Restrictive cardiomyopathy is the second-most-common form of cardiomyopathy in cats and is characterized by a stiff, noncompliant left ventricle, usually due to increased collagen (ie, scar) formation in the left ventricle. Several forms are recognized, including endomyocarditis/endocardial fibrosis, endomyocardial fibrosis, and myocardial fibrosis. The increased stiffness increases diastolic pressure for any given diastolic volume. As in hypertrophic cardiomyopathy, the result is an increase in left atrial size and left atrial pressure, leading to pulmonary edema and/or pleural effusion (left heart failure). In some cats that have obvious endomyocardial thickening or partial cavity obliteration, the diagnosis of restrictive cardiomyopathy can be readily made using two-dimensional echocardiography. In others the diagnosis can be confirmed only through the use of specialized electrocardiographic techniques (eg, mitral inflow pattern using pulsed wave Doppler or tissue Doppler imaging). A left atrial thrombus may be evident, most commonly in the left auricle. Systolic function is usually preserved. Color flow Doppler echocardiography may demonstrate mitral regurgitation.
Clinical signs of and treatment for heart failure are similar to those for hypertrophic cardiomyopathy; however, the prognosis seems to be worse, especially in cats with CHF. The cause of restrictive cardiomyopathy is unknown.
