Introduction: Ventricular tachycardia (VT) recurrence after catheter ablation remains frequent and improved ablation strategies are needed. The re-entry vulnerability index (RVI) is an activation-repolarization marker to localize critical sites for VT initiation. Its use is limited since current electro-anatomical mapping systems (EAMS) cannot provide global measurement of activation and repolarization times within one beat. Here we aim to (1) Assess a simple methodology to map RVI using sequential EAMS and (2) Provide preliminary results about the algorithm’s ability to localize re-entry initiation sites.
Methods: This mapping method assumes that beats showing similar surface ECGs are representative of the same underlying activation-repolarization dynamics and can be used to estimate RVI. The mean correlation coefficient between single ECG beats and a representative template is used as inclusion/exclusion criterion. In simulation, local action potentials were generated using analytical functions at 257 nodes covering both ventricles. The corresponding unipolar electrograms were measured using a simple model recently validated in-vivo while surface ECGs were computed using ECG-Sim. Data from two catheter ablations were recorded using CARTO3 and analyzed off-line.
Results: Localization of the vulnerable region associated with 5% bottom RVI was accurate (sensitivity>80±8%, specificity>99±1%) for moderate to large repolarization variability (5≤σRT≤20 ms) and moderate level of noise (SNR≥10 dB) but it deteriorated for larger repolarization fluctuations (σRT≥25 ms) and SNR≤5 dB. Sensitivity remained high even when RVI estimates were only moderately accurate (CC>0.67±0.05, MAE<25±1 ms). The number of ectopic beats did not affect the results and the best ECG correlation coefficient was CC=0.95. In the two in-vivo cases analyzed the sites of low RVI and VT exit were close (distance: 6.5 and 5.1 mm).
Conclusion: A simple analytical simulation suggests that RVI can be estimated from sequential EAMS and first results during in-vivo VT ablations are encouraging.