BIOPHYSICAL CHARACTERISTICS OF RADIOFREQUENCY LESION FORMATION IN-VIVO - DYNAMICS OF CATHETER TIP-TISSUE CONTACT EVALUATED BY INTRACARDIAC ECHOCARDIOGRAPHY

During clinical radiofrequency catheter ablation a wide range of deliv ered power may be necessary to achieve success despite an apparently s table catheter position on fluoroscopy. The purpose of this study was to use intracardiac echocardiography to characterize the relation betw een catheter tip-tissue contact and the efficiency of heating during a pplications of radiofrequency energy in vivo and to determine whether intracardiac echocardiography could be used prospectively to improve t issue contact. A closed-loop temperature feedback control system was u sed during radiofrequency applications at five anatomic regions in the right atrium of 15 anesthetized dogs to ensure achievement of a prede termined temperature (70 degrees C) at the catheter tip thermistor by automatic adjustment of delivered power (maximum 100 W). The efficienc y-of-heating index was defined as the ratio of steady-state temperatur e (degrees Celsius) to power (watts). Two-dimensional intracardiac ech ocardiography was used to evaluate movement of the catheter tip relati ve to the endocardium. Perpendicular contact was scored as good, avera ge, or poor and lateral catheter sliding as <2, 2 to 5, or >5 mm. Two groups of animals were included: group 1, in which tissue contact was guided by fluoroscopic and electrographic criteria for stability of co ntact, with intracardiac echocardiography used simply to observe the a pplication; and group 2, in which tissue contact was guided by intraca rdiac echocardiography. Of 66 applications, 18 (27.3%) had poor perpen dicular contact on echocardiography, and 12 (18.2%) demonstrated later al sliding of >5 mm even though they had been considered to have good tissue contact by fluoroscopic and electrographic criteria. Perpendicu lar catheter contact and anatomic location were shown to be independen tly related to the efficiency-of-heating index. Applications with good perpendicular contact had a significantly higher efficiency-of-heatin g index and a significantly greater lesion size than those with averag e or poor contact. The percentage of applications having good perpendi cular tissue contact and the lesion size were significantly greater wh en tissue contact was guided by intracardiac echocardiography compared with fluoroscopic and electrographic guidance. This study demonstrate s that variations in catheter tip-tissue contact account for differenc es in the efficiency of tissue heating, independently of the anatomic she of the application. Poor tissue contact was observed by intracardi ac echocardiography and confirmed by indexes of tissue heating in appr oximately one third of radiofrequency applications despite a fluorosco pic appearance and electrographic morphologic appearance suggestive of good tissue contact. There was a significant correlation between echo cardiographic evaluation of tissue contact, parameters of tissue heati ng (efficiency-of-heating index), and lesion size. In addition, intrac ardiac echocardiography could be used prospectively to improve the per centage of good contact applications and increase the lesion size.