Between March 2016 and March 2019, consecutive HOCM patients aged ≥ 18 years who underwent septal myectomy using the mini-invasive surgical instruments in this center were reviewed. Inclusion criteria were the maximum LVOT gradients ≥ 50 mmHg at rest or with provocation and presence of severe limiting 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; and (6) concomitant obstruction of right ventricular outﬂow tract requiring enlargement. Patients who underwent septal myectomy via the transseptal approach through right atrium or via the left atrial approach through interatrial sulcus were also excluded.
2.2 Preoperative evaluation
Preoperative transthoracic echocardiography (TTE) examination was performed to define (1) the location and magnitude of any left ventricular pressure gradient, both at rest and with provocation; (2) the distribution and severity of myocardial hypertrophy; (3) MV anatomy and function; (4) the presence of 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) the presence of intrinsic MV disease including lesions of mitral leaflets and mitral annulus. Resting LVOT velocity was measured by continuous-wave Doppler of the outflow tract from an apical window, and the resting LVOT pressure gradient was estimated by using the modified Bernoulli equation (i.e., gradient = 4v2, where v = peak LVOT velocity). In patients with resting LVOT gradients < 30 mmHg, maneuvers such as the Valsalva maneuver and stand-to-squat were frequently used. In addition, cardiac magnetic resonance was frequently used to measure basal septal thickness and for characterization of 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 included patients signed an informed consent approved by the ethics committee. Data collection was performed by trained staff (two people). The trained staff, however, were not informed of the purpose of this study.
Baseline and surgical characteristics, intraoperative results, and in-hospital results were obtained from our institutional database and were reviewed using a standard data collection form. 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 were surgical death, complete atrioventricular block requiring 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 included 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 obtained through clinic visits or telephone interviews. Follow-up results included survival, reoperation for recurrent LVOT obstruction and/or symptomatic MR, New York Heart Association (NYHA) functional class at the latest follow-up, and 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.
2.4 Surgical procedures
Operations were guided by intraoperative transesophageal echocardiography (TEE), with particular attention paid to ventricular septal anatomy as well as thickness, MV anatomy as well as function, and mitral subvalvular anatomy. The patient was put in the reverse Trendelenburg and left lateral decubitus position. Under general anaesthesia, the heart and ascending aorta were exposed by a median incision with sternotomy, and cardiopulmonary bypass with ascending aortic and right atrial cannulation was established with a left ventricular vent placing via the right superior pulmonary vein. Through a low oblique aortotomy approximately 7-10 mm above the right coronary ostium, the aortic valve leaflets were pulled up to gain access to the outflow tract, the hypertrophic cardiac muscle, anterior MV leaﬂet, and mitral subvalvular apparatus. A head lamp and loupe magnification were used to achieve better inspection of the left ventricular cavity. The mini-invasive surgical instruments (as shown in Figure 1) were used during the resection. Scalpel resection was usually started at the nadir of the right cusp, 5 mm below the aortic valve and extending leftwards to the left trigone. The area of septal excision was lengthened beyond the bases of PMs and toward the apex of the heart. The depth of resection was up to 50% of the basal thickness of the septum. The excision of the hypertrophic muscles as a whole mass was required. In addition, mitral subvalvular anomalies were also corrected, including false cords cutting, retracted secondary chordae cutting, and hypertrophic PM release and/or resection. After resections were completed, the bases of the PMs should be seen by looking through the incision of the aortic root. And then, the outflow tract, mitral and aortic valves were carefully and thoroughly reexplored.
TEE was used after weaning off bypass to measure the maximum gradients and the severity of MR following myectomy. Repeat aortic cross-clamping was immediately performed if there was residual obstruction and/or residual moderate or more MR or if a ventricular septal defect or a left ventricular free wall rupture was observed.
2.5 Statistical analysis
Statistical analysis was performed with the SPSS statistical package version 22.0 (SPSS Inc., Chicago, IL, USA). Categorical data were expressed as frequency distributions and single percentages and were compared 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 and were compared between groups using an independent-samples t-test; non-normally distributed continuous variables were expressed as median and interquartile range (IQR) and were compared between groups with the Wilcoxon rank sum test. A two-sided p-value less than 0.05 was considered statistically significant.