This study was 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 MV between January 2006 and July 2018 at Fundación Cardioinfantil – Instituto de Cardiología. MV exposure was performed using a left atrial (LA) or TS approach. The study included patients with MV stenosis (MVS) or insufficiency (MVI) of any aetiology 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 revascularisation.
Patients who underwent other types of MV access, emergency interventions, history of cardiac arrhythmia, use of devices for rhythm control, resynchronisation 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 selecting 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 decided that there was no need for consent. All methods were performed in accordance with the Declaration of Helsinki
2.2 Surgical technique
Surgical procedures were performed by the Institution's group of nine cardiovascular surgeons throughout the study period. Cardiopulmonary bypass (CPB) was established with arterial cannulation in the ascending aorta and bicaval venous cannulation in all cases, with normothermia or mild hypothermia via active cooling. The cardioplegic solutions used 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 via an antegrade and/or retrograde route.
2.2.1 Left atrium approach
After CPB was established, we performed a vertical left atriotomy anterior to the right superior pulmonary vein and posterior to the interatrial sulcus. The incision was extended superiorly behind the superior vena cava and inferiorly into the oblique fissure. MV retractors were used to expose the left atrium. Left heart venting was achieved via the right superior pulmonary vein, left atrium, pulmonary artery, or aortic root. After completion of the procedure, the left atriotomy was closed using a single layer of nonabsorbable suture.
2.2.2 Superior Transseptal approach
After CPB was established, we performed a vertical right atriotomy parallel to the atrioventricular sulcus. A vertical septal incision was made through the fossa ovalis, avoiding the coronary sinus and extending into the roof of the left atrium. MV retractors were used to expose the left atrium. Left heart venting was achieved via the right superior pulmonary vein, left atrium, pulmonary artery or aortic root. After completion of the procedure, the left atriotomy in the roof of the left atrium, the vertical incision in the interatrial septum and the right atriotomy were closed using a single layer of nonabsorbable suture.
2.3 Echocardiographic and haemodynamic data
Echocardiographic data were obtained from our institutional database. All preoperative studies were performed by our echocardiography laboratory, which is accredited by the Intersocietal Accreditation Commission. The 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 haemodynamically significant CAD identified in the preoperative cardiac catheterisation was recorded in the database. The variables were categorised 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 hospitalisation, 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 via 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 telephone survey.
Continuous variables are presented as medians and interquartile range (IQR). Preoperative and postoperative data were compared using Mann-Whitney U test for continuous variables. Regarding categorical variables, these are expressed as absolute and relative values within each category, groups were compared using the chi-squared test or Fisher's exact test. Statistical significance was assumed at p <0.05. Data processing was performed using the Statistical Package for the Social Sciences - SPSS version 25 software for Windows.
To control the selection bias of the sample, we performed propensity score matching (PSM) using the nearest neighbour method, according to the similarities in the standardised 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 calliper of 0.2 (14).
Variables included in the calculation of the propensity score were sex, age, LVEF, PASP, LAD, preoperative creatinine, preoperative haematocrit, 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 (³moderate), Euroscore II risk (%), diabetes mellitus, hypertension, COPD, stroke, CKD, PAD, pre-surgical use of beta-blockers and statins, MV surgery (valvuloplasty, bioprosthesis or mechanical prosthesis), CABG, aortic valve replacement, and tricuspid valve surgery.
A secondary analysis was performed by splitting the data according to the follow-up time in the first and second halves to check whether consistent results would be obtained compared to the primary outcome analysis.
The Kaplan–Meier method and log-rank test were used to estimate and compare the survival rates between the 2 matched groups.