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.