Recurrent syncope in a patient with an implantable loop recorder: what is the diagnosis?

A 76-year-old woman with a history of hypertension and mastectomy for breast carcinoma was referred for evaluation of recurrent syncope. She characterized a typical episode as a sudden loss of consciousness without a prodrome. There was no sensation of fatigue after the events. Her medical regimen consisted of amlodipine and a hydrochlorothiazide/triamterene combination. Results of physical examination were unremarkable. ECG showed sinus rhythm with a left bundle branch block and normal PR and QT intervals. Results of echocardiogram, exercise stress test, 24-hour Holter monitor, and a head-up tilt-table test were normal. She had no syncope, and no arrhythmias were detected while she wore a 30-day external event recorder. Electrophysiologic study including carotid sinus massage was notable only for spontaneous and pacing-induced atrial Ž brillation. In view of the nonspeciŽ c electrophysiologic study, a loop recorder (Reveal Plus, Medtronic Inc., Minneapolis, MN, USA) was implanted. The loop recorder was implanted on the right side because the patient had undergone a radical mastectomy and was left with little subcutaneous tissue on the left side. The patient had an episode of syncope 6 weeks after the loop recorder was implanted. The retrieved electrogram from the patient-activated event is shown in Figure 1. What is the diagnosis of the implantable loop recording?