An 18-year-old man has palpitations that occur with variable frequency: sometimes several times per day, and often weeks without an occurrence. The onset is typically abrupt, lasting a few seconds to several minutes before abruptly terminating. He describes them as a “rapid fluttering” sensation in his chest with a “full feeling” in his throat.
Associated symptoms include lightheadedness and chest discomfort. He denies chest pain. He had an episode of near-syncope at age 14 and another approximately four weeks ago; the latter prompted him to schedule an appointment in your clinic. He has not been ill recently and has no history to suggest hypovolemia or anemia as a contributing factor for his recent episode of near-syncope.
Medical history is unremarkable, with the exception of tonsillectomy at age 7. He is not taking any medications and has no known drug allergies. Family history is positive for coronary artery disease in his father, which required revascularization at age 62, and diabetes in a grandparent.
Social history reveals he is a full-time undergraduate student at a local junior college. He drinks approximately one six-pack of beer on weekends despite being under age, but denies use of illegal, illicit, or performance-enhancing drugs. The review of systems is noncontributory.
The physical examination reveals a thin, healthy-appearing male in no distress. His blood pressure is 104/62 mm Hg; pulse, 66 beats/min; and respiratory rate, 14 breaths/min. The patient is afebrile.
The chest is clear to auscultation bilaterally with good excursion. The cardiac exam reveals a regular rate and rhythm with no murmurs, rubs, gallops, or extra heart sounds. There is no jugular venous distention or peripheral edema. The remainder of the physical exam shows no abnormalities or deficits.
Despite the “normal” physical, you are concerned about the patient’s history of frequent palpitations and two previous episodes of near-syncope. You order an ECG, the results of which show: a ventricular rate of 66 beats/min; PR interval, 116 ms; QRS duration, 142 ms; QT/QTc interval, 456/478 ms; P axis, 0°; R axis, –7°; and T axis, 105°. What is your interpretation of this ECG?