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.