Restrictive Cardiomyopathy - Feline Cardiomyopathies

Overview

Restrictive cardiomyopathy (RCM) is a series of acquired pathologies of the feline myocardium. The common element is marked diastolic dysfunction without major alteration of systolic function. In RCM, the compliance and distensibility of the ventricular walls is reduced, such that filling of the ventricles in diastole is compromised. This ultimately reduces the amount of blood that the left ventricle (LV) can accept. During the rapid filling phase of diastole, the pressure within the LV rises abruptly, preventing the entry of additional blood from atrial contraction in late diastole. This consequently increases left atrial pressure and the diameter of the left atrium or both atria. Grossly, RCM is characterised by a normal or near-normal appearance of the ventricles with dilation of the left atrium or both atria. The echocardiographic appearance of the cardiac chambers 2D images of cats with early RCM may be normal; however severe diastolic dysfunction may be evident from M-mode and Doppler imaging.

Aetiology

In humans, RCM is usually secondary to systemic infiltrative pathologies (e.g. amyloidosis, sarcoidosis) or radiation exposure; with pathology localized at the myocardial or endomyocardial level. Cats may also have myocardial and endomyocardial forms of RCM, but this seems to occur as a primary cardiomyopathy in cats. However, endomyocardial fibrosis has been associated with viral, hypereosinophilic and immune-mediated pathologies in rare cases.