Persistent atrial standstill in a cat.

A domestic shorthaired cat was presented with a 1-month history of cardiomegaly and recurrent chylothorax. The heart rate was 130 beats/min and no P waves were present on a surface electrocardiogram. Thoracic radiographs and an echocardiogram demonstrated severe biatrial dilatation, pleural effusion and restrictive pleural disease. Permanent atrial standstill was suspected. Pleurocentesis was performed and therapy was started with enalapril, frusemide and aspirin. Intracardiac electrograms revealed no atrial activity, and atrial pacing failed to elicit atrial or ventricular depolarisations. The patient was euthanased. Necropsy showed severe atrial wall thinning with marked cardiocyte loss. Persistent atrial standstill is a rare disease in the cat. Clinical signs may have been due to loss of atrial function, ventricular diastolic dysfunction, bradycardia, neurohormonal activation and reduced atrial natriuretic peptide plasma concentrations.