EXIT SITE OF ISCHEMIC VENTRICULAR TACHYCARDIA: LESSONS FROM SIMULTANEOUS MULTI-ELECTRODE MAPPING ERA APPLIED TO SEQUENTIAL MAPPING ERA

Ventricular tachycardia mapping in the sequential era is dependent on determining the exit site using entrainment mapping and or activation mapping. During entrainment mapping, VT has the potential of degenerating into ventricular fibrillation, requiring cardioversion that may distort the electroanatomic map. In addition entrainment may change the activation sequences and initiate another VT. Thus it is of importance to identify the exit site based on temporal characteristics of the activation map and characterize the exit site. In the era of point by point sequential mapping it is unclear how much time ahead of surface activation is the activation at the exit site. We sought to determine the temporal characteristics of the exit site where successful ablation was performed in relation to the surface activation. Twelve patients with ischemic VT who had multi-electrode simultaneous endocardial mapping during ventricular tachycardia were retrospectively reviewed. 16 VTs induced in these twelve patients were analyzed and the activation sequence in systole, diastole, and the presystolic period was annotated. Activation time in relation to surface activation was characterized at the exit site where ablation was performed. Mapping was performed with a custom-made system consisting of a 112 electrode endocardial array with simultaneous uni and bipolar recording. Filter settings for uni was 0.1 - 200 Hz, bipolar 28 - 700Hz, sampling rate was 1 kHz for uni and 2 kHz for bipolar electrograms.The mean activation time at the exit site was 60 +/− 24 msec ahead of surface VT activation. The range of the timing of the activation at the exit site preceding surface activation was was 18 - 114 ms. The unipolar characteristic at the site was not useful in identifying timing on a consistent basis. The exit site of an ischemic ventricular tachycardia is on average 60 ms ahead of surface activation. This presytolic timing is earlier than what is generally believed in the current sequential mapping era of VT ablation. Our analysis suggests that catheter position at shorter activation times would indicate a location in the post exit site and unlikely to produce a useful outcome.