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Influence of center surgical aortic valve volume on outcomes of transcatheter aortic valve replacement

  • Matthew Gandjian
    Affiliations
    Cardiovascular Outcomes Research Laboratory, David Geffen School of Medicine at UCLA, University of California, Los Angeles, Los Angeles, Calif
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  • Arjun Verma
    Affiliations
    Cardiovascular Outcomes Research Laboratory, David Geffen School of Medicine at UCLA, University of California, Los Angeles, Los Angeles, Calif
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  • Zachary Tran
    Affiliations
    Cardiovascular Outcomes Research Laboratory, David Geffen School of Medicine at UCLA, University of California, Los Angeles, Los Angeles, Calif
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  • Yas Sanaiha
    Affiliations
    Cardiovascular Outcomes Research Laboratory, David Geffen School of Medicine at UCLA, University of California, Los Angeles, Los Angeles, Calif
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  • Peter Downey
    Affiliations
    Cardiovascular Outcomes Research Laboratory, David Geffen School of Medicine at UCLA, University of California, Los Angeles, Los Angeles, Calif
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  • Richard J. Shemin
    Affiliations
    Cardiovascular Outcomes Research Laboratory, David Geffen School of Medicine at UCLA, University of California, Los Angeles, Los Angeles, Calif

    Division of Cardiac Surgery, David Geffen School of Medicine at UCLA, University of California, Los Angeles, Los Angeles, Calif
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  • Peyman Benharash
    Correspondence
    Address for reprints: Peyman Benharash, MD, Division of Cardiac Surgery, David Geffen School of Medicine at UCLA, University of California, Los Angeles, 10833 Le Conte Ave, 64-249 CHS, Los Angeles, CA 90095.
    Affiliations
    Cardiovascular Outcomes Research Laboratory, David Geffen School of Medicine at UCLA, University of California, Los Angeles, Los Angeles, Calif

    Division of Cardiac Surgery, David Geffen School of Medicine at UCLA, University of California, Los Angeles, Los Angeles, Calif
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Open AccessPublished:May 29, 2022DOI:https://doi.org/10.1016/j.xjon.2022.05.010

      Abstract

      Objective

      The utilization of transcatheter aortic valve replacement (TAVR) technology has exceeded that of traditional surgical aortic valve replacement (SAVR). In addition, the role of minimum surgical volume requirements for TAVR centers has recently been disputed. The present work evaluated the association of annual institutional SAVR caseload on outcomes following TAVR.

      Methods

      The 2012-2018 Nationwide Readmissions Database was queried for elective TAVR hospitalizations. The study cohort was split into early (Era 1: 2012-2015) and late (Era 2: 2016-2018) groups. Based on restricted cubic spline modeling of annual hospital SAVR caseload, institutions were dichotomized into low-volume and high-volume centers. Multivariable regressions were used to determine the influence of high-volume status on in-hospital mortality and perioperative complications following TAVR.

      Results

      An estimated 181,740 patients underwent TAVR from 2012 to 2018. Nationwide TAVR volume increased from 5893 in 2012 to 49,983 in 2018. After adjustment for relevant patient and hospital factors, high-volume status did not alter odds of TAVR mortality in Era 1 (adjusted odds ratio, 0.94; P = .52) but was associated decreased likelihood of mortality in Era 2 (adjusted odds ratio, 0.83; P = .047). High-volume status did not influence the risk of perioperative complications during Era 1. However, during Era 2, patients at high-volume centers had significantly lower odds of infectious complications, relative to low-volume hospitals (adjusted odds ratio, 0.78; P = .002).

      Conclusions

      SAVR experience is associated with improved TAVR outcomes in a modern cohort. Our findings suggest the need for continued collaboration between cardiologists and surgeons to maximize patient safety.

      Graphical abstract

      Key Words

      Abbreviations and Acronyms:

      AKI (acute kidney injury), CVA (cerebrovascular accident), ECI (Elixhauser Comorbidity Index), HVH (high-volume hospital), ICD-9/10 (International Classification of Diseases 9th and 10th revisions), LASSO (least absolute shrinkage and selection operator), LOS (length of stay), LVH (low-volume hospital), MI (myocardial infarction), NCD (National Coverage Determination), NPtrend (nonparametric test of trends), NRD (Nationwide Readmissions Database), SAVR (surgical aortic valve replacement), TAVR (transcatheter aortic valve replacement)
      Figure thumbnail fx2
      Contour plot of risk-adjusted TAVR mortality by hospital SAVR and TAVR volumes.
      Surgical aortic valve replacement experience is associated with improved transcatheter aortic valve replacement mortality, suggesting the need for continued collaboration between cardiologists and surgeons.
      The Centers for Medicare and Medicare Services national coverage determination includes minimum surgical volume requirements for new TAVR centers. The role of these volume requirements have been recently disputed. A modern analysis regarding the relevance of SAVR volume requirements in ensuring acceptable TAVR outcomes is warranted.
      Once reserved solely for patients at prohibitive risk for surgical aortic valve replacement (SAVR), transcatheter aortic valve replacement (TAVR) has emerged as an effective treatment strategy for many with severe, symptomatic aortic stenosis.
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      5-Year outcomes of transcatheter aortic valve replacement or surgical aortic valve replacement for high surgical risk patients with aortic stenosis (PARTNER 1): a randomised controlled trial.
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      Recently, new innovations in design coupled with favorable results of randomized clinical trials in low-risk patients have offered increased confidence in this relatively new technology, allowing expanded eligibility for TAVR.
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      The association of transcatheter aortic valve replacement availability and hospital aortic valve replacement volume and mortality in the United States.
      In fact, the number of Medicare beneficiaries receiving TAVR exceeded SAVR for the first time in the United States in 2017.
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      Have TAVR volumes finally outpaced SAVR volumes among Medicare beneficiaries in the United States?.
      Throughout the evolution of TAVR, the concept of shared decision making using a heart team approach has persisted in the United States. Moreover, an advisory panel to the Centers for Medicare & Medicaid Services recommended minimum volume requirements for TAVR, SAVR, and percutaneous coronary interventions to enhance patient safety.
      Centers for Medicare & Medicaid Services
      Medicare coverage database. National coverage determination: transcatheter aortic valve replacement (TAVR) (20.32).
      Created in 2012 and updated in 2018, the national coverage determination for TAVR required a minimum of 50 open heart operations during the year before a TAVR center's opening.
      Centers for Medicare & Medicaid Services
      Medicare coverage database. MEDCAC meeting: transcatheter aortic valve replacement (TAVR) (07/25/2018).
      Although proponents of minimum volume requirements cite reduced mortality at high-volume SAVR centers, others have noted a more complex interaction, suggesting that SAVR volume alone cannot explain observed TAVR outcomes.
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      • McCarthy E.
      • Kim D.
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      • Ramirez-Del Val F.
      • et al.
      Relationship between hospital surgical aortic valve replacement volume and transcatheter aortic valve replacement outcomes.
      ,
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      • Redberg R.F.
      • Carroll J.D.
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      • Laschinger J.
      • Thourani V.
      • et al.
      Association between hospital surgical aortic valve replacement volume and transcatheter aortic valve replacement outcomes.
      In an important commentary, Barker and colleagues postulated the volume–outcome relationship to be the result of earlier adoption of TAVR and improved patient selection strategies at high-volume centers rather than SAVR experience.
      • Barker C.M.
      • Reardon M.J.
      10 000 Hours—is prior experience in cardiac surgery enough?.
      With reduced patient risk and increasing safety profile of TAVR in recent years, a modern analysis regarding the relevance of SAVR volume requirements in ensuring acceptable TAVR outcomes is warranted. In the present study, we sought to evaluate the association of annual hospital SAVR volume on clinical and financial outcomes of TAVR in a contemporary cohort. We hypothesized increasing SAVR caseload to be associated with decreased TAVR mortality and perioperative complications in recent years.

      Methods

      Data Source

      This was a retrospective cohort study using data from the 2012-2018 Nationwide Readmissions Database (NRD). Maintained as a part of the Healthcare Costs and Utilization Project, the NRD is the largest, all-payer, nationally representative readmissions database. Robust survey weights are incorporated into all analyses to provide accurate estimates for up to 57.8% of all United States hospitalizations.
      Agency for Healthcare Research and Quality
      Healthcare cost and utilization project. NRD overview.
      The study was deemed exempt from full review by the Institutional Review Board at the University of California, Los Angeles (IRB No. 17-001112, approved July 26, 2017).

      Study Cohort

      All elective adult (aged 18 years or older) hospitalizations for TAVR were identified using previously validated International Classification of Diseases 9th and 10th revision (ICD-9/10) procedure codes.
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      • Redberg R.F.
      • Carroll J.D.
      • Marinac-Dabic D.
      • Laschinger J.
      • Thourani V.
      • et al.
      Association between hospital surgical aortic valve replacement volume and transcatheter aortic valve replacement outcomes.
      ,
      • Malik A.H.
      • Yandrapalli S.
      • Zaid S.
      • Shetty S.S.
      • Aronow W.S.
      • Ahmad H.
      • et al.
      Valve-in-valve transcatheter implantation versus redo surgical aortic valve replacement.
      Patients with endocarditis as well as those who underwent concomitant open-heart surgery or emergency conversion to sternotomy were excluded to maintain cohort homogeneity (0.4%). Records with missing data for mortality, key demographic characteristics, or hospitalization costs were also excluded (0.6%). Comparison of baseline characteristics between cases with and without missing data is shown in Table E1.

      Variable Definitions

      Patient and hospital characteristics, including age, sex, patient income level, and hospital teaching status, were defined in accordance with the NRD data dictionary. The van Walraven modification of the Elixhauser Comorbidity Index (ECI) was used to estimate the burden of chronic conditions.
      • Van Walraven C.
      • Austin P.C.
      • Jennings A.
      • Quan H.
      • Forster A.J.
      A modification of the elixhauser comorbidity measures into a point system for hospital death using administrative data.
      Briefly, the ECI differentially weighs 31 comorbidities and produces a patient score which ranges from –19 to 89. Additional comorbidities were identified using ICD-9/10 diagnosis codes. Perioperative complications, including cerebrovascular accident (CVA), myocardial infarction (MI), and acute kidney injury (AKI) were similarly ascertained. Using ICD-9/10 diagnosis codes, hemorrhage and accidental puncture were defined as intraoperative events pertaining to any major organ system that complicated the TAVR procedure. Infectious complications were defined as a composite of ICD-9/10 diagnosis codes that have been previously published by our group.
      • Madrigal J.
      • Mukdad L.
      • Han A.Y.
      • Tran Z.
      • Benharash P.
      • St John M.A.
      • et al.
      Impact of hospital volume on outcomes following head and neck cancer surgery and flap reconstruction.
      Hospital SAVR and TAVR volumes were independently calculated as the total number of isolated TAVR and isolated SAVR procedures performed at each institution. Because hospitals are not tracked across calendar years in the NRD, operative volumes were generated annually. NRD-provided discharge weights were incorporated into the calculation for volume in congruence with previously reported methodology for absolute volumes.
      • Gandjian M.
      • Williamson C.
      • Sanaiha Y.
      • Hadaya J.
      • Tran Z.
      • Kim S.T.
      • et al.
      Continued relevance of minimum volume standards for elective esophagectomy: a national perspective.
      Hospitalization costs of index admission were obtained by applying center-specific cost-to-charge ratios to overall charges and inflation adjusted to the 2018 Personal Health Index.
      Using appropriate price indices for expenditure comparisons.
      The primary outcome of interest was in-hospital mortality following TAVR. Secondary outcomes included CVA, MI, AKI, accidental puncture, hemorrhage, and infectious complications as well as length of stay (LOS), costs, and nonhome discharge.

      Temporal Comparison

      To compare the relevance of SAVR volume requirements between a dated and novel cohort of TAVR patients, the study population was split into Era 1 (2012-2015) and Era 2 (2016-2018). This cutoff was chosen to reflect advances in TAVR valve technology and evolving patient candidacy guidelines.

      Designation of High- and Low-Volume Hospitals

      Restricted cubic splines were incorporated into a multivariable regression and used to parametrize the relationship between annual hospital SAVR volume and TAVR mortality. Methods used for covariate selection and model development are described below. A 100-bootstrap simulation integrating a Monte Carlo Markov Chain procedure was subsequently performed to identify the SAVR volume, which corresponded to the point of maximum change in risk-adjusted mortality.
      • Brooks S.
      Markov chain Monte Carlo method and its application.
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      • Roman S.A.
      • Sosa J.A.
      Defining a hospital volume threshold for minimally invasive pancreaticoduodenectomy in the United States.
      • Schlottmann F.
      • Strassle P.D.
      • Charles A.G.
      • Patti M.G.
      Esophageal cancer surgery: spontaneous centralization in the US contributed to reduce mortality without causing health disparities.
      To facilitate analysis of additional TAVR end points, SAVR volume cutoffs were calculated separately in Era 1 and Era 2. Institutions were considered a high-volume hospital (HVH) if they exceeded this threshold or a low-volume hospital (LVH) if their annual SAVR volume fell below the threshold.

      Statistical Analysis

      Categorical variables are reported as percentages. Continuous variables are summarized as means with standard deviation (SD) or median with interquartile range, when non-normally distributed. Normality was visually assessed by generating quantile–quantile plots. The χ2, adjusted Wald, and Mann-Whitney U test were used to compare proportions, means, and medians between groups, respectively. A nonparametric rank-based test by Cuzick was used to assess the statistical significance of nonparametric test of trends (NPtrend).
      • Cuzick J.
      A Wilcoxon-type test for trend.
      Multivariable logistic and linear regression models were developed to characterize the association between high SAVR volume status and outcomes of interest, while adjusting for patient comorbidities as well as hospital TAVR caseload. Model covariates were chosen by applying least absolute shrinkage and selection operator (LASSO) methodology.
      • Tibshirani R.
      Regression shrinkage and selection via the LASSO.
      Briefly, LASSO regularization enhances accuracy and out-of-sample reliability of prediction models by reducing collinearity among selected covariates. LASSO was applied to a training dataset that represented a random 70% sample, whereas model performance was assessed in the remaining 30%. Collinearity between SAVR and TAVR volume was assessed by calculating the variance inflation factor using the collin command in Stata. Both volume variables were retained in the final model because the variance inflation factor was less than 10. Covariates selected using LASSO were subsequently included into multivariable regressions and fit using the entire study cohort. Final models were selected based on evaluation of the receiver-operating characteristics (ie, C statistic) as well as Akaike and Bayesian information criteria. Regression results are reported as adjusted odds ratios (AOR) or beta coefficients with 95% confidence intervals (CI). All statistical analyses were performed using Stata version 16.1 with α = 0.05 set for significance.

      Results

      Study Cohort and Trends

      Of an estimated 181,740 patients who met study criteria, 29.3% underwent TAVR during Era 1, and 70.7% during Era 2. Patients in Era 2 were younger (aged 80 vs 81 years; P < .001), less commonly female (45.8% vs 47.6%; P < .001) and had a lower burden of comorbidities (ECI 5.2 vs 5.3; P < .001), compared with Era 1. A comprehensive comparison of additional baseline characteristics and comorbidities between patients in Eras 1 and 2 are shown in Table E2. Over the study period, nationwide TAVR volume increased dramatically, from 5,893 in 2012 to 49,983 in 2018 (NPtrend < .001) (Figure 1). In addition, the number of unique NRD participating hospitals performing elective TAVR rose from 186 in 2012 to 413 in 2018 (NPtrend < .001). Nationwide SAVR volume increased initially from 28,594 cases in 2012 to 33,200 in 2015, followed by a gradual decline in subsequent years culminating with a total of 27,319 in 2018 (Figure 1).
      Figure thumbnail gr1
      Figure 1Trends in annual surgical aortic valve replacement (SAVR) volume, transcatheter aortic valve replacement (TAVR) volume, and TAVR mortality in the United States from 2012 to 2018.

      Hospital Volumes and Comparison of Patients at LVH and HVH in Both Eras

      Based on restricted cubic spline analysis, the optimal threshold associated with decreased TAVR mortality was set at 140 SAVR cases/year in Era 1 and 85 cases/year in Era 2 (Figure 2). In Era 1, HVHs performed 65.3% of TAVR cases. Compared with LVHs in Era 1, patients at HVHs had comparable distributions of age and sex (Table 1). However, HVH patients had a greater median ECI score (5.4 vs 5.2; P = .012). Specifically, rates of coagulopathy (18.4% vs 15.4%; P < .001) and electrolyte imbalance (21.7% vs 15.4%; P < .001) were greater among HVH patients in Era 1, compared with LVH patients. In Era 2, 63.4% of TAVR patients were managed at HVHs. However, in Era 2, patient age, sex, and ECI score were comparable between patients at LVHs and HVHs (Table 1). The incidence of arrhythmia, chronic lung disease, and electrolyte imbalance was higher among HVH patients, relative to LVH patients (Table 1).
      Figure thumbnail gr2
      Figure 2Spline analysis of risk-adjusted transcatheter aortic valve replacement (TAVR) mortality by annual surgical aortic valve replacement (SAVR) and TAVR volumes in Era 1 and Era 2.
      Table 1Baseline characteristics stratified by low-volume (LVH) and high-volume (HVH) hospital status
      ParameterEra 1P valueEra 2P value
      LVH (n = 18,456)HVH (n = 34,777)LVH (n = 46,998)HVH (n = 81,509)
      Age (y)81.1 ± 9.481.4 ± 7.5.1980.0 ± 8.580.0 ± 7.8.87
      Female sex47.047.9.2945.945.7.61
      ECI score (points)5.2 ± 1.85.4 ± 1.5.0125.2 ± 1.75.2 ± 1.5.13
      Income percentile.019.013
       76th-100th24.627.223.724.6
       51st-75th26.028.226.728.0
       26th-75th25.526.226.228.8
       0-25th23.918.423.318.7
      Payer.22.28
       Private6.45.25.65.8
       Medicare90.992.391.291.6
       Medicaid0.90.71.00.8
       Other1.81.92.31.9
      Comorbidities
       Congestive heart failure31.130.7.8772.472.3.97
       Coronary artery disease61.262.7.1462.263.3.13
       Chronic arrhythmia56.257.0.4951.653.0.017
       Pulmonary circulation disorder16.918.6.1014.915.8.22
       Peripheral vascular disease22.223.4.2819.619.6.93
       Neurologic disorder4.94.3.0914.24.3.52
       Chronic lung disease37.438.1.5426.324.9.014
       Hypothyroidism16.116.9.2116.617.1.29
       End-stage renal disease3.63.6.784.03.8.22
       Liver disease3.02.7.202.32.6.057
       Cancer3.23.2.983.13.4.093
       Coagulopathy15.418.4.01010.311.4.12
       Weight loss3.23.0.511.72.1.028
       Electrolyte imbalance15.421.7<.0019.712.2.035
       Anemia3.23.1.553.33.4.35
      Values are presented as mean ± SD or %. Comparisons were performed independently among patients in Era 1 (2012-2015) and Era 2 (2016-2018). ECI, Elixhauser Comorbidity Index.

      Influence of Volume Designation on In-Hospital Mortality Following TAVR

      Over the study period, in-hospital TAVR mortality declined from 4.5% in 2012 to 1.0% in 2018 (NPtrend < .001) (Figure 1). As displayed in Table 2, there was no difference in mortality between HVHs and LVHs in Era 1. However, a subtle, yet statistically significant difference was noted in Era 2 (1.3% vs 1.0%; P = .007). After adjustment for relevant patient and hospital characteristics, including TAVR volume, HVH status did not alter the risk of mortality in Era 1 (AOR, 0.94; P = .52). Notably, in Era 2, management at HVHs was associated with decreased odds of mortality (AOR, 0.83; P = .047). All model coefficients for the multivariable regression to predict in-hospital mortality following TAVR in each Era can be found in Table 3. In addition, a contour plot of risk-adjusted mortality as a function of TAVR and SAVR volume is shown in Figure 3 and demonstrates a gradual decline in mortality associated with increasing TAVR and SAVR volumes.
      Table 2Comparison of clinical outcomes and resource use in low-volume (LVH) and high-volume (HVH) hospitals
      OutcomeEra 1P valueEra 2P value
      LVH (n = 18,456)HVH (n = 34,777)LVH (n = 46,998)HVH (n = 81,509)
      In-hospital mortality3.02.8.451.31.0.007
      Complications
       Accidental puncture1.61.2.030.90.8.47
       Acute ischemic stroke2.12.2.730.80.8.99
       Acute kidney injury11.010.9.856.26.6.29
       Hemorrhage2.32.4.631.61.9.07
       Myocardial infarction1.01.0.680.60.7.22
       Infectious complication5.86.4.224.33.3<.001
      Length of stay (d)4 (3-7)5 (3-7)<.0012 (1-3)2 (1-4).003
      Costs, in $1000s52.6 (41.2-67.1)51.3 (41.6-65.1).00144.3 (35.1-56.3)45.3 (36.1-56.9)<.001
      Nonhome discharge (%)21.625.5.0079.110.5.002
      values are presented as % or median (interquartile range). Comparisons were separately performed among patients in both Era 1 (2012-2015) and Era 2 (2016-2018).
      Table 3Full multivariable logistic regression demonstrating patient and hospital factors associated with in-hospital mortality following transcatheter aortic valve replacement (TAVR)
      ParameterEra 1 (2012-2015)P valueEra 2 (2016-2018)P value
      High SAVR volume0.94 (0.78-1.14).520.83 (0.69-0.99).047
      Age, per year1.02 (1.01-1.04).0011.04 (1.02-1.05)<.001
      Female sex1.05 (0.90-1.23).511.33 (1.14-1.56)<.001
      ECI score, per point0.61 (0.55-0.69)<.0010.63 (0.57-0.69)<.001
      Income percentile
       76th-100thRefRef
       51st-75th0.96 (0.76-1.21).731.38 (1.11-1.72).004
       26th-50th1.04 (0.83-1.30).741.03 (0.81-1.32).79
       0-25th1.18 (0.94-1.49).151.42 (1.12-1.81).004
      Payer status
       PrivateRefRef
       Medicare1.40 (0.88-2.23).160.89 (0.63-1.24).48
       Medicaid0.84 (0.26-2.72).780.69 (0.30-1.60).39
       Other payer1.16 (0.53-2.54).711.12 (0.60-2.12).73
      Calendar year
       2012Ref
       20130.76 (0.55-1.04).089
       20140.67 (0.49-0.93).018
       20150.48 (0.34-0.68)<.001
       2016Ref
       20170.98 (0.80-1.21).86
       20180.84 (0.68-1.04).12
      Annual TAVR volume, per case0.99 (0.99-1.00).0620.99 (0.99-0.99).003
      Congestive heart failure1.59 (1.24-2.02)<.0012.11 (1.71-2.61)<.001
      Coronary artery disease0.59 (0.50-0.70)<.0010.47 (0.40-0.55)<.001
      Chronic arrhythmia1.73 (1.39-2.14)<.0011.75 (1.46-2.09)<.001
      Pulmonary circulation disorder1.77 (1.33-2.35)<.0011.66 (1.30-2.12)<.001
      Peripheral vascular disease2.22 (1.73-2.86)<.0012.22 (1.80-2.73)<.001
      Neurologic disorder4.78 (3.61-6.33)<.0017.25 (5.86-8.98)<.001
      Chronic lung disease1.54 (1.19-1.99).0011.10 (0.89-1.36).39
      Hypothyroidism0.81 (0.58-1.12).210.82 (0.61-1.11).2
      End-stage renal disease2.85 (1.93-4.20)<.012.35 (1.68-3.29)<.001
      Liver disease8.75 (8.09-12.6)<.0018.26 (5.92-11.5)<.001
      Cancer1.03 (0.60-1.78).921.49 (0.92-2.41).1
      Coagulopathy1.82 (1.40-236)<.0012.19 (1.72-2.78)<.001
      Weight loss3.61 (2.60-5.00)<.0013.85 (2.76-5.37)<.001
      Electrolyte imbalance3.93 (2.92-5.29)<.0018.01 (6.64-9.67)<.001
      Anemia0.50 (0.24-1.04).0640.47 (0.23-1.00).05
      Values are presented as adjusted odds ratio (95% CI). SAVR, Surgical aortic valve replacement; ECI, Elixhauser Comorbidity Index; Ref, reference category.
      Figure thumbnail gr3
      Figure 3Contour plot of risk-adjusted transcatheter aortic valve replacement (TAVR) mortality by hospital surgical aortic valve replacement (SAVR) and TAVR volumes.
      During Era 2, we further examined the relationship between SAVR volume and in-hospital mortality by setting volume cutoffs at 25, 50, and 100 cases per year (2016-2018). We found that 88.4% of centers met the 25 SAVR procedures per year cutoff, 66.3% met the 50 SAVR procedures per year cutoff, and 31.5% met the 100 SAVR procedures per year cutoff. Upon adjusted analysis, only the 100 cases per year SAVR volume cutoff exhibited a statistically significant decrement in TAVR mortality (AOR, 0.80; 95% CI, 0.66-0.97; P = .022).

      Influence of HVH Status on Perioperative Complications and Resource Use

      Rates of accidental puncture were reduced among patients at HVHs (1.2% vs 1.6%; P = .030) during Era 1, but not during Era 2 (0.8% vs 0.9%; P = .47). The incidence of CVA, AKI, hemorrhage and MI were similar between LVHs and HVHs durig both Eras, as shown in Table 2. Although rates of infectious complications were equivalent among patients in HVHs and LVHs during Era 1 (6.4% vs 5.8%; P = .22), patients at HVHs in Era 2 had lower rates, compared with those at LVHs (3.3% vs 4.3%; P < .001). In addition, patients at LVHs experienced longer LOS and accumulated greater hospitalization costs during both Eras, compared with HVH (Table 2). Patients managed at HVHs also faced higher rates of nonhome discharge during both Eras.
      Following multivariable regression, HVH status was not associated with altered odds of any perioperative complication during Era 1 (Table 4). However, during Era 2, patients at HVHs had significantly decreased odds of infectious complications, relative to patients at LVHs (AOR, 0.78; P = .002). Of note, management at HVHs did not influence patient LOS or total index hospitalization costs during either Era 1 or Era 2 (Table 4). Nonetheless, HVH status was associated with a 25% and 13% increment in relative odds of nonhome discharge during Eras 1 and 2, respectively.
      Table 4Risk-adjusted influence of high volume hospital (HVH) status on clinical outcomes and resource use following transcatheter aortic valve replacement (TAVR)
      OutcomeEra 1 (2012-2015)P valueEra 2 (2016-2018)P value
      In-hospital mortality
      Results of logistic regression tests are presented as adjusted odds ratio (95% CI).
      0.94 (0.78-1.14).520.83 (0.69-0.99).047
      Complications
      Results of logistic regression tests are presented as adjusted odds ratio (95% CI).
       Accidental puncture0.83 (0.63-1.10).201.01 (0.80-1.27).91
       Acute ischemic stroke1.13 (0.90-1.42).281.08 (0.81-1.44).57
       Acute kidney injury0.89 (0.76-1.04).141.06 (0.94-1.20).35
       Hemorrhage0.98 (0.77-1.24).860.88 (0.74-1.05).17
       Infectious complication1.13 (0.95-1.34).180.78 (0.66-0.91).002
       Myocardial infarction1.04 (0.77-1.40).811.21 (0.95-1.55).12
      Hospitalization costs ($1000s)
      Results of linear regression tests are presented as β (95% CI).
      +0.2 (-2.7-3.1).890 (-2.4-2.5).97
      Length of stay (d)
      Results of linear regression tests are presented as β (95% CI).
      -0.1 (-0.3-0.5).60-0.1 (-0.2, 0.1).25
      Nonhome discharge
      Results of logistic regression tests are presented as adjusted odds ratio (95% CI).
      1.25 (1.06-1.48).0101.13 (1.01-1.27).029
      Multivariable models included adjustment for all covariates shown in Table 3.
      Results of logistic regression tests are presented as adjusted odds ratio (95% CI).
      Results of linear regression tests are presented as β (95% CI).

      Discussion

      In the present 7-year-study of more than 180,000 TAVR hospitalizations in the United States, we found rapid adoption of TAVR and a recent decline in utilization of SAVR. Although increasing TAVR volume was associated with reduced odds of mortality during the early years following its market introduction, this effect diminished over time (Video 1). In addition, center-level SAVR volume maintains a strong association with improved mortality following TAVR in more recent years. We found high hospital SAVR volume to be associated with decreased risk of infectious complications but equivalent odds of other inferior outcomes despite a greater burden of patient comorbidities. Several of these findings warrant further discussion and have implications relevant to future updates of National Coverage Determination (NCD).
      The rapid adoption of TAVR technology across the United States has been accompanied by major improvements in acute mortality from 4.5% in 2012 to approximately 1% in 2018. Prior studies of the Transcatheter Valve Therapy Registry have demonstrated similar findings using data from a narrower time period.
      • Vemulapalli S.
      • Carroll J.D.
      • Mack M.J.
      • Li Z.
      • Dai D.
      • Kosinski A.S.
      • et al.
      Procedural volume and outcomes for transcatheter aortic-valve replacement.
      Although this observation, in part, is due to inclusion of lower-risk patients in recent years, advances in patient selection as well as technical and manufacturing aspects of TAVR technology cannot be ignored. Early TAVR platforms required large diameter delivery sheaths that warranted alternate access strategies, nearly all of which are associated with increased risk compared with the transfemoral approach.
      • Biancari F.
      • Rosato S.
      • D'Errigo P.
      • Ranucci M.
      • Onorati F.
      • Barbnti M.
      • et al.
      Immediate and intermediate outcome after transapical versus transfemoral transcatheter aortic valve replacement.
      ,
      • Kumar N.
      • Khera R.
      • Fonarow G.C.
      • Bhatt D.L.
      Comparison of outcomes of transfemoral versus transapical approach for transcatheter aortic valve implantation.
      Furthermore, with increasing experience, high-risk features, including dense calcification of the left ventricular outflow tract, have been identified, allowing for better selection of TAVR candidates. Taken together, such advances have allowed for TAVR technology to be adopted into practice for nearly all patients with severe aortic stenosis.
      Although a significant positive volume outcome relationship has been demonstrated in many complex surgical and interventional procedures, the presence of this effect in TAVR has been controversial. A study of early TAVR experience demonstrated higher institutional volumes to be associated with significantly lower rate of death as well as hemorrhagic and vascular complications following TAVR.
      • Carroll J.D.
      • Vemulapalli S.
      • Dai D.
      • Matsouaka R.
      • Blackstone E.
      • Edwards F.
      • et al.
      Procedural experience for transcatheter aortic valve replacement and relation to outcomes: the STS/ACC TVT Registry.
      With aforementioned improvements, some have questioned the relevance of minimum surgical volume requirements set forth by the NCD.
      • Anwaruddin S.
      • Saybolt M.D.
      Improving quality and outcomes in TAVR turning up the volume?.
      Nonetheless, a study of the Transcatheter Valve Therapy Registry reported a persistent conventional positive outcome relationship even after excluding the learning curve period.
      • Vemulapalli S.
      • Carroll J.D.
      • Mack M.J.
      • Li Z.
      • Dai D.
      • Kosinski A.S.
      • et al.
      Procedural volume and outcomes for transcatheter aortic-valve replacement.
      Although our results are congruent with the authors' findings, the present work delves into the potential mechanisms behind the observed relationship. The strong positive association of TAVR mortality and center volume has dissipated in more recent years. This may be due to accumulating operator experience, use of conscious sedation and, of course, lower device-specific risk. With increasing experience, our results suggest continued reductions in mortality and major complications across the United States and the loss of a significant association with annual TAVR volume.
      Perhaps the most significant finding of the present study is the association of center-level SAVR volume with TAVR mortality in the moderate risk era. This relationship was present even after accounting for TAVR volume of each center and validates the close interaction of the 2 technologies as initially hypothesized in the original NCD.
      Centers for Medicare & Medicaid Services
      Medicare coverage database. National coverage determination: transcatheter aortic valve replacement (TAVR) (20.32).
      Other studies of Transcatheter Valve Therapy Registry have failed to account for such cross-volume effect due to methodologic limitations. Systematic variations across hospitals likely result in collinearity between TAVR and SAVR volumes, with large centers having higher procedural volumes for both and more sophisticated perioperative management.
      • Mao J.
      • Redberg R.F.
      • Carroll J.D.
      • Marinac-Dabic D.
      • Laschinger J.
      • Thourani V.
      • et al.
      Association between hospital surgical aortic valve replacement volume and transcatheter aortic valve replacement outcomes.
      ,
      • Vemulapalli S.
      Transcatheter aortic valve replacement and surgical aortic valve replacement volume-outcome relationships: a Pandora's box.
      ,
      • Kundi H.
      • Strom J.B.
      • Valsdottir L.R.
      • Elmariah S.
      • Popma J.J.
      • Shen C.
      • et al.
      Trends in isolated surgical aortic valve replacement according to hospital-based transcatheter aortic valve replacement volumes.
      We especially evaluated the interaction between these modalities and found that emergence of a strong SAVR volume effect on outcomes of TAVR in the latter years of the study. Although the exact reasons for this observation cannot be determined using our dataset, it is possible that hospitals with high surgical expertise in AVR are able to better select patients for TAVR with the heart-team approach. Additionally, the expertise of all members in such a team may help inform the selection of patients who are candidates for alternative surgical intervention, such as video-assisted right minithoracotomy. Our findings provide evidence for the increasing impact of SAVR volume on TAVR-related end points and suggest the need for continued collaboration between cardiologists and surgeons.
      The present study is not without limitations. In addition to shortcomings inherent to a retrospective study, the NRD lacks granular clinical information, including echocardiographic findings, ejection fraction, and degree of aortic stenosis. Furthermore, we are unable to ascertain and adjust for the type of valve that was utilized. Because the NRD does not track hospitals across years, we are unable to assess total operative volume across a period >1 year. For the same reasons, the present study was unable to adjust for institutional or surgeon learning curve.

      Conclusions

      The present study used a nationally representative database to ascertain the influence of institutional SAVR volume on outcomes following TAVR. Using robust statistical techniques to minimize bias in our analyses, we demonstrated the continued relevance of SAVR experience in reducing mortality and perioperative complications in TAVR (Figure 4).
      Figure thumbnail gr4
      Figure 4The study's methods, results, and implications. TAVR, Transcatheter aortic valve replacement. SAVR, surgical aortic valve replacement.

      Conflict of Interest Statement

      Dr Shemin served as a consultant to Edwards LifeSciences and as a co-principal investigator on the PARTNER II Trial. All other authors reported no conflicts of interest.
      The Journal policy requires editors and reviewers to disclose conflicts of interest and to decline handling or reviewing manuscripts for which they may have a conflict of interest. The editors and reviewers of this article have no conflicts of interest.

      Supplementary Data

      Appendix E1

      Table E1Baseline characteristics of study cohort stratified by missingness for key variables, including age, sex, mortality, and hospitalization costs.
      ParameterNot missing (n = 181,740)Missing (n = 1166)P value
      Age (y)80.4 ± 8.180.9 ± 9.6.21
      Female46.347.0.65
      ECI score (points)5.2 ± 1.65.7 ± 1.9.001
      Income percentile<.001
       76th-100th24.955.6
       51st-75th27.527.2
       26th-50th27.39.9
       0-25th20.47.3
      Payer status.63
       Private5.77.3
       Medicare91.592.2
       Medicaid0.80.5
       Other2.00.0
      Comorbidities
       Congestive heart failure71.443.0<.001
       Coronary artery disease62.759.0.19
       Chronic arrhythmia53.756.9.31
       Pulmonary circulation disorder16.214.0.07
       Peripheral vascular disease20.654.1<.001
       Neurologic disorder4.34.3.91
       Chronic lung disease29.128.3.69
       Hypothyroidism16.815.4.24
       End-stage renal disease3.84.8.002
       Liver disease2.65.3.001
       Cancer3.34.0.14
       Coagulopathy12.834.0<.001
       Weight loss2.32.5.58
       Electrolyte imbalance13.713.3.75
       Anemia3.37.9<.001
      Values are presented as mean ± SD or %. ECI, Elixhauser Comorbidity Index.
      Table E2Comparison of patients in Era 1 (2012-2015) and Era 2 (2016-2018)
      ParameterEra 1 (2012-2015) (n = 53,233)Era 2 (2016-2018) (n = 128,507)P value
      Age (y)81.2 ± 7.880.0 ± 8.2<.001
      Female47.645.8<.001
      ECI score (points)5.3 ± 1.65.2 ± 1.6.002
      Income percentile.19
       76th-100th26.324.3
       51st-75th27.427.5
       26th-50th26.027.8
       0-25th20.320.4
      Payer.75
       Private5.65.7
       Medicare91.891.4
       Medicaid0.70.9
       Other1.92.0
      Comorbidities
       Congestive heart failure69.172.3.034
       Coronary artery disease62.262.9.31
       Chronic arrhythmia56.752.5<.001
       Pulmonary circulation disorder18.015.5<.001
       Peripheral vascular disease23.019.6<.001
       Neurologic disorders4.54.3.29
       Chronic lung disease37.925.4<.001
       Hypothyroidism16.716.9.46
       End-stage renal disease3.63.8.17
       Liver disease2.82.5.019
       Cancer3.23.3.55
       Coagulopathy17.411.0<.001
       Weight loss3.01.9<.001
       Electrolyte imbalance19.511.3<.001
       Anemia3.13.4.17
      Values are presented as mean ± SD or %. ECI, Elixhauser Comorbidity Index.

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