IJCS | Volume 33, Nº2, March / April 2020

163 Figure 2 - Increase in the risk (expressed in %) for development of postoperative atrial fibrillation according to the score. Likelihood for the development of postoperative atrial fibrillation (%) Risk score Table 4 - Risk scores and frequency of postoperative atrial fibrillation (n = 1,054) Score Sample (n = 1058) POAF (n) POAF (%) Risk category 0 189 14 7.4 Low 1 and 2 307 36 11.7 Medium 3 to 5 382 181 30.9 High 6 to 8 180 104 57.8 Very high the risk of occurrence of POAF in a sample rather than individually. 21 The incidence of POAF in this study was 25.7%, and when only valve surgeries combined with revascularization were considered, this number was 34.3%. This incidence is similar to the means reported in the literature. 3,22,23 It is worth mentioning that we used continuous monitoring only in the period of intensive therapy and after intermittent electrocardiography, which may have underestimated the cases of asymptomatic POAF. Few studies 24,25 used continuous monitoring and reported prevalence rates of 44% to 64%. Therefore, the literature demonstrates a high prevalence of asymptomatic POAF that is generally greater than 25%, underscoring the need for indetifying factors that contribute to POAF, which was the main objective of this study. The findings of longer hospitalization and increased early and late mortality associated with the occurrence of postoperative arrhythmia are consistent with the findings reported in the literature that strongly suggest that the prognosis of POAF patients is compromised in the long term. 7,25-27 Age greater than 70 years was an important predictor of POAF in this study, adding two points to the score. Age as a predictor of POAF was reported to stratify the risk factors associated with arrhythmia. 16,28 Mathew et al. 26 demonstrated that a one-decade increase in age leads to a 75% increase in the risk of developing POAF; the authors also reported that patients older than 70 years were at high risk regardless of other clinical characteristics. Zaman et al. 28 showed that patients over 60 years of age have a 3.8-fold increased risk for development of AF compared with the population under 60 years, and such risk is likely related to atrial dysfunction and fibrosis. These factors are linearly Ronsoni et al. POAF risk score Int J Cardiovasc Sci. 2020; 33(2):158-166 Original Article