Canis ISSN: 2398-2942

Heart: dilated cardiomyopathy (DCM)

Synonym(s): DCM

Contributor(s): Serena Brownlie, Bruce Keene, Mark Rishniw, Simon Swift, Ruth Willis, Liz Bode

Introduction

  • Common acquired disease, especially large and giant breeds in middle age, some spaniels.
  • Cause: systolic (contractility) failure of left ventricle in classic form, occasionally Arrhythmogenic right ventricular cardiomyopathy (ARVC) form seen.
  • Signs: exercise intolerance, weight loss, dyspnea, cough, arrhythmia. The occult/pre-clinical phase is not associated with clinical signs.
  • Diagnosis: ECG, radiography, echocardiography.
  • Treatment: manage cardiac failure, support myocardial function and control arrhythmias.
  • Prognosis: guarded, survival usually months rather than years but varies with breed.
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Pathogenesis

Etiology

Undefined

Genetic

  • Pure bred dogs are over-represented implying a familial or genetic component.
  • May be autosomal dominant inheritance in some Newfoundland, Boxers and Irish Wolfhound families.
  • Boxer ARVC may be associated with abnormal ryanodine function secondary to calstabin.

Metabolic

  • L-carnitine deficiency Carnitine deficiency within the cardiomyocytes (some Boxers); and possibly other breeds may respond to carnitine supplementation.
  • Carnitine transports long chain fatty acids across mitochondral membranes → energy for myocardium.
  • Deficiency may exist in up to 40% of dogs with cardiomyopathy but most of these have normal plasma carnitine levels.
  • Can only be assessed by endocardial biopsy so treatment may be initiated on a trial basis however the supplement may be expensive.
  • Taurine Taurine is the most abundant free amino acid in the heart.
  • Normal plasma level 63 nmol/l (range 44-224 nmol/l).
  • Taurine deficiency Taurine deficiency most likely to occur in dogs on vegetarian diet, but also seen in some dogs on normal proprietary diets.
  • Low plasma taurine levels recorded in Golden Retrievers Retriever: Golden , American Cocker Spaniels American Cocker Spaniel and Newfoundlands Newfoundland with cardiomyopathy (<60 nmol/l).
  • American Cocker Spaniels American Cocker Spaniel may be taurine Taurine and carnitine deficient. Respond to supplementation.

Toxic

Physical

Other

  • Toxoplasma gondii Toxoplasma gondii , parvovirus Canine parvovirus , borrelia burgdorferi Borrelia burgdorferi.
  • Lymphoma Lymphoma infiltration of myocardium.
  • Tachycardia - supraventricular and ventricular tachycardias can result in a cardiomyopathy if uncontrolled.
    Dilated cardiomyopathy is by definition an idiopathic disease. In cases where an underlying cause has been identified, they should be titled according to the cause, eg tachycardiomyopathy, infiltrative cardiomyopathy.

Predisposing factors

General

  • Breed.
  • Family.

Factors which worsen congestive failure

  • Exertion.
  • Stress.
  • Sudden increase in salt intake.
  • Development of an arrhythmia, eg atrial fibrillation.

Specific

  • Familial basis (breed).
  • Age.

Pathophysiology

  • Metabolic or biochemical lesion affecting cardiac myocyte → failure of contractility/increased work for myocardium → :
    • Increased end-diastolic left ventricular volume and pressure → dilation and non-compensatory eccentric hypertrophy of left ventricle → compromised papillary muscle function and passive dilation of atrioventricular annulus causing mitral regurgitation → increased left atrial pressures → left atrial enlargement → increased pulmonary venous (capillary wedge) pressure and pulmonary edema.
    • Poor cardiac output (CO) due to decreased stroke volume (SV) → increased sympathetic drive → increased heart rate (HR), especially if atrial fibrillation present.
    • Reduced cardiac output with arteriolar constriction to increase vascular resistance (mediated through sympathetic tone, active renin-angiotension-aldosterone system (RAAS) and increased vasopressin release); also venoconstriction → increased venous return → increased stretch of myocardium (preload).
    • Arteriolar constriction increases afterload (left ventricle wall stress) and myocardial workload → further myocardial dysfunction, further dilation.
  • Signs of poor systolic function and vasoconstricted state:
    • Poor pulse.
    • Pale mucous membranes.
    • Delayed capillary refill time.
    • Cold extremities, etc.
  • Left atrial stretch may → supraventricular dysrhythmias, eg atrial fibrillation Heart: atrial fibrillation.
  • Increased myocardial wall stress, poor coronary perfusion of myocardium and diseased myocytes may result in ventricular dysrhythmias Heart: dysrhythmia.
  • Right-sided failure may also result due to myocardial involvement or secondary to the left congestive failure → ascites, hepatomegaly, hepatojugular reflex, pleural effusion Pleural: effusion , pericardial effusion Pericardial disease.
  • Salt and water retention by kidney due to poor renal perfusion → increased sympathetic drive and activation of the RAAS (increased aldosterone) leads to increased venous return (preload) and venous pressure, further stretch of myocardium and predisposition to edema.

Timecourse

  • Weeks-months from onset of signs.
  • Dobermann: rapid, usually <6 weeks survival after diagnosis without ACE inhibition; sudden death common 50% dead in 3 months, 10% live >1 year. Survival may be improved by addition of pimobendan Pimobendan to medication regime.
  • Boxer: variable, may be sudden death from dysrhythmia, may present with congestive heart failure Heart: congestive heart failure.
  • Irish Wolfhound: variable dysrhythmias and progressive cardiac dilatation over several years or sudden death.

Other breeds

  • Survival depends on breed.
  • Cocker Spaniels may survive >12 months.
  • Giant breeds may survive for months to years after diagnosis.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Sanderson S L (2006) Taurine and carnitine in canine cardiomyopathy. Vet Clin North Am Small Anim Pract 36 (6), 1325-1343, vii-viii PubMed.
  • Tidholm A, Jonsson L (2005) Histologic characterization of canine dilated cardiomyopathy. Vet Pathol 42 (1), 1-8 PubMed.
  • O'Grady M R & O'Sullivan (2004) Dilated cardiomyopathy: an update. Vet Clin North Am Small Anim Pract 34 (5), 1187-1207 PubMed.
  • Fuentes V L, Corcoran B, French A, Schober K E, Kleeman R, Justus C (2002) A double-blind, randomized, placebo-controlled study of pimobendan in dogs with dilated cardiomyoathy. J Vet Intern Med 16 (3), 255-261 PubMed.
  • Calvert C A & Wall M (2001) Effects of severity of myocardial failure on heart rate variability in Doberman Pinschers with and without echocardiographic evidence of dilated cardiomyopathy. JAVMA 219 (8), 1084-1088 VetMedResource.
  • Meurs K M, Miller M W & Wright N A (2001) Clinical features of dilated cardiomyopathy in Great Danes with results of a pedigree analysis - 17 cases (1990-2000). JAVMA 218 (5), 729-732 PubMed.
  • Calvert C A, Pickus C W, Jacobs G J & Brown J (1997) Signalment survival and prognostic factors in Doberman Pinschers with endstage cardiomyopathy. JVIM 11 (6), 323-326 PubMed.
  • Kittleson M D, Keene B et al (1997) Results of the multicenter spaniel trial - Taurine and L-carnitine responsive dilated cardiomyopathy in American cocker spaniels with decreased plasma taurine concentration. JVIM 11 (4), 204-211 PubMed.
  • Tidholm A, Svensson H & Sylven C (1997) Survival and prognostic factors in 189 dogs with dilated cardiomyopathy. JAAHA 33 (4), 364-368 PubMed.
  • Tidholm A, Svensson H & Sylven C (1997) A retrospective study of 189 dogs with dilated cardiomyopathy. JAAHA 33 (6), 544-550 PubMed.
  • Kramer G K, Kittleson M D, Fox P R et al (1995) Plasma taurine concentrations in normal dogs and dogs with heart disease. JVIM 9 (4), 253-258 PubMed.
  • Keene B W, Panciera D P et al (1991) Myocardial L-carnitine deficiency in a family of dogs with dilated cardiomyopathy. JAVMA 198 (4), 647-650 PubMed.

Other sources of information

  • For information on Genetic Testing Providers (labs), genetic tests, and tests by breed, visit International Partnership for Dogs: https://dogwellnet.com/.
  • For a list of DNA tests available for certain breeds worldwide, visit Kennel Club Worldwide DNA tests: https://www.thekennelclub.org.uk/health/for-breeders/dna-testing-simple-inherited-disorders/worldwide-dna-tests/.
  • Willis R, Dukes-McEwan J et al (2003) The role of taurine in dilated cardiomyopathy in Newfoundland dogs. VCS Proceedings, Spring meeting, Birmingham.
  • Lombard C W et al (2000) Clinical experience with pimobendan. VCS Proceedings, Spring meeting, Birmingham.
  • Luis Fuentes V, Kleeman R et al (1998) The effect of a novel inodilator pimobendan on heart failure status in Cocker Spaniels and Dobermanns with idiopathic dilated cardiomyopathy. Proc BSAVA Congress. p 284.


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