Abstract
BACKGROUND Real-time monitoring of radiofrequency (RF) abla-tion remains challenging. OBJECTIVE We used intravascular ultrasound (IVUS) to describe atrial wall changes during RF ablation and to assess the extent of RF-induced lesions. METHODS In 9 piglets, RF and IVUS catheters were coupled and introduced into the right atrium. RF applications were performed along the intercaval line. Corresponding IVUS images were analyzed. Wall thickness was correlated with electrogram (EGM) changes (n ¼ 9) and histology (n ¼ 5). RESULTS There were 66 RF applications performed in 57 sites. IVUS provided real-time imaging of the atrial wall during RF application in all but 2 sites. IVUS demonstrated significant (420%) and immediate increase in atrial wall thickness in 71.4% of RF applications. It showed epicardial or intramyocardial effusion in 30% of cases, 2 steam pops, 1 intramural hematoma, and 1 thrombus. EGM amplitude decreased and thickness increased after RF application than at baseline (2.20 1.11 to 0.99 0.62 mV and 1.34 0.53 to 1.93 0.80 mm, respectively; P o .001 for each). However, EGM and thickness changes were poorly correlated (r ¼ 0.43; P o .05). Histologically and echographically measured thicknesses were correlated (r ¼ 0.71; P ¼ .004), but echographic thickness change was not related to histological lesion transmurality. CONCLUSION An IVUS probe coupled to an RF catheter can provide relevant real-time imaging of the atrial wall during ablation. Although thickness change does not appear as a good predictor of the transmural extent, direct visualization and monitoring of RF application may provide new information to guide and secure RF ablation. KEYWORDS Radiofrequency ablation; RF ablation; Transmural extent of RF lesions; Radiofrequency ablation in a porcine model; IVUS imaging of atrial wall; RF lesion extent; Transmural lesion extent; Atrial fibrillation ABBREVIATIONS EGM ¼ electrogram; IVUS ¼ intravascular ultrasound; RA ¼ right atrium; RF ¼ radiofrequency .