777-6 Assessment of Radiofrequency Boiling and Thrombus Formation During Catheter Ablation by Transesophageal Echocardiography

Eighty-four patients (age 43±28 years) suffering from refractory tachycardia underwent RF ablation: 48 patients with an accessory pathway (left side 29, right side 19), 24 patients with ventricular tachycardia (ischemic 13, idiopathic 11) and 12 with junctional tachycardia. Continuous transesophageal echocardiography (TEE) was performed during the procedure — mean duration 124 rain (48–212) — and RF was delivered with an average of 15 applications (1–351) energy of 31.2 Watts (20–40) and temperature of 68°C (47–84) during 48.6min (20–66) with a heparine anticoagulation (ACT×2 to 3).TEE demonstrated a progressive micro-cavitations advent during 29% of the sessions (WPW: 68%; VT: 42%; junctional T: 25%). preceding with an average of 32 sec (10–66), a major rise of impedance (> 200 Ω). No relationship was found between the micro-cavitations appearance and RF success, tip temperature, initial power and anticoagulation level. There is a correlation (r=0.68 p<0.05) between micro-cavitations and both impedance level (≥ 120 Ω) and catheter endocardial-contact estimated by the injury current of the unipolar catheter recording (≥8 mv). A charred thrombus was seen at the catheter tip in all cases when the catheter was withdrawal, micro-thrombus (< 2mm) at the echogenic bubbles appearance and macro-thrombus (>2mm) when impedance increases. In the mean time, if micro-cavitations occur during a first application without or with a slight impedance rise, successive applications with the same catheter lead to an enhancement of echogenic bubbles and finally to the impedance increase.These results suggest that the micro-cavitations observed with TEE during RF ablations are linked to the beginning of a thrombus formation related to endocardial lesions resulting from an overrated catheter contact pressure and tip-delivered energy