ELECTROPHYSIOLOGIC CHARACTERISTICS AND RADIOFREQUENCY CATHETER ABLATION IN ATRIOVENTRICULAR NODE REENTRANT TACHYCARDIA WITH 2ND-DEGREE ATRIOVENTRICULAR-BLOCK

Introduction: Detailed electrophysiologic study of AV nodal reentrant tachycardia (AVNRT) with 2:1 AV block has been limited. Methods and Re sults: Six hundred nine consecutive patients with AVNRT underwent elec trophysiologic study and radiofrequency catheter ablation of the slow pathway. Twenty-six patients with 2:1 AV block during AVNRT were desig nated as group I, and those without this particular finding were desig nated as group II. The major findings of the present study were: (1) g roup I patients had better anterograde and retrograde AV nodal functio n, shorter tachycardia cycle length (during tachycardia with 1:1 condu ction) (307 +/- 30 vs 360 +/- 58 msec, P < 0.001), and higher incidenc e of transient bundle branch block during tachycardia (18/26 vs 43/609 , P < 0.001) than group II patients; (2) 21 (80.8%) group I patients h ad alternans of AA intervals during AVNRT with 2:1 AV block. Longer AH intervals (264 +/- 26 vs 253 +/- 27 msec, P = 0.031) were associated with the blocked beats. However, similar HA intervals (51 +/- 12 vs 50 st 12 msec, P = 0.363) and similar HV intervals (53 +/- 11 vs 52 +/- 12, P = 0.834) were found in the blocked and conducted beats; (3) vent ricular extrastimulation before or during the His-bundle refractory pe riod bundle could convert 2:1 AV block to 1:1 AV conduction. Conclusio ns: Fast reentrant circuit, rather than underlying impaired conduction of the distal AV node or infranodal area, might account for second-de gree AV block during AVNRT, Slow pathway ablation is safe and effectiv e in patients who have AVNRT with 2:1 AV block.