Ablation with an internally irrigated radiofrequency catheter: learning how to avoid steam pops.

Objectives: The aim of this study was to assess the feasibility of using electrode temperature, impedance, and power to predict and thereby potentially prevent steam pops during cooled radiofrequency (RF) ablation.

Background: When myocardial temperature reaches 100 degrees C during RF catheter ablation, steam explosions are seen. Saline-cooled RF ablation reduces temperatures at the electrode-tissue interface, but excessive intramyocardial heating still may occur.

Methods: In anesthetized swine, 26 cooled RF applications were made in the right and left atria while observing with intracardiac echocardiography (ICE). Power delivery was increased gradually until a steam explosion was seen or a maximum output of 50 W was reached.

Results: ICE identified steam explosions in 21 RF applications. Steam explosions were associated with a large impedance increase, >25 Omega in only three cases, whereas small increases <10 Omega (mean 5.3 +/- 2.6 Omega) occurred in 18 cases. Mean electrode temperature at the time of steam explosion was 43.6 degrees C +/- 5.3; 18 of 21 explosions occurred when temperature reached >/=40 degrees C. Mean power and impedance drop were similar for applications with and without steam explosions. Five steam explosions were associated with a sudden drop in electrode temperature.

Conclusions: Steam explosions are common when cooled electrode temperature exceeds 40 degrees C and are not predictable from power or impedance drop. Small impedance rises and sudden drops in measured electrode temperature indicate possible steam formation. Maintaining cooled electrode temperature <40 degrees C during RF likely will reduce the risk of steam explosions.