Intracardiac catheter echocardiographic (9MHz) imaging: In vivo validation and initial clinical applications

Intracardiac echocardiography (ICE) is a new cardiac imaging modality. We previously showed that 12.5 MHz ICE for imaging cardiac anatomy was limited by ultrasonic attenuation in large swine (50-114 kg). The utility of lower frequency (9 MHz) ICE for intracardiac imaging and applications in guiding of radiofrequency catheter ablation was further evaluated in 21 large swine (57-136 kg). With the imaging catheter in the right atrium (RA) or ventricle (RV), all four cardiac chambers, aortic root, valves, and major intracardiac anatomic landmarks (crista terminalis, RA appendage, coronary sinus orifice, interatrial septum and fossa ovalis, right pulmonary veins, superior and inferior caval orifices, and eustachian ridge) were identified in all swine. ICE-guided linear radiofrequency ablations within the RA were accurately sited at pathological autopsy: inferior caval-tricuspid annular isthmus (n=16 swine) between the inferior caval orifice and septal tricuspid leaflet (134/143 lesions, 94%); between the superior and inferior caval orifices along the atrial smooth wall posterior to the crista terminalis, posterior lateral (n=17, 344/350 98%) and vertically medial (n=7, 92/92 100%); and horizontal atrial wall at a level just above the orifice of right pulmonary vein (n=7, 39/39 100%). ICE-guided transseptal puncture and basket catheter placements in atria were all successful (n=13). Clinically, ICE-guided radiofrequency catheter ablations in 10 patients with tachyarrhythmias (total 56 sites including posterior/medial to crista terminalis, lateral tricuspid annulus, RV outflow tract) produced satisfactory results. Thus, 9 MHz ICE improved imaging capabilities (radial depth to 12 cm) and accurately guided catheter ablation with higher resolution of anatomic landmarks in the right heart.