Fig. 7.

Typical trial from experimental Group 6: irrigation with room temperature normal saline at 20 cc/min, blood flow velocity = 0.26 m/s, RF power was fixed at 50 Watts. Note that T₀ rises rapidly to boiling, at which point it abruptly deflects downward. This deflection was coincident with the sudden elaboration of echocardiographic bubbles at the electrode–endocardial interface and an audible “pop.” Trials stopped at this instant (data not shown) showed displacement of the interface thermocouple to a site adjacent to the interface. After a few seconds, T₀ resumes its rise, but at a much slower rate. Note that at the moment that the downward deflection in T₀ occurs, despite continued (constant) power application there is also a downward deflection in T_E, and an insignificant (<10 ohm) rise in circuit impedance. We hypothesize that the drop in T_E was due to temporary displacement of the electrode from endocardial contact by the elaboration of bubbles, increasing its exposure to blood cooling.