Atrial standstill, myocarditis and destruction of cardiac conduction system: clinicopathologic correlation in a dog

A case of permanent atrial standstill is described in a 10-month-old dog with ascites as a presenting complaint. The patient had absence of P waves in all leads in numerous ECG's and had a regular idioventricular rhythm. Pathologically, the patient had multiple areas of atrial and ventricular myocardial necrosis and fibrosis, with chronic active myocarditis and obliteration of the SA and AV node and AV bundle.