Restrictive cardiomyopathy (RCM) is described as a myocardial disorder distinguished by myocardial stiffness, severe diastolic dysfunction (restrictive physiology) and an overall poor prognosis. RCM is frequently subclassified into two forms: myocardial and endomyocardial. Echocardiography is the most common tool used for characterization and diagnosis. Both forms of RCM are characterized by atrial enlargement, normal left ventricular (LV) wall thickness, normal or mildly decreased systolic function, and restrictive LV filling pattern with pulsed Doppler echocardiography. With the endomyocardial form, thick hyperechoic tissues may bridge the LV lumen.
Large epidemiological studies focusing on cardiomyopathies, especially RCM, are not common. This study’s investigators reviewed the clinical archives of a large veterinary clinic and university located in Milan, Italy from 1997-2015 evaluating all cats diagnosed with RCM based on echocardiographic examination. Their study’s population comprised 90 cats (53 male, 37 female). The breed population involved were primarily domestic shorthair cats (n=60), followed by Persians (n=15), longhair cats (n=11; with four Norwegian Forest Cats, four Birmans and three Maine Coons), three Siamese and one Chartreux.
The large majority of cats had clinical signs at presentation (n=87; 97%). Only three cats were asymptomatic. Seventy-five cats (83%) presented with respiratory distress. A minority of cats had a murmur (n=9; 10%). Twelve cats (13%) showed supraventricular arrhythmias. Thoracic radiographs demonstrated pleural effusion in 44 cases (59%), pulmonary oedema in 19 (25%) and both in 12 cases (16%). On echocardiography, most cats had severe LA enlargement (n=72; 80%) and 25 cats (28%) presented with signs for increased risk of aortic thromboembolism (smoke effect or mural thrombi).
The authors state the results show that RCM is almost primarily diagnosed at a late stage after the development of clinical signs. In addition, the long-term prognosis for cats with RCM is poor (median survival time for cats available for follow up was 69 days). Almost all the cats exhibited signs of congestive heart failure along with cardiogenic thromboembolism and cardiac-related deaths occurred in 50 cats. Survival was better in cats not exhibiting respiratory distress though this was found in a minority of the cases. A heart murmur was rarely identified in cats with RCM and the authors comment that the presence or absence of a heart murmur is not a useful screening tool in cats. Treatment in this population of cats was primarily loop diuretics, ACE inhibitors and anti-thrombotic treatment. (VT)