Two ripples in a pond: The subtleties of mapping observations in localizing premature ventricular complex sites

We read with interest the study by Arps et al.1 and technique using ripple mapping that can be used to differentiate successful premature ventricular complex (PVC) sites with high accuracy. Ripple mapping (CARTO-3©; Biosense Webster Inc) is a visual dynamic display of activation and voltage that does not require local activation time annotation or a window of interest as it displays the entire electrogram (EGM) relative to a fiduciary stable time or reference point. In this study, the earliest ripple signal (ERS) that was concordant to the earliest activation (EA) chamber predicted ablation success, compared to discordance. EA was defined using unipolar −dV/dTmaximal. We congratulate the authors for highlighting this technique and suggest annotating all local activation times to first bipolar deflection along with assessment of the earliest sites with unipolar −dV/dT relative to the timing of the QRS. Based on the study by Higuchi et al.,2 we have also found that when the first bipolar deflection correlates with unipolar dV/dT, it predicts success from an endocardial exit site (median of 3.5 ms). However, intramural sites are characterized by a delay from the first bipolar deflection to the unipolar −dV/dT (median 25.5 ms).2 Finally and importantly, this delay was also observed in failed cases (median 12.5 ms), however, the discriminating factor was that the first bipolar deflection was late to surface QRS in these cases as opposed to successful intramural cases where the first bipolar deflection was early. We wish to comment on two nuanced points regarding this concept. The first specific nuance is related to the earliest local bipolar EGM-unipolar −dV/dT discrepancy, but yet success, relating to specific anatomical scenarios such as the coronary cusps compared to typical close and concordant timing of bipolar and unipolar dV/dT breakouts that is commonly seen other sites such as the right ventricular outflow tract (RVOT). If conventional unipolar -dV/dT is used alone in coronary cusp cases, the successful true site of origin may appear on-time or late and appear as a discouraging ablation site. It is possible that this discrepancy may be anatomically related to the thin limbs of myocardial strands on the underside of the base of the coronary cusps distant from the septal myocardium where large-volume depolarization occurs. Regardless of endocardial or intramural sites, it appears first bipolar deflection is a better guide than unipolar −dV/dT. In cases of discordance, did the authors target the ERS or EA site first and was ablation performed on both sides regardless of initial ablation response? The second nuance is if the authors observed two or more different sites simultaneously ripple ahead of unipolar annotation on the mapping surface? This is important as mid-myocardial or deeper origins may be able to be differentiated with ripple mapping. Ripple discrepancy with a single ripple origin ahead of the earliest unipolar EGM may have a different connotation than two (or more) ripples ahead of the earliest unipolar EGM activation. We have observed a phenomenon where deep foci can not only appear on the surface displaced from the intramural site but the finding of dual breakouts sites are commonly seen from deeper foci. Dual simultaneous origins using ripple mapping may differentiate contralateral versus subendocardial origins in the ipsilateral mapped chamber.3 In essence, discrepancy may not always mean an inaccessible or unsuccessful focus but the need to identify the shortest anatomic distance and site overlying the focus. Additionally, it highlights the long electrophysiological distance between the ripple or earliest bipolar to steepest unipolar EGM deflection at the discrepant site may be successfully targeted if it is a coronary cusp or intramural site. Kumaraswamy Nanthakumar is a consultant to Biosense Webster; Dr Robert D. Anderson is a recipient of the Royal Australasian College of Physicians (RACP) Bushell Travelling Fellowship and the Miriam L. Burnett electrophysiology fellowship. The remaining authors declare no conflict of interest.

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