Prevalence and significance of exit block during arrhythmias arising in pulmonary veins

Exit Block. Introduction: Recent studies described the occurrence of conduc tion block within pulmonary veins, The purpose of this study was to evaluat e the prevalence of exit block during arrhythmias that arise in pulmonary v eins. Methods and Results: Twenty-five patients with atrial tachycardia/fibrillat ion underwent successful ablation of 28 arrhythmogenic foci within a pulmon ary vein. The prevalence of exit block in the pulmonary veins was determine d in 28 arrhythmogenic pulmonary veins and 40 nonarrhythmogenic pulmonary v eins. During isolated premature depolarizations, exit block in a pulmonary vein was observed at 50% of arrhythmogenic pulmonary vein sites and was nev er observed within pulmonary veins that did not generate a tachycardia (P < 0.01). During tachycardia, exit block from a pulmonary vein was observed i n 61% of the arrhythmogenic pulmonary veins. The mean cycle length of the p ulmonary vein tachycardias associated with exit block was significantly sho rter than the cycle length of tachycardias that were not associated with ex it block (163 +/- 32 vs 251 +/- 35 msec, P < 0.001). Exit block in two pulm onary veins during the same episode of tachycardia was observed in 3 of the 28 arrhythmogenic pulmonary veins (11%) in three different patients. Simul taneous recordings in the two pulmonary veins demonstrated bursts of tachyc ardia in both veins that were not synchronized. Radiofrequency catheter abl ation of the arrhythmogenic site in one of the pulmonary veins eliminated s pontaneous recurrences of tachycardia from the other pulmonary vein. Conclusion: Exit block from pulmonary veins is a common observation during tachycardias generated within pulmonary veins and indicates that an arrhyth mogenic pulmonary vein has been identified. The occurrence of exit block in more than one pulmonary vein most likely is attributable to simultaneous t achycardias, one or both of which may be tachycardia induced and perpetuate d by the other.