TRANSESOPHAGEAL ECHOCARDIOGRAPHY DURING RADIOFREQUENCY CATHETER ABLATION OF VENTRICULAR-TACHYCARDIA

Radiofrequency lesion formation requires stable catheter tip/endocardi al contact. Energy delivery is limited when temperatures are > 100-deg rees-C due to coagulum formation at the catheter tip. Transesophageal echocardiographic imaging may be useful for monitoring catheter positi on and detecting boiling. Transesophageal echocardiographic images wer e recorded during production of 22 radiofrequency lesions in bovine my ocardium in a saline bath. Lesion size, tissue temperature and appeara nce of echo contrast (bubbles) were assessed. In 11 patients, transeso phageal echocardiography was used to guide catheter movement and detec t boiling during radiofrequency ablation for ventricular tachycardia. In the tissue bath, the appearance of echo bubbles was associated with visual bubbling at the catheter tip, tissue temperatures > 60-degrees -C and larger lesions (284 +/- 165 vs 30 +/- 54 mm3; p < 0.001). In hu mans, transesophageal images easily identified the catheter tip in eit her ventricle and enabled continuous observation of electrode-tissue c ontact during radiofrequency application. Transesophageal echocardiogr aphic bubbles appeared in 59 of 217 radiofrequency applications (27%). Continued radiofrequency application after appearance of bubbles was followed by an increase in impedance. Prolonged placement of the probe in heavily sedated patients resulted in a mild sore throat, but no ot her complications. Transesophageal echocardiographic imaging enables c ontinuous monitoring of catheter position during radiofrequency energy application. The abrupt appearance of echo bubbles indicates boiling and impending coagulum formation at the catheter tip.