Concomitant Septal Myectomy in Patients Undergoing Aortic Valve Replacement for Severe Aortic Stenosis

Abstract

Background: Patients with severe aortic stenosis (AS) are often found to have asymmetric septal hypertrophy (ASH). With low sensitivity of echocardiography for detecting dynamic left ventricular outflow tract (LVOT) obstruction in severe AS, we adopted a routine intraoperative inspection of LVOT strategy for aortic valve replacement (AVR), and performed concomitant septal myectomy (CSM) as necessary. We sought to (1) evaluate surgical outcomes of CSM, (2) suggest preoperative echocardiographic parameters that correlate with findings of ASH, and (3) determine the predictors of CSM.

Methods and Results: A single surgeon performed AVR for moderate-to-severe AS in 301 patients from 2007 to 2012. CSM was performed in 35 (11.6%) patients, resulting in AVR vs. AVR+CSM groups. Echocardiographic parameters, including the ratio of LVOT to aortic annular diameter (LVOT/AA), were compared. Mortality rate was comparable between groups (P=0.37). There were no postoperative complications related to CSM. The AVR+CSM group had a smaller LVOT/AA ratio (P=0.0012). The predictor of CSM was implanted valve size ≤21 mm (odds ratio 3.2, confidence interval 1.54–6.65, P=0.002).

Conclusions: CSM can be performed safely at the time of AVR. The preoperative echocardiographic LVOT/AA ratio may help in detecting ASH. As an implanted valve size ≤21 mm was the only risk factor for CSM, careful assessment of LVOT is important in patients with a small aortic annulus. (Circ J 2015; 79: 375–380)

Asymmetric septal hypertrophy (ASH) was previously reported to be present in approximately 10% of cases of hemodynamically significant valvular aortic stenosis (AS).¹ This type of hypertrophy combined with severe AS can be easily overlooked at the time of aortic valve replacement (AVR), which can lead to residual left ventricular outflow track (LVOT) obstruction following AVR and a deteriorating postoperative course.^2,3 Although the indication for concomitant septal myectomy (CSM) at the time of AVR remains controversial, there have been suggestions supporting the necessity of direct inspection of LVOT at the time of AVR to assess the severity of ASH,^4–6 because of the low sensitivity of echocardiography for detecting dynamic LVOT obstruction in the setting of severe AS. We adopted the strategy of performing a direct visual and manual inspection of the LVOT in the operation room in all patients at the time of AVR and performed CSM in patients who were found to have ASH at the time of AVR, irrespective of their echocardiographic findings. Thus the aims of the current study were to: (1) evaluate the surgical outcomes of CSM, (2) suggest preoperative echocardiographic parameters that could predict the intraoperative finding of ASH requiring CSM, and (3) determine the other predictors of CSM at the time of AVR.

Methods

Study Population

We adopted our intraoperative inspection strategy to detect ASH at the time of AVR in 2007 and until June 2012, inspection was performed in 301 patients by a cardiac surgeon (S.J.P.). We excluded patients who were diagnosed with hypertrophic obstructive cardiomyopathy or had known septal hypertrophy. CSM was performed in 35 patients on the basis of the intraoperative inspection (AVR+CSM group) and the other patients were grouped as AVR alone (n=266). The Institutional Review Board of the Mayo clinic approved this study (IRB no. 104291).

Operative Technique

Median sternotomy was performed in all patients. After establishing standard extracorporeal circulation, cardiac arrest was induced with cold blood cardioplegia. Calcified native aortic valve (AV) was excised through oblique aortotomy and the aortic annulus (AA) was debrided carefully. Next, the LVOT was inspected visually and manually. If prominent septal bulging was detected, we performed standard septal myectomy avoiding conduction tissue injury. Prosthetic AV was placed in the annulus using standard technique.

Echocardiographic Evaluation

The pathology of the AV was preoperatively confirmed by transthoracic echocardiography (TTE). Severe AS was diagnosed with TTE by measuring the AV peak transvalvular pressure gradient, mean transvalvular pressure gradient and the AV orifice area in the systolic phase. Combined aortic regurgitation was graded from trivial (+1) to severe (+4) based on the regurgitant flow acceleration. Ventricular septal diameter and posterior free wall diameter were also measured preoperatively in the parasternal long-axis view. If the septal-free wall ratio was greater than 1.3, ASH was considered to be present. LVOT diameter at the level of 1–2 cm below the AA at end-diastole in the parasternal long-axis view (Figure 1) were measured retrospectively by an echocardiographer who was unaware of the surgical procedures and the LVOT diameter to AA ratio (LVOT/AA ratio) was calculated. As the LVOT was inspected only through the AA in the operating room, we hypothesized that the LVOT/AA ratio on preoperative echocardiography would correlate with the finding on intraoperative inspection of ASH requiring CSM.

Figure 1.

Echocardiographic measurement of left ventricular outflow tract/aortic annulus (LVOT/AA). A, LVOT; B, AA; LVOT/AA=A/B.

Patient Follow-up

Last follow-up was obtained by social security death index, postal questionnaire and review of medical records. Follow-up was completed in 100%. Mean follow-up duration was 2.3±1.6 years.

Statistical Analysis

Statistical analyses were performed using SAS 9.13 (SAS Institute, Cary, NC, USA). Data are expressed as mean±standard deviation for continuous variables and as numbers and percentages for categorical variables. Preoperative and postoperative measurements were compared using Student’s paired-t test. Chi-square test or Fisher’s exact test was used to compare the categorical variables and to assess statistical significance between the 2 groups. P<0.05 was considered statistically significant for all comparisons. Multivariate analysis was performed for the overall patient group using a Cox proportional hazards model. Variables were included in multivariate analysis if univariate significance was <0.05. The survival rate was calculated using Kaplan-Meier analysis. The follow-up period for each patient was calculated from the date of operation to the date of death or last contact.

Results

The preoperative baseline characteristics of the patients are summarized in Table 1. There were more female patients in the AVR+CSM group (P=0.0026) and body surface area (BSA) was significantly smaller in the AVR+CSM group (P=0.0049). Except for these characteristics, there were no significant differences in the baseline characteristics of the 2 groups. Etiology of AS was mostly degenerative valve disease in both groups. Moderate-to-severe aortic regurgitation was concomitant in 74 patients in the AVR group and in 10 in AVR+CSM group. As shown in Table 2, aortic cross-clamp and total bypass times were not different between groups. The mean mass of the resected septal muscle for the patients in the AVR+CSM group was 1.03±0.6 g. Patients in the AVR+CSM group tended to have a smaller prosthetic valve compared with the AVR group (P=0.002). Concomitant procedures were performed in 65% of the patients in both groups. The most common concomitant procedure was coronary artery bypass grafting. There were 6 in hospital deaths, only in the AVR group, and the overall survival rate was comparable between groups (P=0.68) (Figure 2). The postoperative complication rate was comparable between groups in terms of re-exploration for bleeding, stroke, atrial fibrillation and renal failure. Complete atrioventricular block requiring permanent pacemaker occurred in only 3 patients in the AVR group, which did not show any statistical significance (P=0.83).

Table 1. Preoperative Characteristics of Patients With Severe AS

Variable	AVR group (n=266)	AVR+CSM group (n=35)	P value
Age (years)	71.4±11.4	74.4±10.9	0.084
Female, n (%)	90 (33.8)	21 (60)	0.0026*
Body surface area, m2	1.97±0.2	1.85±0.2	0.0049*
Hypertension	205 (77.0)	27 (77.1)	0.99
Diabetes mellitus	67 (25.2)	11 (31.4)	0.43
Hypercholesterolemia	40 (15.1)	1 (2.8)	0.57
Chronic lung disease	53 (19.7)	8 (22.8)	0.24
Chronic renal insufficiency	6 (2.3)	1 (2.8)	0.82
Peripheral vascular disease	31 (11.6)	7 (20)	0.16
Cerebrovascular accident	18 (19.1)	3 (8.6)	0.84
NYHA class III, IV	172 (64.7)	23 (65.7)	0.90
Etiology, n (%)			0.42
Degenerative	180 (67.7)	28 (80)
Rheumatic	10 (3.76)	1 (2.8)
Bicuspid	55 (20.7)	4 (11.4)
LVEF (%)	55.4±15.2	63.2±13.3	<0.001
Aortic regurgitation			0.97
Trivial to mild	150 (56.4)	20 (57.1)
Moderate to severe	74 (27.8)	10 (28.6)
AV mean PG (mmHg)	47.1±16.2	51.9±20.1	0.11
LV mass	263.3±80	246.1±86.8	0.23
LV mass index	132.8±37.5	129.3±36.1	0.65
LVESD	36.1±10.1	30.7±7.6	0.0012*
LVEDD	52.1±8.3	48.8±6.0	0.01*

*P<0.05. AS, aortic stenosis; AV, aortic valve; LV, left ventricle; LVEF, left ventricular ejection fraction; LVEDD, left ventricular end-diastolic dimension; LVESD, left ventricular end-systolic dimension; NYHA, New York Heart Association; PG, pressure gradient.

Table 2. Operative and Postoperative Data of Patients Undergoing Surgical Treatment of AS

Variable	AVR group (n=266)	AVR+CSM group (n=35)	P value
Cardiopulmonary bypass time (min)	111.2±64.7	104.9±48.9	0.79
Aortic cross-clamp time (min)	81.7±40	81.2±34.5	0.89
Implant valve size ≤21 mm	92 (34.5)	22 (62.8)	0.002*
Concomitant procedures, n (%)	175 (65.8)	23 (65.7)	1.0
CABG	134	16
Ascending aorta replacement	18	1
Mitral repair or replacement	17	5
Tricuspid repair or replacement	6	1
Early death, n (%)	6 (2.26)	0	0.37
Late death, n (%)	52 (19.5)	6 (17.1)	0.73
Cardiac death	11 (4.1)	3 (8.6)	0.42
Postoperative complications, n (%)
Re-exploration for bleeding	20 (7.5)	1 (2.8)	0.31
AVB requiring PPM	3 (1.1)	0	0.83
Stroke	8 (3.0)	2 (5.7)	0.34
Atrial fibrillation	72 (27.1)	10 (28.6)	0.85
Renal failure	18 (6.8)	2 (5.7)	0.81

*P<0.05. AVB, atrioventricular block; CABG, coronary artery bypass grafting; PPM, permanent pacemaker. Other abbreviation as in Table 1.

Figure 2.

Overall survival curve. AVR, aortic valve replacement; CSM, concomitant septal myectomy.

Postoperative data from the last echocardiographic follow-up are shown in Table 3. Different from the preoperative echocardiographic findings in which LV end-systolic and end-diastolic dimensions (LVESD, LVEDD) were significantly smaller in AVR+CSM group, these dimensions became comparable postoperatively.

Table 3. Postoperative Echocardiographic Data of Patients Undergoing Surgical Treatment of AS

Variable	AVR group	AVR+CSM group	P value
LVEF	55.3±13.6	58.8±13.6	0.15
LV mass	231.1±86.1	222.5±77.1	0.91
LV mass index	115.3±39.1	122.3±43.3	0.49
LVESD	35.0±9.7	31.6±7.8	0.31
LVEDD	50.7±7.7	48.4±8.0	0.54
AV mean PG	16.7±6.9	16.4±6.3	0.85
TTE follow-up duration	24±16.7	23.6±14.3	0.92

TTE, transthoracic echocardiography. Other abbreviations as in Table 1.

Preoperative TTE Parameter (LVOT/AA) and Intraoperative Findings

The LVOT/AA ratio in the diastolic phase in the AVR+CSM group was 0.81±0.11, which was significantly smaller than in the AVR group (0.89±0.09, P<0.001). This corroborated the high correlation between intraoperative inspection of the LVOT and the LVOT/AA value on preoperative TTE.

Univariate and Multivariate Analysis for Risk Factor of CSM at the Time of AVR

To determine the risk factors contributing to ASH requiring CSM at the time of AVR, univariate and multivariate analyses were performed. In the univariate analysis, sex, BSA, implant valve size ≤21 mm, preoperative LVESD and LVEDD, and the LVOT/AA ratio were found to be significant risk factors for CSM. For the multivariate analysis, we excluded the LVOT/AA ratio, which was the strongest risk factor from the univariate analysis, because this variable was obtained retrospectively to determine the preoperative echocardiographic parameter that correlates with the intraoperative inspection findings and may represent the presence of ASH. Multivariate analysis demonstrated that small implant valve size (≤21 mm) was the only risk factor for CSM (odds ratio 3.2, confidence interval 1.54–6.65, P=0.002). These findings are summarized in Table 4. The best cutoff point for predicting CSM at the time of AVR was LVOT/AA <0.7.

Table 4. Univariate and Multivariate Analyses for Risk Factors of ASH Requiring CSM in Patients Undergoing Surgical Treatment of AS

Variable	Odds ratio	95% CI	P value
Univariate analysis
Age	1.03	0.99–1.06	0.14
Sex	2.93	1.42–6.04	0.004*
BSA	0.11	0.02–0.53	0.006*
Diabetes	0.73	0.34–1.58	0.43
Hypertension	1.0	0.43–2.3	0.99
Renal failure	0.78	0.09–6.71	0.83
NYHA III, IV	1.05	0.5–2.2	0.90
Trans AV PG	1.02	1–1.04	0.11
Implanted valve size ≤21 mm	3.2	1.54–6.65	0.002
LVEF	1.05	1.01–1.08	0.008*
LV mass index	1	0.99–1.01	0.62
LVESD	0.93	0.88–0.98	0.005*
LVEDD	0.95	0.91–1	0.032
IVS	1.09	0.91–1.29	0.35
LVOT/AA	0.39	0.25–0.59	<0.001*
Multivariate analysis
Implanted valve size ≤21 mm	3.2	1.54–6.65	0.002*

*P<0.05. ASH, asymmetric septal hypertrophy; BSA, body surface area; CI, confidence interval; CSM, concomitant septal myectomy; IVS, interventricular septum; LVOT/AA, left ventricular outflow tract/aortic annulus. Other abbreviations as in Table 1.

Discussion

Significant ASH in patients with severe AS occurs in approximately 10% of cases.^4,7 In our study, it was 11.6% (35 of 301 patients), which is comparable. Considering that the incidence of valvular AS is increasing and most common among valvular heart disease,⁸ ASH combined with severe AS is not a rare condition. The strategy for managing ASH at the time of AV surgery remains controversial because there has not been an evaluation in a large cohort or in a randomized controlled trial. Some studies recommend no routine resection of ASH at the time of AV surgery because of possible CSM-related complications such as the need for permanent pacemaker or septal perforation.⁹ or suggest CSM only in the limited cases of dynamic LVOT obstruction with septal anterior motion.⁴

However, there are several reasons to advocate CSM with AVR. First of all, CSM could eliminate any potential subaortic gradient unmasked after AVR. In the setting of combined ASH with severe AS, operative relief of AS only will unmask residual subaortic stenosis by ASH and this can lead to deleterious clinical outcomes in the early and late postoperative period.^10–12 Also, septal hypertrophy and small LV cavity diameter, as shown in the present AVR+CSM group, may be related to poor outcome in the long term if it remains.¹³

CSM also could promote significant LV regression after surgery and it is a relatively safe procedure with an acceptable, low risk.^6,14,15 As shown in our study results, CSM did not add any postoperative complications or contribute to prolonged operation time. However, we failed to demonstrate differences between groups in the current study regarding the echocardiographic variables estimating regression of LV hypertrophy after surgery. Regarding regression of LV hypertrophy, Seo et al insist that LV diastolic dysfunction persists for up to 5 years after uneventful AVR because of inadequate or incomplete regression of LV hypertrophy,¹⁶ and Di Tommaso et al reported the benefit of CSM on LV regression.⁴ The mean follow-up duration in the present study was 2.3±1.6 years, so longer follow-up might be necessary to clarify this issue.

The remaining issue associated with this surgical approach is how the coexistence of ASH with severe AS can be diagnosed precisely before AV surgery. Pressure gradient itself is not reliable for detecting coexisting subaortic obstruction in the setting of severe AS.¹⁷ Despite recent technical advances with 3D echocardiography,¹⁸ transesophageal echocardiography as well as TTE may fail to detect ASH preoperatively. Therefore, some authors suggest that both visual and manual inspection of LVOT intraoperatively are important and the decision on whether to perform CSM at the time of AVR should be made by the operator based on the inspection after excision of the native AV.^4,6,14 We began a strategy of inspecting the LVOT to detect ASH at the time of AV surgery in all patients regardless of their preoperative echocardiographic findings from 2007 onward. Based on the intraoperative findings, we performed CSM. The inspection could be subjective, so we aimed to find some echocardiographic parameters that correlated and corroborated the surgeon’s inspection findings. As shown in our study results, the preoperative LVOT/AA ratio strongly correlated with the intraoperative finding of a requirement for CSM. This suggests that the diagnostic acuity of TTE regarding ASH combined with severe AS may improve by using this parameter.

Study Limitations

First, this study was a retrospective observational study, not a randomized controlled study. So the comparison between groups could be biased with potential compounding factors. Second, the study population was relatively small, partly because of strict inclusion criteria, which were adopted to improve the homogeneity of the study population and to verify the strategy of our surgical approach to ASH with severe AS. Also, the follow-up duration was relatively short because the intraoperative inspection strategy was introduced only 5 years prior. Longer follow-up with a larger population may provide enough statistical power to demonstrate differences in LV regression between CSM+AVR and AVR alone as previously reported.

Conclusions

Intraoperative findings of ASH in patients undergoing AVR for moderate-to-severe AS do not seem to be uncommon, and CSM for ASH can be performed without additional risks. Preoperative echocardiographic measurement of the LVOT/AA ratio may be helpful in corroborating the intraoperative finding of ASH. As the implanted valve size ≤21 mm was the only risk factor for CSM, a careful assessment of the LVOT is important in patients with a small AA and small LVOT/AA ratio (LVOT/AA <0.7) at the time of AVR.

Disclosures

None related to this study.

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