Train stimulation at the atria for prevention of atrioventricular tachycardia: dependence on accessory pathway location.

In 12 patients with accessory pathway-mediated supraventricular tachycardia, programmed electrical stimulation with a rapid train of 10 stimuli was assessed for prevention of tachycardia induction. Tachycardia was induced with one or two extrastimuli from both the right and the left atrium (by way of the coronary sinus). Preventive train stimulation, with the train delivered after the tachycardia-initiating stimulus, was attempted at the site of tachycardia induction as well as at the opposite site. Prevention at the site of tachycardia induction was successful in all patients when the length of the train (90 ms) exceeded the effective refractory period of the tachycardia-initiating stimulus to achieve single atrial capture within the "preventive zone." However, in patients with a left-sided accessory pathway, preventive stimulation at the right atrium failed when tachycardia was induced from the coronary sinus because of interatrial conduction delay. It is concluded that train stimulation is an effective mode for supraventricular tachycardia prevention, yet the site of preventive stimulation should lie as close as possible to the anatomic site of the reentrant circuit to reduce interatrial conduction delay.