USE OF DOUBLE VENTRICULAR EXTRASTIMULATION TO DETERMINE THE PREEXCITATION INDEX IN ATRIOVENTRICULAR NODAL REENTRANT TACHYCARDIA

The ability of single paced ventricular beats during tachycardia to pe netrate the tachycardia circuit and reset the subsequent atrial depola rization (atrial preexcitation), enabling calculation of the ''preexci tation index,'' can be helpful in analyzing supraventricular tachycard ias. However, the ventricular refractory period often prevents ventric ular capture of beats with the necessary prematurity to demonstrate at rial preexcitation, particularly in atrioventricular nodal reentrant t achycardia (AVNRT). We hypothesized that the use of double premature s timuli could overcome this limitation. In 25 consecutive patients with either AVNRT or atrioventricular reciprocating tachycardia (AVRT) we attempted to demonstrate atrial preexcitation with single and double v entricular extrastimuli. Whereas atrial preexcitation with a single ex trastimulus could only be achieved in 3 of 11 patients with A VNRT, al l but 1 patient demonstrated atrial preexcitation with the use of doub le ventricular extrastimuli. On the other hand, in all but 1 patient w ith AVRT, atrial preexcitation could be achieved with single and doubl e extrastimuli. A formula was derived for obtaining a preexcitation in dex with double extrastimuli and shown to correspond closely with the preexcitation index obtained with ct single extrastimulus in the 16 pa tients in whom atrial preexcitation could be achieved with single and double extrastimuli. Thus, this technique significantly enhances the a bility to achieve atrial preexcitation and to calculate the preexcitat ion index in patients with AVNRT, and thus may be useful in decipherin g tachycardia mechanism in some patients, as well as being a useful te chnique in studying the electrophysiological properties of the antegra de and retrograde limbs of AVNRT.