Popping phenomena in temperature-controlled radiofrequency ablation: When and why do they occur?

During temperature-controlled radiofrequency (RF) ablation a popping sound sometimes occurs. This popping phenomenon is know to be associated with unw anted effects like blood boiling, endocardial rupture, catheter dislocation , and impedance rise. The present in vitro study determined the influence o f cooling, electrode contact, and tip temperature on the occurrence of popp ing phenomena. Pieces of porcine ventricle were immersed in a bath of salin e solution at 37 degrees C. Forty-two RF ablations were performed with diff erent electrode-tissue contact forces (i.e., 0.0-0.44N) in a temperature-co ntrolled mode (70 degrees C setpoint, 30 s, 50 W maximum polyer output, 4-m m tip, thermocouple). Half of the 42 ablations were performed with fluid fl ow (0.1 m/s, group I), the other half without flow (group nl. In group I, m ean tip temperature and power were 55.6 +/- 8.5 degrees C and 36.2 +/- 13.8 W,resulting in a lesion volume of 121 +/- 57 mm(3). In group II, the respe ctive values were 67.3 +/- 1.5 degrees C and 9.9 +/- 5.2 W resulting in a v olume of 42 +/- 18 mm(3). The differences between groups were statistically significant. Overall, ten popping phenomenas occurred in group I and none in group II. Pops occurred significantly more often when the contact force was < 0.1 N (8/10) and the tip temperature was < 60 degrees C (8/10). Two e ndocardial ruptures occurred, both were associated with a popping phenomeno n. Using temperature control, the probability of pops is significantly high er when the ablation electrode and the endocardial tissue surface are expo sed to fluid flow and the electrode-tissue contact is poor. Under these con ditions the tissue temperature can be much higher than the temperature meas ured at the tip electrode and can potentially reach 100 degrees C causing i ntramyocardial steam formation and a popping phenomenon.