High-Intensity Ultrasound Catheter Ablation: Transmural Ventricular Lesions Through Transducer-Tissue Contact Sensing.

BACKGROUND: High-intensity ultrasound (HIU) ablation can produce deep myocardial lesions but has been limited by the directional, side-facing transducer orientation, yielding inconsistent myocardial targeting with lesion efficiencies <75% and transmurality <60%. OBJECTIVE: We designed HIU catheters and a real-time contact sensing method to guide energy delivery, aiming for a device capable of deep ventricular tachycardia (VT) ablation and septal reduction therapy in hypertrophic cardiomyopathy (HCM). We hypothesized that contact sensing guided HIU (CSG-HIU) would create larger, deeper, and more transmural lesions than standard HIU (Std-HIU) in a terminal swine model. METHODS: Transducer dimensions (5x6 mm) and frequency (5 MHz) were selected from 3D acoustic simulations. Three contact sensing modalities (pulse-echo, and bipolar or unipolar impedance via transducer-side microelectrodes) were validated ex-vivo. The best method was then used in a prospective in-vivo swine study comparing Std-HIU (n=10) to CSG-HIU (n=13) ablation of the ventricular septum. RESULTS: Ex-vivo, bipolar impedance performed best, with a 600 Ω threshold showing 100% sensitivity and specificity for stable contact. In-vivo, versus Std-HIU, CSG-HIU improved lesion efficiency (100 vs 50%, p=0.007), with larger volumes (2071±1231 vs. 568±890 mm3, p=0.005), deeper lesions (15±3 vs. 6±6 mm, p<0.001), and transmurality in 69 vs 20% of swine (p=0.030). No sustained atrioventricular block, ventricular septal defects, or procedural mortality occurred. CONCLUSIONS: Real-time bipolar impedance CSG-HIU overcomes historical directional limitations, achieving 100% lesion efficiency and more predictable transmurality.