Impact of the ECG for detection of intraatrial conduction block after atrial flutter ablation.

Induction of complete bidirectional conduction block via the posterior isthmus of the right atrium is introduced as a standard endpoint for catheter ablation of atrial flutter. The present study sought to investigate the impact of changes in P wave duration and morphology detected by the surface ECG during coronary sinus and posterolateral right atrial stimulation as a marker for conduction block. Morphology and duration changes of the paced P wave before and after radiofrequency catheter (RFC) ablation were estimated in 22 patients referred for ablation of atrial flutter. We looked for a morphology change of the terminal portion in the 12-lead ECG and an increment of P wave duration. In 16 of 22 patients in whom atrial flutter ablation resulted in a complete bidirectional block, the conduction block was unidirectional in 4 patients and conduction times remained unchanged in 2 patients. After induction of complete bidirectional block a change of the terminal portion of the P wave towards a more positive morphology in one or more inferior leads was detected in 14 (88%) of 16 patients during coronary sinus stimulation and in 15 (94%) of 16 patients during posterolateral right atrial stimulation. These changes were predominantly observed in the inferior leads. Positive morphology changes of the terminal P wave portion in the inferior leads indicating conduction block with a sensitivity of 86% and a specificity of 100% were observed. An increment of 10 ms or more in P wave duration indicates conduction block with a specificity of 100% and a sensitivity of 67%. There was a significantly larger increment of P wave duration during coronary sinus (CS) stimulation compared to posterolateral right atrial stimulation (38 +/- 21 vs 16 +/- 21 ms). The analysis of P wave duration and morphology in the inferior leads of the surface ECG is a reliable tool to assess the intraatrial conduction after atrial flutter ablation. Different conduction during coronary sinus and posterolateral right atrial pacing may cause a different P wave duration after ablation.