Discussion
In patients with IMR, the current ACC/AHA practice guidelines do not specify whether to repair or replace the mitral valve to treat severe IMR [17]. In reality, the decision to repair or replace the mitral valve depends on multiple factors, including the clinical presentation and patient comorbidities. While mitral repair for IMR usually comprises an undersized ring annuloplasty, the decision with regards to technique may also be influenced, particularly, when there is more complex pathology (severe tethering, basal aneurysm/or dyskinesis, coaptation depth greater than 10 mm, or a markedly dilated left ventricle), by the “repairability” of the valve, which is in part dependent on the surgeon’s experience in mitral valve repair. The controversy over the relative benefits and risks of mitral repair in this challenging patient population have led some surgeons to consider chordal-sparing mitral valve replacement as the most conservative approach to minimize the risk of early or late failure of valve repair. This strategy is supported by a randomized controlled trial conducted by the Cardiothoracic Surgical Trials Network (CTSN) which reported no difference in LV reverse remodeling or survival either at 12 months [16], or at 24 months [18] between patients who had mitral valve repair and those who underwent chordal-sparing mitral valve replacement. However, the recurrence of either moderate or severe mitral regurgitation was considerably higher in the repair group than in the replacement group (32.6% vs. 2.3%, P<0.001 at 12 months [16] and 58.8% vs. 3.8%, P<0.001 at 24 months [18]). While mortality did not differ between groups in the CTSN trial, the trial was not powered to detect differences in survival. In contrast, a recent meta-analysis that included this CTSN trial [19] and previous five meta-analyses [20-24] reported lower 30-day mortality associated with MVr compared to MVR.
Likewise, our findings are in line with multiple retrospective studies [8-10, 12], which have suggested higher mortality with MVR compared to MVr.
The observed hospital mortality of MVR and MVr in our study (5.8% and 13.3% for repair and replacement groups, respectively) are comparable to those reported by Grossi et al. (10% and 20%) [13] Milano et al. (6.3% and 18.9%) [14], and Magne et al. (9.7% and 17.4%) [15], for repair and replacement groups, respectively, in a similar era. Gillinov et al. [8] reported a 13% overall 30-day mortality (both repair and replacement) in all patients undergoing surgery for IMR, which is comparable to our overall 30-day mortality (10%). A report from the Society of Thoracic Surgeons (STS) database [25] which included 26,463 patients undergoing MVR/MVr + CABG operations between mid-2011 and mid-2014 reported mortality rates of 4.9% and 8.7% for repair and replacement with CABG, respectively, indicating a continued improvement in early survival outcomes with time.
In our study, mortality was predicted by urgent surgery, LVEF less than 40%, and age. Thourani and associates [9] reported increasing age (OR 1.53 per 10-year increments in age), urgent (OR 3.03) and emergent surgery (OR 9.18), and mitral valve replacement (OR 1.72) as independent predictors of mortality. Similarly, Maltais et al. [28] reported that redo surgery (hazard ratio = 3.39; P < .001) age (hazard ratio = 1.5; P = 0.03), urgent or emergent surgery (hazard ratio = 2.08; P = 0.007) and low LVEF (hazard ratio = 1.31; P = 0.026) were the only independent predictors of one-year survival. In this study, the performance of mitral valve repair versus replacement did not affect survival.
Moreover, data from both randomized trials [16] and observational studies [29] have noted a higher rate of recurrent mitral regurgitation with mitral valve repair, and recurrent MR of moderate or greater severity has been independently associated with worse long-term outcomes [29]. However, improved late survival after MVr has been reported both by a retrospective study [10] and a meta-analysis of nine studies, despite significant rates of recurrent mitral regurgitation after repair. Nevertheless, we believe that the decision between MVr and a chordal-sparing MVP may be best decided based on individual patient demographics, anatomic factors, and the surgeon’s experience.
Our study has several strengths. First, previous observational studies are limited by the inclusion of some patients with nonischemic mitral regurgitation. In our study, we rigorously reviewed the preoperative recent cardiac imaging, pathology reports, and operative notes to verify a purely ischemic etiology. Second, all data were prospectively collected by a single independent, experienced operator. Therefore, the probability of selection, information, or ascertainment bias is reduced. Third, we had very low missing data (<1%) for all variables collected in the database. Because this study focused on short-term (30-day) operative outcomes, loss to follow-up was not an issue. The main limitation of our study is the lack of long-term survival and echocardiography data. However, our primary aim was to compare short-term hospital outcomes between MVr and MVR in patients with IMR.