Septal Reduction Using Transvenous Intramyocardial Cerclage Radiofrequency Ablation: Preclinical Feasibility

Abstract

Debulking of left ventricular septal mass is typically accomplished using surgical myectomy, which is morbid, or using transcoronary alcohol septal ablation, which can result in geographic miss and occasional catastrophic nontarget coronary injury. The authors developed and tested operational parameters in vitro and vivo for a device to accomplish transvenous intraseptal radiofrequency ablation to reduce ventricular septal mass using a technique derived from mitral cerclage, which the authors call cerclage ablation. Cerclage ablation appeared feasible in vitro and safe and effective in vivo. Cerclage ablation is an attractive new approach to debulk the interventricular septum in obstructive hypertrophic cardiomyopathy. These data support clinical investigation.

Keywords: AV, atrioventricular; CT, computed tomography; HCM, hypertrophic cardiomyopathy; RF, radiofrequency; TTE, transthoracic echocardiography; echocardiography; hypertrophic cardiomyopathy; mitral cerclage; radiofrequency ablation; ventricular septum.

Graphical abstract

Figure 1

Cerclage RF Catheter System (A) Multipolar type catheter design. (B) Monopolar type catheter design. (C) The prototype of the monopolar electrode catheter. (D) Overall picture of the catheter system. (E) Radiofrequency (RF) generator used in this study.

Figure 2

Ex Vivo Experiments to Determine Relationships Between RF Ablation and Myocardial Response (A) Radiofrequency (RF) energy was delivered in temperature-controlled mode for 10 min with or without saline irrigation through the catheter (1 ml/min). (B) The result of ex vivo experiments to determine the relationships between RF ablation and swine myocardial response (p < 0.05 in differences among all groups of volume or maximal diameter of volume only except the difference between 75°C irrigation and 85°C nonirrigation groups). Red squares indicate the maximal diameter of the ablated myocardium.

Figure 3

Representative Porcine Septal Venograms The average diameter of the septal veins was 1.5 ± 0.4 mm, and the average length was 6.6 ± 2.4 mm (n = 10).

Figure 4

Serial Change of Septal Reduction After Cerclage RF Ablation (A) Baseline (11.5 mm), (B) 2 weeks’ follow-up (9.4 mm), and (C) 8 weeks’ follow-up (7.6 mm, in subject #2). (D) Comparison at baseline and last follow-up of septal thickness in all animals (n = 7), (E) baseline (15.6 mm due to radiofrequency [RF]-induced edema, noninjured part 11.6 mm), (F) 8 weeks’ follow-up (7.4 mm), (G) long-axis view on computed tomography at 8 weeks (5.5 mm), and (H) short-axis view on computed tomography in subject #5.

Figure 5

ECG Data in the in Vivo Experiments There was no high-degree atrioventricular block during and after the procedure, and there was a temporary slight QRS widening, but it recovered in all cases. The baseline electrocardiograms of cases #1 and #2 are missing data. ECG = electrocardiogram.

Figure 6

Gross Pathology and Histological Finding After Cerclage RF Septal Ablation (A) The heart was harvested after 8 weeks’ follow-up and sliced at the target septum that showed a large area of coagulated necrotic region. The arrow indicates the ablated lesion. The boxed area is shown enlarged in B. (B) The asterisk indicates the site of the ablation catheter. The boxed area is shown in greater magnification in C. Judging from the catheter position, asymmetric ablation has occurred in favor of endocardial sparing with regard to the ablated territory. (C) The heart sliced at the target septum showed a large area of coagulated necrotic region. (D) The left anterior descending coronary artery (arrow) close to the ablated zone was patent. (E) In a beating heart experiment, using an ablation catheter with a 15-mm–long electrode coil, when ablation was done for 15 min at 75°C with saline irrigation through the catheter (1 ml/min), the length of the ablated region was about 15 mm and the width was about 12 mm. RF = radiofrequency.