Impact of Lowering Irrigation Flow Rate on Atrial Lesion Formation in Thin Atrial Tissue: Preliminary Observations From Experimental and Clinical Studies

Objectives The authors sought to investigate the effect of low irrigation flow rate on lesion characteristics and ablation outcomes in a clinicopathological study. Background Irrigated ablation produces deeper lesions compared with nonirrigated ablation, which may not be desirable in the thin-walled posterior left atrium (LA), where collateral esophageal injury is possible. Methods Lesions were placed on the smooth posterior right atrium in 20 swine and posterior LA in 60 patients at a maximum power of 20 to 25 W with either: 1) power-controlled ablation at an irrigation flow rate of 17 ml/min (high-flow group 10 swine; n = 40) or 2) temperature-controlled ablation at an irrigation flow rate of 2 ml/min (low-flow group 10 swine; n = 20). Safety and efficacy was also compared in 326 patients undergoing AF ablation using high-flow (n = 160) or low-flow settings (n = 166) for posterior LA ablation. Results Low-flow, compared with high-flow, lesions in swine had a higher incidence of lesions with: impedance fall ≥10 Ω, loss of pace capture, electrograms characteristic of transmural lesions, and visible lesions on anatomic inspection (p < 0.05 for all). Low-flow lesions had a maximal diameter at the endocardial surface, whereas high-flow lesions had a maximal diameter at the epicardial surface. In humans, impedance, pace capture, and transmurality data also strongly favored low-flow lesions. There was no difference in acute pulmonary vein isolation, complications, or 12-month arrhythmia-free survival between the groups. Conclusions Low-flow irrigated ablation provides favorable lesion characteristics for posterior LA ablation without increasing the risk of adverse events.