Partial cavotricuspid isthmus block before ablation in patients with typical atrial flutter

OBJECTIVES The purpose of this study was to prospectively evaluate preexist ing partial isthmus block in the context of an electrophysiologically direc ted linear ablation strategy ibr typical atrial flutter (AF). BACKGROUND Double potentials (DPs) separated by an isoelectric interval hav e been recognized as markers of local block However, the presence and signi ficance of DPs in the cavotricuspid isthmus during AF before ablation have not been evaluated. METHODS Thirty consecutive patients with AF (counterclockwise: 24, clockwis e: 6) were studied during AF. Sequential withdrawal mapping was performed i n the cavotricuspid isthmus from the tricuspid valve (TV) to the inferior v ena cava (IVC) edge with electrograms coinciding with the center of the sur face electrocardiographic plateau during counterclockwise AF or with the in itial downslope of the positive flutter wave during clockwise AF. Atrial el ectrograms along this line were categorized as double, single or fractionat ed potentials (SPs or FPs). After demarcation of the zone of contiguous DPs , radiofrequency (RF) catheter ablation was performed during AF only at sit es with SPs or FPs (other than DPs) on the mapped line. If isthmus conducti on still persisted after AF termination, additional RF applications were de livered using the same electrophysiologic strategy of avoiding DPs with an isoelectric interval during low lateral right atrial pacing for filling in the gap of residual conduction. RESULTS Before ablation, no DPs were recorded in the isthmus in 19 patients (63%); DPs were recorded only at the IVC edge in five patients, and only a t the TV edge in one patient. A contiguous line of DPs extending through mo re than half the isthmus to the IVC edge was documented in five patients (1 7%: group DP). In group DP, AF was terminated with 1.4 +/- 0.5 applications (vs. 5.8 +/- 3.5 in the remaining patients: p < 0.01). Complete isthmus bl ock was achieved with a total of 3.4 +/- 0.5 applications (vs. 12 +/- 6 in the remaining patients: p < CONCLUSIONS Seventeen percent of patients undergoing ablation of AF have pr eexisting partial isthmus block indicated by a large contiguous zone of DPs separated by an isoelectric interval. Electrophysiologically directed line ar ablation avoiding confluent DPs can prevent unnecessary applications for effective cure of AF. (C) 1999 by the American College of Cardiology.