In this retrospective propensity score-matched cohort study, atrial fibrillation with PHTN had a higher risk-adjusted POD, compared with non-atrial fibrillation patients underwent non-cardiac, non-obstetric surgery. This association was reliable in additional models.
In our study, 29% (151/518) of patients with PHTN and atrial fibrillation, which was higher than the proportion of patients reported in previous studies. They reported that 4%-16% of patients with PHTN had atrial fibrillation[7]. The main reason for this gap may be that with advances in technology, smart devices can easily be used in large-scale population screening for undiagnosed atrial fibrillation. Another reason may be related to obesity. The average BMI of patients in this study was greater than 31 kg/m2, which was confirmed in other studies[14]. Studies found that the occurrence of perioperative atrial fibrillation associated with POD, but most of them focused on cardiac surgery[15–18].
The incidence of POD in the present study was 5.8%, which was different from the literature reported before, this discrepancy may be due to anesthesia, surgery and study populations[19–21]. Delirium varies significantly between surgical populations. In high-risk surgery, 36% − 40% of adult patients developed to postoperative delirium, whereas in low-risk surgery, the prevalence of delirium is 5% − 10%[22]. Most POD studies focused on the elderly, hip and cardiac surgery[20, 23, 24]. However, the patients only recruited were an adult underwent non-cardiac, non-obstetric surgery in this study, and the time and method for POD assessment was not provided in sufficient detail in the original paper[10], which may lead to the differences in the incidence rate of POD.
It is still unclear the mechanism of atrial fibrillation associated with POD in patients with PHTN. Vascular-mediated cognitive decline is one of the aspects in most studied[25–28], the rate of cardio-embolic stroke attributable to atrial fibrillation will continue rising with the aging of the population[28, 29]. The simultaneous conditions of atrial fibrillation leading to micro-embolization phenomena could be responsible for the occurrence of delirium[18]. These micro-emboli could lead to low perfusion of some brain regions and cerebral ischemia, which could represent the mechanisms for the onset of delirium. Published studies have revealed the presence of micro-emboli during cardiac surgery detected by imaging exams such as trans-cranial Doppler, but the results remain contradictory[30]. Another heart rate variability analysis found that preoperative high-frequency power was significantly lower in delirium patients than in non-delirium patients. Preoperative measurement of heart rate variability may be a useful predictor of delirium[31]. Therefore, abnormal autonomic activity may also be one of the mechanisms of postoperative delirium.
Fátima R et al. found that atrial fibrillation after surgery was identified as an independent risk factor for delirium after cardiac surgery, but persistent preoperative atrial fibrillation was not a predictor of delirium after intervention[18]. The occurrence of postoperative atrial fibrillation and its association with delirium favors the hypothesis of cerebral embolism and/or hypotension leading to a reduction of cerebral perfusion that can explain the pathophysiology of delirium[32, 33]. However, We found that preoperative atrial fibrillation is an independent risk factor for POD, and the results of multi-model adjustment after controlling for confounding factors are still robust ( OR = 3.64, 95% CI: 1.1–12.11, P = 0.035). The sensitivity analysis results also support our results (OR = 3.14, 95% CI: 1.08–9.13, P = 0.035). In addition, our results are consistent with previous studies, they believe that preoperative atrial fibrillation is one of the main inducing factors and independent predictors of postoperative delirium[15, 16], and can even be used as a non-mental predictor of postoperative delirium[6].
Whatever, we still need high attention to vascular-mediated cognitive decline in patients with atrial fibrillation. Preventing postoperative delirium and cognitive decline in patients with atrial fibrillation is an important goal of ongoing research. Better methods to prevent vascular brain injury will be necessary to prevent an increasing neurologic burden that will accompany the expected increase in the prevalence of atrial fibrillation in the coming decades. What’s more, we need to explore some biomarkers-based risk predictors for early detection of postoperative cognitive injury. In addition, preoperative atrial fibrillation is inevitable. We should pay attention to effective prevention of atrial fibrillation while focusing on prevention of complications. Studies have shown that effective prevention can reduce cardiovascular mortality and hospitalization rates in patients with a history of atrial fibrillation[34].
We acknowledge limitations with our secondary analysis in a retrospective study. First, the potential for residual confounding may exist, as with all retrospective analyses. We adjusted as many possible confounders as we could and balanced participants in the propensity score-matched cohorts in this study. Second, the study population was comprised only patients with PTHN underwent elective non-cardiac, non-obstetric surgery; therefore, our findings may not be generalizable to other patients. In addition, the study cohort included very few patients with severe PHTN (PASP ≥ 59 mmHg), likely due to the lower prevalence of severe PHTN and the tendency to avoid elective surgery in such high-risk patients. We did not do any subgroup analysis. Nevertheless, our results remained robust and reliable in adjusted multivariable logistic regression analysis. Third, the original study did not include a matched case control cohort of non-PHTN patients, and thus cannot make conclusions about outcome differences between patients with and without PHTN. Finally, we were unable to distinguish the number of patients with postoperative atrial fibrillation due to the lack of a specific description of the type of new postoperative arrhythmias in the original article, so no further analysis of the association between postoperative atrial fibrillation and POD was performed.