Prognosis and Survival in Cats With Restrictive Cardiomyopathy

Restrictive cardiomyopathy (RCM) is a serious condition in cats that typically carries a poor prognosis. The disorder is characterized by myocardial stiffness and severe diastolic dysfunction.

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Researchers in Italy and the United Kingdom recently performed a retrospective study to further understand survival and prognostic factors associated with RCM using records from 90 feline patients.

Study Design

Patient records from 2 veterinary clinics in Milan, Italy were searched to identify cats with an echocardiographic diagnosis of RCM. Diagnostic criteria for RCM included the following:

• Left atrial or bi-atrial enlargement
• Normal left ventricular wall thickness
• Restrictive left ventricular filling pattern
• Normal or mildly decreased systolic function

Left atrial enlargement was defined as an increased left atrial to aortic root ratio ranging from 1.5 to more than 2.0.

Patients were excluded from the study if they had another cardiomyopathy in addition to RCM, congenital heart disease, systemic hypertension, hyperthyroidism, or incomplete medical records. Thyroxine (T₄) levels were tested for all cats over 10 years of age, and thoracic radiography was performed for all cats with respiratory distress. The investigators obtained follow-up patient information via medical records or telephone calls to owners.

Results

Ninety cats were diagnosed with RCM at the 2 clinics between 1997 and 2015. Most patients were male domestic shorthair cats, and mean age and median weight at initial presentation were 10 years and 3.8 kg, respectively.

The most common presenting signs and radiographic findings were respiratory distress (83%), pleural effusion (62%), and pulmonary edema (34%), while supraventricular arrhythmia (13%) and murmur (10%) were detected infrequently. Echocardiography revealed that a restrictive pattern or severe left atrial enlargement was each present in 72 cats, while 25 cats showed signs of increased risk of arterial thromboembolism, such as mural thrombi or smoke effect.

Standard treatment for all 90 cats included furosemide and angiotensin-converting enzyme inhibitors, and cats with supraventricular arrhythmias also were administered diltiazem. Patients with moderate to severe atrial dilation or increased risk of arterial thromboembolism were administered antithrombotic treatment using low-dose aspirin or clopidogrel.

Follow-up information was available for 60 cats. Of these, 50 had died from cardiac-related causes, 5 from unrelated causes, and 5 were still alive at the time of publication. Median survival time was 69 days. None of the cats transitioned from RCM to another cardiomyopathy. Cats presenting with respiratory distress had a shorter median survival (64 days) compared with cats without respiratory distress (466 days), and respiratory distress was the most significant predictor of survival on univariate and multivariate Cox analyses.

Take-home Message

Results from this large-scale retrospective study indicated that RCM is typically diagnosed during the late stage when cats have developed serious sequelae, including congestive heart failure signs and cardiogenic thromboembolism. Furthermore, the authors confirmed that RCM was associated with a poor long-term prognosis, as most cats survived approximately 2 months after presentation. Respiratory distress at presentation was the most significant negative prognostic factor.

Dr. Stilwell received her DVM from Auburn University, followed by a MS in fisheries and aquatic sciences and a PhD in veterinary medical sciences from the University of Florida. She provides freelance medical writing and aquatic veterinary consulting services through her business, Seastar Communications and Consulting.