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 x 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] mm(3); 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.