Echocardiographic features of second degree atrioventricular block.

Echocardiographic studies demonstrated abnormalities of motion of the pulmonary valve, the aortic root and valve, the mitral and tricuspid valves, the left ventricle, and the left atrium in two patients with second-degree atrioventricular block. During Wenckebach 3:2 atrioventricular conduction, ventricular beats exhibited alternately long and short periods of systolic opening of the pulmonary and aortic valves and alternately large and small left ventricular stroke volumes. During 4:3 and 3:2 Wenckebach atrioventricular conduction, the left ventricular stroke volume was directly proportional to the preceding end-diastolic volume. During 2:1 atrioventricular conduction, the blocked atrial contractions may produce movements of the left atrial wall, thereby revealing the true atrial rate when the blocked P waves are obscured in the electrocardiogram by their superimposition on preceding T waves.