Dilated Cardiomyopathy

Also know as: DCM — Congestive Cardiomyopathy

Introduction

This disease is the most common form of cardiomyopathy in dogs.

Dilated cardiomyopathy (DCM) is characterized by progressive systolic dysfunction (loss of myocardial contractile function) and ventricular dilation (eccentric hypertrophy).

Signalment

Giant and large breeds (e.g. Doberman Pinscher, Irish Wolfhound and Great Dane) are most at risk.

Prevalence increases with age and the typical age at diagnosis is 6-8 years.

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

• 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.

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

Dogs:

Poor: Most breeds survive 6-12 months and in Dobermans and Boxers the prognosis is grave.

Cats:

Good: When cardiomyopathy results from taurine deficiency, but grave in other causes of cardiomyopathy.

Dilated Cardiomyopathy Learning Resources
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Flashcards Test your knowledge using flashcard type questions	Myocardial Pathology Flashcards

References

Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company

Ettinger, S.J, Feldman, E.C. (2005) Textbook of Veterinary Internal Medicine (6th edition, volume 2) W.B. Saunders Company

Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition) Mosby Elsevier

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