Clinical and Pathological Findings in 2 Rats (Rattus norvegicus) With Dilated Cardiomyopathy

Abstract

Two 2-year-old intact female rats (Rattus norvegicus) were presented with severe dyspnea and tachypnea. In rat 1, radiographic evaluation of the thorax revealed severe pleural effusion, and cardiomegaly was suspected, suggesting a severe congestive heart failure. Echocardiography and computed tomography (CT) revealed bilateral pleural effusion, severe dilated cardiomyopathy (DCM), hepatomegaly, and mild abdominal effusion. Thoracocentesis and cytological examination revealed a chylous effusion. The patient was treated with a low-fat diet, octreotide, and medication to treat heart disease (furosemide, benazepril, pimobendan, and digoxin). However, because of worsening clinical signs, the animal was euthanized 5 days following the initiation of treatment. At necropsy, the heart was enlarged and rounded, with evident dilation of both ventricles, and the final diagnosis determined to be a DCM and myocardial fibrosis. The cardiac disease appeared to cause a chronic passive liver and lung congestion that, finally, resulted in both pleural and abdominal effusions. In rat 2, radiographic analysis of the thorax revealed pleural effusion and (conceivably) cardiomegaly, suggesting a severe congestive heart failure. Echocardiography and CT revealed pleural effusion and severe DCM of 4 chambers without effective contractility. Thoracocentesis was performed on the patient with the subsequent cytological examination of aspirated fluid being assessed as a transudate rich in macrophages and cells compatible with mastocytes. Cardiac medications were initiated, and the patient was monitored on a weekly basis. The rat died 27 days after the initial diagnosis due to respiratory failure. During the necropsy examination, it was determined that the rat’s heart was rounded, with enlargement of the left ventricle and thinning of the ventricular wall. The final disease diagnosis following the postmortem examination of rat 2 was a DCM and myocardial degeneration, which caused a chronic passive liver and lung congestion that resulted in a pleural effusion, hindering normal pulmonary activity. There is a paucity of published articles that describe DCM in rats. Recommended treatment of cardiovascular disease in this species is largely extrapolated from data obtained from cats, dogs, and ferrets. Further studies are warranted to detail the efficacy of therapeutic agents to treat cardiac disease in pet rats.