Estimation of atrial response to entrainment pacing using electrograms recorded from remote sites

Introduction: Assessing the entrainment response by measuring postpacing in tervals (PPIs) at the pacing site facilitates localization of reentrant cir cuits, but may be technically difficult. Methods and Results: There were 269 right atrial sites entrained in 21 circ uits in congenital heart patients left atrial (LA) electrograms were record ed. Entrainment response was measured by two methods: (1) PPI-tachycardia c ycle length, and (2) the difference in latencies between the stimulus artif act and the pacing site electrogram, referenced to the LA electrogram. PPI also was measured from the LA as an index of antidromic activation. Among 4 3 pacing sites with antidromic LA activation, half showed a discrepancy gre ater than or equal to 25 msec between methods 1 and 2, At the other 226 sit es, agreement between the two methods was high (mean discrepancy -3 +/- 8 m sec, r = 0.975, 0 sites with discrepancy greater than or equal to 25 msec), Correcting all sites by LA antidromicity reduced the mean discrepancy to 1 +/- 6 msec and improved correlation (r = 0.988). Conclusion: LA electrograms can be used to estimate right atrial entrainmen t response, if antidromic activation of the LA is recognized and taken into account.