Vectorcardiography shows cardiac memory and repolarization heterogeneity after ablation of accessory pathways not apparent on ECG.

BACKGROUND Pacing induced cardiac memory is an established phenomenon, but following successful WPW ablation, cardiac memory was present on ECG in variable proportions of patients depending on accessory pathway (AP) location. We hypothesized that vectorcardiography (VCG), which is more sensitive than ECG, would show cardiac memory after WPW ablation independent of AP location. METHODS Thirty-six patients were followed after successful AP ablation, 11 with overt posteroseptal (PS), 13 with overt left-sided (LS) and 12 with concealed APs (controls). VCGs were recorded the day before and after the procedure, ≥ once/week for 6-8 weeks and after ≥ 3 months. T vector and T-vector loop parameters were analyzed and compared. RESULTS After ablation of overt APs, there was a correlation between the directions of the preexcited maximum QRS-vector and the post-ablation maximum T-vector, confirming the presence of cardiac memory. Ablation of overt APs was followed by cardiac memory apparent in different directions. Thus, ablation of PS APs was followed by most pronounced changes in T-vector elevation and LS APs with significant changes only in T-vector azimuth. Cardiac memory disappeared within a month in > 80% of cases. Furthermore, T-vector loop morphology changes suggested a period of repolarization heterogeneity immediately after ablation of overt APs. CONCLUSIONS According to VCG analysis cardiac memory was present after ablation of overt APs independent of location as consistently as after ventricular pacing, and disappeared within a similar time frame during normal ventricular activation. In addition, signs of transient repolarization heterogeneity were observed after ablation of overt APs.