Dilated Cardiomyopathy in Dogs (DCM): Symptoms, Diagnosis and Treatment

What is dilated cardiomyopathy?

Dilated cardiomyopathy (DCM) is a primary disease of the heart muscle characterised by ventricular dilation (especially the left ventricle) and reduced systolic function (pumping ability). The heart becomes large and weak, leading to congestive heart failure and/or potentially fatal arrhythmias.

Most affected breeds

• Dobermann: the most affected breed; an estimated 50–60 % will develop DCM during their lifetime. High rate of sudden cardiac death from ventricular fibrillation.
• Boxer: arrhythmogenic right ventricular cardiomyopathy (ARVC) with distinct features.
• Great Dane, Newfoundland, Irish Wolfhound.
• Golden Retriever, Cocker Spaniel: possible taurine-associated forms, particularly in dogs on grain-free or legume-heavy diets.

The hidden phase: the greatest danger

DCM has a long occult (subclinical) phase (years) during which the heart is already enlarged but the dog shows no outward signs. In Dobermanns, 30–40 % of dogs in the occult phase die suddenly before developing clinical symptoms. This is why annual Holter + echocardiography screening in predisposed breeds is so important.

Symptoms

• Occult phase: no symptoms (but Holter-detectable arrhythmias and echocardiographic dilation present).
• Early clinical phase: exercise intolerance, nocturnal cough, rapid fatigue.
• Left-sided failure: cough, dyspnoea, tachypnoea, orthopnoea.
• Right-sided failure: ascites, limb oedema.
• Syncope, visible arrhythmias.
• Sudden cardiac death without prior warning (especially in Dobermanns).

Diagnosis

• Echocardiography: dilated left ventricle, reduced fractional shortening (<20–25 % in large breeds), depressed systolic function.
• 24-hour Holter: detects ventricular tachyarrhythmias. In Dobermanns, >50 VPCs/24h is a diagnostic criterion even before visible cardiac dilation on echo.
• Thoracic radiographs: cardiomegaly, pulmonary oedema.
• Biomarkers: cardiac troponin I (cTnI), NT-proBNP — elevated in active DCM.

Treatment

Occult phase

The PROTECT study (2012) demonstrated that pimobendan started in the occult phase (when echocardiography shows dilation) delays onset of heart failure by ~9 months in Dobermanns. It is now the standard of care in the occult phase with cardiac dilation.

Clinical phase (heart failure)

• Pimobendan: positive inotrope + vasodilator. First-line at all clinical stages.
• Furosemide: loop diuretic for pulmonary oedema and ascites.
• ACE inhibitors (benazepril, enalapril): reduce preload.
• Antiarrhythmics (sotalol, mexiletine, amiodarone): for ventricular tachyarrhythmias in Dobermanns and Boxers.
• Low-sodium diet. Taurine and L-carnitine supplementation in breeds with possible deficiency.

Screening in predisposed breeds

Veterinary cardiology associations recommend for Dobermanns an annual Holter + echocardiogram from 3–4 years of age to detect the disease in the occult phase when treatment is most effective. Similar protocols exist for Boxers and Great Danes.