LAUSR

BACKGROUND Radiofrequency (RF) ablation of epicardial and mid-myocardial ventricular arrhythmias (VAs) is limited by lesion depth. OBJECTIVES To generate deep, mid-interventricular septal (IVS) lesions using high-intensity ultrasound (US) from an endocardial catheter-based approach. METHODS Irrigated US catheters (12 Fr) were fabricated with 3x5 mm transducers of 5.0, 6.5 and 8.0 MHz frequencies, and compared in an ex vivo perfused myocardial ablation model. In vivo septal ablation in swine (n=12) was performed via femoral venous access to the right ventricle. Lesions were characterized by echocardiography, cardiac MRI and electroanatomic voltage mapping pre- and post-ablation, and at 30 days. Four animals were euthanized immediately post-ablation to compare acute and chronic lesion histology and gross pathology. RESULTS In ex vivo models, maximal lesion depth and volume was achieved by 6.5 MHz catheters, which were used in vivo. Lesion depth by gross pathology was similar post-ablation (10.8[95% CI:9.9,12.4] mm) and at 30 days (11.2[CI:10.6,12.4] mm, p=0.56). Lesion volume decreased post-ablation to 30 days (255[CI:198,440] to 162[CI:133,234] mm3 p=0.05), yet transmurality increased 58%(CI:50,76) to 81%(CI:74,93), attributable to a reduction in IVS thickness (16.0±1.7 to 10.6±2.4 mm, p=0.007). MRI confirmed dense septal ablation by delayed enhancement, with increased T1 time post-ablation and at 30 days, and increased T2 time only post-ablation. Voltage mapping of both sides of IVS demonstrated reduced unipolar (but not bipolar) voltage along the IVS. CONCLUSIONS High-intensity US catheter ablation may be an effective treatment for mid-myocardial or epicardial VAs from an endocardial approach.