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Heart: restrictive cardiomyopathy (RCM)

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Synonym(s): Unclassified cardiomyopathy


Introduction

  • Cause: restrictive cardiomyopathy (RCM) is intrinsic pathology in the heart muscle wall or the endocardial surface that results in diastolic dysfunction (impaired relaxation/filling) sometimes secondary to endomycardial fibrosis.
  • Signs: usually vague chronic course of weight loss, anorexia, lethargy, +/- dyspnea if there is congestive heart failure. Many cats with RCM can have a completely normal cardiac auscultation. If there is an ausculation abnormality, the most common is a murmur (36%), a gallop rhythm (23%) or an arrhythmia (14%).
  • Diagnosis: radiography, echocardiography, NT-proBNP is helpful for moderate to severe cases.
  • Treatment: depends on the stage of the disease. It should be noted that there is not currently a consensus amongst cardiologists on therapy for cats with RCM. Majority of cardiologists would recommend the following:
    • Mild asymptomatic cases - no therapy.
    • Asymptomatic but with left atrial enlargement +/- spontaneous contrast - clopidogrel +/- aspirin.
    • Cases with active or historical congestive heart failure (CHF) - diuretics, vasodilators.
    • Cases with active or historical aortic thromboembolism (ATE) - analgesia, anti-thrombotic therapy (thrombolytic therapy is not currently recommended by most cardiologists), clopidogrel +/- aspirin, physical therapy.
  • Prognosis: generally poor, thromboembolism is a risk in many cases.

Pathogenesis

Etiology

  • The etiology in cats is predominantly unknown (about 50% of cases in humans are also of unknown or idiopathic causes).
  • Theories that exist include:
    • Activated eosinophils have been shown to cause cardiac damage and some forms of endomyocarditis in humans have been associated with hypereosinophilia. A very small number of cats with RCM have had hypereosinophilia Hypereosinophilia but there currently is no direct cause/effect that has been established and eosinophils are rarely noted in feline heart muscle cells that have had histologic evaluation and a diagnosis of RCM.
    • Viral or immune mediated destruction of the endomyocardium - endomycarditis Endomyocardial disease (inflammation in the heart) has been demonstrated in a very small number of cases of feline RCM. Some parvoviral material has been isolated in some cases, but again, cause and effect has not been established. A recent paper that looked at 41 cases of RCM in Japan failed to show any viral material or signs of endomyocarditis.

Pathophysiology

  • Endocardial, subendocardial or myocardial fibrosis  →  prevents stretch (compliance), of left ventricle and ventricular filling.
  • Abnormal blood flows  →  predispose to formation of thromboemboli Thromboembolism: aorta.
  • Lack of compliance of left ventricle and reduced ventricular filling  →   left atrial dilation, decreased preload, decreased cardiac output and increased pulmonary venous pressure  →  pulmonary edema and pleural effusion (seen commonly with left-sided failure in cats).
  • Turbulence  →  damages cardiac endothelium  →  endocardial collagen induces platelet adhesion and aggregation, extrinsic pathway activation Hemostatic disorders: acquired.
  • Circulation of blood through heart is abnormal  →  areas of sluggish flow allow aggregation of platelets particularly in dilated left atrium.
  • Higher levels of serotonin in felines due to larger platelets than dogs and humans, felines more sensitive to effects of serotonin  →  higher susceptibility to aggregation.

Timecourse

  • The largest and most recent study in cats with RCM presenting with clinical signs (some cats had more than 1 presenting sign) had a median survival time of 69 days. Prognosis again depends upon presenting clinical signs:
    • Cats with CHF or ATE averaged 64 days.
    • Asymptomatic cats averaged 466 days.

Diagnosis

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Treatment

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Chetboul V Passavin P, Trehiou-Sechi E, Gouni V, Poissonnier C, Pouchelon J L, Desquilbet L (2019) Clinical, epidemiological and echocardiographic features and prognostic factors in cats with restrictive cardiomyopathy: A retrospective study of 92 cases (2001-2015). J Vet Intern Med 33(3), 1222-1231 PubMed.
  • Locatelli C, Pradelli D, Campo G, Spalla I, Savarese A, Brambilla PG, Bussadori C (2018) Survival and prognostic factors in cats with restrictive cardiomyopathy: a review of 90 cases. J Feline Med Surg 20(12):1138-1143 PubMed.
  • Fox P R, Schober K A (2015) Management of asymptomatic (occult) feline cardiomyopathy: Challenges and realities. J Vet Cardiol 17 (Suppl 1:S), 150-158 PubMed.

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