Double-QRS Complex Revealing a Multilayer Intramural-Epicardial Ventricular Tachycardia Circuit in Cardiac Sarcoidosis

BACKGROUND: Cardiac sarcoidosis can create multilayer intramural-epicardial conduction pathways that manifest as subtle electrocardiographic abnormalities during sinus rhythm. A second low-amplitude deflection following the QRS complex ("double-QRS") has been observed clinically, but its electrophysiological mechanism remains unclear. CASE SUMMARY: A 67-year-old man with cardiac sarcoidosis exhibited a sinus-rhythm double-QRS pattern that changed in timing and polarity after corticosteroid therapy and preceded sustained monomorphic ventricular tachycardia. High-density mapping identified 2 intramural-epicardial connections linking a broad intramural septal corridor to epicardial breakthrough sites at the anterior right ventricular outflow tract and inferior right ventricle. Entrainment confirmed a multilayer reentry circuit. Ablation targeting the intramural isthmus and epicardial exits modified the double-QRS timing, and definitive bipolar ablation eliminated all inducible ventricular tachycardia and abolished the double-QRS pattern. DISCUSSION: A sinus-rhythm double-QRS complex may reflect delayed epicardial activation through intramural-epicardial pathways. TAKE-HOME MESSAGE: Resolution of a double-QRS complex after ablation supports its role as a surface electrocardiographic marker of multilayer conduction.