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OBJECTIVE: Minimally invasive mitral valve surgery (MIMVS) is a safe and feasible technique for mitral valve repair and replacement with reported benefits including shorter hospital stays and decreased bleeding. This study’s objective was to apply an evidence-based approach to better define populations benefiting from MIMVS.
METHODS: A single institution’s STS Adult Cardiac Surgery Database was retrospectively reviewed for patients undergoing mitral valve surgery from 2002-2015. Concomitant operations, cardiogenic shock, age <40 years, or salvage operation were exclusion criteria (N= 2,879). Patients were stratified by age group and surgical approach - median sternotomy (N=2255) vs minimally invasive port access (MIS; N=858). Chi-squared and logistic regression analyses were applied to identify associations between surgical approach and outcomes (Table 1).
RESULTS: MIS decreased in older cohorts and patients with comorbidities. Controlling for differences in baseline characteristics, MIS was associated with 66% reduction in the likelihood of postoperative renal failure (p=0.008) and halved the likelihood of prolonged intubation (p<0.0005). Logistic regression identified older age, diabetes, and moderate to severe lung disease as statistically significant predictors of postoperative renal failure and prolonged intubation; preoperative dialysis was also significantly associated with prolonged intubation. There were significant reductions in length of stay (LOS) of at least 2.8 days across all groups and decreased blood transfusions in older cohorts.
A subgroup analysis of patients without diabetes, dialysis-dependence or moderate to severe lung disease revealed significant reductions in postoperative renal failure (3.9% v 0.7%, p<0.0005), pacemaker requirement (2.7% v 1.3%, p=0.03), 30 day mortality (3.8% v 1.2%, p<0.0005), and ventilator times (13.1% v 5.1%, p<0.0005), associated with MIS. Diabetic patients had no significant differences in outcomes related to surgical approach, though LOS was significantly shorter with MIS (15.7 v 9.6 days, p=0.001).
CONCLUSIONS: MIMVS confers significant benefits to patients without major comorbidities and has equivalent outcomes to open surgery in those with comorbidities. It is associated with significantly reduced LOS across all groups. MIMVS should be considered in all patients requiring mitral valve surgery.

Table 1: Demographics and Outcomes Stratified by Surgical Approach

Age Groups:	Group 1 : 40-54 Yrs (N=686)	Group 2: 55-64 Yrs (N=768)	Group 3: 65-74 Yrs (N=728)	Group 4: >75 Yrs (N=697)
Pre-existing Diabetes (open v MIS)	11.6% v 4.3% (p=0.001)	22.1% v 10.5% (p<0.0005)	24.3% v 13.2% (p=0.001)	23.1% v 6.4% (p<0.0005)
Renal failure on dialysis (open v MIS)	10.5% v 1.4% (p=0.001)	7.0% v 2.1% (p=0.03)	3.9 v 0% (p=0.03	2.4% v 0% (p=0.22)
Moderate-severe lung disease (open v MIS)	6.2% v 2.5% (p=0.02)	8.2% v 4.6% (p=0.08)	7.7% v 2.6% (p=0.004)	9.6% v 8.2% (p=0.031)
30 day readmission (open v MIS)	8.6% v 6.9% (p=0.44)	6.6% v 3.4% (p=0.07)	5.9 v 5.0% (0.55)	4.8% v 1.9% (p=0.16)
Postoperative renal failure (open v MIS)	1.8% v 2.0% (p=0.84)	4.3% v 0.4% (p=0.004)	7.6% v 1.1% (p=0.001)	9.5% v 1.8% (p=0.007)
Postoperative Stroke (open v MIS)	0.7% v 0.8% (p=0.84)	2.1% v 0.4% (p=0.09)	3.3% v 2.6% (p=0.64)	3.9% v 1.8% (p=0.28)
30 day mortality (open v MIS)	2.5% v 1.2% (p=0.26)	3.4% v 0% (p=0.004)	5.4% v 3.7% (p=0.36)	8.5% v 3.6% (p=0.08)
Prolonged intubation (open v MIS)	12.2 v 3.3% (p<0.005)	14.0% v 4.6% (p<0.005)	20.4% v 9.9% (p<0.005)	26.9% v 15.5% (p=0.01)
Length of stay, days (open v MIS)	9.6 v 6.8 (p<0.005)	10.9 v 7.4 (p<0.005)	12.7 v 8.4 (p<0.005)	14.0 v 10.4 (p<0.005)