BackgroundRadiofrequency catheter ablation requires precise positioning of the ablation electrode. Fluoroscopically guided catheter manipulation has limitations, and there are risks of radiation exposure. The purpose of this study was to examine the feasibility of guiding catheter ablation within the right atrium with catheter-based intracardiac echocardiography.Methods and ResultsA 10F, 10-MHz intracardiac imaging catheter was used to direct an ablation electrode at four or five anatomic landmarks in the right atrium. Thirty-eight radiofrequency energy applications were performed in nine anesthetized dogs, and 38 lesions were identified on pathological examination. Lesions were created a mean of 1.9±2.1 mm from the ultrasound-guided site. Twenty-six of 38 lesions (68%) were less than 2.2 mm from the imaged site. Intracardiac echocardiography also was used to confirm stable electrode- endocardial contact in 37 energy applications (97%) and identified catheter movement in 9 energy applications (24%). Discrete lesions, microcavitations, and thrombi were observed in 13 (34%), 23 (61%), and 19 (50%) of 38 energy applications, respectively. Microcavitations predicted the appearance of thrombus. Fluoroscopy time required to create four or five lesions decreased from 23 minutes in the first study to less than 2 minutes in the last five studies.ConclusionsCatheter-based intracardiac echocardiography can accurately guide catheter ablation directed at anatomic landmarks and potentially reduce ionizing radiation exposure. Intracardiac imaging can be used to confirm endocardial contact, identify electrode movement, and directly visualize lesions. Intracardiac echocardiography also can be used to identify microcavitations, which predict thrombus formation during radiofrequency energy applications.