Abstract
Eleven patients with an atrioventricular accessory pathway were studied by programmed electrical stimulation to determine if reentrant tachycardia can be prevented in these patients by delivery of a single atrial extrastimulus, applied at a critical time after the tachycardia-initiating stimulus (or stimuli), or by delivery of a train of stimuli. In all 11 patients, reentrant tachycardia could reproducibly be induced from high right atrium with a single premature beat, and in all patients initiation of tachycardia could be prevented from the same site by a second premature beat. This second extrastimulus was effective if delivered within a zone which began 10 ms outside the effective refractory period of the tachycardia-initiating stimulus, and averaged 61 ms in width. It was termed the “preventive zone”. In 7 patients the effect of train stimulation to the high right atrium was studied. In all 7, results were concordant with those obtained by single-beat stimulation. Any train to achieve single atrial capture within the preventive zone was effective in preventing tachycardia. Prevention was always possible with a single atrial extrastimulus or with single-capture train stimulation, whereas termination of an ongoing tachycardia required at least 2 atrial extrastimuli, or stimulation from the right ventricle.
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