Loss of LV capture with BiV pacing

The top line of this tracing shows one lead from the surface electrocardiogram (ECG). The middle portion of the tracing shows the pacemaker event markers obtained by telemetry. The bottom line of the tracing shows the intracardiac electrogram. The arrow above the tracing indicates the time point at which capture of the left ventricle (LV) by the biventricular (BiV) pacemaker is lost. The changes with loss of capture are subtle in the surface ECG tracing. The event markers and the intracardiac electrogram document the loss of capture.