Volume-Outcome Relationships for Mitral Valve Surgery

On September 28, 2019, the article, “Surgical Volume Matters When It Comes to Repair of Primary MR," was published in TCTMD. The story highlights a presentation from Dr. Vinay Badhwar at TCT 2019 that showed the volume of mitral valve repair or replacement at both the hospital and surgeon levels was inversely related to the success of the mitral valve repair rate.

Dr. James R. Edgerton describes the article, what it means for the cardiothoracic surgery specialty, and his view on the topic of a volume-outcome relationship in mitral valve surgery.

Volume-Outcome Relationships for Mitral Valve Surgery

STS is perhaps the preeminent organization and leader in quality assurance; quality is at the core of the Society’s mission statement. The organization is a leader in transparency. Its Adult Cardiac Surgery Database (ACSD) is the envy of other organizations, and more than 95% of cardiac surgery programs participate in it voluntarily.  

Volume-outcome relationships are a frequent area of investigation in quality assurance initiatives, and these relationships have been defined for many major operations. In the adult cardiac arena, these include coronary artery bypass (CABG), aortic valve replacement (AVR), and transcatheter aortic valve replacement (TAVR), but not previously for mitral valve (MV) surgery.

Recently, STS undertook a 24-month examination of volume-outcome relationships for MV surgery. Data from the STS ACSD were linked to Centers for Medicare & Medicaid Services (CMS) data and included 55,311 patients operated on for primary isolated mitral regurgitation (MR) at 1,094 hospitals in the US by 2,410 surgeons. The findings were presented at the TCT meeting in September by Vinay Badhwar, MD, from West Virginia University School of Medicine in Morgantown, who chairs the STS Council on Quality, Research, and Patient Safety.

In an effort to reflect total annual mitral experience, the volume component included all isolated MV repairs and replacements for primary MR. Outcomes were reported on hospital and surgeon levels for: 

Primary outcome:
•    Operative mortality of isolated MV surgery for primary MR 

Secondary outcomes: 
•    30-day composite mortality/morbidity (bleeding, stroke, prolonged ventilation, renal failure, wound infection)
•    1-year mortality, reoperation, and heart failure related re-hospitalization
•    Rate of successful repair of primary MR (residual MR ≤ mild/1+)

Successful repair was determined by post-operative echocardiogram. When no post-operative echocardiogram was available, a post-repair intraoperative echocardiogram was used. 

And there was good news! More than 80% of degenerative mitral valves undergo the preferred method of repair, which has better outcomes than replacement. Reoperation and re-repair were infrequent—1% or less at 1 year. Additionally, as discussed in a post-presentation panel discussion, there are many more competent and capable facilities accessible to patients than previously thought. It is preferable to intervene surgically prior to the occurrence of atrial and ventricular remodeling with their attendant complications. Unfortunately, patients are being referred for mitral surgery later than optimal in their disease process. Only 4% are referred when their symptoms are minimal or nonexistent. "… patients continue to be referred late when symptoms are more advanced, particularly even in the highest-volume centers,” said Dr. Badhwar.

Volume should be only one of the criteria considered when referring patients for isolated MV surgery for primary degenerative MR.  

James R. Edgerton, MD

Data were reported in quartiles, and the lowest volume and highest volume quartiles were compared statistically for both hospitals and surgeons. The repair rate in the lowest vs. highest volume quartile was 68.3% vs. 84.5% (p< 0.0001). Hospitals and surgeons performed <10.9 and <5.3 procedures, respectively, in the lowest quartile and >46.4 and >20.9, respectively, in the highest quartile. A statistically significant volume-outcome relationship exists at both the hospital and surgeon levels for operative mortality, 1-year mortality, 30-day composite of mortality/morbidity, and rate of successful repair. Highest volume hospitals and surgeons demonstrated outcomes superior to lowest volume hospitals and surgeons. The annual hospital volume inflection point for improved outcomes was 75 MV cases for hospitals and 35 MV cases for surgeons. Results leveled out for higher case volumes. There were no volume outcome differences for MV reoperations or heart failure related readmissions. 

These data fill a void by describing a volume-outcome relationship within a large contemporary national cohort with data derived primarily from clinical rather than administrative databases. Overall, the data demonstrate that patients are receiving excellent care with an increasing rate of mitral valves successfully repaired. It will be useful for future guideline and consensus statements. However, more information is needed, and the outcomes should be applied to referral patterns with some caution. Certainly, there are surgeons achieving high quality outcomes in lower volume centers. Thus, currently, volume should be only one of the criteria considered when referring patients for isolated MV surgery for primary degenerative MR.  

Future dialogue should center on how to better identify high quality in lower-volume programs, perhaps by coupling cumulative sum charts or variable life-adjusted displays with observed-to-expected ratios. Dialogue also should address how to ensure access to high-quality care and how to extend the highest level of care to more hospitals by more surgeons. Perhaps the latter may be achieved by simplification of the surgical techniques coupled with improved teaching methodology, which may include remote proctoring and mentoring. To be sure, STS will be leading the way to enhancing the ability of cardiothoracic surgeons to provide ever-improving quality care for our patients.


Please note: A paper featuring this research is being submitted for publication. Dr. Edgerton is an author on the paper. 


James R. Edgerton, MD, is the Senior Clinical Scientist in the Department of Epidemiology at Baylor Scott & White Health in Dallas, TX. After a long surgical career distinguished by developing innovative techniques to achieve the ablation of atrial arrhythmias, Dr. Edgerton now focuses his attention on research, publication, and teaching. He maintains an active research program, publishes avidly in peer reviewed journals, and lectures internationally. Dr. Edgerton has held leadership positions in The Society of Thoracic Surgeons, American Association of Thoracic Surgeons, International Society for Minimally Invasive Cardiac Surgery, and the Heart Rhythm Society.