Enlargement of left ventricular outflow tract using an autologous pericardial patch for anterior mitral valve leaflet and septal myectomy through trans‐mitral approach for the treatment of hypertrophic obstructive cardiomyopathy

Modified Morrow procedure is the gold standard of surgical intervention for hypertrophic obstructive cardiomyopathy (HOCM). However, there are certain cases without complete relief of obstruction through trans‐aortic approach, we, therefore, described an unusual technique. We aimed to retrospectively analyze this series of patients to reveal its safety and efficiency.


| INTRODUCTION
Hypertrophic cardiomyopathy is one of the most common heritable heart diseases with an incidence of about one in 500 individuals. 1,2 The morphologic and functional feature differs according to the site of the hypertrophic lesions, including the left and/or right ventricular.
Hypertrophic obstructive cardiomyopathy (HOCM) is one form of hypertrophic cardiomyopathy with specific pathophysiological characteristic, that is the obstruction of the left ventricular outflow tract (LVOT) with/without concomitant mitral regurgitation (MR), caused by the thickened septal muscle and systolic anterior motion (SAM) of anterior mitral leaflet. [3][4][5] For patients with obstruction of LVOT and/or mitral valve regurgitation, symptomatic signs just like dyspnea, chest pain, and syncope are more likely occurred and these patients often do not respond adequately to drug therapy, such as beta-blockade, diltiazem, and so forth. Therefore, these patients remain significantly symptomatic and have a dissatisfactory long-term prognosis, which means high mortality and morbidity than hypertrophic cardiomyopathy patients without the obstruction of LVOT. 2,6 Current invasive treatments include alcohol septal ablation and surgical myectomy, especially surgical myectomy of the thicken LVOT muscle has been approved to have the most satisfactory results. 7,8 For a long time, the modified Morrow procedure has been the gold standard of surgical treatment, which was performed through the trans-aortic approach.
In fact, in addition to modified Morrow operation through the transaortic approach, there are other approaches, including the tans-apical and trans-mitral approach. [9][10][11][12][13] In clinical practice, we found many special cases, such as the aortic valve annulus is very small, the angle between the aortic valve annulus and the mitral valve annulus is less than 120 degrees, the anterior mitral leaflet is too long, and so forth.
It is difficult for these cases to completely resolve the obstruction of LVOT and SAM of anterior mitral leaflet by only resecting the hypertrophic LVOT muscle through tans-aortic approach without mitral valve replacement. Thus, we prefer trans-mitral approach to perform septal myectomy and mitral valves repair. In this study, we aimed to review the results and experiences of these cases in our center.

| Patients and characteristics
Between January 2016 and December 2019, a total of 247 consecutive HOCM patients were operated in our center through different approaches. Sixteen of them underwent surgical enlargement of LVOT using an autologous pericardial patch for anterior mitral valve leaflet and septal myectomy through trans-mitral approach and were recruited in this study. Baseline characteristics were extracted from our hospital medical records. In this case series, seven of them were male, the average age was 47.94 ± 12.79 years. All patients were diagnosed via transthoracic echocardiography (TTE) before operation and transesophageal echocardiography (TEE) during operation. Preoperative and postoperative peak LVOT gradient, SAM sign, MR grade, and maximum thickness of septal were measured for each patient to evaluate surgical results. Postoperative TTE was performed for each patient 3 months after the operation and then every 6 months during follow-up until December 2020.
The surgical indication for these patients is the LVOT peak pressure gradient >50 mmHg with/without MR and symptomatic due to failed drug therapy. Patients indicated for modified Morrow procedure through trans-aortic approach were excluded from this series.
The pathological features of each patient recruited in this series are listed in Table 1. Aortic cross-clamp time and postoperative complications were collected to evaluate surgical safety.
This study was approved by the ethics committee of Zhongshan Hospital Fudan University, all patients gave their informed consent.

| Operative technique
The surgery was conventional median sternotomy. Ascending aorta, superior and inferior vena cava were cannulated, after initiation of the cardiopulmonary bypass, aorta was cross-clamped and cold blood cardioplegia was introduced. We preferred a trans-right atrium and atrial septum approach to expose the anterior leaflet of mitral valve.
The incision of mitral valve was at the root of the anterior leaflet, about 2-5 mm to the annulus, leaving an edge to repair. It usually carried from the right fibrous trigone to the left without freeing the whole anterior leaflet. After this incision, the anterior leaflet attachments would be released, and the ventricular septum and bottom of the anterior papillary muscle could be exposed clearly. Septal muscle myectomy was carried from the nadir of the right aortic valve sinus to the left fibrous trigone, papillary muscle attachments were released at the same time. The depth of septal muscle resection was measured by TEE before operation and mainly depended on surgeons' experiences. The resection should be carefully carried to avoid injuring the aortic valve, atrioventricular, and interventricular conduction beam.
After septal myectomy, the anterior leaflet was reattached to the residual leaflet rim by using a prepared fusiform autologous peri-

| Statistical analysis
Continuous variables were expressed as mean ± standard error of the

| Perioperative results
There was no patient who died in this series, the overall mortality rate

| Follow-up results
All patients underwent routine TTE examination 3 months after the

| DISCUSSION
HOCM is common hereditary heart disease with nonspecific symptoms, just like dyspnea, chest pain, and syncope on exercise. 1,2,6 For patients without relieving symptoms after regular drug treatment, surgical intervention is required. In this retrospective study, we described a trans-mitral approach through the base of the anterior mitral valve leaflet, with a special way to reattach the anterior mitral valve leaflet, for some special types of HOCM patients. The results confirmed that using this special technique to treat HOCM patients in this series is feasible and reliable.
Although there are many different surgical approaches and methods, the modified Morrow procedure through trans-aortic approach is still considered as the gold standard surgical treatment, showing a verified surgical result and good remission of symptoms for a long time. 8,9,11 The trans-mitral approach was first described in 1963 by Lillehei and Levy. 10 They chose this approach for HOCM patients just because of suboptimal exposure through the traditional trans-aortic approach. As we all know, a satisfactory procedure for HOCM consists of three major goals: completely thickened septal muscle resection, dealing with the anterior mitral valve leaflet to avoid postoperative SAM, and release of abnormal papillary muscle and chordae attachments. 8,9,[11][12][13] Compared with the traditional trans-aortic approach via the aortic incision, the trans-mitral approach via the base of the anterior mitral leaflet provided a more clear panoramic exposure of the interventricular septum, making myectomy easily and avoiding heart block, 14,15 through this approach, experienced surgeons could even identify the pale fibrous hinges subaortic hit caused by SAM. [16][17][18] Also, this approach provided a wide vision of the anterior papillary muscles and its base. This allowed surgeons to completely address mitral valve abnormalities, release any abnormal papillary muscle, and chordae insertion to avoid postoperative SAM simultaneously. [16][17][18] According to the literatures, [3][4][5]  que. It really works for some cases, but not for the patients with a small angle between the aortic valve annulus and the mitral valve annulus plane, therefore we preferred the technique described by Chitwood 17,18 and make some modifications for our cases. Chitwood made the mitral valve incision at the base of the anterior mitral valve leaflet and resuspended it using a 4-0 PTFE suture, they interposed a pericardial patch between the annulus and cut leaflet edge when the anterior leaflet has been shortened. However, for these specific cases in our study, isolated myectomy often could not relieve LVOT obstruction and mitral valve SAM completely, in avoiding of mitral valve replacement and postoperative SAM, we reattach the anterior mitral valve leaflet to the residual leaflet rim by using a prepared fusiform autologous pericardial patch in all cases. We strongly recommend that the width of the patch should be as wide as possible to ensure that the root of the anterior mitral valve leaflet is sufficiently billowing away from the LVOT during the systolic period. The LVOT obstruction and mitral valve SAM were completely resolved during follow up in our cases, with no severe complications after operation and no occurrence MR.
The limitation of our study was the small-sized patient population and lack of long-term follow up since the cohort of cases was rare. For each case, we planted a flexible band annuloplasty to increase the height of the leaflet coaptation to avoid the recurrence MR, and during a mean follow-up of 34.25 ± 12.85 months (range, , no patient had more than moderate MR, but the long-term prognosis accompany with the pericardial patch getting calcification is unknown.
Although modified Morrow procedure is still the gold standard surgical intervention for HOCM, enlargement of LVOT using an autologous pericardial patch for the anterior mitral valve leaflet and septal myectomy through trans-mitral approach is feasible and reliable for certain cases. Since the pathology of different HOCM forms ZHANG ET AL.
| 4201 varies in patients, a personalized procedure plan should be prepared and the one in our study could be a proper choice.

| CONCLUSIONS
Enlargement of LVOT using an autologous pericardial patch for the anterior mitral valve leaflet and septal myectomy through a transmitral approach is feasible and reliable for the treatment of certain types of HOCM cases.