High-intensity ultrasound catheter ablation achieves deep mid-myocardial lesions in vivo

Background: Radiofrequency ablation of epicardial and mid-myocardial ventricular arrhythmias is limited by lesion depth. Objective: The purpose of this study was to generate deep mid-interventricular septal (IVS) lesions using high-intensity ultrasound (US) from an endocardial catheter-based approach. Methods: Irrigated US catheters (12 F) were fabricated with 3 × 5 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 magnetic resonance imaging, 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 mm; 95% confidence interval [CI] 9.9–12.4 mm) and at 30 days (11.2 mm; 95% CI 10.6–12.4 mm) (P =.56). Lesion volume decreased post-ablation to 30 days (from 255 [95% CI 198–440] to 162 [95% CI 133–234] mm³; P =.05), yet transmurality increased from 58% (95% CI 50%–76%) to 81% (95% CI 74%–93%), attributable to a reduction in IVS thickness (from 16.0 ± 1.7 to 10.6 ± 2.4 mm; P =.007). Magnetic resonance imaging 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. Conclusion: High-intensity US catheter ablation may be an effective treatment of mid-myocardial or epicardial ventricular arrhythmias from an endocardial approach.