Feasibility of Unipolar Signal Guided Ablation in Creating Contiguous Lines of Conduction Block: A Proof-of-Concept Study.

Background: Modification of the atrial unipolar electrogram (Uni-_EGM) with loss of the near-field negative component in response to radiofrequency ablation reflects transmural loss of tissue conductivity.

Objective: The present study sought to investigate feasibility of Uni-_EGM morphology guided radiofrequency ablation (RFA) in generating contiguous, transmural lesions that result in conduction block. This method was compared with ablation guided by standard Ablation Index parameters.

Methods: In a beating heart swine model, linear transcaval ablation was performed using an irrigated ablation catheter with standard and high power RFA. First, an optimal Uni-_EGM endpoint for predicting a transmural lesion was determined by single RF applications in the smooth and trabeculated portions of the right atrium. We compared termination of RF energy immediately upon observing consistent loss of the negative component (s-wave) on the local unipolar electrogram (U₊₀) versus extending RF delivery for an additional 3 seconds beyond (U₊₃). Next, linear ablation was achieved with either target Ablation Index (AI₄₀₀) or unipolar electrogram (U₊₃) based techniques. The latter method relied upon Uni-_EGM morphology to both direct catheter positioning at sites of contiguous and viable tissue and to titrate RF delivery. Bidirectional block was demonstrated with standard EP pacing maneuvers, high density activation mapping and pathology.

Results: Extending RF delivery for 3 additional seconds (U₊₃) after consistent loss of the negative component on the Uni-_EGM proved an optimal endpoint, predicting a transmural lesion with 94% sensitivity and 100% specificity. It was observed that with increasing distance from site of radiofrequency application, the near field s-wave on the Uni-_EGM grows in magnitude while an acute current of injury pattern diminishes. Uni-_EGM based technique resulted in equal efficacy in producing ablation lines with complete bidirectional block, compared with target AI guided ablation. With standard power, Uni-_EGM guided ablation resulted in significantly less energy delivered per RF application.

Conclusions: We demonstrate that Uni-_EGM can successfully guide ablation yielding conduction lines of block. Uni-_EGM morphology reflects local tissue activation and its modification in response to thermal injury can serve as an endpoint to ensure adequate yet avoid excess RF delivery. The near-field s-wave on the Uni-_EGM indicates viable tissue, and in conjunction with an acute current of injury identified contiguous, conductive tissue for targeting. Characterization of unipolar electrogram morphology with respect to myocardial electrical properties and understanding its modification in response to injury may lend to continued pursuit for safer, more effective ablation strategies.