Cardiac memory after radiofrequency ablation of accessory pathways: the post-ablation T wave does not forget the pre-excited QRS.

INTRODUCTION

Normalization of the pre-excited QRS following ablation is accompanied by repolarization changes but their directional relationship to changes in ventricular activation has not been well characterized.

METHODS

Accordingly, we measured QRS and T wave vectors and QRS-T angles from 12 lead ECG recordings immediately before and after accessory pathway (AP) radiofrequency ablation in 100 consecutive patients. Patients with bundle branch block, intraventricular conduction defect or intermittent pre-excitation were excluded, leaving a study group of 45 patients: 35 with pre-excitation and 10 with concealed APs.

RESULTS

With AP ablation, changes occurred in the QRS and T wave vectors and QRS-T angles that were essentially equal and opposite, so that the newly normalized QRS complex and QRS vector were accompanied by a T wave whose vector approximated that of the pre-ablation QRS vector. This tended to maintain a large QRS-T angle: 72 degrees +/- 50 degrees before, and 54 degrees +/- 34 degrees after QRS normalization (p = NS). A QRS-T angle >40 degrees was found before and after ablation in 22/35 patients (63%) with baseline pre-excitation; but never in patients with a concealed AP (p = 0.001). The angle between the pre-excited QRS and the post-ablation T wave was 35 degrees +/- 37 degrees, and </=40 degrees in 25/35 patients (71%). The change in T wave axis with QRS normalization correlated in magnitude with the QRS-T angle before ablation (r = 0.73, p < 0.0001). The change in QRS axis correlated with the QRS-T angle after ablation (r = 0.37, p < 0.03). Shorter AP effective refractory periods (ERPs) correlated with wider QRS-T angles after ablation (r = -0.39, p < 0.03). The ECG leads manifesting these changes depend on AP location.

CONCLUSION

T-wave changes after ablation of APs (1) are dependent on anterograde AP conduction at baseline and are not observed with concealed APs; (2) correlate in magnitude directly with the change in QRS axis and inversely with the anterograde AP-ERP; (3) are related to AP location. With termination of pre-excitation secondary repolarization changes immediately disappear and the post ablation T wave axis approximates that of the pre-excited QRS. Recognition of this sequence may prevent unnecessary clinical interventions.