Abnormal transmitral flow: what is the rhythm?

Abstract

Echocardiography was performed on 78-year-old woman for the follow-up of moderate mitral valve regurgitation (MR). A single-lead electrocardiographic (ECG) tracing showed bradycardia with irregular heart rhythm between 46 and 53 beats per minute. The echocardiographic image of pulsed wave Doppler at mitral inflow is displayed in Panel. There was a progressive shortening of the interval between E (early) and A (late) diastolic filling waves, followed by an absent A wave. A gradual shortening of the A-A wave interval was also noted. The interval between A wave and MR envelope remains constant. This typical pattern is consistent with Wenckebach phenomenon in sinoatrial (SA) exit block. SA exit block is due to failed propagation of pacemaker impulses beyond the SA node. In Type I second-degree SA block (Wenckebach), there is a progressive delay in the conduction from the SA node to the atrium until one impulse is completely blocked, leading to intermittent failure of atrial depolarization and ensuing absence of A wave in the Doppler inflow pattern. Moreover, the A-A wave interval is gradually decreased (i.e. the atrial rate accelerates) as the increment in the conduction delay from the SA node to the atrium becomes progressively smaller.