Multicomponent local ventricular electrograms during left bundle branch area pacing.

A 63-year-old woman with sick sinus syndrome and recurrent syncope underwent left bundle branch area pacing lead implantation using a continuous pacing and recording technique. Multicomponent local ventricular electrograms were observed during left ventricular septal pacing, nonselective left bundle branch pacing, and selective left bundle branch pacing, challenging the specificity of discrete electrograms for selective capture. Potential mechanisms included overlapping potentials from distinct septal sources and far-field contributions. These findings suggested that selective left bundle branch capture should be confirmed through comprehensive unipolar threshold testing and systematic analysis of output-dependent electrophysiological transitions rather than electrogram morphology alone.