How to use bipolar and unipolar electrograms for selecting successful ablation sites of ventricular premature contractions

Background: Local activation time is often determined by the maximal negative of the extracellular unipolar potential (−dV/dT_max). While this is accurate in 2-dimensional uniform tissue, propagation through nonuniform or 3-dimensional structures have shown discordance between −dV/dT_max and local activation time. Objective: The purpose of this study was to examine the relationship between bipolar and unipolar electrograms for selecting successful ablation sites of endocardial (superficial) vs intramural (deep) ventricular premature contractions (VPCs). Methods: This cohort consisted of 66 patients with VPCs presenting for ablation in a bigeminy, trigeminy, or quadrigeminy pattern. VPCs were classified as endocardial if ablation at the earliest endocardial site resulted in immediate suppression (<10 seconds) or as intramural if ablation resulted in delayed suppression (≥10 seconds), required multiple applications, or was not achieved. Unipolar and bipolar electrograms were analyzed. Results: In endocardial VPCs, the first rapid bipolar deflection corresponded with unipolar −dV/dT_max, occurring 20.5 ms (17.8–26.0 ms) and 16.0 ms (6.8–22.0 ms), respectively, before the QRS onset. In successfully ablated intramural VPCs, the first rapid bipolar deflection preceded the QRS onset by 14.0 ms (11.2–22.6 ms) and coincided with the first rapid unipolar deflection, although −dV/dT_max occurred 10.5 ms (0.0–20.8 ms) after the QRS onset and often coincided with far-field activity. In unsuccessfully ablated intramural VPCs, the first rapid bipolar deflection to QRS onset interval was shorter in comparison to successfully ablated intramural VPCs (1.5 ms vs 14.0 ms; P <.001) while the unipolar −dV/dT_max to QRS onset interval was similar (P =.095). Conclusion: Mapping of VPCs should be guided by the first rapid bipolar deflection that corresponds to a similarly early unipolar deflection but not with −dV/dT_max.