Rare Forms of Preexcitation

Abstract

A 16-year-old boy was brought to the hospital when he complained of chest pain while at a basketball game. In the emergency room, he was noted to have a wide complex tachycardia. The ECG at presentation is shown in Figure 1. He was cardioverted after administration of 150 mg of intravenous amiodarone. His ECG after cardioversion is shown in Figure 2. His physical examination and developmental evaluation were significant for obesity, synophrys, mild fifth digit clinodactyly, and subnormal intelligence. Cardiac magnetic resonance imaging with contrast showed massive left ventricular hypertrophy (LVH), with preserved ejection fraction, and several areas of delayed hyperenhancement in the subendocardium. Cardiac catheterization showed no obstructive coronary artery disease or anomalous coronary arteries. What are the diagnostic considerations for this constellation of findings of massive LVH, subendocardial necrosis, and abnormal ECGs? Figure 1. Wide complex tachycardia at presentation. Figure 2. Sinus rhythm ECG showing ventricular preexcitation and normal axis (see text for further details). The ECG in Figure 1 displays a wide complex tachycardia, with a right-bundle branch block morphology with a QRS complex duration >120 ms. A wide complex tachycardia with a right-bundle branch block morphology could be secondary to ventricular tachycardia originating from the left ventricle or a preexcited tachycardia in the presence of a left-sided bypass tract. However, the QS complex in lead V6 rules out a left-sided atrioventricular bypass tract, because such bypass tracts do not have the left ventricle apex as their ventricular insertion site, which is necessary to produce a QS complex in V6. A left-sided nodofascicular bypass tract with insertion in the distal His-Purkinje system can produce QS complexes in lead V6, but these are extraordinarily rare and occur more frequently on the right side. Initial R wave in lead aVR,1 a QS complex in lead …