We reviewed data for consecutive HOCM patients aged ≥ 18 years who underwent septal myectomy using the mini-invasive surgical instruments in our center between March 2016 and March 2019. Inclusion criteria included: (1) the maximum LVOT gradients ≥ 50 mmHg at rest or with provocation; and (2) presence of severe symptoms refractory to maximum pharmacologic therapy with non-vasodilating β-blockers and/or calcium channel blockers. Exclusion criteria included: (1) organic mitral valve (MV) lesions (rheumatic, degenerative, ischemic, infective, and mitral annulus calcification); (2) previous valvular surgery; (3) LVOT obstruction secondary to hypertensive heart disease or severe aortic stenosis; (4) concomitant coronary artery disease requiring bypass grafting; (5) concomitant modiﬁed Maze procedure; (6) concomitant obstruction of right ventricular outﬂow tract requiring enlargement; and (7) patients who underwent septal myectomy via the transseptal approach through right atrium or via the left atrial approach through interatrial sulcus.
2.2 Preoperative evaluation
Preoperative transthoracic echocardiography (TTE) examination aided in defining: (1) the location and magnitude of left ventricular pressure gradient, both at rest and with provocation; (2) the distribution and severity of myocardial hypertrophy; (3) MV anatomy and function; (4) mitral subvalvular anomalies, including abnormal chordae tendineae attached to the ventricular septum or free wall (false cords), fibrotic and retracted secondary chordae inserted on the anterior mitral leaflet body, and papillary muscle (PM) abnormalities (hypertrophy, and direct insertion into the anterior mitral valve leaflet); and (5) intrinsic MV diseases, including lesions of mitral leaflets and mitral annulus. Resting LVOT velocity was evaluated via continuous-wave Doppler of the outflow tract from an apical window. An estimate of the resting LVOT pressure gradient was established using the modified Bernoulli equation (i.e., gradient = 4v2, where v = peak LVOT velocity). For symptomatic patients with resting LVOT gradients < 30 mmHg, the Valsalva maneuver and stand-to-squat were frequently employed. Furthermore, we relied on cardiac magnetic resonance frequently to measure basal septal thickness and characterize PM morphology and location within the left ventricular cavity, PM thickness, and PM mobility.
2.3 Study protocol
This study protocol was approved by the ethics committee of Zhongshan Hospital Fudan University and was consistent with the Declaration of Helsinki. All enrolled patients signed an informed consent approved by the ethics committee. Two trained staff actively collected all data; however, they were not informed of the purpose of this study so as not to bias the results.
Using a standard data collection form, the baseline and surgical characteristics, intraoperative and in-hospital results were collected retrospectively from our institutional database, then reviewed. Intraoperative results included: the incidence of repeat aortic cross-clamping (due to inadequate septal myectomy, iatrogenic free wall rupture, iatrogenic septal perforation, and iatrogenic aortic valve perforation) and transesophageal echocardiography data, including the maximum LVOT gradient, interventricular septal thickness, systolic anterior motion (SAM), the severity of MR, and aortic regurgitation. In-hospital results included: surgical death, complete atrioventricular block requiring a permanent pacemaker, new-onset atrial fibrillation, complete left bundle branch block, new-onset cerebrovascular adverse events, prolonged mechanical ventilation (> 72 hours), redo for bleeding, and postoperative hospital stay. Surgical death was defined as all deaths within 30 days of operation regardless where death occurred and all in-hospital deaths after 30 days among patients who had not been discharged after the initial operation.
Patients were regularly followed up at 3 and 6 months following myectomy and in 6-month intervals thereafter. Follow-up data were collected prospectively through clinic visits or telephone interviews, including results on the survival, reoperation for recurrent LVOT obstruction and/or symptomatic MR, New York Heart Association (NYHA) functional class at the latest follow-up. Also, echocardiographic data at the latest follow-up including residual obstruction (the maximum gradient ≥ 30 mmHg), septal thickness, SAM, residual MR, and ventricular septal defect were also recorded. In addition, the incidence of major adverse events (including deaths, complete atrioventricular block, residual obstruction, and residual moderate or more MR) per surgeon was calculated and compared.
2.4 Surgical procedures
Operations were guided by intraoperative transesophageal echocardiography (TEE). Particular attention was paid to ventricular septal anatomy as well as thickness, MV anatomy and function, and mitral subvalvular anatomy. Each patient was put in the reverse Trendelenburg and left lateral decubitus position. Under general anaesthesia, the heart and ascending aorta were exposed via a median incision with sternotomy. Cardiopulmonary bypass with ascending aortic and right atrial cannulation was established with a left ventricular vent placing via the right superior pulmonary vein. Employing a low oblique aortotomy (approximately 7-10 mm above the right coronary ostium), the aortic valve leaflets were pulled up to permit access to the outflow tract, the hypertrophic cardiac muscle, anterior MV leaﬂet, and mitral subvalvular apparatus. We then used a headlamp and loupe magnification to achieve a better inspection of the left ventricular cavity. The mini-invasive surgical instruments (see Figure 1) were applied in the resection process. Scalpel resection was usually initiated at the nadir of the right cusp, 5 mm below the aortic valve, extending leftwards to the left trigone. The septal excision area was lengthened beyond the bases of PMs and toward the heart apex. The resection depth was up to 50% of the basal septum thickness. The excision of the hypertrophic muscles as a whole mass was necessary. Moreover, mitral subvalvular anomalies were corrected, including false cords cutting, retracted secondary chordae cutting, and hypertrophic PM release and/or resection. After completing the resections, the bases of the PMs were visible through the incision of the aortic root. The outflow tract, mitral and aortic valves were precisely and extensive re-explored.
We employed TEE after weaning off bypass to evaluate the maximum gradients and the severity of MR following myectomy. Immediately, repeat aortic cross-clamping was performed if there was residual obstruction and/or residual moderate or more MR or a ventricular septal defect or a left ventricular free wall rupture.
2.5 Statistical analysis
All statistical data were analyzed with the SPSS statistical package version 22.0 (SPSS Inc., Chicago, IL, USA). Categorical data were expressed as frequency distributions; comparison of single percentages was achieved between groups using Fisher’s exact test if the expected frequency was < 5 or the chi-square test. Normally distributed continuous variables were expressed as the mean ± standard deviation; here, comparisons between groups were established using an independent-samples t-test. Non-normally distributed continuous variables were expressed as the median and interquartile range (IQR); here comparison between groups was achieved using the Wilcoxon rank sum test. A two-sided p-value less than 0.05 was considered statistically significant.