Dilated Cardiomyopathy

Also know as: DCM — Congestive Cardiomyopathy

Introduction

Dilated cardiomyopathy (DCM) is characterized by progressive systolic dysfunction (loss of myocardial contractile function) and ventricular dilation (eccentric hypertrophy). This is the most common form of cardiomyopathy in dogs. There are breed predispositions and familial distributions, suggesting an underlying causal genetic mutation. An autosomal dominant inheritance pattern with incomplete and age-dependent penetrance has been reported.

Signalment

Giant and large breeds are most at risk. Predisposed breeds include: Irish Wolfhound, Great Dane, Newfoundland, Leonberger, St. Bernard, Dobermann Pinscher, Boxer, Dogue de Bordeaux and the Portuguese Water dog.

Prevalence increases with age and the typical age at diagnosis is 6-8 years. A severe juvenile form is recognized in the Portuguese Water dog.

Male dogs are more frequently affected than females, particularly in Doberman Pinschers.

Clinical Signs

The natural history of the disease is described in two phases.

The asymptomatic (occult) phase is when no clinical signs are apparent, but there may be structural, functional or electrical abnormalities. These include increased left ventricular and left atrial internal diameter, reduced myocardial contractility and ventricular premature contractions. The duration of this occult phase is variable and can last from months to years.

The overt clinical phase is when clinical signs, such as congestive heart failure (CHF), syncope and exercise intolerance, develop. Arrhythmias are common in this stage.

Diagnosis

History and Physical Examination

Asymptomatic (occult) phase

• Physical examination may be unremarkable
• Soft, systolic heart murmur
• Arrhythmia with pulse deficits

Overt clinical phase

• History may include: exercise intolerance, lethargy, anorexia, muscle wasting (cardiac cachexia), syncope, abdominal distension (ascites)
• Systolic heart murmur
• Arrhythmia with pulse deficits
• Increased respiratory rate and effort, increased bronchovesicular sounds, pulmonary crackles (left-sided congestive heart failure)
• Weakness
• Jugular venous distension and/or jugular pulsation, hepatomegaly, ascites (right-sided congestive heart failure)

Thoracic Radiographs

Radiographs are performed in the clinical phase to diagnose congestive heart failure and monitor response to treatment.

Electrocardiography (ECG)

A normal ECG does not rule out the presence of DCM, but is the test of choice for detecting arrhythmias. In the occult phase, arrhythmias may be the first indication of disease. The following are associated with a high index of suspicion for occult DCM:

• One or more VPC in an at-risk breed
• Atrial fibrillation appears to be an early sign of disease in Irish Wolfhounds, whereas other breeds develop atrial fibrillation in advanced disease.
• 24 hour Holter ECG recording:
  • Greater than 100 VPCs is suggestive of DCM or ARVC
  • Between 50 and 100 VPCs in an at-risk breed is suspicious. Holter recording should be repeated in 3-6 months.

During the clinical phase, the following may be detected:

• Occasional VPCs or superventricular premature complexes (SVPCs)
• Ventricular tachycardia
• Atrial fibrillation
• Left bundle branch block morphology

Echocardiography

Echocardiographic changes may include left ventricular dilation (increased left ventricular end-diastolic diameter), systolic dysfunction (reduced myocardial contractility), mitral regurgitation secondary to dilation of the mitral annulus and atrial enlargement.

Blood Tests

Changes on serum biochemistry analysis may include azotemia, this is common in dogs receiving diuretic therapy and is usually pre-renal in nature. Electrolyte abnormalities, such as mild hyponatraemia and hypokalaemia, are also common in dogs with congestive heart failure.

Cardiac biomarkers, NT-proBNP and cardiac troponin I (cTnI), may be helpful in detecting DCM. Troponin I may be elevated in cardiac disease and will also be elevated as a consequence of haemodynamically significant arrhythmias. Plasma concentrations of NT-proBNP may be elevated in pre-clinical disease and increase with severity. It is important to note that neither biomarker is specific to DCM and merely indicates the heart is under stress/stretch (NT-proBNP) or that there is damage to cardiomyocytes (cTnI).

Taurine deficiency may contribute to a DCM phenotype in the American Cocker Spaniel, Dalmatian, Labrador Retriever and Golden Retriever. Most dogs with taurine-deficient DCM will have plasma taurine levels <25nmol/L. This is important to recognize, as in these cases cardiac function and prognosis can be substantially improved by taurine supplementation.

Treatment and Control

Asymptomatic (Ocult) phase

Pimobendan has recently been demonstrated to prolong the time to onset of clinical signs and extend survival in Dobermans with asymptomatic (occult) DCM.

Clinical phase

In the clinical phase, treatment involves the use of diuretics, ACE inhibitors and positive inotropes. Antiarrhythmic drugs may also be necessary.

Prognosis

Prognosis from the onset of occult DCM is variable and can be years. Once clinical signs have developed, the prognosis is poor with a median survival time of 3-6 month depending on the breed. Death is usually due to refractory congestive heart failure or sudden death. The prevalence of sudden death is particularly high in Doberman Pinschers with DCM (30-50%).

Dilated Cardiomyopathy Learning Resources
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References

Tilley, L.P, Smith, F.W.K., Oyama, M.A, Sleeper, M.M (2008) Manual of Canine and Feline Cardiology (Fourth Edition) W.B. Saunders Company

Watson, P.. (2012) Efficacy of Pimobendan in the Prevention of Congestive Heart Failure or Sudden Death in Doberman Pinschers with Preclinical Dilated Cardiomyopathy (The PROTECT Study). Journal of Veterinary Internal Medicine 26(6):

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