LGL-Phenocopy With Dual AV Nodal Physiology and Malignant SVT: A Diagnostic Pitfall With Sudden Deaths.

BACKGROUND: The short PR interval without preexcitation (Lown-Ganong-Levine-phenocopy) is often considered benign, but its association with malignant substrates is underappreciated. CASE SUMMARY: A 45-year-old man with no previous cardiac history presented with palpitations, dyspnea, and diaphoresis. Electrocardiogram (ECG) during symptoms showed supraventricular tachycardia at ∼220 beats/min with a Hisian extrasystole and QRS variability. Postconversion ECG revealed short PR and dual atrioventricular nodal physiology. Echocardiography showed subtle nonterritorial hypokinesia. Family history included sudden cardiac death in 3 siblings. DISCUSSION: This case demonstrates that Lown-Ganong-Levine-phenocopy with dual atrioventricular nodal physiology and Hisian extrasystoles can be a red flag for a lethal inherited arrhythmogenic substrate requiring comprehensive evaluation including cardiac magnetic resonance, genetic testing, and family screening. TAKE-HOME MESSAGES: A short PR pattern with a malignant family history warrants comprehensive evaluation. Surface ECG red flags should not be ignored even when the resting ECG appears benign.