Hypertrophic obstructive cardiomyopathy (HCM) is a genetic and familial condition with variable clinical evolution. It is characterized by left ventricular hypertrophy (LVH) in the absence of other etiologies, such as aortic stenosis or sustained arterial hypertension. HCM can vary morphologically, with common forms being basal, midventricular, apical, and diffuse. The basal septal hypertrophy phenotype is the most common, while the midventricular variant accounts for up to 9.4% in Japanese series. Less commonly, the apical form predominates, with hypertrophy concentrated in the apex, causing diastolic dysfunction without obstructive gradients. 

This variability results in a range of clinical presentations, from asymptomatic patients to cases of sudden death. The primary prognostic factor in HCM is obstruction of the left ventricular outflow tract (LVOT), making most medical and surgical treatments focus on reducing this obstruction. Extended septal myectomy (ESM) is the treatment of choice for patients with HCM and an LVOT gradient >50 mmHg (at rest or with stress) who remain symptomatic despite optimal medical management. New therapies/procedures for HCM have been developed, reducing the incidence of HCM advancing to the “burn out” phase, where cardiac transplantation becomes necessary. 

Li et al. developed a device using negative pressure and aspiration, comprising a bullet-headed resection tube, a multifunctional handle, and a catheter connecting the device chambers. The resection tube itself includes an outer layer, a tubular blade, a piercing needle, and a multi-porous tunnel. Using this device, they completed and published their initial cases of transapical beating-heart septal myectomy (TA-BSM) in patients with resting HCM and obstruction, avoiding median sternotomy and cardiopulmonary bypass (CPB). 

This study aims to evaluate TA-BSM outcomes in patients with resting or provoked LVOT gradients >50 mmHg and a maximum septal thickness >15 mm, with symptoms refractory to medical treatment. Patients were divided into two groups: the latent obstruction group (patients with provoked obstruction despite low resting gradient <30 mmHg) and the resting obstruction group (patients with resting LVOT obstruction with a gradient >30 mmHg). A total of 120 patients participated in the study, with 33 in the latent obstruction group and 87 in the resting obstruction group. 

The primary objective was procedural success, defined as a maximum LVOT gradient (after provocation) of less than 30 mmHg, residual mitral regurgitation grade ≤1+, and absence of mortality at six months post-procedure. Secondary objectives included a composite of adverse events: 30-day mortality, iatrogenic ventricular septal defect, left ventricular apical tear, conversion to median sternotomy, iatrogenic valvular injury, device-related embolization, or stroke. 

The procedure is performed under general anesthesia, using a left mini-thoracotomy to access the left ventricular apex. A standard transapical approach is employed, with tobacco-pouch sutures reinforced with Teflon patches for the apical puncture and subsequent dilation of the incision. Guided by intraoperative 3D transesophageal echocardiography (TEE), the device location is determined in both depth (mid-esophageal long-axis view) and resection window orientation (transgastric short-axis view). The initial resection is performed on the basal anterior septum, 5–10 mm below the right coronary sinus (mid-esophageal long-axis view) and extending to the septum midpoint (transgastric short-axis view). Morphological and hemodynamic characteristics, including septal thickness, LVOT gradient, and residual mitral regurgitation, are assessed after each resection. On average, 3-6 resections are necessary to achieve technical success. After completing the resections, an isoproterenol challenge is performed; if the provoked gradient exceeds 30 mmHg, additional resection is required. 

A propensity score-matched analysis revealed significant differences in pre-procedure characteristics. Patients with resting obstruction had a greater septal thickness (22 mm vs 20 mm; p = .029), larger left atrial size (p = .027), and a higher rate of mitral regurgitation >2+ (90.8% vs 63.6%; p < .001). Patients with latent obstruction showed more mitral subvalvular anomalies (30.3% vs 6.9%; p = .003). No significant differences were found in other clinical characteristics, including age, symptoms, comorbidities, and medical history. The primary goal was achieved in 31/33 (93.9%) latent obstruction patients and 80/87 (92%) resting obstruction patients. Secondary outcomes included one case of 30-day mortality, one iatrogenic ventricular septal defect, one left ventricular apical tear, two median sternotomy conversions, one iatrogenic valvular injury, and five device-related embolizations, although not all were associated with stroke. No differences were observed between groups in myocardial weight resected, ICU stay, or rates of left bundle branch block. The duration of mechanical ventilation was significantly shorter in patients with latent obstruction (2.9 h vs 4.3 h; p < .010). 

The authors conclude that TA-BSM yields favorable results according to reference standards. The findings support using this device in symptomatic patients with latent obstruction regardless of resting LVOT gradients. However, larger series with long-term follow-up are necessary. 

COMMENTARY: 

This study presents disruptive findings for the future of invasive HCM management. Other approaches/modalities emerging for HCM treatment include transaortic myectomy via right anterior mini-thoracotomy and transmitral myectomy. Unfortunately, the outcomes of these approaches have not yet been rigorously studied. Transmitral myectomy, while advantageous in cases requiring mitral valve replacement, requires detachment and reattachment of the anterior mitral leaflet in patients with a normal valve, which may distort the valve leaflets, leading to higher rates of residual mitral regurgitation. 

This study offers a promising minimally invasive solution. Li et al.’s team from Wuhan, China, recently described a novel transapical beating-heart septal myectomy technique. This procedure is made possible by an innovative instrument with a bullet-headed resection tube. Close communication with the echocardiographer is necessary to guide septal resection, avoiding injury to other intracardiac structures. Similar to thoracoscopic and anterior mini-thoracotomy approaches, this minimally invasive beating-heart access allows for faster postoperative recovery with less pain. Additionally, avoiding CPB can reduce risks of bleeding, AF, stroke, and other complications associated with cannulation and CPB itself. 

Surgical treatment of HCM remains the choice for patients who are symptomatic despite optimal medical management. This study shows that TA-BSM yields favorable results according to reference standards and allows real-time visualization of gradient resolution. 

However, this study has limitations: it is a single-center study with all procedures performed by a single surgeon, a relatively small sample size favoring selection bias, and this procedure is not feasible for patients requiring other types of concomitant cardiac surgery. Additionally, high-quality TEE imaging is required for precise localization and resection of hypertrophied myocardium, necessitating close cooperation with the echocardiographer. 

REFERENCE: 

Li J, Wei X. Transapical beating-heart septal myectomy for hypertrophic cardiomyopathy with latent obstruction. Eur J Cardiothorac Surg 2024; doi:10.1093/ejcts/ezad425.