Abstract
Case presentation A 15-year-old boy was referred to our institution because of a single episode of rapid nonsyncopal palpitations in the absence of structural heart disease. A regular wide QRS complex tachycardia (210 beats/min, left-bundle-branchblock morphology) (Figure 1A) that was terminated by a bolus of intravenous adenosine in his hospital of origin was documented. An electrophysiological study was subsequently performed. A traumatic right bundle branch block developed during catheter positioning and was present throughout the entire procedure. The baseline sinus cycle length and atrial-His (AH) and His-ventricular intervals were 810, 95, and 45 ms, respectively. Dual atrioventricular (AV) node physiology and a single AV nodal echo beat were demonstrated. Ventricular pacing during sinus rhythm showed ventriculoatrial conduction that was concentric and decremental. During isoproterenol infusion, a sustained tachycardia (Figure 1B) with QRS and cycle length alternans was reproducibly induced by programmed atrial stimulation. Induction of the tachycardia by atrial extrastimulus testing and the response to a single premature atrial extrastimulus introduced during His refractoriness were repeatedly observed (Figure 2). Overdrive ventricular pacing during tachycardia at a pacing cycle length of 10–20 ms below the atrial rate failed to affect the atria. What is the mechanism of the tachycardia? What is the cause of QRS and cycle length alternans?
Published Version
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