Critical appraisal of electrogram-based depth estimation and lesion assessment in ventricular ablation

Abstract

We read with interest the article by Jeong et al. titled “Quantitative analyses of the distal bipolar electrogram for focal premature ventricular contraction ablation” published in the Journal of Arrhythmia.¹ While the authors present novel quantitative parameters for analyzing bipolar electrograms, several of their key conclusions warrant critical examination against established research findings.

The authors propose that a 4 mm depth threshold distinguishes “true” near-field from far-field bipolar electrograms, calculating this based on a 9.8 ms timing difference and an assumed conduction velocity of 40 cm/s. However, this conclusion conflicts with substantial evidence regarding ventricular conduction velocities and radiofrequency lesion characteristics. Recent extensive reviews prove that there is a great variability in human ventricular conduction velocities, where longitudinal velocities vary between 50 and 95 cm/s and transverse velocities range between 14 and 45 cm/s.² The value of 40 cm/s assumed by the authors seems to be quite smaller than the measured values, which may overestimate the distance reflected by their time differences.

Moreover, the investigation of the depth of the lesions made by radiofrequency ablation proves that efficient lesions are made up to 3–5 mm. Contact force, however, is a major determinant of lesion dimensions, with the depth of the lesion assuming a power function (Lesion depth = 3.17 × CF^0.14).³ The author used magnetic navigation sources with inherently lower contact force that could have produced shallower lesions than their postulated 4 mm threshold, and could be the reason why ablations failed in some places classified as “far-field”.

The authors conclude that the extent of fractionation does not have any definite implication in differentiating between successful and unsuccessful ablation sites, as it has been the practice in focal PVC ablation. Such observation is contrary to numerous reports that have shown the significance of fractionated electrograms in the ablation of ventricular arrhythmias. Large-scale studies using ultrahigh-density mapping have shown that highly fractionated potentials (>10 fractionations) are consistently found in all critical ventricular tachycardia isthmus areas during substrate mapping.⁴ While the authors correctly note that idiopathic focal PVCs differ mechanistically from scar-related ventricular tachycardia, recent evidence suggests that local substrate abnormalities, reflected by electrogram fractionation, may still play important roles in focal PVC origins.

Although the authors give their reasoning only to bipolar electrograms, discrediting unipolar recordings as of “limited utility,” this opinion is not corroborated with the new data on the complementary nature of bipolar–unipolar analysis. Emerging evidence has suggested that particular unipolar electrogram patterns, including the negative concordance pattern (NCP) and notched morphologies, could serve as useful information to guide the successful ablation of PVC. In a large study of tricuspid annular PVCs, negative concordance patterns on both unipolar and bipolar electrograms with a difference in timing had a sensitivity of 73.1% and specificity of 87.7% in predicting successful ablation.⁵ In summary, although the authors speak only in favor of bipolar electrograms and diminish the role of unipolar recordings, this point of view does not take into consideration the accumulating body of evidence on the synergistic value of combining both modalities.

Finally, although the method of quantifying bipolar electrograms offered by Jeong et al. is rather interesting, their major findings about the 4 mm depth threshold, rejection of fractionated electrograms, and the sole use of bipolar parameters contradict a significant body of existing evidence. Before these parameters can be used clinically, they must be prospectively validated in larger, multi-center studies. Future studies ought to include thorough analysis of electrograms bearing the features of both unipolar and bipolar signals, verified conduction velocity, and the impact of contact force on lesion creation.

No funding was received for the preparation or submission of this letter.

Authors declare no conflict of interests for this article.

As this is a commentary on a published study and no new data were collected or analyzed, ethics approval was not required.