Dilated cardiomyopathy

What it is

Dilated cardiomyopathy (DCM) is a disease of the heart muscle in which the ventricles, above all the left, dilate and contract poorly (reduced systolic function). It has a long preclinical (occult) phase in which the only changes are ventricular arrhythmias or mild dilation, followed by an overt phase with congestive heart failure. In most breeds it is considered hereditary. Secondary forms with a similar picture exist: taurine deficiency (described in some breeds and associated with certain diets), tachycardia-induced cardiomyopathy and doxorubicin toxicity.

Who it affects

Large and giant breeds, usually middle-aged to older: Dobermann (very high prevalence), Great Dane, Irish wolfhound, boxer (in which ventricular arrhythmias dominate), Newfoundland and others. Cocker spaniels and some retrievers can develop taurine-responsive forms.

Anatomy involved

• Ventricles: thin walls and dilated chambers, left more than right; the atria dilate secondarily.
• Atrioventricular valves: the stretched annulus prevents the leaflets from closing, causing functional mitral and tricuspid regurgitation without primary valve lesions.
• Conduction: ventricular premature complexes and ventricular tachycardia (Dobermann, boxer) or atrial fibrillation (giant breeds).
• Lungs and serosal cavities: left-sided failure causes pulmonary oedema; right-sided failure causes ascites and pleural effusion.

Clinical signs

In the occult phase there may be no signs, or only syncope; sudden death can be the first event, especially in Dobermanns. In the overt phase: exercise intolerance, weakness, weight loss, tachypnoea, cough, dyspnoea, abdominal distension from ascites, weak and irregular pulse, soft systolic murmur or gallop sound.

Diagnosis

• Echocardiography: dilated left ventricle with reduced fractional shortening and ejection fraction; it is the key test.
• Holter monitoring (24 h): detects ventricular arrhythmias in the occult phase; together with annual echocardiography it is the screening method for Dobermanns.
• Electrocardiogram: atrial fibrillation, ventricular premature complexes.
• Thoracic radiographs: generalised cardiomegaly and signs of congestion (pulmonary oedema, pleural effusion).
• Biomarkers: NT-proBNP and cardiac troponin I support screening. Plasma or whole-blood taurine is measured when diet or breed suggests deficiency.

Treatment

In the occult phase, pimobendan delays the onset of heart failure in Dobermanns, and significant ventricular arrhythmias are treated (sotalol, mexiletine, amiodarone). In heart failure: pimobendan, furosemide, an ACE inhibitor and spironolactone; heart rate control in atrial fibrillation (diltiazem, digoxin). Dietary change and taurine supplementation can reverse taurine-related cases. The prognosis of overt hereditary DCM is poor, especially in Dobermanns.

In the cat

Until the late 1980s DCM was a common heart disease in cats. In 1987 most cases were shown to be caused by taurine deficiency, an amino acid that is essential for the cat because it synthesises very little, and supplementation reversed the disease. Since commercial cat foods have been supplemented with taurine, feline DCM has been uncommon. Today it is seen mainly as an idiopathic form, as the end stage of other cardiomyopathies (for example hypertrophic cardiomyopathy progressing to systolic dysfunction) and occasionally in cats on taurine-deficient home-made or vegetarian diets.

The signs are those of feline heart failure: tachypnoea, dyspnoea from pleural effusion or pulmonary oedema, lethargy, anorexia and hypothermia; it can also present with arterial thromboembolism. Echocardiography shows a dilated, hypokinetic left ventricle with large atria. Besides treatment of heart failure (furosemide, pimobendan, an ACE inhibitor and thromboprophylaxis with clopidogrel), taurine is measured and supplemented while results are awaited. Cats with taurine deficiency can improve within weeks; in idiopathic forms the prognosis is poor.

Key studies in the cat

• Pion et al. (1987) found low plasma taurine with echocardiographic myocardial failure in 21 cats fed commercial foods and in 2 of 11 cats fed a diet marginally low in taurine for 4 years. Taurine supplementation normalised left ventricular function in both groups. This study established the link between taurine deficiency and feline DCM.
• Pion et al. (1992), prospective study of 37 cats with DCM. Most had low plasma taurine and a diet history compatible with deficiency, and their findings matched those of 33 earlier cases reviewed retrospectively. With taurine supplementation 38% died in the first 30 days, but 59% improved markedly, clinically and on echocardiography, and stayed stable after the other drugs were withdrawn. One-year survival was 58%, compared with 13% in the historical group.
• Hambrook and Bennett (2012), retrospective study of 32 cats with DCM that did not respond to taurine, all on furosemide, taurine and an ACE inhibitor. Median survival was 49 days with pimobendan and 12 days without. Hypothermia and fractional shortening below 20% indicated a poor prognosis. It is small and not randomised.