Effects of seasonal and climate variations on in-hospital mortality and length of stay in patients with type A aortic dissection

Acute aortic dissection (AAD) is one of the cardiovascular diseases associated with the highest risk of mortality. Especially, Stanford type A AAD is life-threatening that requires emergency surgical intervention [1]. Therefore, identification of risk factors affecting the outcomes is valuable for risk stratification and prognostication. Previous studies have reported that the incidence of cardiovascular disorders including coronary heart disease, stroke, supra-ventricular tachycardia and heart failure are associated with distinct seasonal variations [2‐4], with peak hospital admission reported during the winter. Also, a peak incidence of type A AAD has been observed in winter but lowest in the summer, while the average temperature on the day of patient admission with AAD is higher than that without AAD [5‐8]. Nevertheless, evidence is lacking on the association of seasonal and climate variations with in-hospital mortality and length of stay (LOS) in postoperative patients with AAD, which formed the basis of this study.

This study was approved by the ethics committee of Fujian Medical University, China.

The occurrence of AAD is multifactorial but primarily associated with three key factors: weakened aortic wall, damaged vascular endothelial resulting in the formation of the vascular endothelial slap, and the extension of endothelial damage due to hypertension [12]. Previous studies have demonstrated the relationship between numerous cardiovascular disorders with seasonal and climatic variations, including external environmental factors such as temperature and UV radiation, lifestyle factors such as diet, obesity, exercise and smoking, and other factors such as blood pressure, serum cholesterol, glucose tolerance, coagulation, acute and chronic infections [13, 14]. All these risk factors are more common in the winter and may account for seasonal variations in the incidence of AAD [15, 16]. Several studies have also suggested a possible seasonal effect on the onset of AAD, given an observed higher incidence of AAD in the winter and a lower incidence of AAD in the summer [5‐8]. During the winter, the human sympathetic nervous system is activated with an increased catecholamine secretion to cope with the low temperature, resulting in increased heart rate, peripheral vascular resistance, and systemic blood pressure. High blood pressure then leads to increased blood friction against the vascular wall and surface shear stress, which enhances the occurrence and rupture of aortic dissection [17]. To date, limited studies have explored the impacts of seasonal and climatic variations on the postoperative outcomes of AAD patients.

A significant increase in the incidence of non-accidental mortality in the general population has been reported during the transitional season. A study has demonstrated a higher mortality rate during the seasonal transition from hot to cold (autumn) than that from cold to hot (spring) in Russia [18]. Also, large diurnal temperature variation leading to increased risk of cardiac mortality in autumn has also been observed [19, 20]. Unlike the regular seasonal and climatical patterns in the incidence of AAD, our univariate and multivariate regression analysis revealed patients with onset of AAD in autumn were significantly associated with a higher risk of mortality, although no significant link between other climatic factors and in-hospital mortality, such as the average minimum temperature on the day of onset of AAD, average daily temperature difference and average AQI. Numerous studies have shown that seasonal meteorological variations affect blood pressure readings in hypertensive and normotensive individuals [21‐23]. In China, the weather becomes cool and humid in autumn due to frequent rainfalls and the atmospheric pressure (AP) fluctuates intensely [24]. The reduction in temperature and fluctuation in AP may lead to increased sympathetic activity, resulting in increased vasoconstriction or vasospasm and higher blood pressure consequently [25]. Also, the fluctuation of AP may increase the risk of rupture of the abdominal aortic aneurysm [26, 27]. Similarly, drastic fluctuations of systolic blood pressure in patients with AAD as a result of an increased alteration of AP in autumn may cause a greater risk of postoperative rupture of residual endothelial dissection, leading to a significantly higher in-hospital mortality rate in our study. Alternatively, other meteorological risk factors such as humidity, rainfall, etc. may also contribute to the impacts of seasonal and climatic variations on the prognosis of patients [28]. On the other hand, our analyses also revealed that coronary heart disease and admissions from outpatient settings were adverse factors associated with an increase of postoperative in-hospital mortality, suggesting that timely intervention of coronary heart disease and emergency surgery may reduce postoperative mortality.

Our analyses have also revealed that factors including the onset of AAD in autumn and hypertension were independent risk factors associated with a prolonged hospital LOS. Understandably, due to the significantly higher in-hospital mortality rate in autumn, the corresponding severe postoperative patients resulted in the increased LOS.

In patients undergoing surgery for AAD, factors including admission in autumn, coronary heart disease, renal dysfunction, malperfusion syndromes and admission from outpatient settings are associated with increased risk of postoperative in-hospital mortality. Meanwhile, patients with hypertension and admitted in autumn have longer hospital LOS following surgery for AAD. The temperature transition in autumn may be a factor that increases the risk of in-hospital mortality from type A AAD, especially in patients complicated with coronary heart disease, renal dysfunction, malperfusion syndromes. Urgent surgery for type A AAD is very necessary. Nevertheless, further studies are warranted to validate our findings.