Conclusions
MV surgery, including MVr, has continued to evolve over the past several decades[1,17]. MVr is widely accepted as both preferable and superior to replacement when the repair is expected to feasible, durable, and associated with a low morbidity and mortality[18]. In our recently published series of 446 patients undergoing MVr, survival was excellent at 97%, 96%, 95%, and 94% at 1,3, 5, and 10 years, and the cumulative incidence of progression of mitral regurgitation (MR) with mortality as a competing risk was 4.7%, 10.5%, 21.1%, and 35.8% at 1, 3, 5, and 10 years[14]. Other contemporary studies have also demonstrated excellent survival and low rates of MR recurrence, suggesting that in the era of evolving technologies, the excellent results obtained with surgical MVr should not be forgotten[19-21].
The optimal approach to the MV remains debatable. Minimally invasive approaches to the MV were developed, and continue to be developed and improved, with the hope of decreasing the morbidity and mortality associated with a standard sternotomy approach. While there are strong proponents of the minimally invasive approach, demonstrating a clear benefit over standard sternotomy has been difficult. Results of comparative studies are often contradictory, however, several studies suggest a minimally invasive approach can be associated with less blood product use, equivalent or shorter lengths of stay, decreased hospital readmissions, and equivalent perioperative morbidity and mortality[5-7,9-12]. The long-term benefits of minimally invasive MV approach when compared to a sternotomy approach are even less clear with far fewer studies with a comparator group and long-term outcomes. This is made more difficult by the lack of randomized controlled trials, and given lack of surgeon equipoise, the unlikelihood that an appropriately designed trial will be conducted.
The present study used a propensity score model to compare long term survival, need of mitral reoperation, and progression of mitral regurgitation with two surgical approaches to MVr, the standard sternotomy, and our preferred minimally invasive approach, the small right anterior thoracotomy. The principle findings of our study were that overall survival was at least equivalent between groups, and there were no differences in the need for MV reoperation or progression of mitral regurgitation over time between groups.
Overall survival was excellent with both surgical approaches, and is comparable to other reports[5,6,9,10,12]. Perioperative mortality was 1.5% in the sternotomy group and 0.4% in the small right anterior thoracotomy group, and 10-year survival was 91.4% in the sternotomy group and 97.0% in the small right anterior thoracotomy group. After propensity adjustment on baseline factors predictive of operative approach, there was a protective benefit for the small right anterior thoracotomy approach, which was independent of the type of MVr (HR 0.32, 95% CI 0.13-0.82, p=0.018). This protective benefit, while statistically significant, should be viewed with caution and should not be interpreted to suggest that a right anterior thoracotomy approach is superior to a standard sternotomy approach.
One should carefully interpret these results within the context of this study. The higher mortality rates in the sternotomy group likely reflects their sicker nature and inclusion of those needing coronary revascularization, despite risk adjustment. This is seen in our sensitivity analysis with lessening of survival “benefit” with removal of coronary revascularization patients indicating, albeit a good logistic model, all bias was not removed. However, the analysis does strongly support equivalent long-term survival between these two operative approaches. Patient selection (body habitus, anatomy, etc) partially accounts for our excellent minimally invasive results, for which we offer no apologies.
Our rates of MV reoperation and progression of MR over time are somewhat difficult to interpret in the context of the literature as we appropriately included death as a competing outcome. That said, the important finding here is that after risk adjustment for differences in selection of operative approach, there does not seem to be any more or less need for MV reoperation or progression of MR in either group.
There are numerous limitations to this study, some of which are discussed above. This was a retrospective cohort study from a single center and has the inherent limitations of this type of analysis. Selection to a surgical approach was not randomized and was highly biased based on preoperative characteristics. While we have attempted to adjust for these baseline differences with our statistical modeling, inherently not all bias is removed.
In conclusion, MVr via a small right anterior thoracotomy incision in select patients can be performed with surgical results and survival that are equivalent to the sternotomy approach. Growing evidence supports the safety and durability of less invasive MVr, making it the preferred approach of many experienced MV surgeons.