IJCS | Volume 33, Nº2, March / April 2020

161 Table 1 - Characteristics of the sample and univariate analysis Variable Total (n = 1054) POAF (n = 272) Non-POAF (n = 782) RR 95% CI p Age ≥ 70 years 281 (26.8%) 141 (41.9%) 167 (21.2%) 2.67 1.99-3.59 < 0.0001 Mean age ± SD 60.1 ± 12.1 Male 690 (65.2%) 182 (66.9%) 508 (64.6%) 1.1 0.82-1.48 0.507 Type of surgery Revascularization 675 (63.8%) 141 (51.8%) 534 (67.9%) 1 Valve surgery 306 (28.9%) 105 (38.6%) 201 (25.6%) 1.98 1.45-2.70 < 0.001 Combined 77 (7.3%) 26 (9.6%) 51 (6.5%) 1.93 1.11-3.28 0.14 Mitral valve disease 109 (10.3%) 46 (16.9%) 63 (8%) 2.33 1.55-3.51 < 0.001 Absence of beta-blocker 454 (42.9%) 197 (72.4%) 257 (32.7%) 5.40 3.98-7.33 < 0.001 Water balance > 1,500 mL 685 (64.7%) 203 (74.6%) 482 (61.3%) 1.85 1.36-2.52 < 0.001 *p-values: Fisher’s exact test; POAF: postoperative atrial fibrillation; CI: confidence interval. Table 2 - Logistic regression and multivariate risk score (derivation – n = 448) Variable B p RR 95% CI Points Age ≥ 70 years 0.96 < 0.001 2.67 1.59-4.48 2 Mitral valve disease 0.77 0.03 2.18 1.08-4.35 1 Absence of beta-blocker 0.91 < 0.001 2.49 1.53-4.03 1.5 Water balance > 1,500 ml 0.5 0.06 1.65 0.96-2.83 0.5 Constant -2.471 < 0.001 0.08 and validation cohorts. Using the variables described, multiple logistic regression was performed, resulting in a recalibrated risk score based on the importance of the coefficient β of the logistic equation (Table 3). Variables related to the development of POAF included age (≥ 70 years), mitral valve disease, the non-use or discontinuation of beta-blockers and a positive water balance greater than 1500 mL. The area under the ROC curve of the obtained model was 0.76 (95% Cl 0.72- 0.79) (Figure 1). Table 4 and Figure 2 present the risk of POAF according to the score and the classification of this risk (additive score). There was a progressive increase in the proportion of the event, exhibited by an increase in the score: very low risk (score 0) = 0.0%; low risk (score 1 and 2) = 3.9%; intermediate risk (score 3 to 5) = 10.9%; and high risk (score 6 to 8) = 60.0%; p < 0.0001. The logistic equation should be used for risk assessment in the development of POAF individually (Table 3). In the total sample, 46.8% of the operated patients had low andmedium risk. The score predicted POAF in 7.4% of individuals at low risk and 11.7% of those at medium risk; 17% of the total sample was classified as very high risk. To test the calibration of the final score, the observed POAF was compared with that predicted in each of the four classification intervals of the score, resulting in a predicted/observed correlation coefficient of 0.99 with x² = 0.98 (p = 0.98) (Hosmer-Lemeshow test) (Figure 3). Ronsoni et al. POAF risk score Int J Cardiovasc Sci. 2020; 33(2):158-166 Original Article