Limitations of studies
Limitations of this study are related to several limitations of the included studies. Firstly, available literature remains limited and data are derived from observational retrospective studies of relatively small cohorts of patients. Several studies included the control group of patients who underwent full sternotomy for a comparison; however, these groups of patients were not truly comparable in several aspects as they included patients with combined procedures and are biased with selection of patients for the minimally invasive David procedure. In addition, improved surgeon’s experience with the minimal access during the study period might have influenced outcomes, particularly timings of surgery. Furthermore, one of main limitations of these studies is that we still do not have available long-term follow-up data with echocardiographic findings. Interestingly, Monsefi and colleagues reported mid-term results with a mean follow-up of 3±2 years with completeness of 96%.11 Importantly, they reported 5-year freedom from reoperation of 93%  and 0% late mortality in their series with unremarkable predischarge echocardiographic findings in 99% of patients.11 However, the results were not propensity matched to the full sternotomy group as there were significantly more patients with type A aortic dissection (14% vs. 4%, p=0.03) and concomitant coronary artery bypass grafting (CABG) in the conventional group (21% vs. 4%, p<0.01).11
Two studies included propensity-matched analysis; however, these studies included carefully selected patients with many patients exclude from analysis.14, 15 While Charchyan and colleagues compared their results to 30 matched patients who underwent full sternotomy, they also included a significant number of patients with combined procedures which could influence outcomes (arch replacement 6.6% vs 9.9%, CABG 0% vs 9.9%, mitral valve reconstruction 9.9% vs 6.6%).15 They provide mid-term results with a mean follow-up of 13.8±10.3 months in the minimally invasive group, but unfortunately they did not report follow-up echocardiographic findings.15 Similarly, Hou and colleagues matched their results to 52 patients who underwent full sternotomy; however, they excluded around 21% (52 out of 269) of patients from their study.14  They also included patients with combined procedures in their propensity-matched analysis when compared to the full sternotomy group (7.7% vs. 11.5%).14  However, one of the strengths of their study is that they provided echocardiographic data after the average cumulative follow-up of 9 months, although with completeness of 91%.14 
Further large prospective randomized studies with long-term follow-up are still needed to confirm durability of minimal access technique and to investigate for which subgroups of patients this technique could be particularly useful.