How narrow is narrow QRS in premature ventricular contractions? A novel variant of SCN5A-associated MEPPC

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  Figure 1. The patient’s initial (A), 48 hours after flecainide (B), and postinterruption follow-up electrocardiograms (ECGs) (C). A: The initial ECG showed a sinus rhythm at 42 beats per minute (red arrow), with P waves buried in consecutive ventricular escape beats with premature ventricular contractions (PVCs). The QRS complexes were wide with a left bundle branch block morphology, suggesting the involvement of the proximal Purkinje system near the His bundle, with propagation exiting to the right bundle. These PVCs were followed by a 6-beat run of nonsustained polymorphic ventricular tachycardia. B: After flecainide, sinus rhythm was restored with 1:1 AV conduction, accompanied by left bundle branch block morphology (QRS duration of 150 ms) and nonspecific ST-segment and T-wave changes. C: The third ECG mirrored the initial pattern of ventricular escape beats with PVCs. However, the ectopic beats now displayed a right bundle branch block morphology with a narrower QRS duration than baseline, further supporting their origin from Purkinje-related ectopic activity. AV = atrioventricular.