Procedural Volume and Outcomes After Septal Reduction Therapies in Hypertrophic Obstructive Cardiomyopathy

Abstract

Background

Septal myectomy and alcohol septal ablation (ASA) are septal reduction therapies for patients with symptomatic obstructive hypertrophic cardiomyopathy. Operator and hospital volume may influence outcomes, but contemporary data on this relationship are limited.

Methods and Results

This retrospective cohort study used data from the Vizient Clinical Data Base (2016–2022). Patients with undergoing septal myectomy and ASA were identified using International Classification of Diseases, Tenth Revision, Clinical Modification (ICD‐10‐CM) codes and stratified into low‐, medium‐, and high‐volume groups based on annualized operator and hospital volumes. The outcomes were 30‐day in‐hospital mortality and 90‐day readmission, analyzed using multivariable adjusted logistic and Cox models. Among 5725 patients with hypertrophic cardiomyopathy (3990 septal myectomy; 1735 ASA), most operators and hospitals performed <10 procedures annually. For septal myectomy, low‐volume operators were associated with higher odds of 30‐day mortality (adjusted odds ratio [aOR], 1.86 [95% CI, 1.11–3.15]) and greater risk for 90‐day readmission (aOR, 1.51 [95% CI, 1.22–1.88]), and medium‐volume operators had higher odds of 30‐day mortality (aOR, 1.93 [95% CI, 1.05–3.55]). Medium‐volume hospitals had higher 30‐day mortality (aOR, 2.29 [95% CI, 1.32–3.99]), with low‐volume hospitals showing greater risk for 90‐day readmission (aOR, 1.60 [95% CI, 1.14–2.23]). For ASA, low‐ and medium‐volume operators had increased 30‐day mortality (aOR, 2.99 [95% CI, 1.15–7.75] and aOR, 3.86 [95% CI, 1.30–11.46]), but the risk of 90‐day readmission was similar. Hospital volumes did not significantly impact outcomes for ASA.

Conclusions

Low operator and hospital volumes were associated with worse outcomes for septal reduction therapies, emphasizing the need to refer patients with hypertrophic cardiomyopathy to high‐volume centers with experienced operators.

Nonstandard Abbreviations and Acronyms

HCM

hypertrophic cardiomyopathy

Clinical Perspective.

What Is New?

• In this extensive contemporary nationwide database, 5725 patients underwent septal reduction therapy between 2016 and 2022, which included data from >150 academic medical centers and >500 operators; >90% of these procedures were performed in hospitals or by operators who conducted <10 procedures per year.

• Septal myectomy performed by low‐volume operators and hospitals was associated with approximately twice the risk of 30‐day in‐hospital mortality and higher odds of postoperative complications compared with high‐volume counterparts.

• For alcohol septal ablation, low‐ and medium‐volume operators had a 3‐ to 4‐fold higher risk of 30‐day in‐hospital mortality and greater odds of complications such as bleeding, acute renal failure, and 90‐day readmission compared with high‐volume operators, although hospital center volume did not significantly affect these outcomes.

What Are the Clinical Implications?

• Low‐volume centers and surgeons for septal myectomy, as well as interventionalists with low annual volumes for alcohol septal ablation, were associated with higher short‐term morbidity, mortality, and 90‐day readmissions.

• Important quality standards should include patient outcomes (such as complication rates, long‐term survival, and quality of life improvements), operator experience and skill, patient selection criteria, and comprehensive postprocedure follow‐up as a part of evaluation for septal reduction therapies.

• According to the 2024 American College of Cardiology/American Heart Association guidelines, patients with hypertrophic cardiomyopathy who are candidates for septal reduction therapy should be referred to a center of excellence for hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is a common inherited cardiac disease that affects an estimated ≈20 million people worldwide and ≈750 000 individuals in the United States. ¹ , ² , ³ Nearly 70% of patients with HCM are reported to have left ventricular outflow tract (LVOT) obstruction, ¹ which is associated with worse prognosis and overall survival. ⁴ Alleviating LVOT obstruction in patients with HCM improves their survival to that of the general population. ⁵ , ⁶ Septal reduction therapies, such as septal myectomy and alcohol septal ablation, are preferred surgical versus interventional modalities to reduce LVOT obstruction among symptomatic patients with obstructive HCM refractory to standard medical management. ³ Identifying the determinants of adverse clinical outcomes among patients with HCM undergoing septal reduction therapies may guide clinical practice to further improve outcomes.

Apart from patient‐level factors, surgical center volume and operator volume have been shown to be important determinants of postprocedural outcomes in a wide range of cardiac procedures. ⁷ , ⁸ , ⁹ , ¹⁰ , ¹¹ , ¹² , ¹³ , ¹⁴ Evidence from prior observational studies supports that patients with HCM undergoing septal reduction therapies at high‐volume centers have better survival and lower risk of postprocedural complications compared with patients having surgery at lower‐volume centers. ³ , ¹² , ¹³ , ¹⁴ , ¹⁵ Based on these prior studies, the current American College of Cardiology/American Heart Association and European Society of Cardiology HCM guidelines recommend the referral of patients to comprehensive high‐volume HCM centers with experienced operators for septal reduction therapies. ³ , ¹⁶ , ¹⁷ However, the prior studies were limited by institutional‐level data with the use of inpatient or registry databases, without assessment of operator‐level data. ¹² , ¹³ , ¹⁴ , ¹⁸ Thus, there is a lack of contemporary data on the role of center volume in clinical outcomes of patients with HCM undergoing septal reduction therapies from a patient‐level nationwide database. Furthermore, the role of operator experience in the context of septal reduction therapies for patients with HCM has not been explored.

This nationwide study of patients with HCM undergoing septal reduction therapies using contemporary nationwide patient‐level data aimed to examine (1) the association between operator‐ and center‐based procedural volume and 30‐day mortality after septal myectomy and alcohol septal ablation and (2) the association between operator‐ and center‐based procedural volume and risk of postprocedural complications including stroke, bleeding, acute renal failure, permanent pacemaker and implantable cardioverter‐defibrillator, and 90‐day readmission after septal myectomy and alcohol septal ablation.

METHODS

Transparency and Openness Promotion

The data that support the findings of this study are available from the corresponding author (parora@uabmc.edu) upon reasonable request.

Data Source

This study used data from the Vizient Clinical Data Base. In brief, the Vizient Clinical Data Base is a large consortium‐based database that comprises demographics, comorbidities, clinical outcomes, procedures, medications, costs, and readmission data from patients hospitalized in US academic centers and affiliated hospitals. ¹⁹ , ²⁰ , ²¹ , ²² The Vizient Clinical Data Base is the expansion of the University Hospital Consortium. ²³ The University Hospital Consortium was initiated in 1984 as a nonprofit organization that included 43 academic hospitals from ≈24 states. ²⁴ The University Hospital Consortium was transitioned to the Vizient Clinical Data Base, which incorporates data from >1000 academic medical centers (>95%) and community hospitals from all 50 states across the United States. ²¹ , ²³ , ²⁵ The Vizient Clinical Data Base contains longitudinal encounters for each individual patient across multiple clinical settings in the specific hospital system. All patient, hospital, and operator data were deidentified before extraction for analysis. This study was designated exempt by the institutional review board of the University of Alabama at Birmingham because it involved deidentified data.

Study Population

Patients with HCM aged between 18 and 80 years who underwent septal reduction therapies between January 1, 2016 and December 31, 2022 (last date with available data in the Vizient Clinical Data Base) were identified. Individuals aged <18 years were excluded because the society recommendations for diagnostic workup and management strategies for HCM are different for this age group. ³ A validated strategy using International Classification of Diseases, Tenth Revision, Clinical Modification (ICD‐10‐CM) coding strategies was used to identify the study population. ¹⁴ , ¹⁸ , ²⁶ In brief, all patients with HCM (ICD‐10‐CM: I42.1 and I42.2) who were admitted for septal myectomy (ICD‐10‐Procedure Coding System [ICD‐10‐PCS]: 02BM0ZZ, 02BL0ZZ, 025L0ZZ, 025M0ZZ) or alcohol septal ablation (ICD‐10‐PCS: 025M3ZZ, 025L3ZZ, 02BL3ZZ, 02BM3ZZ) were identified in the Vizient Clinical Data Base. Patients who had both septal reduction therapies at the same encounter were excluded. Demographic information such as age, sex, race, income, insurance status, hospital volume, and operator volume were provided by each participating health care facility through electronic health records to the Vizient Clinical Data Base. The clinical comorbidities used in the study were derived using the Elixhauser method for quantification of coexisting conditions and provided by the Vizient Clinical Data Base. ²⁷ Each patient's unique identifier was linked longitudinally for up to 90 days across same‐hospital data in the Vizient Clinical Data Base. Using these follow‐up data, each patient with HCM who underwent septal myectomy or alcohol septal ablation was assessed for the first occurrence of hospitalization or emergency department visit to examine readmission after septal reduction therapy.

Procedure Volume Assessment

The Vizient Clinical Data Base provides data on the frequency of septal reduction therapy per quarter for each hospital or operator. Annual hospital volume for each septal reduction therapy (septal myectomy or alcohol septal ablation) was calculated by dividing the total number of respective procedures within a hospital by the number of quarters between the first and last case by that hospital and then multiplied by 4, as outlined previously. ¹⁰ , ¹² , ¹³ , ¹⁸ , ²⁶ Similarly, the annual operator volume for septal myectomy or alcohol septal ablation was calculated by dividing the total number of procedures by the specific operator within the study duration by the number of quarters between the first and last case by that operator and then multiplied by 4. Because the Vizient Clinical Data Base used a unique patient, hospital, and operator identifier, the study had no overlap at patient‐level data within the same institutions.

Hospitals and operators were categorized into 3 groups based on the tertiles of annualized volume for septal myectomy or alcohol septal ablation. Hospitals conducting septal myectomy were classified as low‐volume (tertile 1: <2 procedures per year), medium‐volume (tertile 2: 2–4 procedures per year), and high‐volume (tertile 3: >4 procedures per year) hospitals. Similarly, operators performing septal myectomy were stratified into low‐ (<3 procedures per year), medium‐ (3–4 procedures per year), and high‐volume (>4 procedures per year) categories. Hospitals in which <2, 2 to 4, and >4 alcohol septal ablations were performed each year were classified as low‐, medium‐, and high‐volume centers, respectively. Last, operators were categorized as low, medium, and high volume if they performed <4, 4, and >4 alcohol septal ablations per year, respectively.

Outcomes

The primary outcome of our study was 30‐day in‐hospital mortality following septal reduction therapies. Secondary outcomes included permanent pacemaker or implantable cardioverter‐defibrillator placement, acute renal failure, stroke, major bleeding, and 90‐day readmission. Additional exploratory outcomes included length of stay, hospitalization cost to produce care, discharge disposition, and cause‐specific readmission. Outcomes were defined using ICD‐10‐CM codes, as outlined in Table S1.

Statistical Analysis

Analyses were conducted in the septal myectomy and alcohol septal ablation cohorts by hospital and operator volume separately. For descriptive statistics, the baseline characteristics of patients undergoing septal myectomy and alcohol septal ablation were divided across tertiles of annualized hospital volume. Similarly, the baseline characteristics of those undergoing septal myectomy and alcohol septal ablation were compared across tertiles of annualized operator volume. Continuous variables were presented as median with interquartile range and compared using the Mann‐Whitney test. Categorical variables were presented as frequency with percentages and compared using the Pearson χ² test.

Because there was a lack of time‐to‐event data, the 30‐day outcomes were calculated within each cohort of septal myectomy and alcohol septal ablation stratified by the tertiles of hospital and operator procedural volume. The first and third tertiles based on volume were defined as the lowest and highest procedure volume, respectively, for each analysis. The volume–outcome (primary and secondary) relationship using tertiles of the annualized hospital or operator procedural volume was analyzed using incrementally adjusted logistic regression models. The highest procedure volume tertile was used as a reference. The following models were used to assess the relationship of volume status with outcomes: (1) unadjusted models; (2) age, sex, and race‐adjusted models; and (3) multivariable adjusted models. To identify relevant variables for the multivariable adjusted models, a parsimonious set of variables in addition to age, sex, and race was selected using backward elimination, implementing a retention threshold of P<0.01. ²⁸ , ²⁹ The covariates included in the backward elimination models were peripheral vascular disease, prior history of cardiovascular event, valvular heart disease, diabetes, chronic pulmonary disease, hypertension, obesity, heart failure, chronic kidney disease, hospital size and region, income status, and primary insurance status.

The association between hospital and operator procedural volume as a continuous variable and 30‐day mortality was also assessed using generalized linear mixed models with random effects from a well‐established and implemented methodology. ¹⁰ In brief, the generalized mixed models using the eneralized linear mixed models (GLIMMIX) procedure, including a logit link function with a binary distribution, were used. This procedure used a 3‐level hierarchical structure consisting of patients, operators, and hospitals, incorporating random intercepts at the operator and hospital levels with a covariance matrix to account for interhospital and nested operator variability. The nonlinear associations were explored as unadjusted as well as multivariable adjusted (variables derived through backward elimination strategy) incorporating restricted cubic splines. The restricted cubic spline models with 3 knots were used based on the annualized hospital and operator volume distribution. The relationship was plotted as an unadjusted and adjusted odds ratio (OR) with a 95% CI of 30‐day mortality on the y axis with the procedural volume on the x axis for both septal myectomy and alcohol septal ablation. Moreover, the relative difference in the adjusted odds of 30‐day mortality was calculated as follows: ([odds of 30‐day in‐hospital mortality with an annualized procedural volume of x]−[odds of 30‐day in‐hospital mortality with an annualized procedural volume of y]/[odds of 30‐day in‐hospital mortality with an annualized procedural volume of x]), where x denotes the median annualized volume in the lowest tertile and y denotes the median annualized volume in the highest tertile. The Δ method was used to calculate the 95% CI for the difference in the adjusted risk of 30‐day mortality between an annualized procedural volume of x and volume of y. ¹⁰

The survival curves for 90‐day readmission stratified by tertiles of hospital and operator volume were plotted using the Kaplan‐Meier method for both septal myectomy and alcohol septal ablation. The log‐rank test was used to compare the survival. Additionally, the Cox proportional hazard modeling was used to estimate the relationship between hospital and operator volume strata with 90‐day readmission. The covariates in the Cox models included demographics, comorbidities, and other variables similar to those used in the primary analyses. A P value of <0.05 was considered statistically significant. All analysis was conducted with SAS 9.4 (Cary, NC).

To examine the effect of current HCM guidelines' cutoff of ≥10 procedures per year on clinical outcomes, ³ , ¹⁷ sensitivity analyses were conducted by stratifying operator and hospital volume in 2 groups (<10 or ≥10 procedures per year) among patients with HCM undergoing septal myectomy and alcohol septal ablation. The association between operator and hospital volume with 30‐day mortality, postoperative complications, and 90‐day readmission was assessed using similar modeling strategies as primary analyses.

RESULTS

The study population included a total of 5725 patients with HCM undergoing septal reduction therapies from >150 centers comprising >500 operators from January 2016 to December 2022. Within the study cohort, the septal myectomy cohort included data from 3990 patients, 494 surgeons, and 123 institutions. Similarly, the alcohol septal ablation cohort comprised data from 1735 patients, 332 interventionalists, and 103 hospitals. A total of 476 (96.4%) operators and 112 (91.1%) hospitals performed <10 septal myectomies (Figure S1A and S1B). There were 326 (98.2%) operators and 98 (95.1%) hospitals that performed <10 alcohol septal ablations annually (Figure S2A and S2B). The median number of septal myectomies performed with low‐, medium‐, and high‐volume operators were 1.71 (1.23–2.15), 4.00 (3.52–4.00), and 20.29 (9.14–74.43), respectively. Similarly, low‐, medium‐, and high‐volume hospitals conducted 1.2 (0.92–1.60), 2.86 (2.52–3.57), and 21.7 (7.85–76.48), respectively. For alcohol septal ablation, the median annual procedure volume for low‐, medium‐, and high‐volume operators performed 2.25 (1.67–3.20), 4.00 (4.00–4.00), and 9.57 (4.57–12.96), respectively, and for low‐, medium‐, and high‐volume hospitals was 1.50 (1.22–1.71), 2.96 (2.67–3.54), and 8.32 (6.62–14.07), respectively.

Baseline Characteristics

Table 1 and Table S2 outline the baseline characteristics stratified by tertiles of operator and hospital volumes, respectively, for patients who have undergone septal myectomy. Compared with low‐ and medium‐volume operators, patients who presented to high‐volume operators were ~1 year younger (P<0.001), and a greater proportion were men (P<0.001). Compared with high operator volume, low‐ and medium‐volume operators had a greater proportion of non‐White individuals (21.7%, 21.6%, and 17.3% in low‐, medium‐, and high‐volume operators, respectively; P<0.001). Patients who underwent septal myectomy with low‐versus high‐volume operators were more likely to have peripheral vascular disease (21.6% versus 12.4%, P<0.001), chronic renal disease (10.5% versus 7.7%, P=0.01), valvular heart disease (79.4% versus 73.0%, P<0.001), and chronic pulmonary disease (24.8% versus 19.2%, P=0.003). Moreover, patients receiving septal myectomy with high‐volume operators were more likely to present to academic hospitals (P<0.001) and hospitals with large bed sizes (P<0.001), to have private insurance (P<0.001), and to have higher income compared with the lower tertiles (P<0.001).

Table 1.

Descriptive Statistics for Participants Undergoing Septal Myectomy Procedure Stratified by Tertiles of Annualized Operator Volume

Variables	Overall	Tertile 1 (<3 procedures per y)	Tertile 2 (3–4 procedures per y)	Tertile 3 (>4 procedures per y)	P value
Patient characteristics
Age, y	60.5 (50.6–69.0)	62.6 (52.5–72.0)	61.2 (51.9–69.0)	59.7 (50.0–68.1)	<0.001
Women	2109 (52.9)	426 (58.1)	277 (59.2)	1406 (50.4)	<0.001
Race
Black	283 (7.1)	75 (10.2)	51 (10.9)	157 (5.6)	<0.0001
White	3247 (81.4)	574 (78.3)	367 (78.4)	2306 (82.7)
Other	460 (11.5)	84 (11.5)	50 (10.7)	326 (11.7)
Primary payer
Commercial/private	1912 (47.9)	276 (37.7)	186 (39.7)	1450 (52.0)	<0.001
Medicare/Medicaid	1837 (46.0)	408 (55.7)	255 (54.5)	1174 (42.1)
Other	241 (6.01)	49 (6.7)	27 (5.8)	165 (5.9)
Income quartile
<50 001	929 (23.3)	160 (21.8)	122 (26.1)	647 (23.2)	0.03
50 001–65 000	1034 (25.9)	220 (30.0)	123 (26.3)	691 (24.8)
65 001–90 000	1084 (27.2)	190 (25.9)	130 (27.8)	764 (27.4)
>90 001	943 (23.6)	163 (22.2)	93 (19.9)	687 (24.6)
ICU d	2 (1–3)	2 (1–5)	2 (1–4)	2 (1–3)	<0.001
LOS d	6 (5–9)	7 (5–11)	7 (5–11)	6 (5–8)	<0.001
LOS d	8.5 ± 8.6	10.1 ± 10.8	10.1 ± 9.6	7.8 ± 7.7	<0.001
LOS ≥8 d	1384 (35.7)	342 (46.7)	212 (45.3)	830 (29.8)	<0.001
Total hospital cost	47 521 ± 50 061	57 144 ± 57 114	62 617 ± 60 024	42 520 ± 45 205	<0.001
Comorbidities
Peripheral vascular disease	579 (14.5)	158 (21.6)	75 (16.0)	346 (12.4)	<0.001
Valvular heart disease	2982 (75.7)	582 (79.4)	364 (77.8)	2036 (73.0)	<0.001
Diabetes	263 (6.6)	53 (7.2)	37 (7.9)	173 (6.2)	0.29
Chronic pulmonary disease	811 (20.3)	182 (24.8)	95 (20.3)	534 (19.2)	0.003
Chronic heart failure	1808 (45.3)	335 (45.7)	204 (43.6)	1269 (45.5)	0.72
Obesity	1426 (35.7)	278 (37.9)	190 (40.6)	958 (34.3)	0.01
Hypertension	1608 (40.3)	315 (42.9)	203 (43.4)	1090 (39.1)	0.06
Chronic renal disease	344 (8.6)	77 (10.5)	51 (10.9)	216 (7.7)	0.01
Hospital characteristics
Academic hospital	3782 (94.8)	629 (85.8)	418 (89.3)	2735 (98.1)	<0.001
Region
Midwest	1504 (37.7)	20 (32.7)	85 (18.2)	1179 (42.3)	<0.001
Northeast	1051 (26.3)	114 (15.6)	82 (17.5)	855 (30.7)
South	918 (23.0)	241 (32.9)	185 (39.5)	492 (17.6)
West	517 (13.0)	138 (18.8)	116 (24.8)	263 (9.4)
Bed size
<500	846 (21.2)	122 (16.6)	117 (25.0)	607 (21.8)	<0.001
500–750	749 (18.8)	245 (33.4)	178 (38.0)	326 (11.7)
751–1000	1007 (25.2)	193 (26.3)	104 (22.2)	710 (25.5)
>1000	1388 (34.8)	173 (23.6)	69 (14.7)	1146 (41.1)

Baseline characteristics for participants who underwent septal myectomy stratified by tertiles of operator volume (<3, 3 to 4, and >4 procedures). Data from the Vizient Clinical Data Base used with permission of Vizient, Inc. All rights reserved. Data are presented in number (percentage) or mean±SD or median (interquartile range). ICU indicates intensive care unit; and LOS, length of stay.

Table 2 and Table S3 compare the baseline characteristics of patients who received alcohol septal ablation according to the tertiles of operator and hospital volumes, respectively. Patients who underwent alcohol septal ablation with low‐ versus high‐volume operators were nearly 2 years older (≈71 versus ≈69 years, P<0.01). Similar to the study cohort with septal myectomy, patients who underwent alcohol septal ablation were predominantly women (~69%) and White (~81%). Compared with high‐volume operators, patients undergoing alcohol septal ablation with low‐volume operators were more likely to have peripheral vascular disease (10.4% versus 6.6%, P=0.03), valvular heart disease (46.9% versus 38.1%, P=0.002), chronic pulmonary disease (12.2% versus 9.8%, P=0.01), obesity (28.6% versus 18.8%, P<0.001), and chronic heart failure (46.9% versus 37.1%, P<0.001). Patients who underwent alcohol septal ablation with high‐volume operators were more likely to present at large teaching hospitals (P=0.26), have private insurance (P<0.001), and have a higher income (P=0.18).

Table 2.

Descriptive Statistics for Participants Undergoing Alcohol Septal Ablation Procedure Stratified by Tertiles of Annualized Operator Volume

Variables	Overall	Tertile 1 (<4 procedures per y)	Tertile 2 (4 procedures per y)	Tertile 3 (>4 procedures per y)	P value
Patient characteristics
Age, y	69.9 (61.7–77.3)	70.8 (62.7–78.5)	69.8 (61.3–78.2)	69.5 (60.8–76.4)	0.01
Women	1206 (69.5)	459 (70.2)	172 (68.5)	575 (69.3)	0.87
Race
Black	142 (8.2)	54 (8.3)	24 (9.6)	64 (7.7)	0.86
White	1413 (81.4)	536 (82.0)	201 (80.0)	676 (81.5)
Other	180 (10.4)	64 (9.7)	26 (10.4)	90 (10.8)
Primary payer
Commercial/private	402 (23.2)	135 (20.6)	55 (21.9)	212 (25.5)	<0.001
Medicare/Medicaid	1258 (72.5)	473 (72.3)	182 (72.5)	603 (72.7)
Other	75 (4.3)	46 (7.1)	14 (5.6)	15 (1.8)
Income quartile
50 001	396 (22.8)	170 (26.0)	51 (20.3)	175 (21.1)	0.18
50 001–65 000	437 (25.2)	160 (24.5)	66 (26.3)	211 (25.4)
65 001–90 000	499 (28.8)	190 (29.1)	75 (29.9)	234 (28.2)
>90 001	403 (23.2)	134 (20.4)	59 (23.5)	210 (25.3)
ICU d	1 (0–2)	1 (0–2)	1 (0–2)	0.5 (0–2)	<0.001
LOS d	3 (2–4)	3 (2–5)	3 (2–5)	2 (2–3)	<0.001
LOS d	4.4 ± 7.0	5.1 ± 7.9	5.3 ± 9.0	3.6 ± 5.2	<0.001
LOS ≥8 d	536 (30.9)	252 (38.5)	94 (37.5)	190 (22.9)	<0.001
Total hospital cost	23 307 ± 33 746	25 797 ± 42 963	28 037 ± 36 120	19 871 ± 22 854	<0.001
Comorbidities
Peripheral vascular disease	145 (8.4)	68 (10.4)	22 (8.8)	55 (6.6)	0.03
Valvular heart disease	725 (41.8)	307 (46.9)	102 (40.6)	316 (38.1)	0.002
Diabetes	194 (11.2)	80 (12.2)	33 (13.2)	81 (9.8)	0.18
Chronic pulmonary disease	441 (25.4)	188 (28.8)	69 (27.5)	184 (22.2)	0.01
Chronic heart failure	729 (42.0)	307 (46.9)	114 (45.4)	308 (37.1)	<0.001
Obesity	401 (23.1)	187 (28.6)	58 (23.1)	156 (18.8)	<0.001
Hypertension	721 (41.6)	275 (42.1)	101 (40.2)	345 (41.6)	0.88
Chronic renal disease	222 (12.8)	85 (13.0)	34 (13.6)	103 (12.4)	0.87
Hospital characteristics
Academic hospital	1572 (90.6)	583 (89.1)	229 (91.2)	760 (91.6)	0.26
Region
Midwest	286 (16.5)	174 (26.6)	67 (26.7)	45 (5.4)	<0.001
Northeast	458 (26.4)	116 (17.7)	43 (17.1)	299 (36.0)
South	626 (36.1)	268 (41.0)	79 (31.5)	279 (33.6)
West	365 (21.0)	96 (14.7)	62 (24.7)	207 (24.9)
Bed size
<500	315 (18.2)	108 (16.5)	51 (20.3)	156 (18.8)	<0.001
500–750	550 (31.7)	191 (29.2)	109 (43.4)	250 (30.1)
751–1000	574 (33.1)	146 (22.3)	64 (25.5)	364 (43.9)
>1000	296 (17.0)	209 (32.0)	27 (10.8)	60 (7.2)

Baseline characteristics for participants who underwent septal myectomy stratified by tertiles of operator volume (<3, 3 to 4, and >4 procedures). Data from the Vizient Clinical Data Base used with permission of Vizient, Inc. All rights reserved. Data are presented in number (percentage) or mean±SD or median (interquartile range). ICU indicates intensive care unit; and LOS, length of stay.

Septal Myectomy

There were 26, 16, and 43 events of 30‐day in‐hospital mortality with low‐, medium‐, and high‐volume operators (3.6% versus 3.4% versus 1.5%, P<0.001), respectively (Table 3). Compared with high‐volume operators, patients who underwent septal myectomy with low‐volume (adjusted OR [aOR], 1.86 [95% CI, 1.11–3.15]; P=0.02] and medium‐volume (aOR, 1.93 [95% CI, 1.05–3.55]; P=0.04] operators had greater odds of 30‐day in‐hospital mortality (Table 3). The continuous relationship between operator volume and 30‐day in‐hospital mortality is depicted using restricted cubic spline modeling in Figure 1A. The odds of 30‐day in‐hospital mortality decreased as the annualized operator volume increased. The relative difference in the adjusted odds for 30‐day in‐hospital mortality between the median annual operator volume in low‐ and high‐volume tertiles was 54.0% (95% CI, 52.0–56.3).

Table 3.

Association Between Operator Volume and Outcomes After Septal Myectomy (Third Tertile^* as Reference)

Outcome	Events, n (%)	Odds ratio (95% CI)
		Model 1†	Model 2‡	Model 3§
30‐d in‐hospital mortality
First tertile	26 (3.6)	2.35 (1.43–3.85), <0.001‖	2.15 (1.31–3.55), 0.002‖	1.86 (1.11–3.15), 0.02‖
Second tertile	16 (3.4)	2.26 (1.26–4.05), <0.001‖	2.19 (1.22–3.94), 0.008‖	1.93 (1.05–3.55), 0.04‖
Third tertile	43 (1.5)	Referent
P value	<0.001
PPM/ICD7
First tertile	40 (5.5)	1.15 (0.80–1.66), 0.44	1.24 (0.86–1.79), 0.25	1.29 (0.89–1.87), 0.17
Second tertile	34 (7.3)	1.56 (1.06–2.31), 0.02‖	1.66 (1.12–2.46), 0.01‖	1.70 (1.14–2.52), 0.009‖
Third tertile	133 (4.8)	Referent
P value	0.07
Stroke
First tertile	48 (6.6)	1.40 (1.00–1.97), 0.06	1.17 (0.82–1.65), 0.39	1.27 (0.89–1.80), 0.19
Second tertile	37 (7.9)	1.71 (1.17–2.50), 0.005‖	1.59 (1.08–2.34), 0.02‖	1.73 (1.17–2.54), 0.006‖
Third tertile	133 (4.8)	Referent
P value	0.008
Bleeding
First tertile	50 (6.8)	1.99 (1.40–2.82), <0.001‖	1.88 (1.32–2.69), 0.002‖	1.89 (1.31–2.72), 0.001‖
Second tertile	27 (5.8)	1.66 (1.08–2.58), 0.001‖	1.64 (1.06–2.55), 0.006‖	1.66 (1.06–2.60), 0.003‖
Third tertile	99 (3.6)	Referent
P value	<0.001
Acute renal failure
First tertile	145 (19.8)	1.57 (1.27–1.94), <0.001‖	1.42 (1.14–1.76), 0.002‖	1.49 (1.19–1.88), 0.006‖
Second tertile	90 (19.2)	1.52 (1.18–1.96), 0.001‖	1.44 (1.11–1.86), 0.006‖	1.50 (1.15–1.97), 0.003‖
Third tertile	378 (13.6)	Referent
P value	<0.001

Association between hospital volume and outcomes after undergoing septal myectomy stratified by tertile. Measured outcomes include 30‐d in‐hospital mortality, permanent pacemaker, stroke, bleeding, acute renal failure, and 90‐d readmission. Data from the Vizient Clinical Data Base used with permission of Vizient, Inc. All rights reserved. PPM/ICD indicates permanent pacemaker/implantable cardioverter defibrillator.

^*Tertiles were created using annualized hospital volumes.

^† Model 1 is an unadjusted model showing the association between hospital volume tertiles and outcomes.

^‡ Model 2 is an adjusted model for demographic variables including age, race, and sex.

^§ Model 3 is a fully adjusted model with age, sex, Association of American Medical Colleges (AAMC) hospital status, heart failure history, and history of chronic renal failure.

^‖ Statistically Significant P Value.

Figure 1. Unadjusted and adjusted association of annualized operator and hospital volume with 30‐day in‐hospital mortality among patients undergoing septal reduction therapies.

A, Unadjusted (red line) and adjusted (blue line) association of annualized operator volume with 30‐day in‐hospital mortality among patients undergoing septal myectomy. B, Unadjusted (red line) and adjusted (blue line) association of annualized hospital volume with 30‐day in‐hospital mortality among patients undergoing septal myectomy. The models were adjusted for age, race, sex, hospital status, chronic heart failure, and chronic renal disease. The 95% CIs are represented as shaded regions. Solid black circles represent scatter plots for the events. C, Unadjusted (red line) and adjusted (blue line) association of annualized operator volume with 30‐day in‐hospital mortality among patients undergoing alcohol septal ablation. D, Unadjusted (red line) and adjusted (blue line) association of annualized hospital volume with 30‐day in‐hospital mortality among patient undergoing alcohol septal ablation. The models were adjusted for age, sex, hospital status, chronic heart failure, and chronic renal disease. The 95% CIs are represented as shaded regions. Solid black circles represent scatter plots for the events.

Similarly, patients who underwent septal myectomy at high‐volume hospitals had a lower mortality rate compared with medium‐ and low‐volume hospitals (1.7% in high‐volume hospitals versus 4.5% in medium‐volume hospitals versus 3.5% in low‐volume hospitals) (Table S4). Compared with patients who had surgery at high‐volume centers, the adjusted odds ratio of 30‐day in‐hospital mortality after septal myectomy was 1.34 (95% CI, 0.57–3.12; P=0.5) and 2.29 (95% CI; 1.32–3.99; P=0.003) among patients who had surgery at low‐ and medium‐volume centers, respectively. As outlined in Figure 1B, the relative reduction in the adjusted odds of 30‐day in‐hospital mortality between the median of annualized hospital volume in low‐and high‐volume tertiles was 51.0% (95% CI, 44.3–57.7).

Patients who underwent septal myectomy with low‐volume operators were associated with higher odds of postoperative bleeding (aOR, 1.89 [95% CI, 1.31–2.72]; P=0.001) and acute renal failure (aOR, 1.49 [95% CI, 1.19–1.88]; P=0.006) compared with high‐volume operators (Table 3). The odds of complications such as acute stroke (aOR, 1.73 [95% CI, 1.17–2.54]; P=0.006) or placement of a permanent pacemaker/implantable cardioverter‐defibrillator (aOR, 1.70 [95% CI, 1.14–2.52]; P=0.009) were higher in patients who had surgery by medium‐volume operators compared with high‐volume operators (Table 3). Similarly, there were greater odds of postoperative bleeding (aOR, 1.86 [95% CI, 1.06–3.26]; P=0.03) among patients who had surgery at low‐volume centers compared with high‐volume centers (Table S4).

The rate of 90‐day readmission after septal myectomy was lower in patients who received their surgery with high‐volume operators as compared with medium‐ and low‐volume operators (11.0% versus 15.4% and 16.9%, P<0.001) (Table S5). Compared with patients undergoing septal myectomy with high‐volume operators, the hazard ratio (HR) of 90‐day readmission was higher in patients who had surgery by medium‐ (adjusted (HR), 1.35 [95% CI, 1.04–1.75]; P=0.02) and low‐volume operators (adjusted HR, 1.51 (95% CI, 1.22–1.88]; P<0.001) (Table S5). Figure 2A shows the Kaplan‐Meier curve of 90‐day readmission stratified by tertiles of annualized operator volume. Similar to operator volume, we noticed incrementally increasing HRs for 90‐day readmission in patients undergoing surgery performed by medium‐ (adjusted HR, 1.40 [95% CI, 1.09–1.81]; P=0.01) and low‐volume (adjusted HR, 1.60 [95% CI, 1.14–2.23]) centers as compared with high‐volume centers (Table S6). The Kaplan‐Meier curve of 90‐day readmission by tertiles of annualized hospital volume is depicted in Figure 2B.

Figure 2. Adjusted Kaplan‐Meier survival curves for 90‐day readmission stratified by the tertiles of annualized operator and hospital volume among patients undergoing septal reduction therapies.

A, Adjusted Kaplan‐Meier curves for 90‐day readmission stratified into low (red), medium (green), and high (blue) tertiles of annualized operator volume among patients receiving septal myectomy. B, Adjusted Kaplan‐Meier curves for 90‐day readmission stratified into low (red), medium (green), and high (blue) tertiles of annualized hospital volume among patients receiving septal myectomy. The models were adjusted for age, race, sex, hospital status, chronic heart failure, and chronic renal disease. C, Adjusted Kaplan‐Meier curves for 90‐day readmission stratified into low (red), medium (green), and high (blue) tertiles among patients receiving alcohol septal ablation. D, Adjusted Kaplan‐Meier curves for 90‐day readmission stratified into low (red), medium (green), and high (blue) tertiles among patients receiving alcohol septal ablation. The models were adjusted for age, sex, hospital status, chronic heart failure, and chronic renal disease.

Alcohol Septal Ablation

The low‐, medium‐, and high‐volume operators showed increasing rates of 30‐day mortality (2.6% versus 3.2% versus 0.7%, respectively; P=0.005) (Table 4). Compared with patients who had surgery by an operator with high volume, alcohol septal ablation with a low‐ (aOR, 2.99 [95% CI, 1.15–7.75]; P=0.03) and medium‐volume (aOR, 3.86 [95% CI, 1.30–11.46]; P=0.01) operator was associated with higher odds of 30‐day in‐hospital mortality, respectively. As depicted in Figure 1C, we observed a 48.6% (95% CI, 35.7–61.4) relative reduction in the adjusted odds of 30‐day in‐hospital mortality between median annualized operator volume in low‐ and high‐volume tertiles. On the contrary, patients who had surgery at low‐, medium‐, and high‐volume hospitals showed similar rates of 30‐day in‐hospital mortality (1.8% versus 2.0% versus 1.7%, respectively) (Table 4). The adjusted odds of 30‐day in‐hospital mortality were similar among patients who had surgery at low‐ (aOR, 0.81 [95% CI, 0.27–2.48]; P=0.73) and medium‐ (aOR, 1.42 [95% CI, 0.58–3.46]; P=0.42) volume hospitals compared with high‐volume hospitals (Table 4). Figure 1D outlines the relationship between hospital volume and 30‐day in‐hospital mortality using restricted cubic spline modeling. There is a nonsignificant relationship between the rates of 30‐day mortality versus annualized hospital volume. There was a nonlinear but statistically nonsignificant relationship between hospital volume and the rate of 30‐day in‐hospital mortality.

Table 4.

Association Between Operator Volume and Outcomes After Alcohol Septal Ablation (Third Tertile^* as Reference)

Outcome	Events, n (%)	Odds ratio (95% CI)
		Model 1†	Model 2‡	Model 3§
30‐d in‐hospital mortality
First tertile	17 (2.6)	3.67 (1.44–9.35), 0.007‖	3.96 (1.54–10.14), 0.004‖	2.99 (1.15–7.75), 0.025‖
Second tertile	8 (3.2)	4.52 (1.55–13.16), 0.006‖	4.67 (1.60–13.64), 0.005‖	3.86 (1.30–11.46), 0.012‖
Third tertile	6 (0.7)	Referent
P value	0.005
PPM/ICD
First tertile	43 (6.6)	1.20 (0.78–1.84), 0.41	1.32 (0.85–2.05), 0.21	1.28 (0.82–1.98), 0.27
Second tertile	16 (6.4)	1.16 (0.65–2.09), 0.62	1.20 (0.66–2.17), 0.55	1.17 (0.64–2.12), 0.61
Third tertile	46 (5.5)	Referent
P value	0.69
Stroke
First tertile	28 (4.3)	1.33 (0.78–2.28), 0.30	1.24 (0.72–2.14), 0.43	0.98 (0.54–1.79), 0.60
Second tertile	11 (4.4)	1.36 (0.67–2.79), 0.40	1.31 (0.64–2.69), 0.46	1.20 (0.54–2.67), 0.52
Third tertile	27 (3.3)	Referent
P value	0.52
Bleeding
First tertile	18 (2.8)	1.28 (0.66–2.47), 0.47	1.24 (0.64–2.42), 0.52	1.08 (0.55–2.11), 0.78
Second tertile	17 (6.8)	3.28 (1.67–6.46), <0.001‖	3.22 (1.63–6.37), <0.001‖	2.99 (1.50–5.95), <0.001‖
Third tertile	18 (2.2)	Referent
P value	<0.001
Acute renal failure
First tertile	63 (11.0)	1.86 (1.25–2.77), 0.002‖	1.83 (1.23–2.72), 0.003‖	1.66 (1.12–2.49), 0.012‖
Second tertile	27 (10.8)	2.10 (1.28–3.47), 0.003‖	2.06 (1.25–3.40), 0.005‖	1.95 (1.17–3.23), 0.009‖
Third tertile	45 (5.4)	Referent
P value	0.002

Association between hospital volume and outcomes after undergoing alcohol septal ablation stratified by tertile. Measured outcomes include death, permanent pacemaker, stroke, bleeding, acute renal failure, and 90‐day readmission. Data from the Vizient Clinical Data Base used with permission of Vizient, Inc. All rights reserved. PPM/ICD indicates permanent pacemaker/implantable cardioverter defibrillator.

^*Tertiles were created using annualized hospital volumes.

^† Model 1 is an unadjusted model showing the association between hospital volume tertiles and outcomes.

^‡ Model 2 is an adjusted model for demographic variables in the form of age, race, and sex.

^§ Model 3 is a fully adjusted model with age, sex, Association of American Medical Colleges (AAMC) hospital status, heart failure history, and history of chronic renal failure.

^‖ Statistically Significant P Value.

Patients who underwent the procedure with a low‐ (aOR, 1.66 [95% CI, 1.12–2.49]; P=0.012) and medium‐ (aOR, 1.95 [95% CI, 1.17–3.23]; P=0.009) volume operator had a higher odds of postoperative acute renal failure compared with high‐volume operators (Table 4). There were greater odds of postoperative bleeding among patients who had surgery by a medium‐volume operator compared with a high‐volume operator (aOR, 2.99 [95% CI, 1.50–5.95]; P<0.001). However, we did not observe any significant associations of postoperative complications with hospital volume (Table S7).

The adjusted hazard ratio for 90‐day readmission in patients operated on by low‐ and medium‐volume operators was 1.31 (95% CI, 0.96–1.77; P=0.08) and 1.47 (95% CI, 0.99–2.17; P=0.06), respectively, compared with higher‐volume operators (Table S8). The Kaplan‐Meier curve of 90‐day readmission by tertiles of annualized operator volume is outlined in Figure 2C. However, the rate of 90‐day readmissions after alcohol septal ablation was similar among low‐, medium‐, and high‐volume hospitals (11.9% versus 12.3%, 11.7%, respectively) (Table S9). The risk of 90‐day readmission was similar among patients who had their procedure at a medium‐ (adjusted HR, 1.01 [95% CI, 0.72–1.43]; P=0.95) and low‐volume hospital (adjusted HR, 0.91 [95% CI, 0.60–1.39]; P=0.67) compared with higher‐volume hospitals (Table S9). Figure 2D depicts the Kaplan‐Meier curve of 90‐day readmission by tertiles of annualized hospital volume.

Sensitivity Analysis: Procedural Volume and Outcomes Stratified by 10 Cases per Year

In the sensitivity analysis, the odds of 30‐day in‐hospital mortality were higher in patients operated on at low‐volume hospitals (aOR, 1.87 [95% CI, 1.15–3.05]) and by low‐volume operators (aOR, 1.69 [95% CI, 1.06–2.71]) compared with their respective high‐volume counterparts, and remained significantly higher for septal myectomy (Figure 3A and 3B). However, the odds of 30‐day mortality did not vary by hospital and operator volume among patients undergoing alcohol septal ablation (Figure 3C and 3D). Moreover, the risk of 90‐day readmission after septal myectomy was higher among centers or operators performing <10 cases per year (Figure 4A and 4B). Similarly, the risk of 90‐day readmission after alcohol septal ablation was higher among hospitals performing <10 cases/year but remained nonsignificant by operators (Figure 4C and 4D).

Figure 3. Association of clinical outcomes with operators and hospitals performing <10 vs ≥10 procedures per year.

A, Forest plot of the odds ratio and 95% CI for the association of the clinical outcomes including 30‐day mortality, acute renal failure, permanent pacemaker implantation/implantable cardioverter defibrillator, acute bleeding, and any stroke with operator volume (low volume: <10 septal myectomies per year and high volume: ≥10 septal myectomies per year). B, Forest plot of the odds ratio and 95% CI for the association of the clinical outcomes including 30‐day mortality, acute renal failure, permanent pacemaker implantation/implantable cardioverter defibrillator, acute bleeding, and any stroke with hospital volume (low volume: <10 septal myectomies per year and high volume: ≥10 septal myectomies per year). The models were adjusted for age, race, sex, hospital status, chronic heart failure, and chronic renal disease. Ten or more septal myectomies per year were taken as the reference. C, Forest plot of the odds ratio and 95% CI for the association of the clinical outcomes including 30‐day mortality, acute renal failure, permanent pacemaker implantation/implantable cardioverter defibrillator, acute bleeding, and any stroke with operator volume (low volume: <10 septal myectomies per year and high volume: ≥10 septal myectomies per year). D, Forest plot of the odds ratio and 95% CI for the association of the clinical outcomes including 30‐day mortality, acute renal failure, permanent pacemaker implantation/implantable cardioverter defibrillator, acute bleeding, and any stroke with hospital volume (low volume: <10 septal myectomies per year and high volume: ≥10 septal myectomies per year). The models were adjusted for age, sex, hospital status, chronic heart failure, and chronic renal disease. Ten or more alcohol septal ablations per year was taken as the reference.

Figure 4. Kaplan‐Meier survival curves for 90‐day readmission stratified by high (≥10) vs low (<10) annualized operator and hospital volume among patients undergoing septal reduction therapies.

A, Adjusted Kaplan‐Meier curves for 90‐day readmission stratified into low (red) and high (blue) annualized operator volume among patients receiving septal myectomy. B, Adjusted Kaplan‐Meier curves for 90‐day readmission stratified into low (red) and high (blue) tertiles of annualized hospital volume among patients receiving septal myectomy. The models were adjusted for age, race, sex, hospital status, chronic heart failure, and chronic renal disease. C, Adjusted Kaplan Meier curves for 90‐day readmission stratified into low (red) and high (blue) annualized operator volume among patients receiving alcohol septal ablation. D, Adjusted Kaplan‐Meier curves for 90‐day readmission stratified into low (red) and high (blue) annualized hospital volume among patients receiving alcohol septal ablation. The models were adjusted for age, sex, hospital status, chronic heart failure, and chronic renal disease.

DISCUSSION

This large contemporary nationwide database incorporating data from >150 Academic Medical Centers and >500 operators provided several insights into the role of center and operator volume in determining clinical outcomes for patients with HCM undergoing septal reduction therapies. First, >91% of institutions and ≈96% of surgeons perform <10 septal myectomy per year, whereas >95% of hospitals and ≈98% of operators perform <10 alcohol septal ablation per year in the United States. Second, low‐ (<2 procedures per year) and medium‐ (2–4 procedures per year) volume centers and low‐ (<3 procedures per year) and medium‐ (3–4 procedures per year) volume operators for septal myectomy were associated with a ≈2‐fold greater risk of 30‐day in‐hospital mortality compared with their high‐volume counterparts. Moreover, low operator and hospital volume for septal myectomy were associated with greater odds of postoperative complications examined in this study. Third, consistent with the septal myectomy analysis, low (<4 procedures per year) and medium (4 procedures/year) operator volume for alcohol septal ablation was associated with a 3‐ to 4‐fold higher odds of 30‐day in‐hospital mortality compared with high‐volume (>4 procedures per year) operators. The odds of complications after alcohol septal ablation, such as bleeding, acute renal failure, and 90‐day readmission, were higher with low‐ and medium‐volume operators compared with high‐volume operators. However, the 30‐day mortality and complications did not vary by hospital center volumes among patients undergoing alcohol septal ablation.

The findings from our study may have several underlying explanations. Although septal reduction therapies such as septal myectomy and alcohol septal ablation have been shown to improve overall survival among patients with HCM, ³ , ¹⁶ , ¹⁷ these procedures are technically intricate and require extensive training. Therefore, the HCM guidelines have highlighted that these procedures “should be performed at experienced centers with expert operators.” ³ , ¹⁶ , ¹⁷ As highlighted previously, ¹³ the observed findings could be attributed to the learning curve for operators or institutions performing technically complex procedures such as septal myectomy, emphasizing the importance of procedural volumes. The findings of increased mortality rates as well as complications with decreasing operator volumes may reflect the skills and experience of the operator to deal with the inherent difficulties in the myocardium resection for septal myectomy and the selection of an appropriate septal perforator for alcohol septal ablation. ³⁰ , ³¹ Furthermore, expert surgeons with higher annualized procedural volumes are more likely to perform septal myectomy in eligible patients with HCM while limiting excessive septal wall dissection. Similarly, the impact of operator volume on overall mortality, postoperative complications, as well as the risk of readmission outlines the underlying learning curve to perform an appropriate alcohol septal ablation. ³¹ Furthermore, the interventionalists with more experience are likely to select appropriate patients who will benefit from septal ablation. The volume of septal myectomy performed by centers, rather than alcohol septal ablations, was more critical in achieving better clinical outcomes. This observation underscores the importance of a center's experience in managing underlying comorbidities and handling peri‐ and postoperative complications during septal myectomy. Similar rates of postoperative outcomes after alcohol septal ablation by hospital volumes could be due to the wide availability of catheter‐based techniques as well as the relatively noninvasive nature of the procedure in resourceful hospitals.

In recognition of the role of operator and center volumes in determining clinical outcomes in patients with HCM undergoing septal reduction therapies, the 2011 American College of Cardiology/American Heart Association guidelines for HCM ¹⁶ recommended an operator volume of at least 20 procedures or institutional experience of at least 50 procedures to define the HCM center of excellence. The 2014 European Society of Cardiology guidelines suggest a more relaxed threshold to define an experienced operator by considering a minimum annual caseload of 10 per operator, which was considered reasonable to justify the sustainability of the HCM center. ¹⁷ However, the recently updated 2024 American Heart Association/American College of Cardiology guidelines for HCM did not outline specific cutoffs but highlighted that high‐volume comprehensive HCM centers should be preferred for patients undergoing septal reduction therapies. ³ As depicted previously, ¹² , ¹³ , ¹⁴ , ¹⁸ our study highlights that >90% of centers were performing <10 cases per year in the United States. Moreover, our study is the first to outline that only ≈4% of surgeons and 2% of interventionalists perform >10 cases of septal reduction therapies in the United States among those within the Vizient Clinical Data Base.

The current study adds to prior literature ¹² , ¹³ , ¹⁴ , ¹⁸ by underscoring a relatively greater rate of short‐term mortality among low‐volume centers compared with high‐volume centers, especially for septal myectomy. Septal reduction therapies were found to be relatively safe, with low postoperative mortality, complications, and risk of 90‐day readmission when performed at high‐volume institutions and with high‐volume operators. Altibi et al ¹⁴ used data from the National Readmission Database from 2010 to 2019 to demonstrate that higher hospital volume was associated with lower in‐hospital morbidity and mortality following septal reduction therapies. Moreover, Altibi et al ¹⁴ noted that >90% of hospitals performed <10 procedures per year, which was consistent with our observation. Similarly, Hadaya et al ¹⁸ showed a significant association between hospital volume and in‐hospital mortality using the National Readmission Database from 2016 to 2019, albeit in patients undergoing septal myectomy. Kim et al ¹³ examined the National Inpatient Sample from 2003 to 2011 and showed that ~60% of hospitals performed ≤10 septal reduction therapies annually. Furthermore, Kim et al ¹³ noted a significant trend in increasing hospital volume with improving in‐hospital outcomes among hospitalizations for septal myectomy but not with alcohol septal ablation, consistent with our observations. Observational studies based on the Society of Thoracic Surgeons Database ¹² , ³² showed <1% operative mortality among patients undergoing septal myectomy if they were performed at high‐volume hospitals (ie, >10 procedures per year). However, none of the studies, to our knowledge, examined the relationship between operator volume and short‐term morbidity and mortality.

Our study has several public health implications. As outlined previously, ¹² , ¹³ , ¹⁴ , ¹⁸ as well as by our study, a volume–mortality association exists for septal reduction therapies. The current HCM guidelines ¹⁶ , ¹⁷ recommend a threshold for the procedure rate per year (ie, >10 cases per year) to improve clinical outcomes after septal reduction therapies. However, the current study highlights that >90% of hospitals in the United States perform <10 annualized procedural volumes. Considering the intricacies of performing septal reduction therapies, guidelines should formulate a volume threshold for operators and centers when recommending septal reduction therapies. At the operator level, focused training in septal reduction therapies could be included in the trainees' curriculum. Given that septal reduction therapies are elective procedures, all efforts must be taken to refer patients to a center of excellence for these procedures. Furthermore, guidelines may recommend specific parameters based on the expertise of the center for performing septal reduction therapies, similar to the guideline recommendations for aortic aneurysms. ³³ The Hypertrophic Cardiomyopathy Association has been instrumental in assigning a hospital as a center of excellence based on expertise, volume of care, quality research, and facilities. This study highlights the need for societies formulating HCM guidelines to work with organizations such as the Hypertrophic Cardiomyopathy Association to develop stringent and objective criteria to determine the requirements for obtaining the certification of an HCM center of excellence. Implementation of these operator and hospital‐level changes may translate into improved care for patients with HCM requiring septal reduction therapies. Notably, a registry for examining and improving the care of patients with HCM receiving septal reduction therapies is lacking. The establishment of such a registry may facilitate the exploration of determinants of clinical outcomes among patients with HCM undergoing septal reduction therapies. Finally, the 2024 HCM guidelines have highlighted the role and benefits of newer cardiac myosin inhibitors in managing symptomatic patients with HCM. The use of these inhibitors is expected to decrease the number of patients requiring septal reduction therapies, supporting the case for referrals to the center of excellence with expert operators. ³ With the evolving landscape of septal reduction therapies, the importance of achieving optimal patient outcomes has become increasingly critical.

Limitations

This study is subject to several limitations. First, our study is unable to provide alternative strategies among patients who were unable to get access to the high‐volume centers offering septal reduction therapies. Second, the use of administrative databases using ICD‐10‐CM coding strategies and characterization of hospital mix have been acknowledged in previous studies. ¹² , ¹³ , ¹⁸ Third, residual confounding by unaccounted factors, such as preexisting conduction abnormalities, individual symptoms, anatomical variances including LVOT gradient, septal thickness, mitral valve anatomy, present medications, and the risk of sudden cardiac death were not assessed. Fourth, there could be a referral bias toward septal reduction therapies, which could not be addressed due to insufficient information on the timing of HCM diagnosis. Fifth, although all‐cause in‐hospital mortality is reported, data on the cause of death were not available. Sixth, additional diagnostic tests, such as genetic analysis and cardiac imaging, were absent. Seventh, the readmission data lack clinically important information such as symptomatic status and severity of disease on presentation. Furthermore, hemodynamic and imaging assessments, including transthoracic echocardiography, angiography, pre‐ and postprocedural LVOT gradient, severity of mitral regurgitation, and cardiac magnetic resonance imaging, were not accessible. The limited patient data hindered the assessment of preoperative risk metrics, such as the Society of Thoracic Surgery risk calculator score, duration of the procedure, cumulative volume beyond study time, and long‐term follow‐up. The operator‐based analyses could only account for procedures that were performed in a single institution and did not include data on interinstitutional procedures potentially performed by the same operator. Moreover, the data on multiple operators, outlining primary versus secondary, were not available, which limit the ability to characterize operator‐based clinical outcomes. Despite these limitations, administrative databases such as the Vizient Clinical Data Base have demonstrated similar discrimination capabilities in assessing outcomes as traditional clinical databases.

CONCLUSIONS

In this nationwide study from 2016 through 2022, <5% of operators and institutions conducting septal reduction therapies performed ≥10 procedures per year, depicting discordance with the current recommendations by the HCM guidelines. Low‐volume centers and surgeons for septal myectomy were associated with higher short‐term morbidity, mortality, and 90‐day readmissions. Interventionalists with low annualized volume for alcohol septal ablation rather than hospitals were associated with higher short‐term morbidity, mortality, and 90‐day readmissions. When considering septal reduction therapies, the relevant metrics for establishing quality standards may also include patient outcomes (eg, complication rates, long‐term survival rates, and patient‐centered outcomes such as improvement in quality of life), operator experience and skill, patient selection criteria, and postprocedure follow‐up.

Sources of Funding

G.A. is supported by the National Heart, Lung, and Blood Institute of the National Institutes of Health awards R01HL160982, R01HL163852, and R01HL163081. N.P. is supported by the National Institutes of Health grant T32HL007457.

Disclosures

Dr Arora reports grant support from Merck Sharp and Dohme LLC and Bristol‐Myers Squibb, and consulting income from Bristol‐Myers Squibb, which are all unrelated to this work. The remaining authors have no disclosures to report.

Supporting information

Tables S1–S9

Figures S1–S2