SUMMARYWe studied the electrophysiologic effects of intravenous adenosine triphosphate disodium (ATP-2Na) on 15 patients with paroxysmal supraventricular tachycardias (PSVTs). One patient had sinus node (SN) reentry and 2 patients had intraatrial (IA) reentry. Five patients had AV nodal reentry and 7 patients had atrioventricular reentrant tachycardias (AVRTs) with accessory pathways (APs). ATP-2Na was injected during ventricular pacing (VP) in patients with AVRTs with APs. A bolus injection of ATP-2Na terminated all the PSVTs within 40 sec except in one case of IA reentry. The sites of block at the termination were the atrium in SN reentry and IA reentry, between A and H (AH) block or between H and A (HA) block in AV nodal reentry and AH block in all the AVRTs with APs. ATP-2Na during VP in patients with AVRTs with APs produced the changes of atrial activation sequences in 3 patients, induction of PSVT in 2 patients and a Mobitz type II VA block in 2 patients. The former two phenomena suggested a retrograde AV nodal block and raised the possibility of a simple test for retrograde atrial fusion during VP in patients with WPW syndrome. Chest discomfort of short duration was most commonly noted after ATP-2Na. Inosine pretreatment potentiated the effects of ATP-2Na. This combination may further alleviate the side effects of ATP-2Na, while preserving the effective action of ATP-2Na for rapid termination of PSVTs. Additional Indexing Words: Electrophysiologic effectsParoxysmal supraventricular tachycardias Ventricular pacing ATP-2Na potentiation by inosine

We studied the electrophysiologic effects of intravenous adenosine triphosphate disodium (ATP-2Na) on 17 patients with paroxysmal supraventricular tachycardias (PSVTs). One patient had sinus node (SN) reentry, two had intraatrial (IA) reentry, 7 patients had AV nodal reentry and seven had atrioventricular reentrant tachycardias (AVRTs) with accessory pathways (APs). ATP-2Na was injected during ventricular pacing in patients with AV nodal reentry and AVRTs with APs. A bolus injection of ATP-2Na terminated all the PSVTs within 50 s except for one case of IA reentry (case 2). The sites of block at termination were the atrium in SN reentry and IA reentry, between A and H (AH) or between H and A (HA) in AV nodal reentry, and AH block in all the PSVTs with APs. The sites of action on the patients with AV nodal reentry were both the antegrade and retrograde pathways, while the modes of block were Mobitz type I and type II, respectively. ATP-2Na during ventricular pacing in patients with AV nodal reentry produced Mobitz type II ventriculoatrial block (VAB) in four of seven cases. ATP-2Na during ventricular pacing in patients with AVRTs with APs produced changes of atrial activation sequences in two patients, induction of PSVT in two patients, and Mobitz type II VA block in three patients. The former two phenomena suggested a retrograde AV nodal block and raised the possibility of a simple test for retrograde atrial fusion during ventricular pacing in patients with WPW syndrome. Chest discomfort of short duration was most commonly noted after ATP-2Na administration.

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