Outcomes of Surgical Myectomy and Mitral Valve Repair for Hypertrophic Cardiomyopathy with or without Marked Septal Hypertrophy
ABSTRACT
Background
This study reports a single institution’s clinical and echocardiographic outcomes for septal myectomy with or without concomitant mitral valve interventions in patients with hypertrophic cardiomyopathy (HCM). and left ventricular outflow tract obstruction (LVOTO).
Methods
Consecutive patients who underwent transaortic septal myectomy with or without subvalvular mitral apparatus intervention for HCM between October 2019 and March 2024 were included. All patients underwent transesophageal echocardiography and cardiac magnetic resonance imaging to confirm the pathology, measure intracavitary gradients, and assess mitral valve morphology. Patients were analyzed as an entire cohort and stratified by the presence of marked (>15mm) or only mild (≤15mm) septal hypertrophy.
Results
Sixty-one patients (32 males) were included, of whom 28 (45.9%) had mild septal hypertrophy. Follow-up was 100% complete and averaged 26.9 ± 16.2 months. In addition to septal myectomy, 32 patients (52.5%) underwent concomitant papillary muscle realignment, and aberrant chordae were resected in 40 patients (65.6%). All patients with a septal thickness ≤ 15mm had a mitral valve repair intervention. Thirty-day and 2-year mortality were 1.6% and 3.3%, respectively. There were no post-operative ventricular septal defects, including in the thin septum subgroup. Peak left ventricular outflow tract gradients were significantly reduced with surgery, both at rest (47.2±34.7 mmHg pre-operatively versus 8.8±12.3 post-operatively, p < 0.001) and under stress (114.2±58.7 mmHg pre-operatively versus 17.6±18.5 post-operatively, p < 0.001).
Conclusions
In patients with symptomatic HCM, even in those without marked septal hypertrophy, septal myectomy with a concomitant mitral valve apparatus intervention is safe and provides excellent relief of LVOTO.
Graphical abstract
INTRODUCTION
Hypertrophic cardiomyopathy (HCM) is an inherited myocardial disease characterized by pathological left ventricular hypertrophy in the absence of another cardiac, systemic, or metabolic etiology.1, 2, 3 In the 2024 Canadian Cardiovascular Society Clinical Update on Hypertrophic Cardiomyopathy2, the proposed diagnostic criteria for HCM in adults are: A) End-diastolic left ventricular wall thickening in one or more myocardial segments measuring ≥ 15mm or ≥ 13mm in the presence of a family history of HCM and/or a pathogenic genetic variant causing HCM and B) Absence of another etiology for left ventricular hypertrophy.
While HCM morphology and location of hypertrophy are variable, 75% of HCM patients develop some degree of left ventricular outflow tract (LVOT) obstruction.4 Two principal mechanisms can cause LVOT obstruction: 1) basal septal hypertrophy leading to narrowing of the LVOT and, with turbulent flow, subsequent anterior displacement of the mitral valve leaflets; and 2) aberrant subvalvular mitral apparatus and anterior displacement of the papillary muscles causing systolic anterior motion (SAM) of the anterior mitral valve leaflet (AMVL).5,6
In patients with significant basal septal hypertrophy in whom optimal medical therapy failed to alleviate symptoms, septal myectomy is indicated.1,2,7 In contrast, in patients with LVOT obstruction but with mild septal hypertrophy, isolated myectomy may not suffice to relieve obstruction, and concomitant mitral valve apparatus interventions are often warranted.8
This study aims to report our institution’s clinical and echocardiographic outcomes of septal myectomy, with or without concomitant mitral valve interventions, in patients with obstructive HCM and varying degrees of septal hypertrophy. It focuses on a diverse cohort, including patients with (> 15 mm) and without (≤ 15 mm) marked septal hypertrophy, and highlights the importance of addressing the mitral valve apparatus in achieving optimal outcomes. This work expands the understanding of surgical approaches in obstructive HCM, emphasizing the need for tailored interventions based on individual anatomical and functional characteristics. We provide a detailed surgical technique description with an additional focus on patients with only mild septal thickening and an abnormal mitral valve apparatus.
MATERIALS AND METHODS
Patient Selection and Follow-Up
All consecutive patients who underwent surgical septal myectomy for primary LVOT obstruction, with or without concomitant cardiac procedures, at our institution between October 2019 and March 2024, were included in this cohort. During the same period, 18 alcohol septal ablations (age range 48-87 years) were performed by one operator in our center (personal communication; unpublished data).
All patients underwent a trial of medical therapy, namely with a beta-blocker and disopyramide, prior to surgical consideration. Because Mavacamten was only approved for use in Canada as of November 20229, most patients were not treated with this medication.
A multidisciplinary team of cardiologists, cardiac surgeons, and anesthesiologists reviewed all patients prior to surgery, with a specific focus on their imaging findings, and confirmed their suitability for surgical treatment. The pre-operative assessment included a transthoracic echocardiogram (TTE) for initial diagnosis. Once surgical intervention was indicated, a transesophageal echocardiogram (TEE) and a cardiac magnetic resonance imaging (MRI) scan were performed, to provide information regarding the septum dimensions and the left ventricle (LV), mitral and aortic valves, papillary muscles, and chordae. Indications for surgery included severe heart failure symptoms caused by dynamic subaortic obstruction refractory to medical therapy, patients with LVOT obstruction unable to tolerate medical therapy, and patients with significant LVOT obstruction undergoing concomitant cardiac surgery.
Post-operatively, patients were followed in clinic and had serial echocardiograms at 1 month, 6 months, 12 months, and annually thereafter. Post-operative Holter monitoring was performed in selected patients, at the discretion of the referring cardiologist. Patients with an implantable cardioverter-defibrillator (ICD) were followed by an electrophysiologist. ICD printouts were not reviewed for this study. Malignant arrhythmias were defined as potentially life-threatening ventricular arrhythmias, including ventricular tachycardia and ventricular fibrillation, that result in a hemodynamic compromise.1
Surgical Technique
In this cohort, septal myectomy was performed by a group of 4 surgeons, either individually or in pairs, with the corresponding author involved in all cases. After general anesthesia induction, a TEE is performed to assess the LVOT morphology. More specifically, TEE serves to evaluate septal thickness and morphology, the mitral valve and its subvalvular apparatus, and the LV dimensions, and to confirm the pathology and LVOT gradient before and after provocation with isoproterenol. All patients are operated through a midline sternotomy, and intravenous isoproterenol (2 to 8 mcg/min to obtain a heart rate of 100 beats-per-minute and a systolic blood pressure ≤ 80 mmHg) is only initiated after intravenous heparin has been administered and cannulation has been performed. Cardiopulmonary bypass (CPB) is then initiated. The interventricular septum is exposed through a transverse aortotomy incision and suspension of the noncoronary aortic valve leaflet. The basal septum is incised, using a #15 scalpel blade, parallel to the LVOT, about 2-3 mm below the insertion of the aortic valve leaflets, at the mid-point of the right coronary cusp, and progressing counterclockwise. The depth of the incision is determined by pre- and intra-operative echocardiography. It is essential to know the dimensions of the septum that need to be resected, including its depth and thickness, prior to proceeding with the myectomy. The incision is carried towards the lateral portion of the mitral annulus, and the desired portion of the resected interventricular septum is developed towards the apex of the heart. In all cases, the septal resection extends to the insertion of the anterolateral papillary muscle in order to mobilize it away from the septum. Accessory trabeculae are resected, and the anterolateral papillary muscle is extensively freed from the lateral left ventricular wall. The mitral valve apparatus is then examined, and any aberrant secondary chordae that are fibrotic or thickened, as well as any accessory papillary muscles, are also resected. The papillary muscles are realigned when necessary; to this end, we use a pledgeted horizontal mattress prolene or Goretex suture from the anterolateral to the posteromedial papillary muscle, being cognizant to incorporate enough tissues to avoid tearing of the sutures, but not enough to cause papillary muscle necrosis (video). A post-CPB TEE is performed, with isoproterenol provocation, in all cases to confirm the absence of SAM of the AMVL, new ventricular septal defect, new aortic insufficiency, or residual mitral regurgitation and LVOT obstruction. We deem that a peak gradient of 20 mmHg or less during provocation is satisfactory; however, this cut-off is not fixed and is assessed on a case-by-case basis. Further details on the surgical technique are provided in the supplemental video.
Echocardiographic Imaging
All patients underwent pre-, intra-, and post-operative echocardiography, which confirmed the presence, severity, and mechanism of LVOT obstruction, as well as the morphology of the mitral valve. Echocardiographic measurements were performed by board-certified cardiac anesthesiologists and echocardiographers, following the American Society of Echocardiography guidelines.10,11 Septal thickness was measured at the basal and mid-cavity levels, in the mid-esophageal long axis view on pre-operative TTE and was confirmed on TEE. The left ventricular end-diastolic diameter, the anterior and posterior mitral leaflet length, the aorto-mitral angle, and the distance between the mitral leaflet coaptation point and the interventricular septum (C-Sept) were also acquired. Furthermore, MRI was performed in almost all patients pre-operatively to confirm the septum dimensions and for assessment of the LVOT surrounding structures. SAM was defined as the obstruction of the LVOT by any portion of the AMVL against the septum during systole while not on CPB. Post-operative septal thickness was assessed on TTE.
Statistical Analysis
Continuous variables were described as a mean with standard deviation, and categorical variables as frequency and percentages. Continuous and categorical variables were compared between groups using a Student’s t-test and a χ2 test or Fisher’s exact test, respectively. Pre- and post-operative LVOT gradients were assessed with a paired Student’s t-test. A subgroup analysis was performed for patients with mild septal hypertrophy, defined as an interventricular septum ≤ 15 mm7. Survival analysis with Kaplan-Meier estimates were used to determine the freedom from a composite of death, heart failure hospitalization, and malignant ventricular arrhythmias during follow-up, stratified by septal thickness. Kaplan-Meier curves were compared with a log-rank test. A P-value < 0.05 was considered statistically significant. All analyses were conducted using SAS On Demand for Academics (SAS Institute Inc., Cary, North Carolina, USA).
RESULTS
A total of 61 patients were included in the cohort. Twenty-eight patients had a septal thickness of ≤ 15 mm and 33 patients were > 15 mm. Patient baseline characteristics and operative data are summarized in Table 1. The mean age of the cohort was 57.7 ± 13.8 and 32 (52.5%) were males. Eleven (17.7%) patients suffered from a prior aborted sudden cardiac death, and most patients (75.7%) presented with symptoms of New York Heart Association (NYHA) class II or higher. Among the 6 patients (9.8%) with NHYA class I symptoms, the primary indication for surgery was severe coronary artery disease in 4 and aortic stenosis in 2 (Supplemental Table S1). Furthermore, 2 of these 6 patients had a documented family history of HCM. With regards to the 19 patients (31.1%) with NYHA class II symptoms, the primary surgical indication was valvular heart disease in 10, severe coronary disease in 2, and syncopal or anginal symptoms attributable to HCM in 7 patients.
Table 1. Baseline and Operative Characteristics of the entire cohort and of patients with a thin septum (≤ 15mm)
| Variable | Entire Cohort (N = 61) | Septum > 15mm (N = 33) | Septum ≤ 15mm (N = 28) |
|---|---|---|---|
| Age (years), mean ± SD | 57.7 ± 13.8 | 57.7 ± 13 | 57.6 ± 15 |
| Male sex, n (%) | 32 (52.5) | 20 (60.6) | 12 (41.4) |
| Pre-operative medication, n (%) | |||
| Beta-Blockers | 43 (71.7) | 26 (78.8) | 17 (60.7) |
| Disopyramide | 18 (29.5) | 13 (39.4) | 5 (17.9) |
| NYHA Class, n (%) | |||
| I | 6 (9.7) | 2 (6.5) | 4 (14.3) |
| II | 19 (30.6) | 11 (35.5) | 8 (28.6) |
| III | 27 (43.5) | 17 (54.8) | 10 (35.7) |
| IV | 1 (1.6) | 1 (3.2) | 0 (0) |
| Not reported | 8 (12.9) | 2 (6.1) | 6 (21.4) |
| Prior Aborted Sudden Cardiac Death, n (%) | 11 (17.7) | 6 (18.2) | 5 (17.9) |
| Previous Cardiac Surgery | 2 | 1 (3.0) | 1 (3.6) |
| Prior myectomy | 1 (1.6) | 1 (3.0) | 0 (0) |
| Other cardiac surgery | 1 (1.6) | 0 (0) | 1 (3.6) |
| Prior Atrial Fibrillation | 13 (21) | 6 (18.2) | 7 (25) |
| Urgency, n (%) | |||
| Elective | 46 (75.4) | 25 (75.8) | 21 (75) |
| Urgent | 15 (24.6) | 8 (24.2) | 7 (25) |
| Transaortic Approach, n (%) | 61 (100) | 33 (100) | 28 (100) |
| Subvalvular Mitral Apparatus Intervention, n (%) | |||
| Chordal Resection | 40 (65.6) | 25 (75.8) | 15 (53.6) |
| Papillary Muscle Realignment | 32 (52.5) | 23 (69.7) | 9 (32.1) |
| Cardiopulmonary Bypass Time (min), mean ± SD | 122.6 ± 47.5 | 120.8 ± 53.2 | 124.7 ± 40.8 |
| Cross-clamp Time (min), mean ± SD | 93.2 ± 34.1 | 89.8 ± 36.6 | 97.1 ± 31.1 |
| Concomitant Procedure, n (%) | 46 (75.4) | 23 (69.7) | 23 (82.1) |
| CABG | 12 (19.7) | 3 (9.1) | 9 (32.1) |
| AVR | 12 (20) | 3 (9.1) | 9 (32.1) |
| Surgical Ablation | 4 (6.7) | 1 (3.0) | 3 (10.7) |
| Mitral valve replacement | 5 (8.2) | 3 (9.1) | 2 (7.1) |
AVR: Aortic valve replacement; CABG: Coronary Artery Bypass Grafting; NYHA: New York Heart Association; SD: Standard Deviation.
All patients underwent septal myectomy via a transaortic approach and 46 (75.4%) received concomitant procedures. With regards to subvalvular mitral apparatus interventions, all patients had anterolateral papillary muscle mobilization, while 40 (65.6%) and 32 (52.5%) patients underwent chordal resection and papillary muscle realignment, respectively. Forty-six patients (75.4%) underwent surgery under an elective setting. Among the 15 patients (24.6%) whose surgery was classified as urgent, the reason for urgency was decompensated valvular heart disease in 6 patients (9.8%) and severe or acute coronary artery disease in 4 patients (6.6%). The 5 other patients had expedited surgery due to debilitating worsening of their symptoms. None of the patients from this cohort required emergent surgery.
Table 2 summarizes the baseline and post-operative echocardiographic characteristics of the entire cohort, and of patients stratified by septal thickness. Preoperative resting and provoked peak LVOT gradients were 47.2 ± 34.7 mmHg and 114.2 ± 58.7 mmHg, respectively, for the entire cohort, and were not significantly different between patients with or without marked septal hypertrophy. In the entire cohort, peak left ventricular outflow tract gradients were significantly reduced with surgery, both at rest (47.2 ± 34.7 mmHg pre-operatively versus 8.8 ± 12.3 post-operatively, p < 0.0001) and under stress (114.2 ± 58.7 mmHg pre-operatively versus 17.6 ± 18.5 post-operatively, p < 0.0001). In patients with a septum > 15 mm, pre-operative gradients at rest and under stress were 51.3 ± 35.1 and 108.7 ± 54.9, respectively, while corresponding post-operative gradients were 11.0 ± 13.9 and 15.5 ± 20.3, respectively (p < 0.0001). Patients with a septum ≤ 15 mm had pre-operative gradients at rest and under stress of 40.8 ± 33.8 and 123.7 ± 65.5, and post-operative gradients of 4.5 ± 6.9 and 10.4 ± 13.6 at rest and under stress, respectively (p = 0.003 for rest gradients and p < 0.0001 for stress gradients).
Table 2. Echocardiography Characteristics at baseline and after surgery, for the entire cohort and for patients with a thin septum
| Variable | Entire Cohort (N = 61) | Septum > 15mm (N = 33) | Septum ≤ 15mm (N = 28) |
|---|---|---|---|
| Pre-operative Data | |||
| LV ejection fraction (%), mean ± SD | 60.7 ± 7.5 | 60.8 ± 5.6 | 60.6 ± 9.5 |
| Septal wall thickness (cm), mean ± SD | 1.6 ± 0.5 | 2.0 ± 0.3 | 1.15 ± 0.18 |
| Resting peak LVOT gradients (mmHg), mean ± SD | 47.2 ± 34.7 | 51.3 ± 35.1 | 40.8 ± 33.8 |
| Induced LVOT gradients (mmHg), mean ± SD & | 114.2 ± 58.7 | 108.7 ± 54.9 | 123.7 ± 65.5 |
| ≥ 2+ Mitral valve regurgitation, n (%) | 10 (16.4) | 8 (24.2) | 5 (17.8) |
| Systolic anterior motion of the AMVL, n (%) | 42 (68.9) | 28 (84.9) | 14 (50) |
| Left atrial volume index (mL/m2), mean ± SD | 41.9 ± 17.1 | 48.4 ± 19.8 | 34.7 ± 9.7 |
| Post-operative Data t | |||
| Septal wall thickness (cm), mean ± SD | 1.3 ± 0.4 | 1.4 ± 0.5 | 1.08 ± 0.21 |
| Resting peak LVOT gradients (mmHg), mean ± SD | 8.8 ± 12.3 | 11.0 ± 13.9 | 4.5 ± 6.9 |
| Induced LVOT gradients (mmHg), mean ± SD & | 14.0 ± 18.5 | 15.5 ± 20.3 | 10.4 ± 13.6 |
| ≥ 2+ Mitral valve regurgitation, n (%) | 6 (10.5) | 3 (9.1) | 3 (12) |
| Systolic anterior motion of the AMVL, n (%) | 11 (20.3) ∗ | 8 (15.4) ∗ | 3 (13) ∗ |
| Left atrial volume index (mL/m2), mean ± SD | 41.7 ± 17.2 | 47.5 ± 18.6 | 34.2 ± 11.7 |
| Ventricular septal defect, n (%) | 0 (0) | 0 (0) | 0 (0) |
t Four patients had missing post-operative echocardiographic data.
&Induced gradients were provoked with either exercise, dobutamine or isoproterenol.*For post-operative systolic anterior motion (SAM), patients who underwent mitral valve replacement were excluded. Therefore, the numbers at risk for SAM were 54 and 23 for the entire cohort and for patients with a thin septum, respectively. AMVL: Anterior mitral valve leaflet; LV: Left ventricular; LVOT: Left ventricular outflow tract; SD: Standard Deviation.
Although 11 patients (20.3%) had SAM post-operatively, there was no difference in post-operative gradients, both at rest and under stress, compared to patients without post-operative SAM (Supplemental Table S2). The average peak gradients at rest were 7.2 ± 14.0 mmHg and 9.3 ± 14.5 mmHg for patients with and without SAM, respectively (p = 0.68) and the average peak gradients under stress were 8.7 ± 13.0 mmHg and 16.6 ± 20.5 mmHg, respectively (p = 0.36).
Median follow-up was 26.9 months (Table 3). One patient died in hospital (1.6% mortality) due to severe cardiogenic shock, and one patient died during follow-up of an unknown cause. There were no new ventricular septal defects in the entire cohort. Among the entire cohort, two (3.3%) patients had a secondary prevention ICD, one for a prior history of aborted sudden cardiac death pre-operatively and the other for post-operative sustained ventricular tachycardia, as recommended in the 2024 Clinical Practice Updated on Hypertrophic Cardiomyopathy2. With regards to post-operative permanent pacemaker implantation, this was required in 3 (4.9%) patients due to the presence or suspicion for intermittent high-grade atrioventricular block.
Table 3. Outcomes of surgical myectomy for the entire cohort and for patients with a thin septum
| Variable | Entire Cohort (N = 61) | Septum > 15mm (N = 33) | Septum ≤ 15mm (N = 28) | P-value |
|---|---|---|---|---|
| Median Follow-up (months) | 26.9 ± 16.2 | 23.1 ± 16.6 | 27.7 ± 15.6 | 0.33 |
| 30-day mortality, n (%) | 1 (1.6)∗ | 1 (3.0) | 0 (0) | > 0.99 |
| Medium-term mortality, n (%) | 2 (3.3)t | 2 (6.1) | 0 (0) | 0.5 |
| Cerebrovascular accident, n (%) | 0 (0) | 0 (0) | 0 (0) | > 0.99 |
| Acute Kidney Injury requiring dialysis, n (%) | 3 (4.9) | 2 (6.1) | 1 (3.6) | > 0.99 |
| Permanent pacemaker implantation, n (%) | 3 (4.9) | 2 (6.1) | 1 (3.6) | > 0.99 |
| Implantable Cardiac Defibrillator, n (%) | 2 (3.3) | 1 (3.0) | 1 (3.6) | > 0.99 |
| Cardiovascular rehospitalization, n (%) | 5 (8.2) | 4 (13.3) | 1 (3.7) | 0.36 |
| Malignant ventricular arrhythmia, n (%) | 1 (1.6) | 1 (3.0) | 0 (0) | > 0.99 |
* Cause of death: Severe cardiogenic shock.
t Cause of death unknown.
Rehospitalization for cardiovascular causes occurred in 5 (8.2%) patients. One patient (1.6%) experienced an aborted sudden cardiac death at follow-up. She suffered from a ventricular fibrillation cardiac arrest, which was successfully defibrillated through an ICD shock. The patient was readmitted briefly for monitoring but did not require further resuscitation. The freedom from a surgical failure, defined by the SHARE registry as a composite of death, heart failure hospitalization, and malignant ventricular arrhythmias,12 was 94.8% and 92.4% for the entire cohort, at 12 and 24 months of follow-up, respectively. When stratified by septal thickness, freedom from surgical failure was higher in patients with a septal thickness ≤ 15 mm (P-value = 0.022; Figure 2). With regards to functional status at follow-up, 91.2% of patients had NYHA class I or II symptoms, 5 patients (8.8%) had NYHA class III symptoms while none were NYHA IV (Figure 3).
Figure 1. Average pre- and post-operative peak gradients at rest and under stress for the entire surgical cohort, for patients with a septum > 15 mm and for those with a septum ≤ 15mm preoperatively.
Figure 2. Kaplan-Meier curves for freedom from surgical failure, stratified by septal thickness > 15 mm (blue) and ≤ 15 mm (yellow). Shaded areas represent the 95% confidence intervals. Surgical failure was defined as a composite of death, heart failure hospitalization, and malignant ventricular arrhythmia at follow-up.
Figure 3. New York Heart Association (NYHA) functional status at baseline and at last follow-up. Numbers (percentages) represent the frequency for each NYHA class in the entire cohort.
DISCUSSION
In this study, septal myectomy with or without concomitant mitral valve apparatus intervention was safe and significantly decreased LVOT gradients in patients with symptomatic obstructive hypertrophic cardiomyopathy with varying degrees of interventricular septal thickening, including patients with only mild hypertrophy.
Moreover, 2 of the 5 patients who underwent mitral valve replacement were planned pre-operatively, due to organic disease. The remaining 3 patients had residual moderate-to-severe or severe MR after the first CBP run, thereby requiring a mitral valve replacement. These patients had a largely abnormal subvalvular mitral apparatus, with a known low threshold and preoperative discussion to replace their mitral valves.
The present HCM cohort also highlights that there was markedly improved symptomatology and LVOT gradients after corrective surgery even in patients who had presented with mild septal thickening and symptomatic LVOT obstruction. In our cohort, while all patients underwent a septal myectomy, some of those with a pre-operative septal thickness ≤ 15mm underwent a limited septal myectomy, sometimes by resecting only a few millimeters. Among patients with a septal thickness ≤ 15mm, the average septal resection was 7 mm in thickness. In these patients, understanding the mechanism of LVOT obstruction and consequent remodeling of the abnormal mitral valve apparatus is paramount. Risk factors for LVOT obstruction through SAM of the AMVL include a tall posterior mitral valve leaflet, a small aorto-mitral angle, anterior displacement of the anterolateral papillary muscle, interventricular septal thickening, a short distance between the mitral valve leaflet coaptation point and the interventricular septum (C-Sept), and a small left ventricular cavity.13, 14, 15 Critical values for these variables have been previously described and are summarized in Table 4.
Table 4. Echocardiographic risk factors for left ventricular outflow tract obstruction through systolic anterior motion of the anterior mitral valve leaflet in hypertrophic cardiomyopathy
| Variable | Definition | TEE view | Critical value | Miscellaneous information |
|---|---|---|---|---|
| Anterior leaflet length | Distance between the mitral annulus and the tip of the leaflet | Mid-esophageal long-axis | Shorter values are worse (no validated cut off value) | Measured in diastole |
| Posterior leaflet length | Distance between the mitral annulus and the tip of the leaflet | Mid-esophageal long-axis | > 15mm | Measured in diastole |
| AL/PL ratio | Ratio of the anterior leaflet to posterior leaflet length | Not applicable. Calculated from the AL and PL lengths | ≤ 1.3 | – |
| Left ventricular end diastolic diameter | Internal mid-cavitary diameter of the left ventricle at end-diastole | Mid-esophageal two chamber or trans gastric mid-papillary short-axis | < 45mm | Can also be measured with M-mode |
| Coaptation-Septum distance | Distance between coaptation point to the septum | Mid-esophageal long-axis | < 25mm | Measured in mid-systole, just before the onset of SAM |
| Aorto-mitral angle | Angle created between the mitral annular plane and the aortic annular plane | Mid-esophageal long-axis | < 120° | The border between the mitral and aortic annuli is the hinge point of the aorto-mitral curtain |
| Septal thickness | Interventricular septal thickness | Mid-esophageal long-axis | ≥ 13 mm | Measured in diastole |
Clinical and echocardiographic results of this cohort compare to previously published outcomes.16 In a series of 507 myectomies, Rastegar and colleagues describe a 30-day mortality of 0.8% and a 5-year and 10-year survival of 94% (95% confidence interval [CI]: 89-96%) and 91% (95% CI: 84-95%), respectively, which matches the age- and sex-matched survival in the general U.S. population.17 Similarly, Vriesendorp et al. described a cohort of 98 patients who underwent septal myectomy with AMLV extension with autologous pericardium.18 This concomitant procedure was performed to stiffen the midsegment of the AMVL, and resulted in significant reduction of SAM and no operative mortality. Transaortic chordal cutting has also been described as an adjunct intervention to septal myectomy, particularly for patients with mild septal hypertrophy. In a cohort of 39 consecutive HCM patients, Ferrazzi et al. report a decrease in resting LVOT gradient from 82 ± 43 mm Hg to 9 ± 5 mm Hg (p < 0.001) and a decrease in septal thickness from 17 ± 1 mm to 14 ± 2 mm (p < 0.001), with no operative mortality.8 Nonetheless, these series arguably represent outcomes of higher volume centers. In a United-States Nationwide-based study including 6386 patients who underwent septal myectomy for HCM between 2003 and 2011, hospital volume was an independent predictor of in-hospital all-cause mortality.19 In this cohort, in-hospital mortality was 5.2%. In a more recent report from the Society of Thoracic Surgery database with 5935 patients with HCM, overall early mortality was 2.6%.20 Lower annual case volume was, again, consistently associated with higher rate of early mortality (odds ratio, 5.4; 95% CI 3.0-9.9; P < 0.001).
This study has several limitations. First, the sample size is small due to the relatively rare nature of the disease, thereby limiting the statistical power of the study. Second, as depicted by the variability in concomitant procedures, this HCM cohort is somewhat heterogeneous, and may not be perfectly generalizable to all HCM patients. Furthermore, it is possible that the improvement in some patients’ symptoms was partly attributable to the concomitant procedure they received, thereby confounding their outcome. For example, 7 (11.5%) patients presented with angina as their primary symptom. Among these, 3 had concomitant obstructive coronary artery disease and underwent coronary artery bypass grafting surgery at time of septal myectomy, which may have contributed to the improvement of symptoms post-operatively. Third, some patients had a degree of aortic stenosis, which, in certain cases can preclude the diagnosis of HCM. Nevertheless, aortic stenosis and HCM may still coexist and can be reliably distinguished with appropriate diagnostic methods.21, 22, 23 Our patients were followed by a multi-disciplinary team including cardiologists specialized in HCM, who were instrumental in confirming the HCM diagnosis in this subset of patients, despite the cooccurrence of their aortic stenosis. Furthermore, among the 3 patients who had severe concomitant aortic stenosis, 2 had cardiac MRI findings in keeping with HCM, and the third patient had a left ventricular morphology strongly suggestive of HCM, with a pronounced basal bulge. Fourth, because this is a recent cohort, median follow-up is only 26.9 months. However, all patients continue to be followed longitudinally at our institution. Despite these limitations, this cohort provides a modern and comprehensive clinical and echocardiographic follow-up after surgical management of LVOT obstruction in HCM, and highlights the role of correction of the mitral valve apparatus, especially in patients with mild septal thickening. The study provides strong evidence of the medium-term efficacy and safety of these combined procedures, particularly in more complex cases.
CONCLUSION
In this cohort of patients with symptomatic obstructive HCM, septal myectomy with or without concomitant mitral valve apparatus intervention was safe and provided excellent relief of LVOT obstruction. Surgery reduced LVOT gradients in patients with HCM and LVOT obstruction but with no significant septal hypertrophy, by addressing the root anatomical cause of LVOT obstruction. This cohort highlights how, in a subset of patients including those without marked septal hypertrophy, addressing the abnormal mitral valve is paramount to relieve the LVOT obstruction. Specific echocardiographic predictors for SAM and LVOT obstruction in HCM patients with mild septal hypertrophy remain to be validated with larger cohorts.