Background : Several methods including ‘differential pacing’ and ‘polarity reversal of the local electrograms have been reported to confirm conduction block of the cavotricuspid isthmus in the ablation of isthmus-dependent atrial flutter. It is well known that the flutter cycle length (FCL) itself is the conduction time around the tricuspid annulus. We have noticed that it takes the similar conduction time to the FCL when pacing is done from one side of the complete line of block after the ablation.
Methods and results : Linear ablation of the cavotricuspid isthmus was performed in 35 patients with isthmus dependant atrial flutter. Mean value of the shortest and the longest flutter cycle lengths were 216 ± 25.5 ms, 238 ± 27.5 ms, respectively. Seven of those were clockwise flutter. Differential pacing, pacing from the right atrium near the posterolateral tricuspid annulus with the distal and then proximal electrodes, was performed in all cases to confirm counterclockwise conduction block of the isthmus. The interval between the pacing stimulus and the first component of the split local electrograms on the line of block was measured (SD1). Then the interval between the pacing stimulus and second component was measured which suggested the local activation of the contralateral side of the ablation line (SD2). The sum of both intervals was the same as or very close (≤ about 10%) to the shortest flutter cycle lengths in 24 of 27 patients reviewed retrospectively and in 8 patients prospectively (FCL=SD1+SD2).
Conclusion : If the FCL is very close to the sum of SD1 and SD2 after making a line of block, additional tests may not be needed to confirm unidirectional conduction block in the pacing direction
|
