Differences in Short-Term Outcomes and Hospital-Based Resource Utilization Between Septal Reduction Strategies for Hypertrophic Obstructive Cardiomyopathy

Srikanth Yandrapalli, MD1;  Prakash Harikrishnan, MD2;  Gabriela Andries, MD3; Wilbert S. Aronow, MD1;  Julio A. Panza, MD1;  Srihari S. Naidu, MD1

Peer Reviewed

Original Contribution

Differences in Short-Term Outcomes and Hospital-Based Resource Utilization Between Septal Reduction Strategies for Hypertrophic Obstructive Cardiomyopathy

Srikanth Yandrapalli, MD¹; Prakash Harikrishnan, MD²; Gabriela Andries, MD³; Wilbert S. Aronow, MD¹; Julio A. Panza, MD¹; Srihari S. Naidu, MD¹

Keywords

hypertrophic cardiomyopathy

septal myectomy

Alcohol septal ablation

left ventricular hypertrophy

January 2022

ISSN 1557-2501

Index J INVASIVE CARDIOL 2022;34(1):E8-E13. doi: 10.25270/jic/21.00097. Epub 2021 December 12.

Abstract

Background. Given clinical equipoise in a subset of obstructive hypertrophic cardiomyopathy (OHCM) patients who are candidates for both alcohol septal ablation (ASA) or septal myectomy (SM), other considerations such as cost, readmissions, and hospital length of stay (LOS) may be important to optimize healthcare resource utilization and inform shared decision making. Methods. In this retrospective observational analysis of the United States Nationwide Readmissions Database years 2012-2014, we identified adults who underwent isolated septal reduction (SR) for OHCM. We studied the differences in short-term outcomes (inpatient mortality and 90-day readmission rate) and in-hospital resource utilization (LOS and costs) between the SR strategies. Results. Of the 2250 patients in this study, ASA was performed in 1113 (49.5%) and SM in 1137 (50.5%). Inpatient mortality occurred in 21 patients (0.9%), with similar rates between strategies (10 SM patients [0.9%] vs 11 ASA patients [1.0%]; P=.30). Of the 2229 patients who survived to discharge, 298 (13.4%) were readmitted 386 times within 90 days with a similar readmission rate between SM (14.9%) and ASA (11.8%; P=.16). During the index admission, average LOS and cost were significantly lower for ASA (3.9 days, United States [US] $20,322) compared with SM (7.6 days, US $39,470; P<.001). Average LOS and cost during 90-day readmissions were similar between ASA and SM. Combining index admissions and readmissions, patients undergoing ASA had significantly lower LOS and hospitalization costs. Conclusions. In this non-randomized observational study of OHCM patients undergoing isolated septal reduction, ASA was associated with similar short-term outcomes, including mortality, but substantially lower hospitalization costs and LOS compared with SM.

J INVASIVE CARDIOL 2022;34(1):E8-E13. Epub 2021 December 12.

Key words: alcohol septal ablation, hypertrophic cardiomyopathy, obstructive hypertrophic cardiomyopathy, outcomes, septal myectomy, septal reduction

Introduction

Hypertrophic cardiomyopathy (HCM) is an inherited genetic disease of cardiac myofilaments characterized by unexplained left ventricular hypertrophy. The disease is associated with left ventricular outflow tract obstruction (LVOTO) in a majority of patients, resulting in progressive symptoms of dyspnea, angina, and syncope.^1,2 In obstructive HCM (OHCM) patients with resting or provokable gradients and symptoms refractory to optimal medical therapy, septal reduction with either alcohol septal ablation (ASA) or surgical septal myectomy (SM) should be considered to improve function and quality of life, and perhaps survival.^3,4 SM has historically been considered the gold-standard treatment for LVOTO reduction in OHCM, although there have been no prospective randomized trials comparing clinical outcomes between the 2 strategies.^2,3,5,6 Most observational series and meta-analyses suggest similar outcomes, including a low rate of sudden cardiac death and all-cause mortality, between both therapies when performed at high-volume centers of excellence.^7-11

Several clinical and anatomical criteria guide the selection of either ASA or SM for LVOTO reduction in OHCM.³ For example, those who require other surgical correction, such as coronary artery bypass grafting or mitral or aortic valve replacement, would be preferentially slated for SM. In patients who are eligible for both ASA and SM, however, a clinical equipoise exists regarding which strategy to choose. In such situations, other considerations such as procedural and hospitalization costs, short-term readmissions that could be procedure related, and hospital length of stay (LOS) may be useful determinants in the current era to optimize healthcare resource utilization and inform shared decision making. In this study of a nationally representative database, we investigated differences in short-term outcomes including periprocedural mortality, short-term readmission rates, and LOS and healthcare costs associated with the different invasive septal reduction strategies for OHCM.

Methods

Data source and study design. For this retrospective observational study, data were obtained from the publicly available and deidentified United States (US) Nationwide Readmissions Database (NRD) from 2012 through 2014. The NRD is part of the Healthcare Cost and Utilization Project (HCUP) that is sponsored by the Agency for Healthcare Research and Quality and is a database of all-payer hospital inpatient stays.¹² The NRD is drawn from HCUP State Inpatient Databases, which contain verified patient linkage numbers that can be used to track a person across admissions while maintaining privacy. Such a tracking strategy can also be used to generate national estimates of readmissions. Unweighted, the NRD contains data from approximately 14-15 million discharges from participating states that are geographically dispersed and account for around 50% of the total US resident population and hospitalizations. When weighted to provide national estimates, the NRD contains roughly 36 million discharges.¹² The verified patient linkage numbers are unique to individual years and the NRD does not allow for multiyear follow-up.

The NRD years utilized for this study contain data on patient and hospital demographics, diagnostic and procedural International Classification of Diseases, Ninth Edition, Clinical Modification (ICD-9-CM) codes, Elixhauser comorbidities and Healthcare Cost and Utilization Project Clinical Classification Software data, hospital outcomes including LOS, hospital charges, disposition, and mortality status. The Agency for Healthcare Research and Quality provides cost-to-charge ratios, which can be used to estimate costs of hospitalizations from total charges provided by the hospital.¹³

Ethics. As this study used only data that were previously deidentified and available from a publicly available database, the study was deemed not to be human studies research and therefore institutional review board approval was not required.

Study population. The study sample included all adult patients (≥18 years) who were hospitalized with a primary discharge diagnosis of hypertrophic cardiomyopathy (ICD-9 CM 425) between January and September in years 2012 to 2014. This period was chosen for the study as it is the most recently available data that allows analysis using ICD-9 codes. More recent NRD data utilized ICD-10 coding, which was not previously studied or validated to identify OHCM populations. We only included patients admitted between January and September in this study to allow for detection of 90-day readmission events after discharge, which can occur in months October to December for patients discharged in September. Among these patients, those undergoing ASA (ICD-9-CM 37.34) or SM (ICD-9-CM 37.33) were then identified if the specified ICD-9 CM codes were present in any of the procedural fields. Similar strategies to identify OHCM patients undergoing septal reduction procedures were utilized previously.¹⁴ Isolated ASA and SM cases were identified in this cohort by excluding patients undergoing other open chest procedures like coronary artery bypass grafting (ICD-9 CM 36.x1), valve surgery (ICD-9 CM 35.1x, 35.2x), and thoracic vascular surgery (ICD-9 CM 38.x5) or thoracic aortic aneurysm (ICD-9 CM 414.x) undergoing repair (ICD-9 CM 39.57). We excluded patients undergoing these surgical procedures and studied an isolated septal reduction cohort to minimize the selection of patients who were referred for SM as they required other surgeries and to avoid the influence that concomitant surgeries can have on the outcomes studied.

In the resulting study cohorts, baseline patient characteristics identified were age, sex, comorbidities, and in-hospital complications as listed in Table 1. The Elixhauser comorbidity data were extracted from the NRD. Appropriate ICD-9-CM and the HCUP Clinical Classification Software codes were used to identify comorbidities and in-hospital complications.

Study outcomes. Main short-term outcomes studied were the differences in in-hospital mortality, 90-day readmission rates in survivors, LOS and costs of hospitalization for initial admission, readmissions, and combined initial admission and readmission. These were compared between ASA and SM groups. Methodology described by the HCUP was used to identify 90-day readmissions.¹² We studied 90-day readmission rates because hospitalizations from complications that could arise directly from the procedures (heart block, arrhythmias, heart failure, and other procedure-related complications) usually occur in the short-term period following the septal reduction procedure and should be adequately identified within a 90-day postprocedural period. This short-term postprocedural follow-up period is in line with the aim of our study, ie, to primarily identify differences in short-term outcomes between ASA and SM, which could be related to the procedure. Longer follow-ups are not feasible utilizing the NRD, as it is a yearly database. To identify costs of hospitalization, hospital-reported charges (variable TOTCHG) were multiplied with the cost-to-charge ratios developed and reported by the Agency for Healthcare Research and Quality. Costs were then inflation adjusted with January 2014 as the reference.¹⁵ Etiologies of readmissions were classified by identifying the ICD-9-CM diagnosis codes of the primary discharge diagnosis of each individual readmission.

Statistical analysis. Weighted data were used for all statistical analyses. Since the NRD has a complex semi-random multistage sampling survey design, survey-design based descriptive analytic tests were used for all analyses. Baseline patient characteristics, comorbidities and complications, and in-hospital mortality and 90-day readmission rates were compared between patients undergoing either SM or ASA using the survey-design specific Rao-Scott Chi-Square test for categorical variables. Differences in age, LOS, and hospitalization costs were compared between ASA and SM groups with the survey-design specific student’s t test. Categorical variables are expressed as percentages and continuous variables as mean (standard error [SE]). A P-value of <.05 was considered to be significant and all reported P-values are 2-sided. Statistical analyses were performed using IBM SPSS Statistics 25.0 (IBM Corporation).

Results

Baseline characteristics and in-hospital complications. Our final study sample included 2250 patients who underwent isolated septal reduction (ASA or SM) for OHCM. Mean age was 58 (SE, 0.6) years and the majority (56.5%) were female. The type of septal reduction procedure performed was almost evenly distributed, with ASA performed in 49.5% (n = 1113) and SM in 50.5% (n = 1137). Baseline characteristics and periprocedural complications are presented in Table 1. Patients undergoing ASA were on average 11 years older than those undergoing SM. Most baseline comorbidities were similarly prevalent between the ASA and SM groups except for a higher prevalence of hypertension, coronary artery disease, prior percutaneous coronary intervention, chronic kidney disease, and cancer in patients undergoing ASA. Patients undergoing isolated SM were more likely to be smokers, had higher atrial fibrillation rate, and had a higher prevalence of related coagulopathy compared with those undergoing ASA. In-hospital complications, like acute kidney injury, cardiogenic shock, and implantable cardioverter defibrillator rates, were similar between the groups. Patients undergoing ASA had higher rates of ventricular tachycardia and permanent pacemaker implantation (Table 1).

In-hospital mortality. All-cause in-hospital mortality occurred in 21 patients (0.9%) undergoing septal reduction and was similar between ASA (n = 11; 1%) and SM (n = 10; 0.9%) (P=.30) (Table 2).

90-day readmission rates. For readmission analysis, a total of 2229 patients were studied after excluding patients who died during the index admission. Among these patients, 298 patients (13.4%) had a 90-day readmission with a total of 386 readmissions within 90 days from discharge. Readmission rates were statistically similar between patients undergoing ASA (11.8%) or SM (14.9%; P=.16) (Table 2).

Length of stay. Average LOS for the overall cohort and intergroup comparisons is presented in Table 2. During index admission, average LOS with ASA was 3.9 (SE, 0.2) days and 7.6 (SE, 0.3) days with SM, significantly higher with SM compared to ASA (P<.001) (Table 2). Average LOS during 90-day readmissions was similar between ASA and SM (Table 2). The average LOS for combined index admissions and readmissions was significantly higher with SM (7.0 [SE, 0.3] days) compared with ASA (4.3 [SE, 0.4] days; P<.001) (Table 2).

Costs. Average costs for the overall cohort and intergroup comparisons are presented in Table 2. During the index admission, average cost with ASA was US $20,322 (SE, $1090) and US $39,470 (SE, $1417) with SM, significantly higher with isolated SM compared with ASA (P<.001) (Table 2). Average cost during 90-day readmissions was similar between ASA and SM. The average cost for combined index admissions and readmissions was significantly higher with SM (US $34,742 [SE, $1444]) compared with ASA (US $20,670 [SE, $1299]) (P<.001) (Table 2).

Etiologies for readmissions. Cardiovascular causes were the most frequent readmission etiologies in both groups. In patients undergoing ASA, 60% of the 163 90-day readmissions were for cardiovascular causes, primarily arrhythmias in 28 (17%) and heart failure in 15 (9%). In patients undergoing isolated SM, 111 (49%) of the 227 90-day readmissions were for cardiovascular causes, primarily arrhythmias in 31 (14%) and heart failure in 18 (8%). Of all the readmissions, 29 (7.3%) were for atrial fibrillation/flutter, 15 (3.8%) were for complete atrioventricular block, and 10 (2.5%) were for ventricular arrhythmias.

Discussion

In this study of a large nationally representative sample of patients undergoing isolated septal reduction for OHCM in the United States, we report several noteworthy findings. First, among patients requiring isolated septal reduction therapy, the 2 procedures appear evenly split in prevalence. Second, and consistent with national guidelines, patients undergoing ASA are roughly a decade older and have a higher prevalence of significant comorbidities. Third, and despite the above-mentioned demographic differences, patients undergoing ASA and isolated SM had similarly low in-hospital mortality and 90-day readmission rates. And finally, patients undergoing ASA had substantially lower average LOS and hospitalization costs during the procedural admissions, but statistically similar LOS and hospitalization costs, during subsequent 90-day readmissions. To the best of our knowledge, this is the largest national study to report these short-term outcomes and hospitalization cost comparisons in OHCM patients undergoing septal reduction procedures.

In the present age, choice of septal reduction procedure is largely guided by patient age, left ventricular and coronary anatomy, severity of hemodynamics, pre-existing conduction disease, and clinical comorbidity status.^3,16 SM has been considered the gold-standard therapy for LVOTO reduction and has been shown to reduce the LVOT gradients to a greater extent than ASA.^6,11,17-19However, the long-term clinical implications of these findings were not established in any randomized clinical trials that compared these septal reduction strategies with each other. Several observation data and single-center studies have demonstrated comparative clinical efficacy of ASA and SM in the long term despite an increased need for reintervention and pacemaker implantation with ASA therapy.^7,10,19-22 More recent data from specialized and experienced centers have confirmed the procedural safety of ASA and the rarity of previously documented complications with ASA, like heart block, ventricular arrhythmias, and need for permanent pacemaker placement.^8,9,23-27 Moreover, it does appear that much of the difference is age related, given the older cohort with higher frequency of comorbidities.

With the growing body of evidence regarding clinical safety and efficacy of individual septal reduction strategies, other important considerations, such as in-hospital morbidity and mortality, length of stay, readmissions and hospital-based costs, and other periprocedural complication rates, can aid in the physician-patient discussion and decision-making process regarding the selection of either ASA or SM. In our study, in-hospital mortality and 90-day readmission rate were similar between ASA and SM, and periprocedural complications, like implantable cardioverter defibrillator implantation, acute kidney injury, and cardiogenic shock, were also similar between ASA and SM. There was a higher incidence of pacemaker implantation and periprocedural ventricular tachycardia with ASA, but these did not translate into increased hospital costs, LOS, or mortality.

In addition, cost data and LOS are particularly important in the current era to appropriately utilize healthcare resources while providing optimal therapies. Indeed, with the growing prevalence of HCM centers of excellence, and increased awareness of HCM and associated heart failure burden, these procedures are likely to increase in volume in the next decade, with financial implications on a population basis to health insurers. In our study, we demonstrate that the hospital-based costs of ASA were almost half of those with SM, despite the higher incidence of pacemaker placement. This significant difference persisted even after including all of the readmission costs in the short-term post procedure for either strategy. These data are particularly important when making cost-effective consensus recommendations for strategy selection in patients eligible for both ASA and SM.

Study strengths. Important strengths of our study are the utilization of a nationally representative administrative database to identify a large group of OHCM patients undergoing septal reduction to characterize the clinical comorbidities and short-term outcomes and hospital-based resource utilization differences between these procedures at a national level. These databases were validated for research in OHCM patients in prior studies, and the utilization of an administrative database improves the accuracy of estimated hospitalization costs.

Study limitations. Our study has several important limitations. First, we studied only postprocedural short-term hospital-based mortality and cost differences in a 90-day period following septal reduction procedures. While a 90-day follow-up might not be sufficient to analyze overall healthcare cost differences between ASA and SM, the outcomes evaluated in our analysis are in line with our study objective to identify differences in the short-term hospital-based outcomes and resource utilization. As the NRD captures only inpatient data, we were unable to account for costs and resource utilization in the ambulatory setting. While this limitation could affect certain study outcomes, short-term procedure-related complications after septal reduction are typically managed in the hospital setting rather than the ambulatory setting.

Our analysis does not account for costs of cardiac electronic device implantation that could have occurred after a 90-day period. Costs of implanted cardiac electronic devices within the 90-day follow-up period utilized in this study should be typically included within the hospitalization costs for procedure-related complications that occurred in the short-term postprocedural period. The need for permanent pacemaker implantation (in around 10% of patients undergoing ASA) usually occurs in the short term following the procedure. Administrative databases lack important clinical data regarding the myocardial and coronary anatomy and LVOTO gradients in OHCM, which can influence the selection of procedures. Second, using billing codes to identify comorbidities, complications, and causes of readmissions can result in misclassification bias. Third, the NRD does not report out-of-hospital and emergency room mortality data, which could influence the readmission rates. Finally, because of the limited follow-up period after the index admission, we cannot ascertain long-term outcomes, either in terms of the magnitude of hemodynamic relief of LVOTO with each intervention, or of the long-term morbidity and mortality. These outcomes, however, were extensively evaluated in previous studies discussed above.

Conclusion

In OHCM patients undergoing isolated septal reduction, ASA was associated with similar short-term (90-day) outcomes, including mortality, but substantially lower hospital-based costs and LOS compared with SM. These data may inform decision making in a subset of patients eligible for both procedures based on anatomic considerations and can be utilized to optimize healthcare resource utilization.

Affiliations and Disclosures

From the ¹Department of Cardiology, Westchester Medical Center and New York Medical College, Valhalla, New York; ²Division of Cardiology, Medical College of Georgia, Augusta, Georgia; and the ³Division of Cardiology, Newark Beth Israel Medical Center, Newark, New Jersey.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.

Manuscript accepted March 26, 2021.

Address for correspondence: Srikanth Yandrapalli, MD, Department of Cardiology, Westchester Medical Center and New York Medical College, 100 Woods Rd, Macy Pavilion, Valhalla, NY 10595. Email: srikanth.yn@gmail.com

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