To evaluate the electrophysiological and histological characteristics of the atrioventricular node (AVN) and His bundle (His) post the temporal and spatial change of pulse field ablation (PFA) in canine.

A stable biphasic square wave pulse width (100 ms) was delivered with output 2 000 V (± 1 000) V from a novel contact-force sensing focal PFA catheter in a bipolar electrode arrangement. After mapping the site with the highest his potential navigated by a 3-dimensional electroanatomical mapping system in 6 canines. Sites 1 was defined as those 0~2 mm away from the highest His potential. Then the PFA catheter was moved to map the sites 2 which with his potential were ≥6 mm far from the highest His potential, and the sites 3 were without His. The one and consecutive 3 pulse train deliveries were applied in sites 1, 2 and 3 in sequence, and were named in sequence as 1PFA-1 site, 3PFA-1 site, 1PFA-2 site, 3PFA-2 site, 1PFA-3 site and 3PFA-3 site. The safe distance in vivo was defined as the shortest width between the sites 3, without high-degree atrioventricular block (AVB) or complete bundle brunch block post PFA, to the sites 1. Estimated the range of estimated lesion was confirmed after simulation of focal ablation catheter placed on the surface of atrial musculature tissue in vitro in a computational model. The cardiac specimens were sectioned for histopathological analysis such as depth and width of ablation in 24 h post the PFA procedure.

①The transient Ⅲ-degree AVB reproducibly occurred in 6 1PFA-1 sites, 6 3PFA-1 sites and 2 3PFA-2 sites. Right bundle branch block (RBBB) occurred in 6 1PFA-1 sites, 6 1PFA-2 sites, 2 1PFA-3 sites, 6 3PFA-1 sites, 4 3PFA-2 sites and 3 3PFA-3 sites. ②The duration of transient Ⅲ-degree AVB and RBBB were sorted as follows: 3PFA-1 sites>1PFA-1 sites>3PFA-2 sites [(4.15±0.58) min vs. (2.97±0.46) min vs. (1.35±0.21) min, P<0.01]. The transient duration of RBBB in 1PFA-1 sites was longer than that in 1PFA-2 sites followed by 1PFA-3 sites, and it was reoccurred in 1PFA-3 sites [1PFA: (2.01±0.81) min vs. (1.07±0.63) min vs. (0.40±0.14) min; 3PFA: [(4.53±0.80) min vs. (3.27±0.17) min vs. (0.43±0.12)] min, P<0.05]. The duration of RBBB either in 3PFA-1 sites or 3PFA-2 sites was longer than that in 1PFA-1 sites [(4.53±0.80) min vs. (2.01±0.81) min, P<0.01] and 1PFA-2 sites [(3.27±0.17) min vs. (1.07±0.63) min, P<0.01]. The safe distance in vivo was 10.0-14.1 mm. A maximal transmural lesion producing a width of 14 mm by histology was comparable to irreversible damage width in a computational model in vitro.

PFA can produce transmural lesions near AVN- His region, and PFA-related Ⅲ-degree AVB or RBBB was site and dose dependent.