Abstract Body (Do not enter title and authors here): Background:
High-intensity ultrasound (HIU) catheter ablation produces deeper lesions than radiofrequency and may serve as a new modality for interventricular septal (IVS) reduction in hypertrophic cardiomyopathy (HCM). A proprietary “contact sensing” algorithm was developed to confirm orientation of the side-facing transducer toward the IVS.

Hypothesis:
Contact sensing will improve HIU ablation efficacy, resulting in larger and more consistent IVS lesions.

Methods:
A total of 31 healthy swine underwent HIU catheter (Fig A) ablation via femoral venous access targeting the RV side of the IVS. In 13 of the 31 swine, continuous transducer-tissue contact was monitored to confirm tissue contact (Fig B) and optimize catheter positioning prior to ablation. Each swine underwent 8-16 HIU sonications. Animals were euthanized immediately post-ablation, and lesion presence, dimensions, volume, and location were assessed by gross pathology. Lesion metrics are reported as mean ± standard deviation. Group comparisons (with vs. without contact sensing) were performed using unpaired, two-tailed homoscedastic t-tests for continuous variables and chi-squared tests for categorical outcomes.

Results:
Contact sensing increased lesion volume from 657 ± 901 to 2071 ± 1230 mm³ (p=0.001) and lesion depth from 7 ± 7 mm to 15 ± 3 mm (p=0.001; Fig C,D). Spline analysis of gross pathology showed that the lesion area on the LV side of the IVS increased from 22 ± 23% without sensing to 55 ± 19% with sensing (p=0.0004; Fig C,D). Transient atrio-ventricular block occurred in both groups (Fig D) and resolved with catheter repositioning. Sustained AVB occurred in one swine without contact sensing.

Conclusion:
HIU transducer-tissue contact sensing significantly improved HIU ablation efficacy, producing larger, deeper, and more optimally located lesions for HCM septal reduction. Survival studies will confirm the degree of septal reduction.