IJCS | Volume 33, Nº2, March / April 2020

159 in the perioperative period and a positive water balance greater than 1,500 mL in the 48 after surgery. 14 To this end, we sought to create and validate a risk stratification score of POAF, using preoperative and early postoperative indicators in patients undergoing cardiac surgery. Material And Methods Population and sample The present study consists of a prospective analysis of 1,054 patients at the Institute of Cardiology of Rio Grande do Sul/University Foundation of Cardiology ( Instituto de Cardiologia do Rio Grande do Sul/Fundação Universitária de Cardiologia - lClFUC). Study sample consisted of patients who underwent valve surgery and/or myocardial revascularization at the ICIFUC, andwas collected during two periods, between 2002 and 2005 (n = 448 patients) and between 2010 and 2011 (n = 606 patients). Study design This was an observational prospective cohort study. Inclusion criteria Patients aged 18 years or older who underwent valve surgery (mitral and/or aortic valve replacement) and/ or myocardial revascularization surgery were included. Patients who underwent additional procedure associated with any of these surgeries were also included. Exclusion criteria Patients who underwent emergency procedures, and patientswithAF(detectedbystandardelectrocardiography and 24-h ambulatory electrocardiographic monitoring) were excluded. Study variables The following variableswere evaluated in the validation cohort: gender, age, presence of mitral valve disease (severe regurgitation and/or severe stenosis), use of beta- blockers in the preoperative period, discontinuation of beta-blocker therapy in the postoperative period, presence of a positive water balance greater than 1,500 mL within 48 hours after surgery, duration of hospitalization and in-hospital mortality. Outcome The diagnosis of POAF was considered an outcome in the perioperative period. POAF was desfined as an episode of arrhythmia, with electrocardiographic tracing with an irregular baseline secondary to disorganized atrial activity, which is referred to as the so-called “f” waves generating variable RR cycles. Episodes of POAF lasting longer than 15 minutes or requiring medical intervention were considered in the study due to the symptomatology or hemodynamic instability. Patients were monitored continuously for 72 hours, and daily electrocardiograms were obtained during hospitalization. In case of cardiovascular symptoms, additional monitoring was performed. Procedures Anesthesia and cardiopulmonary bypass (CPB) were performed according to local standard protocols. After cardiac surgery (immediate postoperative period), the patient remaining for 48 hours or longer in the intensive care unit. Statistical analysis Continuous variables with normal distribution were described as means and standard deviations. The hypothesis of normalitywas verified by the Kolmogorov- Smirnov test. Categorical (or categorized continuous) variables were described as counts and percentages and compared using the chi-square test or Fisher’s exact test, when necessary. For construction of the risk score, a derivation cohort was collected between 2002 and 2005, and a validation cohort was collected during 2010-2011. Multivariate analysis with backward selection was applied. Statistical significance was set at p < 0.05. Preliminary model of the risk score Variables used for analysis were selected based on biological plausibility (association with POAF) and data from literature on POAF. A total of 67 variables were studied in the derivation cohort 14 of 448 patients included between 2002 and 2005. Variables associated with POAF were selected in a multiple logistic regression model with backward selection, and those with p-values close to 0.05 in the model were maintained. Then, b coefficient of the logistic Ronsoni et al. POAF risk score Int J Cardiovasc Sci. 2020; 33(2):158-166 Original Article