Coronary atherosclerotic disease (CAD) is the main source of cardiovascular disease (CVD), causing more than 7 million deaths worldwide each year. In recent decades, there have been substantial declines in cardiovascular disease mortality across much of Europe [1]. The latest guidelines from the European Heart Association, published in 2019, indicate that CAD is a pathologic process characterized by atherosclerotic plaque accumulation in the epicardial arteries, which is either obstructive or non-obstructive [2]. Acute coronary syndrome (ACS) refers to an acute ischemic syndrome of the heart caused by new thrombosis secondary to rupture or erosion of an unstable coronary artery atherosclerotic plaque. It includes unstable angina and acute myocardial infarction (AMI), either ST-segment elevation myocardial infarction (STEMI) or non-STEMI (NSTEMI).

AMI is associated with high morbidity and mortality. Mortality is influenced by many factors, including advanced age, smoking status, and the presence of hypertension, diabetes mellitus (DM), dyslipidemia, or obesity. Elevated levels of liver transaminases, specifically alanine aminotransferase (ALT) and aspartate aminotransferase (AST), are used as markers of hepatic dysfunction and have attracted attention as emerging risk factors for CVD.

Recent studies have investigated the role of liver transaminases as independent predictors of cardiac-related morbidity and mortality [3, 4]. Several prospective epidemiologic studies have suggested that hepatic dysfunction is common in cardiac disease [5, 6]. When no other causes of liver injury are identified, elevations of liver aminotransferases are associated with an elevated risk of cardiac-related mortality [7]. The goal of this study was to evaluate the association between elevated liver transaminases and in-hospital all-cause mortality in patients with AMI.

The diagnostic criteria for AMI were in accordance with the 2017 guidelines from the European Society of Cardiology (ESC) [8]. Myocardial injury was defined as at least one cardiac troponin value above the 99th percentile upper reference limit. STEMI was defined as persistent chest discomfort or other symptoms suggestive of ischemia and ST-segment elevation in at least two contiguous leads. Ischemic symptoms in the absence of ST-segment elevation at presentation were designated as NSTEMI [8]. Hypoxic liver injury (HLI) was defined as at least one serum transaminase level more than twice the upper limit of normal (ULN). The ULN for ALT was defined as 50 U/L for men and 40 U/L for women, whereas the ULN for AST was defined as 40 U/L for men and 35 U/L for women. The World Health Organization (WHO) defines impaired fasting glucose as a fasting plasma glucose (FPG) value of 6.1 mmol/L or higher, whereas the American Diabetes Association recommends a cutoff value of 5.6 mmol/L [9]. In this study, we used the WHO cutoff value. Estimated glomerular filtration rate (eGFR) was calculated as 175 × plasma creatinine^–1.234 × age^–0.179 × 0.79 if female [10]. Elevated D-dimer level was defined as a serum concentration ≥ 400 ng/mL and increased fibrinogen was defined as a serum concentration ≥ 3.5 g/L.

One of the most important factors associated with an increased risk of in-hospital mortality in patients with an AMI was an elevated ALT. The liver is a vital organ that is very sensitive to hemodynamic changes because of its complex vascular system and high metabolic activity [11]. Every 10-mm Hg decrease in arterial blood pressure decreases hepatic arterial blood flow by approximately 10% [12]; therefore, abnormal serum transaminases are often observed in patients with AMI. A few recent studies reported that elevated serum transaminases were independently associated with poor clinical outcomes in patients with AMI. The extent of liver injury, in particular in patients with preexisting metabolic syndrome, may have a direct impact on cardiac outcomes [13].

Hypoxic liver injury (HLI) is commonly diagnosed in the emergency room in patients with STEMI (in 22% of patients), and those patients with HLI have higher mortality rate and higher frequency of major adverse cardiovascular events (MACE) after percutaneous coronary intervention [14]. Using multivariable regression analysis, Jantti et al. reported that a > 20% increase in ALT was associated with an increased risk of 90-day mortality independent of other known risk factors [15]. However, the association between liver transaminases and CVD remains a subject of debate. Authors of a narrative review based on prospective data concluded that the available evidence did not support a linear relationship between ALT and CVD events [16]. Differences in the effects of specific aminotransferases have not been clearly elucidated and require further research.

A few potential mechanisms have been proposed to explain the association between elevated ALT levels and increased in-hospital all-cause mortality in patients with AMI. For example, the liver has high metabolic activity and perfusion rates, and acute circulatory changes, such as AMI-related hypotension, will directly influence hepatic blood flow and thereby increase ALT and AST. Liver transaminases may also be elevated because of hepatic congestion from acute right ventricular dysfunction. Current research suggests that venous congestion, reduced capability of hepatocytes to extract oxygen, and reperfusion injury are of particular importance [12]. Although the source of elevated serum transaminases might be ischemic myocardial tissue, increased levels of these enzymes often reflect HLI secondary to both impaired forward perfusion and passive backward congestion, which are prevalent during STEMI [6]. In addition, an analysis of asymptomatic individuals found that increased levels of serum ALT (even high-normal levels) were associated with markers of CVD [17]. It is known that incomplete peripheral lipolysis of very low–density lipoprotein (VLDL) particles over-enriched with triglycerides increases the number of small dense LDL (sdLDL) particles, which carry a disproportionately large amount of LDL-C [17‐19]. ALT levels are directly related to desmosterol: TC ratio, a marker of cholesterol synthetic activity [20], thereby suggesting that ALT elevations are associated with increased hepatic triglyceride and cholesterol output in VLDL particles and lead to increased production of sdLDL [17].

In this study, we found that increased patient age was also significantly associated with mortality, which is consistent with previous reports of higher mortality in elderly patients with AMI [21‐23]. In the CADILLAC trial, both cardiac and noncardiac causes of death were more frequent in older patients [21]. Myocytes are continuously lost as the heart ages, and senescent cells exhibit increased susceptibility to microvasculature reperfusion injury. D-dimer, one of the degradation products of fibrin, is produced when fibrinolytic enzymes degrade fibrin clots produced by thrombin. Choi et al. reported that in STEMI patients undergoing primary percutaneous coronary intervention, high D-dimer levels on admission were associated with a larger myocardial infarction size [24]. In the current study, higher D-dimer levels were associated with higher all-cause in-hospital mortality in patients with AMI; this finding is consistent with the results reported by Kikkert et al. [25].

In the current study, another important predictor of early mortality in patients with AMI was reduced eGFR. A previous study reported that among patients with AMI, any degree of preexisting renal impairment should be considered a potent, independent, and easily identifiable risk factor for cardiovascular complications, with each 10-unit reduction in eGFR being associated with a 10% increased risk for death and nonfatal cardiovascular outcomes [26]. In general, patients with chronic kidney disease have more cardiovascular risk factors and a higher incidence of MACE with AMI and acute kidney injury (AKI) was revealed to be an independent long-term prognostic indicator in patients with STEMI [27]. Even small, subclinical elevations of serum creatinine that do not fulfil the consensus criteria for acute kidney injury have been independently associated with a twofold increased risk of adverse in-hospital outcomes after AMI [28]. Our findings suggested that serum eGFR was an independent predictor of in-hospital all-cause mortality after AMI, with mortality increasing as eGFR decreased. Various factors associated with impaired renal function, such as insulin resistance, oxidative stress, inflammation, endothelial dysfunction, vascular calcifications, and hypercoagulability, may contribute to adverse outcomes in patients with ACS [29].

The 2019 ESC guidelines regarding diabetes, pre-diabetes, and cardiovascular diseases developed in collaboration with the European Association for the Study of Diabetes concluded that patients with DM and established CVD have very high cardiovascular risk [30]. Our findings that elevated FPG, but not DM, was associated with mortality suggest that glycemic control is the critical determinant of the risk of death. Previous studies have shown that severe hyperglycemia on admission was associated with increased in-hospital mortality in AMI patients with or without DM [31, 32]. Hyperglycemia can induce abnormalities in endothelial and vascular smooth muscle cell function, as well as a propensity to thrombosis, thereby contributing to atherosclerosis and its complications [33], as well as hypercoagulability and impaired fibrinolysis [34].

This study had several limitations. As a retrospective study, it relied on the accuracy of data in the medical records. It was also based on data from a single center, whose population consisted primarily of a single ethnic group of individuals located in Northeast China. Because of the climate, diet, and other factors, the incidence of cardiovascular disease in this region is significantly higher than in other regions, and the data may not reflect a general population of patients with AMI. Furthermore, although we excluded patients diagnosed with and treated for various liver diseases (including hepatobiliary malignancies, liver fibrosis and cirrhosis, and viral hepatitis) based on medical records, some factors potentially affecting transaminase levels, such as undiagnosed liver disease or medications affecting liver function, may have remained undetected and therefore not been considered when excluding patients.

This retrospective study focused on non-invasive markers of in-hospital death from any cause after AMI. Increased risk of in-hospital all-cause mortality was significantly associated with increased levels of ALT, older age, FPG, D-dimer, and fibrinogen and decreased eGFR. Our results therefore suggest that elevation of the serum transaminase ALT, which likely reflects HLI, may be a useful marker of increased risk of early mortality in patients with AMI.