What is Dilated Cardiomyopathy?
Dilated Cardiomyopathy (DCM) is a disease process that affects the myocardium of the heart. The heart muscle overtime becomes dilated or stretched and can no longer pump blood efficiently. This disease is characterized by myocardial failure with and increase in end systolic volume with a decrease in shortening fraction. There is no known cause for primary DCM and there are several causes of secondary DCM such as taurine deficiency, carnitine deficiency, infectious myocaritis, adriamycin-induced, and inherited DCM in Portuguese water dogs and Irish wolfhounds. Primary or idiopathic DCM occurs most commonly in middle-aged to older large breed dogs such as Doberman Pinschers, Great Danes, Newfoundlands, Boxers and Irish Wolfhounds. The systolic contractile failure of the heart leads to left and/or right ventricular eccentric hypertrophy. The hemodynamic consequences results from volume overload of the left and/or right sides of heart with the increasing preload overtime. Mitral and tricuspid valve can become insufficient as well as the annulus is stretched and valve leaflets no longer meet. Eventually, left or right-sided congestive heart failure or both can result. In addition, ventricular and atrial arrhythmias may be seen due to myocardial failure, increasing the risk for sudden death. Auscultation can reveal a systolic murmur of mitral or tricuspid valve regurgitation or a gallop rhythm from the third heart sound being heard as blood fills turbulently into a very large ventricle. Arrhythmias such as atrial fibrillation or other atrial or ventricular arrhythmias may be heard.
Clinical signs of DCM are usually not observed by the owner until the animal is in congestive heart failure secondary to preload overload with concurrent mitral or tricuspid valve regurgitation. Left sided heart failure is the most commonly seen as the left side of the heart is most commonly affected. Clinical signs of left heart failure may be subtle such as increased respiratory rate at rest to mild decreases in activity or exercise intolerance. Other clinical signs may include coughing, not sleeping through the night, coughing more at night or decreased appetite. Signs may progress to coughing up pink-tinted foam to fulminate respiratory distress. Clinical signs of right heart failure secondary may include weight gain, abdominal distension, inappetance, difficulty breathing, exercise intolerance and increased lethargy. A way for owners to monitor to their pet at home for early signs of congestive heart failure is to count the resting respiratory rate. This can be done when the pet is sound asleep and the number of breathes per 15 seconds is counted. This number is then multiplied by 4. If this number is consistently above 40 when the pet is sound asleep, this may be an early sign of congestive heart failure and the veterinarian should be contacted. Other signs of DCM may be syncope or sudden death due to atrial or ventricular arrhythmias.
Treatment for this disease is only medical management. A general treatment protocol is the institution of a loop diuretic such as furosemide and an angiotensin converting enzyme (ACE) inhibitor when these patients present in heart failure. Often an agent that increases contractility (positive inotrope) is prescribed. Pimobendan, an inodilator may be used to improve contractility and for vasodilation. Digoxin, a cardiac glyocoside, may also be advocated for its effects on contractility, vagal tone, and baroreceptor activity. In severe or recurrent cases of heart failure, diuretics with effects in the distal nephron, additional positive inotropes, and other afterload reducers may be added for treatment. Finally, β-blockers or calcium channel blockers may be added in cases of tachycardia and other arrhythmias.
Animals diagnosed with symptomatic DCM should have thoracic radiographs, echocardiograms and ECG recordings performed every 3-4 months. Holter monitor, 24 hour ECG monitoring may be recommended in animals with arrhythmias noted from other diagnostic tests. Special testing for taurine levels may be indicated in animals suspected of dilated cardiomyopathy secondary to nutritional deficiencies.