The Innocent Delta Wave in Progressive Cardiomyopathy - Culprit vs Bystander.

A 34-year-old man presented with recurrent palpitations and dyspnea on exertion. Palpitations started at the age of 13 years; he received direct-current cardioversion for unstable tachycardia at 22 years and recently developed an acute ischemic stroke. The admission 12-lead electrocardiogram showed atrial fibrillation, and echocardiography demonstrated a hypertrophic cardiomyopathy (HCM) phenotype with moderate left ventricular systolic dysfunction. His father was diagnosed with HCM and high-grade conduction disease requiring a permanent pacemaker at the age of 46 years. After cardioversion, the sinus rhythm electrocardiogram revealed a short PR interval (from the onset of atrial depolarization to the onset of ventricular depolarization) with ventricular pre-excitation (mid-septal pattern). Electrophysiological study showed a short, fixed His-ventricular (HV) interval of 24 ms that remained unchanged during atrial pacing and after adenosine, with persistence of the pre-excited QRS (ventricular depolarization complex) morphology during junctional beats and no inducible tachycardia. These findings were diagnostic of a fasciculoventricular pathway. Cardiac magnetic resonance imaging revealed asymmetric septal hypertrophy with multifocal late gadolinium enhancement, and targeted genetic testing confirmed a pathogenic PRKAG2 variant (c.905G>A, p.Arg302Gln). Because no ablatable arrhythmic substrate was present, management was directed at heart failure, anticoagulation, rhythm control of atrial fibrillation, and surveillance for progressive conduction disease with cascade family screening. In conclusion, this case illustrates the clinical manifestations of PRKAG2 mutation-associated glycogen-storage cardiomyopathy, a phenocopy of HCM characterized by ventricular pre-excitation and progressive conduction disease, highlighting the convergence of structural, electrophysiological, and genetic mechanisms.