Unipolar electrogram characteristics predictive of successful radiofrequency catheter ablation of accessory pathways

Unipolar Electrogram in Ablation, Introduction: The purpose of this study w as to determine the characteristics of the unipolar electrogram that are mo st helpful in predicting successful radiofrequency ablation of accessory pa thways. Methods and Results: The unipolar electrogram was analyzed at 185 ablation sites in 53 patients; 94 attempts were directed at the site of earliest atr ial activation ("atrial group") and 91 at the site of earliest ventricular activation ("ventricular group"). The electrogram was analyzed for several features, including pattern ("QS" or "initial R"), Unipolar pattern: Overal l, a "QS" pattern was seen at 55% of unsuccessful, 75% of temporarily succe ssful, and 90% of permanently successful sites. For the atrial group, the r espective frequencies were 53%, 77%, and 92%, and for the ventricular group , 57%, 73%, and 86%, The difference in pattern distribution between unsucce ssful and permanently successful sites was significant for all groups: over all, P < 0.0001; atrial group, P = 0.0005; ventricular group, P = 0.02. Abs ence of a "QS" pattern (i.e., "initial R") predicted a 92% chance of unsucc essful ablation, Additional features: Activation times were significantly s horter at permanently successful than at unsuccessful (P < 0.0001) or tempo rarily successful sites (P = 0.0002), No significant differences were found in atrial or ventricular amplitudes or in AN ratios. Intrinsic deflection slew was lower at temporarily successful sites (P = 0.03 vs all other sites ), Conclusion: Ablation at sites revealing an "initial R" pattern (i.e., absen t "QS") is very unlikely to be successful. Activation time is shorter at su ccessful sites. These features are equally applicable when mapping the atri al potential as when mapping the ventricular potential.