ADULT CARDIAC
A Population-Based Analysis of Robotic-Assisted Mitral Valve Repair Subroto Paul, MD, Abby J. Isaacs, MS, Jessica Jalbert, PhD, Nonso C. Osakwe, MD, MPH, Arash Salemi, MD, Leonard N. Girardi, MD, and Art Sedrakyan, MD, PhD Departments of Health Policy and Research and Cardiothoracic Surgery, New York Presbyterian Hospital–Weill Cornell Medical College, New York, New York
Background. Robotic-assisted mitral valve repair is becoming more frequently performed in cardiac surgery. However, little is known about its utilization and safety at a national level. Methods. Patients undergoing mitral valve repair in the United States from 2008 to 2012 were identified in the National Inpatient Sample. Inhospital mortality, complications, length of stay, and cost for patients undergoing robotic-assisted mitral valve repair were compared with patients undergoing nonrobotic procedures. Results. We identified 50,408 isolated mitral valve repair surgeries, of which 3,145 were done with robotic assistance. In a propensity score matched analysis of 631 pairs of patients, we found no difference between patients
undergoing robotic-assisted and nonrobotic-assisted mitral valve repair with respect to inhospital mortality, complications, or composite outcomes in unadjusted or multivariable analyses. Robotic-assisted mitral valve repair surgery was associated with a shorter median length of stay (4 versus 6 days, p < 0.001), and there was no difference in median total costs between the two procedures. Conclusions. In our analysis of a large national database with its inherent limitations, robotic-assisted mitral valve repair was found to be safe, with an acceptable morbidity and mortality profile.
R
of the NIS and the collection and maintenance of data within the database is described elsewhere [8, 9] (available at: http://www.hcup-us.ahrq.gov/nisoverview. jsp). This study was approved by the Institutional Review Board of Weill Cornell Medical College (protocol no. EXE2011-057) and conforms to the data use agreement for the NIS from the Healthcare Cost and Utilization Project.
obotic-assisted surgical technologies are being rapidly adopted in all surgical disciplines. Urologists and gynecologists have been early adopters and account for the majority of more than 459,000 robotic surgeries performed worldwide in 2012. With the ability to perform articulated movements with wristed instruments, the robotic platform facilitates operating, particularly suturing, in small closed spaces. Mitral valve repair is one procedure that may benefit from this technology. Most studies examining the safety of robotic mitral valve surgery come from large single-institution case series. A national perspective on the adoption and safety of mitral valve repair is not known [1–7]. To evaluate national trends in the adoption and safety of robotic-assisted surgery for mitral valve repairs, we performed a population-based analysis using the National (formerly, Nationwide) Inpatient Sample (NIS).
Material and Methods Data Source The NIS is the largest all-payer inpatient care database in the United States and constitutes approximately a 20% stratified sample of all hospital discharges from nongovernment institutions. An extensive description Accepted for publication Dec 16, 2014. Address correspondence to Dr Paul, Division of Thoracic Surgery, Department of Cardiothoracic Surgery, New York Presbyterian Hospital– Weill Cornell Medical College, New York, NY 10065; e-mail: pas2022@ med.cornell.edu.
Ó 2015 by The Society of Thoracic Surgeons Published by Elsevier
(Ann Thorac Surg 2015;99:1546–53) Ó 2015 by The Society of Thoracic Surgeons
Study Cohort The study cohort consisted of all patients with a visit to an Healthcare Cost and Utilization Project NIS-participating hospital undergoing either of the following procedures: robotic-assisted mitral valve repair or nonrobotic-assisted isolated mitral valve repair. International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9CM) codes were used to identify patients undergoing those procedures (Appendix Table 1). We compared robotic-assisted mitral valve repair to any mitral valve repair performed without the aid of robotic assistance. Although the standard approach for a mitral repair is a sternotomy, minimally invasive mitral valve repair through a ministernotomy or minithoractomy has been reported. We are unable to differentiate these approaches, and they are included in the nonrobotic sample of patients. However, they reflect a small proportion of mitral valves performed nationally. We included only procedures performed between October 2008 and 2012 as the codes for robotic-assisted surgery were introduced in October 2008. All patient admissions were elective, and patients were at least 18 years of age at the time of the procedure. 0003-4975/$36.00 http://dx.doi.org/10.1016/j.athoracsur.2014.12.043
PAUL ET AL NIS ANALYSIS OF ROBOTIC-ASSISTED MV REPAIR
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Outcomes
Results
The study outcomes were inhospital mortality, inhospital complications, and a composite outcome consisting of inhospital mortality or stroke or myocardial infarction. We identified patients with the various complications based on previously validated algorithms using ICD-9-CM codes [8, 9].
From October 2008 to December 2012, 50,408 isolated mitral valve repair admissions were identified, of which 3,145 (6.2%) were performed with robotic assistance (Table 1). Patients who underwent robotic-assisted mitral valve repair were younger with a higher proportion of males undergoing the procedure. These patients also had fewer comorbidities than patients who underwent nonrobotic repair and were more likely to have commercial insurance. The characteristics of hospitals performing these robotic-assisted procedures differed. Robotic-assisted mitral valve repair was more likely to be performed in large hospitals and teaching hospitals. Volume differed by region, with the largest volume of procedures performed in the Midwest region. Outcomes were then compared between patients undergoing nonrobotic and robotic-assisted procedures in the raw data and a balanced propensity-matched cohort (Table 2). There was a slightly lower rate of mortality with robotic-assisted surgery (1.3% versus 2.2%, p ¼ 0.048). Patients undergoing robotic-assisted mitral valve repair also had a shorter length of stay (4 versus 7 days, p ¼ 0.004) and more routine discharges than patients undergoing nonrobotic repair (65.1% versus 44.9%, p < 0.001). Only the difference in length of stay (4 versus 6 days, p < 0.001) remained in the propensity-matched cohort. No significant differences were found when the total hospital costs of robotic-assisted and nonrobotic-assisted mitral valve repair procedures were compared. There was no difference in the unadjusted rate of any complication (37.3% versus 37.1%, p ¼ 0.94). Our propensity-matched analysis balanced for multiple patient and hospital factors similarly found no difference in the odds ratio between the mitral valve repair groups with respect to inhospital mortality, complications, or composite outcomes (Table 3). Similar results were obtained with adjusted logistic regression in the full NIS sample and in examining outcomes at hospitals performing both robotic and nonrobotic mitral valve repairs (Appendix Table 3).
Variables We categorized patients according to age (18 to 55, 56 to 64, and 65 or more), sex, race, year of procedure, and insurance status. We identified patients with diagnoses of coronary artery disease, heart failure, hypertension, diabetes mellitus, chronic pulmonary disease, peripheral vascular disease, and chronic renal insufficiency during the index hospitalization, as described before [10]. To summarize a patient’s comorbidity burden, we used information during the hospitalization to calculate the Elixhauser comorbidity score [10, 11]. We also used hospital-level information available in the NIS data to categorize according to their location with respect to the census regions, bed size (small, medium, or large), and teaching hospital status. We additionally included annual hospital valve procedure volume. Before 2012, the NIS included all discharges from a 20% sample of hospitals. It was updated in 2012 to include a 20% sample of discharges across hospitals. We used a weighted estimate of hospital volume in 2012 to accommodate this change. Charge data were provided at the discharge level in the NIS database. Cost is estimated using hospital-specific cost-tocharge ratio, using a preestablished method.
Statistical Analysis Baseline characteristics for the study population are reported and compared using percentages and c2 tests for categorical variables, and medians, interquartile ranges, and Wilcoxon tests for continuous variables. To assess the relationship between exposure to robotic surgery and the outcome in similar patients, we matched patients on their propensity of being treated with robotic surgery using a one-to-one nearest neighbor algorithm [12]. We created the propensity score using a logistic regression model that included age group, sex, year, coronary artery disease, diabetes, chronic pulmonary disease, peripheral vascular disease, renal failure, hospital valve replacement volume, and region. We then assessed balance using absolute difference and postmatch c-statistic (Appendix Table 2). After matching, paired test statistics were used to compare the inhospital outcomes, length of stay, charges, and costs for patients receiving traditional and robotic procedures. All analyses were performed using SAS version 9.3 (SAS Institute, Cary, NC).
Sensitivity Analysis To determine whether the results were sensitive to the methods used, hierarchical logistic regression models, adjusted for the same covariates included in the propensity score, were used to compare the procedures for both the full sample and for only hospitals performing at least one robotic procedure.
Comment The introduction of robotics into surgery has been complex and is still evolving. The first robotic-assisted mitral valve repair was performed in 1998 by Carpentier in France and Mohr in Germany [13, 14]. Several large single-institution series examining the outcomes of robotic-assisted mitral valve surgery have been published. Robotic-assisted mitral valve surgery in these series has, in general, been found to be safe and effective. However, these reports are from high-volume centers with special expertise in valve surgery and other complex cardiac surgical procedures. There are limited national data, however, on the short-term morbidity and mortality after robotic-assisted mitral surgery. We report a population-based analysis of roboticassisted mitral valve surgery using the NIS. The principal finding of our study is that robotic-assisted mitral surgery can be performed safely with a similar
ADULT CARDIAC
Ann Thorac Surg 2015;99:1546–53
ADULT CARDIAC
1548
PAUL ET AL NIS ANALYSIS OF ROBOTIC-ASSISTED MV REPAIR
Ann Thorac Surg 2015;99:1546–53
Table 1. Patient Demographics and Hospital Characteristics in Unmatched National Sample
Patient Demographics Age, years Age group 18–55 years 56–64 years 65 years and above Sexa Female Male Raceb White Not white Year of procedure 2008 (October–December) 2009 2010 2011 2012 Comorbidities Coronary artery disease Congestive heart failurec Hypertension Diabetes mellitusc Chronic pulmonary diseasec Peripheral vascular diseasec Chronic renal insufficiency/failurec Elixhauser comorbidity score Insurance Medicare Medicaid Commercial Other (uninsured) Annual hospital procedure volume Procedure volume
A Population-Based Analysis of Robotic-Assisted Mitral Valve Repair Subroto Paul, MD, Abby J. Isaacs, MS, Jessica Jalbert, PhD, Nonso C. Osakwe, MD, MPH, Arash Salemi, MD, Leonard N. Girardi, MD, and Art Sedrakyan, MD, PhD Departments of Health Policy and Research and Cardiothoracic Surgery, New York Presbyterian Hospital–Weill Cornell Medical College, New York, New York
Background. Robotic-assisted mitral valve repair is becoming more frequently performed in cardiac surgery. However, little is known about its utilization and safety at a national level. Methods. Patients undergoing mitral valve repair in the United States from 2008 to 2012 were identified in the National Inpatient Sample. Inhospital mortality, complications, length of stay, and cost for patients undergoing robotic-assisted mitral valve repair were compared with patients undergoing nonrobotic procedures. Results. We identified 50,408 isolated mitral valve repair surgeries, of which 3,145 were done with robotic assistance. In a propensity score matched analysis of 631 pairs of patients, we found no difference between patients
undergoing robotic-assisted and nonrobotic-assisted mitral valve repair with respect to inhospital mortality, complications, or composite outcomes in unadjusted or multivariable analyses. Robotic-assisted mitral valve repair surgery was associated with a shorter median length of stay (4 versus 6 days, p < 0.001), and there was no difference in median total costs between the two procedures. Conclusions. In our analysis of a large national database with its inherent limitations, robotic-assisted mitral valve repair was found to be safe, with an acceptable morbidity and mortality profile.
R
of the NIS and the collection and maintenance of data within the database is described elsewhere [8, 9] (available at: http://www.hcup-us.ahrq.gov/nisoverview. jsp). This study was approved by the Institutional Review Board of Weill Cornell Medical College (protocol no. EXE2011-057) and conforms to the data use agreement for the NIS from the Healthcare Cost and Utilization Project.
obotic-assisted surgical technologies are being rapidly adopted in all surgical disciplines. Urologists and gynecologists have been early adopters and account for the majority of more than 459,000 robotic surgeries performed worldwide in 2012. With the ability to perform articulated movements with wristed instruments, the robotic platform facilitates operating, particularly suturing, in small closed spaces. Mitral valve repair is one procedure that may benefit from this technology. Most studies examining the safety of robotic mitral valve surgery come from large single-institution case series. A national perspective on the adoption and safety of mitral valve repair is not known [1–7]. To evaluate national trends in the adoption and safety of robotic-assisted surgery for mitral valve repairs, we performed a population-based analysis using the National (formerly, Nationwide) Inpatient Sample (NIS).
Material and Methods Data Source The NIS is the largest all-payer inpatient care database in the United States and constitutes approximately a 20% stratified sample of all hospital discharges from nongovernment institutions. An extensive description Accepted for publication Dec 16, 2014. Address correspondence to Dr Paul, Division of Thoracic Surgery, Department of Cardiothoracic Surgery, New York Presbyterian Hospital– Weill Cornell Medical College, New York, NY 10065; e-mail: pas2022@ med.cornell.edu.
Ó 2015 by The Society of Thoracic Surgeons Published by Elsevier
(Ann Thorac Surg 2015;99:1546–53) Ó 2015 by The Society of Thoracic Surgeons
Study Cohort The study cohort consisted of all patients with a visit to an Healthcare Cost and Utilization Project NIS-participating hospital undergoing either of the following procedures: robotic-assisted mitral valve repair or nonrobotic-assisted isolated mitral valve repair. International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9CM) codes were used to identify patients undergoing those procedures (Appendix Table 1). We compared robotic-assisted mitral valve repair to any mitral valve repair performed without the aid of robotic assistance. Although the standard approach for a mitral repair is a sternotomy, minimally invasive mitral valve repair through a ministernotomy or minithoractomy has been reported. We are unable to differentiate these approaches, and they are included in the nonrobotic sample of patients. However, they reflect a small proportion of mitral valves performed nationally. We included only procedures performed between October 2008 and 2012 as the codes for robotic-assisted surgery were introduced in October 2008. All patient admissions were elective, and patients were at least 18 years of age at the time of the procedure. 0003-4975/$36.00 http://dx.doi.org/10.1016/j.athoracsur.2014.12.043
PAUL ET AL NIS ANALYSIS OF ROBOTIC-ASSISTED MV REPAIR
1547
Outcomes
Results
The study outcomes were inhospital mortality, inhospital complications, and a composite outcome consisting of inhospital mortality or stroke or myocardial infarction. We identified patients with the various complications based on previously validated algorithms using ICD-9-CM codes [8, 9].
From October 2008 to December 2012, 50,408 isolated mitral valve repair admissions were identified, of which 3,145 (6.2%) were performed with robotic assistance (Table 1). Patients who underwent robotic-assisted mitral valve repair were younger with a higher proportion of males undergoing the procedure. These patients also had fewer comorbidities than patients who underwent nonrobotic repair and were more likely to have commercial insurance. The characteristics of hospitals performing these robotic-assisted procedures differed. Robotic-assisted mitral valve repair was more likely to be performed in large hospitals and teaching hospitals. Volume differed by region, with the largest volume of procedures performed in the Midwest region. Outcomes were then compared between patients undergoing nonrobotic and robotic-assisted procedures in the raw data and a balanced propensity-matched cohort (Table 2). There was a slightly lower rate of mortality with robotic-assisted surgery (1.3% versus 2.2%, p ¼ 0.048). Patients undergoing robotic-assisted mitral valve repair also had a shorter length of stay (4 versus 7 days, p ¼ 0.004) and more routine discharges than patients undergoing nonrobotic repair (65.1% versus 44.9%, p < 0.001). Only the difference in length of stay (4 versus 6 days, p < 0.001) remained in the propensity-matched cohort. No significant differences were found when the total hospital costs of robotic-assisted and nonrobotic-assisted mitral valve repair procedures were compared. There was no difference in the unadjusted rate of any complication (37.3% versus 37.1%, p ¼ 0.94). Our propensity-matched analysis balanced for multiple patient and hospital factors similarly found no difference in the odds ratio between the mitral valve repair groups with respect to inhospital mortality, complications, or composite outcomes (Table 3). Similar results were obtained with adjusted logistic regression in the full NIS sample and in examining outcomes at hospitals performing both robotic and nonrobotic mitral valve repairs (Appendix Table 3).
Variables We categorized patients according to age (18 to 55, 56 to 64, and 65 or more), sex, race, year of procedure, and insurance status. We identified patients with diagnoses of coronary artery disease, heart failure, hypertension, diabetes mellitus, chronic pulmonary disease, peripheral vascular disease, and chronic renal insufficiency during the index hospitalization, as described before [10]. To summarize a patient’s comorbidity burden, we used information during the hospitalization to calculate the Elixhauser comorbidity score [10, 11]. We also used hospital-level information available in the NIS data to categorize according to their location with respect to the census regions, bed size (small, medium, or large), and teaching hospital status. We additionally included annual hospital valve procedure volume. Before 2012, the NIS included all discharges from a 20% sample of hospitals. It was updated in 2012 to include a 20% sample of discharges across hospitals. We used a weighted estimate of hospital volume in 2012 to accommodate this change. Charge data were provided at the discharge level in the NIS database. Cost is estimated using hospital-specific cost-tocharge ratio, using a preestablished method.
Statistical Analysis Baseline characteristics for the study population are reported and compared using percentages and c2 tests for categorical variables, and medians, interquartile ranges, and Wilcoxon tests for continuous variables. To assess the relationship between exposure to robotic surgery and the outcome in similar patients, we matched patients on their propensity of being treated with robotic surgery using a one-to-one nearest neighbor algorithm [12]. We created the propensity score using a logistic regression model that included age group, sex, year, coronary artery disease, diabetes, chronic pulmonary disease, peripheral vascular disease, renal failure, hospital valve replacement volume, and region. We then assessed balance using absolute difference and postmatch c-statistic (Appendix Table 2). After matching, paired test statistics were used to compare the inhospital outcomes, length of stay, charges, and costs for patients receiving traditional and robotic procedures. All analyses were performed using SAS version 9.3 (SAS Institute, Cary, NC).
Sensitivity Analysis To determine whether the results were sensitive to the methods used, hierarchical logistic regression models, adjusted for the same covariates included in the propensity score, were used to compare the procedures for both the full sample and for only hospitals performing at least one robotic procedure.
Comment The introduction of robotics into surgery has been complex and is still evolving. The first robotic-assisted mitral valve repair was performed in 1998 by Carpentier in France and Mohr in Germany [13, 14]. Several large single-institution series examining the outcomes of robotic-assisted mitral valve surgery have been published. Robotic-assisted mitral valve surgery in these series has, in general, been found to be safe and effective. However, these reports are from high-volume centers with special expertise in valve surgery and other complex cardiac surgical procedures. There are limited national data, however, on the short-term morbidity and mortality after robotic-assisted mitral surgery. We report a population-based analysis of roboticassisted mitral valve surgery using the NIS. The principal finding of our study is that robotic-assisted mitral surgery can be performed safely with a similar
ADULT CARDIAC
Ann Thorac Surg 2015;99:1546–53
ADULT CARDIAC
1548
PAUL ET AL NIS ANALYSIS OF ROBOTIC-ASSISTED MV REPAIR
Ann Thorac Surg 2015;99:1546–53
Table 1. Patient Demographics and Hospital Characteristics in Unmatched National Sample
Patient Demographics Age, years Age group 18–55 years 56–64 years 65 years and above Sexa Female Male Raceb White Not white Year of procedure 2008 (October–December) 2009 2010 2011 2012 Comorbidities Coronary artery disease Congestive heart failurec Hypertension Diabetes mellitusc Chronic pulmonary diseasec Peripheral vascular diseasec Chronic renal insufficiency/failurec Elixhauser comorbidity score Insurance Medicare Medicaid Commercial Other (uninsured) Annual hospital procedure volume Procedure volume
![[Mitral valve repair versus mitral valve replacement].](/assets/img/hold.png)
