Differential pacing for distinguishing block from persistent conduction through an ablation line

Background-Because complete Linear conduction block is necessary to minimiz e the recurrence of reentrant tachycardias such as typical atrial flutter, we investigated a simple technique to recognize a persistent gap or complet e linear block. Methods and Results-We prospectively evaluated cavotricuspid isthmus conduc tion in 50 patients (age 63 +/- 8 years, 43 men) after radiofrequency ablat ion, The distal and proximal bipoles of a quadripolar catheter placed close to the ablation line were successively stimulated during recording from th e ablation line. We hypothesized that because the initial and terminal comp onents of local potentials reflected activation at the ipsilateral and cont ralateral borders of the ablation lesion, a change to a more proximal pacin g site without moving the catheter would prolong the stimulus to the initia l component timing, whereas the response of the terminal component would de pend on the presence of block or persistent conduction. A shortening or no change in timing of the terminal component would indicate block, whereas le ngthening would indicate persistent gap conduction. The results were compar ed with previously described criteria for isthmus block. Ninety-two sites w ere assessed: 17 before and 75 after the achievement of complete isthmus bl ock The timing of the initial component was delayed by 19 +/- 9 ms, and the terminal component was advanced by 13 +/- 8 ms after block ansi delayed by 12 +/- 9 ms in case of persisting conduction. The sensitivity, specificity , and positive and negative predictive values for linear block were 100%, 7 5%, 94%, and 100%, respectively. Conclusions-An accurate assessment of isthmus block or persistent isthmus c onduction is possible with this technique of differential pacing.