An Incessant Tachycardia: What Is the Mechanism?

A 39-year-old man presented with lifelong palpitations, a mildly reduced left ventricular ejection fraction, and incessant tachycardia. Electrocardiography revealed a regular, one-to-one supraventricular tachycardia with superiorly directed P-waves and a long R-P interval. The differential diagnosis of the tachycardia, response to invasive electrophysiologic maneuvers, and treatment with catheter ablation are discussed.