Can We Predict Mitral Valve Repair Rates by Individual Surgeons' Mitral Volume?

Mitral valve repair is desirable and superior to replacement in nearly all instances of mitral disease. The excellent long-term results have facilitated changing the indications for mitral surgery.¹ Mitral patients can potentially be referred earlier, in a lower functional class or even when asymptomatic, before left ventricular (LV) dysfunction and dilation occur. This synopsis considers clinical and individual surgeon factors that predict mitral repair, which could lead to higher repair rates and improved outcomes.²

Patients and Methods

Patients who underwent an isolated mitral valve operation and were entered into the Society of Thoracic Surgeons database from 2005 through 2007 were studied. Parameters of logistic regression were estimated with the use of general estimating equations methodology. Rates of surgical repair of the mitral valve were plotted against surgeon mitral volume.

In this study, 28,507 patients underwent isolated mitral valve operations (with or without concomitant tricuspid valve or atrial fibrillation surgery), by 1,088 surgeons at 639 centers. Patients who had mitral surgery with concomitant coronary artery bypass grafting (possible ischemic mitral regurgitation) were excluded.

Results

Marked variability was found in the annual frequency of mitral valve repair compared with replacement. The mean repair rate for all surgeons was 41% (range, 0–100%). The median number of isolated mitral valve operations per year was 5 (range, 1–166).

Compared with patients who underwent mitral valve replacement, mitral repair patients were younger and had a lower burden of comorbidities. After risk adjustment, age, sex, race, endocarditis, mitral pathology, urgency, and concomitant tricuspid or atrial fibrillation surgery were independently associated with altered probability of mitral repair. However, increased surgeon mitral volume was the most highly associated predictive factor, with an increased propensity to perform mitral repair both before and after all clinical covariate factor risk adjustments. Furthermore, predictive mitral repair rates increased with increasing surgeon annual mitral valve volume, with a prominent observed threshold effect (Fig. 1).

Fig. 1 The predictive model of mitral valve repairs as a function of the surgeon-specific annual mitral valve volume.

Discussion

Despite the well-known advantages of mitral valve repair, including preservation of LV function, freedom from anticoagulation and reoperation, and a low early and late mortality rate, mitral valve repair is not undertaken universally or uniformly.

The largest positive predictor of and influence for mitral valve repair is a surgeon's annual mitral volume. For example, when a surgeon performed 100 mitral procedures per year, the risk-adjusted odds ratio for a mitral repair was 3.78 times (95% confidence interval, 1.87–7.64) that of a patient operated upon by a surgeon who performed a median number of 5 mitral procedures per year.

Despite the many possible advantages of early mitral repair, the timing of referral for mitral valve surgery remains delayed. At present, the American College of Cardiology/American Heart Association guidelines suggest that patients with significant mitral regurgitation be sent for mitral surgery on the basis of symptoms; or, if asymptomatic, on the basis of LV functional deterioration, LV chamber dilation, or the onset of complications, including atrial fibrillation and pulmonary hypertension.³ Two studies revealed that the rate of adherence to these conservative guidelines for surgical referral of mitral valve disease varied between 2% and 50% of the recommended rate,^4,5 which resulted in significant under-referral for operative intervention in patients with severe mitral regurgitation.

Previously, Birkmeyer and colleagues⁶ found a difference in mortality rate between the lowest and highest hospital volumes for mitral valve replacement. Gammie and associates⁷ also examined fatal outcomes in mitral valve surgery and showed a significant decline in both unadjusted and risk-adjusted mortality rates as hospital mitral procedure volumes increased. However, Gammie's study examined individual surgeons' mitral volume as a predictor of mitral repair rates. Bridgewater and co-authors,⁸ in the United Kingdom, proposed mitral repair best-practice standards of 25 annual mitral repairs per surgeon and 50 mitral repairs by any hospital unit. From this synopsis, it is noted that the inflection point at 40 isolated mitral cases per year could be a potential “minimum annual volume” basis by which to qualify an individual as a “reference” mitral valve surgeon.

Patient and surgeon factors both influence whether patients will undergo surgical mitral valve repair. However, the likelihood of mitral valve repair is very heavily influenced by individual surgeons' mitral valve volume. These findings create an opportunity to improve patient outcomes in mitral valve surgery⁹ through education of the cardiac surgical and cardiology communities.