Lower atmospheric pressure is associated with shallower radiofrequency ablation lesions and more frequent steam pops: an ex vivo porcine study

Background Atmospheric pressure affects the boiling point of water and may influence thermal lesion formation during radiofrequency (RF) ablation. However, whether atmospheric pressure alters RF lesion formation and steam-pop risk under fixed ablation index (AI) targets remains unknown. Methods A total of 360 analyzable lesions were created in 36 ex vivo porcine hearts using the same RF ablation system, which was transported and used consistently at three sites with different atmospheric pressures: Beijing (1,014 hPa), Xining (770 hPa), and Lhasa (650 hPa). At each site, 30 analyzable lesions were obtained at each target AI value (300, 400, 500, and 600). Lesion dimensions, impedance reduction, ablation duration, temperature, and steam-pop occurrence were recorded. Differences among sites were assessed using analysis of variance and Fisher's exact test. A multiple linear regression model was constructed to evaluate the relationship between atmospheric pressure, AI, and lesion volume. Results At fixed AI targets, lesions created at lower-pressure sites were significantly shallower and had smaller volumes (all P < 0.05), whereas surface and maximum diameters remained similar among the three sites. Steam pops occurred in 0/120 (0.0%) RF applications in Beijing, 2/122 (1.6%) in Xining, and 6/126 (4.8%) in Lhasa (overall P = 0.031). Impedance reductions differed significantly among sites at 3 and 10 s (both P < 0.001), but not at 5 s ( P = 0.498). Atmospheric pressure and AI jointly explained 88.4% of the variation in lesion volume (R 2 = 0.884), enabling derivation of a hypothesis-generating AI correction equation. Conclusion Within the natural range of atmospheric pressures examined, lower atmospheric pressure was associated with shallower and smaller-volume RF lesions at fixed AI targets and a higher observed incidence of steam pops. These findings suggest that atmospheric pressure may influence RF lesion formation and steam-pop occurrence, warranting further mechanistic and in vivo validation.