2.1 Patients
This is a retrospective cohort analysis of adult patients (over 18 years of age) who underwent cardiac surgery for the first time for conventional open intervention of the MV between January 2006 and July 2018 at Fundación Cardioinfantil – Institute of Cardiology. MV exposure was performed through a Left Atrial (LA) or TS approach. The study included patients with MV stenosis (MVS) or insufficiency (MVI) of any etiology with indication for MV replacement (MVR) or repair (MVr) as a single procedure or combined with other types of valve surgery at the aortic, tricuspid or both, with and without coronary revascularization.
Patients who underwent other types of MV access, emergency interventions, history of cardiac arrhythmia, use of devices for rhythm control, resynchronization therapy, implantable cardioverter defibrillator (ICD) or both, were excluded from the present study.
We searched for potentially eligible patients by convenience sampling, extracting the information from the institutional electronic medical records and selected the patients who fulfilled the criteria, according to the Consort flow diagram.
2.1 Ethics Statement
The Clinical Research Ethics Committee of our institution approved the study (Act number 11-2017) and considered that there was no need for consent.
2.2 Surgical technique
Surgical procedures were performed by the Institution's group of nine cardiovascular surgeons throughout the study period. In all cases, cardiopulmonary bypass (CPB) was established with arterial cannulation in the ascending aorta and bicaval venous cannulation, with normothermia or mild hypothermia through active cooling. Cardioplegic solutions employed for myocardial protection included HTK solution (custodiol), cristaloid (St Thomas, Del Nido) or blood cardioplegia using St Thomas solution in a 4:1 ratio and Del Nido in a 1:4 ratio, administered by either antegrade and /or retrograde route. In the LA approach, access was achieved through a longitudinal incision posterior to the interatrial groove. For the TS approach a right oblique atriotomy was performed, followed by a longitudinal septal incision in the middle part of the floor of the fossa ovalis extending cranially over the roof of the left atrium.
2.3 Echocardiographic and hemodynamic data
Echocardiographic data was obtained from our institutional database. All preoperative studies were performed by our echocardiography lab, which is accredited by the Intersocietal Accreditation Commission. Variables evaluated were left ventricle ejection fraction (LVEF), pulmonary artery systolic pressure (PASP), left atrial diameter (LAD), type and severity of mitral and other types of valve dysfunction. The presence of hemodynamically significant CAD identified in the preoperative cardiac catheterization was recorded in the database. The variables were categorized to define groups of outcomes, according to the severity of the diagnosis.
2.4 Data and follow-up
Patient records were reviewed to obtain demographic data, prior medical history, and intraoperative variables including type of approach, valve interventions, coronary artery bypass grafting (CABG), myocardial protection strategy, CPB and cross-clamp times. During their hospitalization, all patients were monitored with continuous telemetry and any alteration of the rhythm was recorded in the medical records. Thirty day-postoperative follow-up was included in our database. Long-term follow-up was performed through telephone interviews and outpatient clinic visits. Patients were evaluated for the appearance of atrial fibrillation (Afib), flutter, other supraventricular arrhythmias, bradyarrhythmias or blocks, the use of antiarrhythmics, the need for electrical cardioversion, implantation of permanent pacemaker (PPM), and ICU length of stay.
2.5 Statistical analysis
All preoperative, perioperative and 30-day variables were recorded in our database, which follows the guidelines established by the Society of Thoracic Surgeons. Long-term follow-up variables were recorded by extracting data from institutional registries and by telephone survey.
Continuous variables are presented as mean ± one standard deviation (SD) or as median and interquartile range (IQR). Preoperative and postoperative data were compared using the t- test or the Mann-Whitney U test for continuous variables, according to the sample distribution of normality (Kolmogorov-Smirnoff test) and categorical variables were expressed as the number and percentage of the cases within each category and groups compared using the Chi-square test or the Fisher's exact test. Statistical significance was assumed with p <0.05. Data processing was carried out using the Statistical Package for the Social Sciences - SPSS version 25 software for Windows.
In order to control the selection bias of the sample, we performed a propensity score matching (PSM), using the Nearest Neighbor method, according to the similarities in the standardized differences between a case comparing it with 2 controls (matching 1:2), ordered from highest to lowest, without replacement of the data and setting a reference caliper of 0,2 (14).
Variables included in the calculation of the propensity score were sex, age, LVEF, PASP, LAD, preoperative creatinine, preoperative hematocrit, MVS (absent, mild, moderate, severe), MVI (absent, mild, moderate, severe), aortic valve disease (absent, stenosis, insufficiency, double injury), CAD, 3 Vessel disease and/or left main trunk compromise, TV disease (≥ moderate), Euroscore II risk (%), diabetes mellitus, hypertension, COPD, stroke, CKD, PAD, pre-surgical use of beta-blockers and statins, mitral valve surgery (valvuloplasty, bioprosthesis or mechanical prosthesis), CABG, aortic valve replacement, tricuspid valve surgery.
A secondary analysis was performed splitting the data according to the follow up time in first and second half, to check if consistent results would come up compared to the primary outcomes analysis.
The Kaplan–Meier method and log-rank test were used to estimate and compare the survival rates between the 2 matched groups.