CARDIOVASCULAR JOURNAL OF AFRICA • Volume 34, No 5, November/December 2023 304 AFRICA conditions.23 Studies have shown that the mechanism of POAF includes intra-operative and postoperative phenomena such as inflammation, oxidative stress, sympathetic activation and cardiac ischaemia, and these combine to trigger AF.21 There are many studies investigating the relationship between clinical risk factors, demographic conditions, and pre-, peri- and post-operative biomarkers to predict the development of POAF in CABG patients.24 Recent biomarkers that support clinical outcomes and show solid evidence have broadened the medical field and helped clinicians in many specialities to predict the clinical course.20 Previous studies have shown biomarkers to be used as predictors of patient condition after cardiac surgery.23 In this study, we evaluated the effect of the pre-operative and early postoperative values of RDW, one of the recently used biomarkers, which has been shown to predict the incidence of POAF in patients without a previous history of AF who have undergone isolated CABG with CPB. One potential cause of POAF is post-surgical inflammation, indicated by increased levels of inflammatory biomarkers such as CRP and Il-6.25 Although still a matter of debate, the role of these inflammatory biomarkers in the pathogenesis of POAF remains a subject of intense research.23 Anti-inflammatory agents used after CABG and/or valve surgery are an indication that inflammation plays a contributing role to POAF and reduce the incidence of AF.21 CRP and ESR are acute-phase reactants that increase in response to pro-inflammatory cytokines and other endogenous signals of innate immunity or tissue damage and are widely used as prognostic biomarkers in cardiovascular events.26 High pre-operative CRP levels were associated with POAF after CABG, but all studies emphasised that local stress and inflammation caused by surgery were more important than other causes of inflammation regarding POAF.27 Olesen et al. reported in their study that increased postoperative CRP levels after CABG were associated with POAF.28 Our study, which excluded patients with multiple risk factors for AF, showed high pre-operative and early postoperative CRP and ESR values to be independent risk factors for AF following isolated CABG. PLR and NLR, which are widely used as inflammation biomarkers, are known to be associated with poor prognosis in cardiovascular disease.12 Güngör et al. reported in their study that age and high pre-operative PLR levels were independent predictors of AF after CABG.29 In their systematic review and meta-analysis, Liu et al. emphasised that high pre-operative NLR level was a promising prognostic biomarker in predicting POAF after cardiac surgery, but larger-scale validation studies are needed to confirm the integration of pre-operative NLR testing into routine clinical practice.30 However, PLR and NLR inflammation indices were not evaluated in this study. RDW, which reflects the variability in the size of circulating red blood cells and is mostly used in the differential diagnosis of anaemia, is a new biomarker that has been associated with adverse cardiovascular events (myocardial infarction, atherosclerosis, heart failure, AF and left atrial thrombus) in many studies independently of other haematological indicators.10 Evidence from recent studies shows that RDW is a prognostic marker of AF in a variety of clinical settings.15 The first epidemiological study describing the relationship between RDW and AF was published in 2010 by Horne et al. In this prospective study, a total of 3 927 patients who underwent coronary angiography to define the frequency of cardiovascular disorders and complications (including AF) were evaluated after 30 days and one year, and an increased incidence of AF was observed with high RDW levels.31 Providencia et al. reported in their cross-sectional study that left atrial thrombus was significantly more common in patients with RDW ≥ 15.0% than in patients with a low RDW. This study included 247 patients who presented to the emergency department with symptomatic AF and underwent transoesophageal echocardiography to rule out left atrial appendage thrombus.32 In their retrospective study including 132 patients who underwent elective CABG surgery, Ertaş et al. reported that the risk of new-onset AF increased approximately 1.5 times in patients with RDW > 13.45%.33 Korantzopoulos et al. reported in their prospective study on 109 patients undergoing elective cardiac surgery that patients with RDW > 13.35% had a 46% higher risk of developing POAF during the hospital stay.34 Similarly, Pilling et al. reported that high RDW levels were associated with AF, and high RDW levels predicted new-onset AF in healthy volunteers.35 Jurin et al. reported in a recent study that RDW increased with enlargement of the left atrium and was independently associated with AF progression.36 In our study, the RDW levels in the pre-operative and early postoperative periods were significantly higher in the AF group compared to the non-AF group, and were consistent with previous studies. We also found that increased pre-operative and early postoperative RDW levels were an independent predictor for the development of early POAF in patients who underwent isolated CABG with CPB. In addition, we found that RDW levels were higher in patients with AF who had adverse events (such as stroke, heart failure, thromboembolism, mortality), which makes our study different from other studies. This result suggests that inflammation may be more active in patients in the AF group, reflecting increased RDW levels. Previous studies have shown the association between coronary artery disease and some haematological parameters, including high RDW level.37 Osadnik et al. reported that high RDW values were an independent predictor of mortality in patients with stable coronary artery disease.38 Another study has shown that high RDW value was a strong predictor of mortality and major adverse cardiac events in patients presenting with acute coronary syndrome (ACS).39 Rosas-Cabral et al. reported in their study that increased volume of erythrocyte distribution was associated with short-term cardiovascular mortality in patients with ACS.40 In another meta-analysis study, Abrahan et al. reported that RDW was associated with mortality and risk of major cardiovascular events in patients diagnosed with ACS.39 Our study showed that AF occurring after cardiac surgery was closely associated with high pre-operative and early postoperative RDW levels. This biomarker, like others, has shown good performance in predicting new-onset AF following cardiac surgery, which may offer clinicians the possibility of early intervention and treatment to reduce the incidence of complications related to AF. Limitations of the study A few limitations to our study should be mentioned. The primary limitation is that it included a limited, retrospective study population prone to prejudice, and it was a single-centre study,
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