ACTION OF ATP ON VENTRICULAR AUTOMATICITY

ATP is an effective treatment of supraventricular tachycardia when the atrioventricular (AV) node is part of the reentrant circuit. However, the lower a pacemaker in the pacemaker hierarchy, the more sensitive it is to adenosine. Therefore, we investigated the effects of ATP on v entricular automaticity in in vivo and in vitro conditions. Wide and n arrow QRS complex tachycardia in 46 patients was treated with 6, 12, a nd 18 mg ATP as sequential intravenous (i.v.) bolus. ATP terminated ta chycardias in 67%. Bolus infusion ATP caused less than or equal to 6.4 -s asystole that was self-limited. Perfusion of isolated spontaneously beating guinea pig heart with 100 mu M ATP completely suppressed vent ricular automaticity. After ATP-infusion was discontinued, the first v entricular beat was evident after 3.1 +/- 0.9 s and sinus node activit y recovered with a time constant of 3.0 +/- 1.1 s. Because sinus node and ventricular automaticity recovered within seconds after ATP infusi on was discontinued in vitro, recovery in vivo is also likely to be de termined by the short half-life (+ 1/2) of ATP.