Electrophysiology study (EPS) tracing showing the effects of procainamide on an abnormal His-Purkinje conduction system

These tracings were taken from a 58-year-old male with syncope. The baseline 12-lead electrocardiogram demonstrated sinus rhythm with prolonged atrioventricular (AV) conduction and a left bundle branch block with left axis deviation. Surface leads represented are I, II, III, and V1. Intracardiac tracings shown are the high right atrium (HRA), the distal His bundle electrogram (HIS d), the proximal His bundle electrogram (HIS 2), and the right ventricular apex (RVa). The left side of Panel A shows a baseline HV interval of 68 milliseconds. The right side of Panel A demonstrates prolongation of the HV interval to 100 milliseconds after the administration of procainamide indicating severe His-Purkinje conduction disease. Panel B (same lead schema) demonstrates high right atrial pacing at 400 milliseconds (150 beats per minute) with infra-Hisian block (arrow) after the administration of procainamide, confirming severe His-Purkinje disease.