ELECTROPHYSIOLOGIC CHARACTERISTICS, ELECTROPHARMACOLOGIC RESPONSES AND RADIOFREQUENCY ABLATION IN PATIENTS WITH DECREMENTAL ACCESSORY PATHWAY

Objectives. This study sought to characterize the functional propertie s of decremental accessory atrioventricular (AV) pathways and to inves tigate their pharmacologic responses. Background. Although decremental AV pathways associated with incessant reciprocating tachycardia have been studied extensively, information about the electrophysiologic cha racteristics and pharmacologic responses of anterograde and retrograde decremental AV pathways is limited. Methods. Of 759 consecutive patie nts with accessory pathway-mediated tachyarrhythmia, 74 with decrement al AV pathways were investigated (mean age 43 +/- 18 years). After bas eline electrophysiologic study, the serial drugs adenosine, verapamil and procainamide were tested during atrial and ventricular pacing, Fin ally, radiofrequency catheter ablation was performed. Results. Five pa tients had anterograde decremental conduction over the accessory pathw ay hut had no retrograde conduction. Of the 64 patients with retrograd e decremental conduction over the accessory pathway, anterograde condu ction over the pathway was absent in 41 (64%), intermittent in 5 (8%) and nondecremental in 18 (28%). In the remaining five patients, antero grade and retrograde decremental conduction over the same pathway was found. The anterograde and retrograde conduction properties and extent of decrement did not differ between anterograde and retrograde decrem ental pathways. Posteroseptal pathways had the highest incidences of a nterograde and retrograde decremental conduction, Intravenous adenosin e, procainamide and verapamil caused conduction delay or block, or bot h, in 10 of 10, 10 of 10 and 4 of 10 of the anterograde and 20 of 20, 20 of 20 and 8 of 20 of the retrograde decremental pathways, respectiv ely. All patients had successful ablation of the decremental pathways without complications. During the follow-up period of 31 +/- 19 months , only one patient experienced recurrence. Conclusions. Decremental ac cessory pathways usually had functionally distinct conduction characte ristics in the anterograde and retrograde directions. Their pharmacolo gic responses suggested the heterogeneous mechanisms of decremental co nduction.