Impedance fluctuation and steam pop occurrence during radiofrequency current ablation: An experimental in vitro model.

Abstract

The radiofrequency impedance measurement is one of the basic parameters monitored during ablation procedures. An abrupt rise in impedance is often observed corresponding to a steam pop. The exact correlation between the occurrence of steam pop and subsequent rise in impedance has not been experimentally described so far. To evaluate the relationship between steam pop occurrence and impedance fluctuations observed during radiofrequency ablation (RFA). Porcine heart tissue specimens were appropriately prepared and placed in an experimental setup connected to electrophysiological equipment with 3D anatomical mapping facilities. The RFA lesions were performed in standardized conditions with the use of contact force measurement-enabled open irrigation ablation catheter (ThermoCool SmartTouch™, 3.5 mm tip, F-J curvature; Biosense Webster, Irvine, USA) in the power-control mode. The RFA delivery was stopped when the steam pop occurred. Time taken for the steam pop to occur and to the subsequent abrupt impedance rise was recorded, along with the impedance fluctuations during an application. In total, 25 experimental radiofrequency (RF) current deliveries ended up with steam pops, which occurred after 30-60 s. The time recorded from the beginning of the application up to the steam pop was shorter if increased power was applied (35 W compared to 30 W: 41.5 ±9.9 s compared to 49.9 ±8.2 s; p = 0.046). During all RF applications, impedance significantly but gradually decreased from 122.9 ±7.9 Ω to 87.5 ±3.6 Ω (p < 0.001) with a mean drop rate of 0.8 ±0.2 Ω/s. During all experiments, the abrupt and significant impedance increase (8.2 ±2.0 Ω, p < 0.001) was observed always after steam pop occurrence (207.4 ±155.9 ms). During RF current delivery which ended up with steam pop, an abrupt impedance increase was always registered after the occurrence of this phenomenon. Therefore, the impedance rise observed during steam popping cannot be used for its prediction. The time to steam pop was shorter for applications with increased power but not with greater contact force.