Evaluation of Fast Pathway Function

There is no consensus oti the effect of slow pathway ablation on the electrophysiologic properties of the fast pathway in patients with AV ncxial reentrant tachycardia. Some investigators have demonstrated that ahlation of the slow pathway results In shortening of the fast pathway effective refractory period, while other investigators have not made this observation.' '̂ In the setting of sympathetic stimulation, slow pathway ahlation does not result in shortening of the fast pathway eifective refractory period.'" The results from studies not perfonned in the setting of autonomic blockade have been variable.--̂ -'̂ -'̂ However, the majority of studies perfonned in the setting of autonomic blockade have demonstrated shortening of the fast pathway effective refractory period after complete, but not partial, elimination of slow pathway fimction.**" Among the four studies that have included autonomic blockade as part of the study design, three demonstrated that the fast pathway effective refractory period decreases after complete elimination of slow pathway function.**'" In one study, shortening of the fast pathway effective refractory period after slow pathway ahlation in the setting of atropine and propranolol was not observed." In this report, complete autonomic blockade was not maintained throughout the study, as evidenced by large changes in the sinus cycle length before and after the ablation procedure." If shortening of the fast pathway effective refractory period can be obscured by alterations in autonotnic lone, then complete autonomic blockade throughout the entire study is required. Given that the changes in fast pathway function occur only after complete elimination of slow pathway function and that sympathetic stimulation can obscure these