Transcatheter Myotomy for Left Ventricular Outflow Tract Obstruction
June 1, 2024
By Michael H. Crawford, MD, Editor
SYNOPSIS: Initial experience with a new transcutaneous transcatheter electrosurgery device using intramyocardial guidewires to create left ventricular upper septum myotomies to enlarge the outflow tract in symptomatic patients with hypertrophic cardiomyopathy, and potentially to enhance transcatheter left heart valve replacement when outflow tract obstruction compromises the procedure, is described in this report from a single center.
SOURCE: Greenbaum AB, Ueyama HA, Gleason PT, et al. Transcatheter myotomy to reduce left ventricular outflow tract obstruction. J Am Coll Cardiol 2024;83:1257-1272.
Left ventricular (LV) septal reduction is used to improve symptoms in patients with hypertrophic cardiomyopathy (HCM) and facilitate transcatheter valve replacement (TVR), especially when it is likely to cause an LV outflow tract (OT) obstruction. However, current septal reduction techniques have significant limitations. Thus, this report on an innovative new transcatheter technique for septal myotomy is of interest.
The technique uses intramyocardial guidewires to deploy electrosurgery to create septal scoring along the midline of the endocardium (SESAME), which splays open the myocardium circumferentially to widen the LVOT. This report describes the results in the first 76 patients between 2021 and 2023 treated with SESAME for HCM (n = 11) with gradients > 30 mmHg, and TVR (n = 65), with 34 patients having gradients > 30 mmHg and 31 patients who needed more room for the new valve. The procedure is planned using contrast computed tomography (CT) to identify the cutting plane. It is accom-plished by femoral access under general anesthesia, guided by biplane fluoroscopy, transesophageal echocardiography, and, occasionally, intracardiac echocardiography.
The average age of the patients was 77 years and 82% were women. All but three patients were at prohibitive surgical risk. The procedure was elective in 82% of patients, urgent in 14% of patients, and emergent in three patients. The average procedure time was 174 minutes, with 73 minutes of fluoroscopy time. Myotomy was successful in all patients, and septal thickness by CT decreased from an average of 16 mm to 8.5 mm (P < 0.001). LVOT catheter gradients decreased immediately in 82% of patients, but the decrease in echocardiographic gradients took days. New York Heart Association (NYHA) class III or IV symptoms were present in 91% of the patients at baseline. At 30 days, 52% of the patients were NYHA class II or below (P < 0.001). Thirty-day survival was 100% in the HCM patients and 88% overall. Major adverse cardiovascular events occurred in 24%, but mostly in the TVR patients: ventricular septal defect in three patients, free wall rupture in three patients, stroke in two patients, ventricular tachycardia/ventricular fibrillation in four patients, pacemaker in four patients, and acute kidney injury in three patients. In the total patient population, major vascular complications occurred in 7% and major bleeding occurred in 19%. CT imaging at 43 days showed LVOT enlargement in all, but in 14% of the TVR patients it was not enough to accommodate TVR of the mitral valve. Also, there was no lengthening or deepening of the myotomy incisions. The authors concluded that SESAME is safe and effective for increasing LVOT size and reducing gradients in patients with HCM or LVOT obstruction after TVR and may help facilitate TVR.
COMMENTARY
SESAME was designed to mimic the original surgical myotomy procedure, which eventually was replaced by myectomy. It combines two new technologies: electrosurgery and intramyocardial guidewire navigation. The long incisions splay out the myocardial fibers circumferentially to widen the LVOT without tissue removal. The overall success rate of SESAME is remarkable, especially since 18% of the patients were done under urgent/emergent circumstances. It was highly successful in HCM patients, where there were no deaths in 30 days and no myocardial perforations. I would expect it to compete successfully with surgical septal myectomy and alcohol septal ablation in HCM patients, especially since no HCM patients needed a pacemaker after SESAME. LV wall damage resulting in septal defects and free wall ruptures are a problem in the TVR patients that one hopes can be corrected with further experience. Another unresolved issue is whether embolic protection equipment should be used. There were two strokes within 30 days, but only one was considered atheroembolic. Other hurdles include the technical complexity of the procedure, the need for expert operators, the lack of dedicated equipment for this purpose, and optimal patient selection.
This type of first experience report has several weaknesses that should be considered. It is a retrospective, observational study from one center with no control group that had another septal reduction procedure and there are no long-term data. However, it is innovative, safe, and effective with experienced operators. It seems especially useful for HCM patients and shows promise to address the unforeseen challenges of TVR when septal obstruction complicates the procedure.