3.5 Incidence of major adverse events per surgeon
Six surgeons (total number of procedures during the three-year period of 72, 36, 23, 14, 13, and 10, respectively) have completed 168 transaortic septal myectomy procedures. A total of 11 major adverse events were recorded, including surgical death (one patient), complete atrioventricular block (5), residual obstruction (3), and moderate residual MR (2). As shown in Table 3, no significant difference was found among all surgeons regarding the incidence of major adverse events (p=0.739).
Discussion
In the 1960s, Morrow et al have reported transaortic resection of a small amount of muscle from the proximal ventricular septum, a technique generally described as classic Morrow operation. Over the next decades, myectomy has evolved from the classic Morrow operation to a more extended septal myectomy guided by preoperative cardiovascular magnetic resonance and intraoperative TEE [15-18]. High technical difficulty, however, limited clinical application of the extended septal myectomy procedure. In 2015, Ferrazzi et al proposed the transaortic secondary chordae cutting in addition to a shallow septal myectomy for the treatment of HOCM [8]. It was reported to be associated with favorable results [8, 19]. However, such an approach remained controversial because the secondary chordae maintains ventricular geometry and enhances wall thickening, which may be helpful in the presence of left ventricular dilation and systolic dysfunction [20]. In this study, with the aid of special surgical instruments, transaortic septal myectomy was performed in 168 patients with HOCM and drug refractory symptoms. Favorable results were achieved, including a low surgical mortality (<1%) with no occurrences of deaths or re-interventions at follow-up, a significant improvement of quality of life with recovery from symptoms and NYHA functional class I and II, an effective relief of LVOT obstruction, and a reliable reduction of MR. The observed good survival and a significant improvement in NYHA functional status coincided with an effective relief of LVOT obstruction and a reliable reduction of MR, which confirmed the safety and efficacy of transaortic septal myectomy with the aid of special surgical instruments in the treatment of symptomatic HOCM.
In this series including 168 transaortic myectomy procedures with the aid of special surgical instruments, the mean duration of aortic cross-clamping was 36.0 ± 8.1 minutes (median, 35.0 min), which was significantly lower than the value (median, 68 min) reported from a famous and experienced myectomy center in the same country[21]. The reason for this difference may be that the application of special surgical instruments may be beneficial in reducing the technical challenges of myectomy and shortening operation time.
Note that 7 HOCM patients in this series suffered from midventricular obstruction and underwent transaortic septal myectomy with the aid of special surgical instruments. Favorable results suggested that the application of special surgical instruments made it easy to remove the myocardium at the base of PMs, even to extend to the apex of the left ventricle. The surgical comfort of the operator is essential for a myectomy surgeon, especially for an inexperienced myectomy surgeon. These may attribute to the small operational radius of the special instruments. Moreover, the application of special surgical instruments is beneficial for an adequate length of septal excision, which is extremely important to surgical effect [14].
In addition, six surgeons with greatly varied operation volume have completed 168 myectomy procedures. Favorable results were achieved, and no significant difference was found among six surgeons regarding the incidence of major adverse events, which suggested that the application of special surgical instruments during transaortic septal myectomy may be a promising treatment option for HOCM, with good and reproducible results.
Complete atrioventricular block, left ventricular free wall rupture, aortic valve injury and iatrogenic septal perforation were the main complications of septal myectomy. In the present cohort, the incidence of pacemaker implantation (3.0%) was greater than expected based on other large series [22, 23]. This elevated incidence was attributed to the excessive subaortic resection to the side of the noncoronary valve when the incision beginning just to the right of the nadir of the right aortic sinus was made. More than 41.0% of patients developed complete left bundle branch block after myectomy, which allowed the adoption of conservative surgical strategies in patients with preoperative right bundle branch block. In this series, left ventricular free wall rupture, a rare complication after myectomy, occurred in 2 (1.2%) patients, and was successfully treated under cardiopulmonary bypass and cardioplegic arrest with a double-armed 3-0 polypropylene suture with a pledget placed in a horizontal mattress fashion, similar to the technique described to control a stab wound to the heart in close proximity myectomy to a coronary artery. Left ventricular free wall rupture may be associated with excessive subaortic resection to the mitral anterior commissure when the incision that began just to the right of the nadir of the right aortic sinus was made. Although abnormal papillary muscles were corrected, left ventricular free wall rupture was indicated via operative exploration to not be associated with the excision of muscle bundles. In principle, aortic valve injury and iatrogenic septal perforation were prone to occur in young patients with small aortic roots and old patients without severe septal hypertrophy, respectively. In this series, ventricular septal perforation occurred in one female patient aged 70 years with a preoperative septal thickness of 17.0 mm. Although the perforation was repaired using a bovine pericardium patch, a residual ventricular septal defect was observed during follow-up and may be associated with the thin myocardium surrounding of the perforation and the small patch that was not large enough to extend beyond the edge of the perforation at a certain distance.
This study had some potential limitations. First, this was a single-center, single-armed observational study with a limited sample size, which may have influenced the generalizability of the results. Second, only a minor part of patients received cardiac magnetic resonance imaging, as it did not serve as a regular examination modality in the early times at our institution. Third, a functional capacity assessment tool, such as the 6-minute walking test, and a quality of life assessment tool, such as the SF-36 questionnaire, were not utilized in this study. Finally, the duration of follow-up was relatively short. It needed longer observation to confirm our findings.
Conclusion
The application of special surgical instruments may contribute to reducing the technical difficulty of myectomy. Transaortic septal myectomy procedure with the aid of special surgical instruments achieved favorable and reproducible results, and thus may be a promising treatment option for HOCM.