylor C. Parker, Sarah Bell, DVM, MS, DACVIM, John R. Parker, MD
Cardiomyopathy is defined as degeneration of the heart muscle. As a result of this degeneration, the muscle becomes thinner, particularly the thick muscle wall of the left ventricle. The pressure of the blood inside the heart causes these thin walls to stretch resulting in a much larger heart. This condition is described as dilated cardiomyopathy (DCM).
Dilated cardiomyopathy is the most common cause of heart failure in certain large breeds of dogs. These include Boxer Dogs, Doberman Pinschers, Great Danes, Irish Wolfhounds, and Saint Bernards. Occasionally, German Shepherd Dogs and some medium-sized breeds such as Cocker Spaniels, English Springer Spaniels, and Portuguese Water Dogs are also affected. Small breeds rarely develop DCM. It is more often diagnosed in males than females.
Dilated cardiomyopathy may have a sudden onset of clinical signs; however, the disease has actually been developing slowly and subtly. Some dogs may develop severe congestive heart failure (CHF) in only a few hours. Rapid, heavy breathing, a blue tongue, excessive drooling, or collapse may be the first signs.
Signs may be sudden or progressive in onset. Annual checkups with your veterinarian may lead to a diagnosis of heart problems before clinical signs are present (this is the best time to diagnose a problem). Signs can include:
Before a diagnosis of dilated cardiomyopathy is made, several tests are performed to assess different aspects of heart function.
Auscultation. Listening to the chest with a stethoscope allows your veterinarian to identify murmurs due to the improper closure of heart valves. The murmur's location and intensity help determine its significance. Heart rhythm is also assessed during auscultation, and if there are concerns, your veterinarian may simultaneously palpate or feel the pulse to determine its strength and rhythm. Auscultation is also used to evaluate the lungs.
Blood and urine tests. Liver and kidney function can be a concern, because these organs are often impaired in heart disease.
ProBNP. This is a blood test that measures a specific protein level in the body that changes with structural changes of the heart and heart disease. It is not as reliable a test as some of the others outlined below to indicate the source or an accurate assessment of the severity of the condition.
Chest radiographs (X-rays). Chest radiographs allow your veterinarian to examine the lungs and measure the size and shape of the heart. Dilated cardiomyopathy usually causes obvious enlargement of the heart, particularly the left side.radiograph_vs_illustration_updated2017-01
Electrocardiogram (ECG). This is an assessment based on the electrical activity of the heart. It allows your veterinarian to accurately determine heart rate and to diagnose any abnormal rhythms.
Ultrasound examination (echocardiogram). This gives the most accurate determination of each heart chamber's size and thickness of the heart walls. Measurements of the heart contractions can be taken to evaluate the heart's pumping efficiency.
Holter monitor. This is a portable, wearable device your dog wears for 24 hours. A Holter monitor records the heart rhythm and see if there is a consistency to arrhythmias or abnormal heart beats.
The combination of many of these tests gives your veterinarian the best evaluation of heart function. An accurate diagnosis provides a much better guide to the severity of the disease and the extent of treatment that is necessary. Treatment of the condition without proper diagnosis can potentially be fatal.
There are several drugs used to treat the symptoms of dilated cardiomyopathy. Initial stabilization depends upon the use of:
Diuretics. These are drugs that stimulate the kidneys to remove excess fluid from the body. Furosemide and spironolactone are two commonly used diuretics.
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 in both people and dogs. Enalapril and benazepril are commonly used ACE-inhibitors in dogs, although new ACE-inhibitors continue to be developed and may prove useful for treating dogs.
Cardiac glycosides. These drugs improve heart function in several ways. They slow the heart rate and strengthen heart contractions, so the blood is pumped more effectively. Digoxin is the most common digitalis glycoside used in veterinary medicine. Because of the potential for toxic side-effects., the dose must be closely regulated and monitored through routine blood tests and ECG analyses.
Vasodilators. These drugs dilate the arteries or veins of the body so that the heart does not have to work so hard to pump blood to the body. ACE-inhibitors have vasodilator activity, and are the vasodilators used most widely in the therapy of congestive heart failure associated with DCM.
Bronchodilators. These drugs make breathing easier for dogs experiencing DCM. Bronchodilators include theophylline and aminophylline.
Pimobendan. This drug lowers the pressure in the arteries and veins and improves the heart muscle strength, therefore increasing blood flow to the body. Pimobendan does not appear to induce arrhythmias.
Anti-arrhythmic drugs. Many dogs with DCM have arrhythmias. If arrhythmias are not controlled with the above medications, 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 term can include procainamide, mexiletine, and amiodarone.
Based on your dog’s condition, your veterinarian will choose the appropriate medication(s) to treat your dog with.
Unfortunately, there are no guarantees in medicine. DCM is a serious disease that must be accurately diagnosed and aggressively treated. Some dogs with DCM do well with treatment for a period of time; however, some dogs will never resume a normal lifestyle. Doberman Pinschers have been shown to live as little as 3 months once diagnosed. Other dogs have 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 cardiac medication in the early stages of the disease. Your veterinarian will guide you through the diagnostic and treatment process to ensure that your pet receives the highest standard of care.
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