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Young Woman With Wide QRS Tachycardia and No Structural Heart Disease: Do We Need to Look for Something Else?

A 23-year-old female patient, previously asymptomatic and without structural heart disease, sought the emergency department with well-tolerated palpitations that lasted for 2 hours. The ECG showed a wide QRS complex tachycardia (Fig. 1) with left bundle branch block morphology, superior axis, and late transition in the horizontal plane. The infusion of 6 mg of adenosine reversed the arrhythmia, showing right bundle branch block and T-wave inversion in the anterior wall during sinus rhythm. An echocardiogram and cardiac magnetic resonance imaging showed no structural heart disease; Holter monitoring showed a PR interval of around 200 milliseconds and rare ventricular premature beats. The patient also reported a visual acuity deficit, which began around 6 months before this evaluation. The patient underwent electrophysiological study, which revealed a 76-millisecond HV interval during sinus rhythm. Programmed ventricular pacing (S1: 600 milliseconds, S2: 280 milliseconds) induced a wide QRS tachycardia similar to the clinic one, with 90-millisecond HV interval (Fig. 2). What is the mechanism of the arrhythmia? Do we need to look for something else?