Pleural effusion in two rats (Rattus norvegicus) as a complication of dilated cardiomyopathy

Abstract

Introduction: Dilated cardiomyopathy (DCM) is a myocardial disease characterized by primary systolic dysfunction of the left ventricule with secondary eccentric hypertrophy and left atrial dilation. The right heart chambers are variably involved in this disease. Although DCM begins with an asymptomatic phase, of variable duration, it is a progressive and usually fatal disease that leads to congestive heart failure (CHF), arrhytmias, and often sudden cardiac death. Rats are widely used as experimental models but naturally occuring cardiac disease is poorly described. Clinical case: Two 2-year-old female rats (Rattus norvegicus) were presented to the emergency department with evident dyspnea and tachypnea. Chest X-ray showed a bilateral effusion in both animals. In rat 1, drainage of the effusion yielded a cloudy, offwhite fluid that settled in layers in the drainage container (16 ml). Pleural fluid examination revealed a lymphocyte-rich transudate with high levels of cholesterol (Chol) and triglycerides (Trig) (Chol 27 mg/dL and Trig > 375 mg/dL in pleural fluid; Chol 80 mg/dL and Trig 130 mg/dL in blood). Ultrasonography (US) and computed tomography (CT) of the thorax and abdomen revealed bilateral pleural effusion, severe dilated cardiomyopathy and mild edematous abdominal effusion. Due to ongoing chylous leak the patient was commenced on a low fatty acid diet, octreotide and heart medication (furosemide, benazepril, pimobendan and digoxin). However, because of worsened of clinical signs the animal was euthanized 5 days later. In rat 2, drainage of the effusion yielded a translucent liquid with small amount of blood (3 ml). Pleural fluid examination revealed a transudate rich in macrophages and cells compatible with mastocites. Cardiac ultrasonography and CT revealed a severe dilated cardiomyopathy of four chambers without effective contractility and a clot at the level of the aorta. The patient started with cardiac medication and was monitored weekly. Unfortunately the rat died 27 days later. Conclusion: Many causes have been involved in the development of a DCM, such as chemotherapy, inflammatory process, nutrient deficiencies, but in most cases are considered idiopathic. The DCM seems to be the most common cause of pleural effusions in rats. Although the literature about this disease is scarce in pet rats, the recommended treatment of cardiovascular disease in this species is largely extrapolated from data obtained from the cat, dog, and ferret. Further studies are warranted to detail efficacy of these drugs in pet rats.