European Journal of Cardiovascular Medicine

Acute Myocardial Infarction (AMI) remains a leading cause of morbidity and mortality worldwide, imposing a substantial burden on healthcare systems [1]. The pathophysiology of AMI extends beyond the occlusion of coronary arteries; it involves a complex interplay of neurohormonal activation, systemic inflammation, and metabolic derangement. Immediate risk stratification is crucial for determining the intensity of monitoring and therapeutic intervention. While traditional biomarkers like cardiac troponins and natriuretic peptides are indispensable for diagnosis and hemodynamic assessment, they primarily reflect myocardial necrosis and wall stress [2]. There is a continuous search for novel biomarkers that can capture the broader systemic response to ischemia, particularly the autonomic and inflammatory imbalances that drive poor outcomes.

The autonomic nervous system plays a critical role in cardiac regulation. During acute ischemia, sympathetic overdrive is often accompanied by parasympathetic withdrawal, a state known to predispose the heart to lethal arrhythmias and poor healing [3]. The vagus nerve, the primary component of the parasympathetic system, also regulates the immune response via the "cholinergic anti-inflammatory pathway." Through this mechanism, acetylcholine inhibits the release of pro-inflammatory cytokines like Tumor Necrosis Factor-alpha (TNF-α) and Interleukin-6 (IL-6) [4].

Serum cholinesterase (CHE), also known as butyrylcholinesterase (BChE), is an enzyme synthesized by the liver. Historically, its clinical utility has been limited to diagnosing organophosphate pesticide poisoning and assessing hepatic synthetic function [5]. However, recent physiological insights suggest that CHE may serve as a surrogate marker for parasympathetic tone. Since CHE hydrolyzes acetylcholine, its levels may reflect the body’s attempt to regulate cholinergic activity [6]. Furthermore, because CHE synthesis is downregulated by inflammatory cytokines, low levels may indicate the severity of the systemic inflammatory response syndrome (SIRS) often seen in severe cardiac events [7].

Recent epidemiological studies have hinted at an association between low CHE levels and all-cause mortality in general populations and in patients with chronic heart failure [8, 9]. However, data regarding the specific prognostic value of CHE in the acute phase of myocardial infarction are conflicting. Some studies suggest a rapid decline in CHE correlates with infarct size, while others argue that comorbidities such as subclinical liver disease confound these findings [10]. Specifically, there is a research gap regarding how admission CHE levels correlate with short-term in-hospital Major Adverse Cardiac Events (MACE) independent of traditional risk factors.

Therefore, the aim of this study was to evaluate the diagnostic and prognostic significance of serum cholinesterase in patients with AMI compared to healthy controls and to determine its efficacy in predicting in-hospital complications.

Study Design and Setting
This was a prospective, observational conducted in the Coronary Care Unit (CCU) and the Department of General Medicine at the tertiary care hospital.

Sample Size and Population
Based on a pilot study indicating a mean difference in CHE levels of 2000 U/L between ischemic patients and controls, with a power of 90% and an alpha error of 0.05, a minimum sample size of 90 per group was calculated. We recruited a total of 240 participants, divided into two groups:

• Group A (Study Group): 120 consecutive patients admitted with a diagnosis of Acute Myocardial Infarction (AMI).
• Group B (Control Group): 120 age- and sex-matched healthy volunteers recruited from the hospital's preventative health check-up clinic.

Inclusion and Exclusion Criteria

• Inclusion: Patients aged >18 years meeting the Third Universal Definition of Myocardial Infarction (elevation of cardiac troponin >99th percentile with at least one of the following: symptoms of ischemia, new significant ST-T wave changes, or imaging evidence of new loss of viable myocardium). Both ST-elevation MI (STEMI) and Non-ST-elevation MI (NSTEMI) were included.
• Exclusion: Patients with conditions known to alter serum CHE levels were strictly excluded. This included chronic liver disease (cirrhosis, hepatitis), acute liver failure, malnutrition (BMI < 18.5 kg/m²), pregnancy, active malignancy, recent surgery (<4 weeks), severe renal failure (eGFR < 30 mL/min), sepsis on admission, or history of organophosphate poisoning.

Data Collection and Laboratory Procedures
Demographic data, clinical history, and cardiovascular risk factors (hypertension, diabetes mellitus, smoking, dyslipidemia) were recorded. For Group A, blood samples were drawn within 6 hours of admission (before primary PCI or thrombolysis). For Group B, samples were drawn during the morning check-up.
Serum CHE (butyrylcholinesterase) activity was measured using a kinetic photometric method (butyrylthiocholine substrate) on an automated chemistry analyzer. The reference range for the laboratory was 5,400–13,200 U/L. Other investigations included Complete Blood Count (CBC), renal and liver function tests, high-sensitivity Troponin I (hs-cTnI), CPK-MB, lipid profile, and C-reactive protein (CRP). Transthoracic echocardiography was performed to assess Left Ventricular Ejection Fraction (LVEF).

Outcome Measures
The primary outcome was the comparison of CHE levels between Group A and Group B. The secondary outcome was the association of CHE levels with in-hospital Major Adverse Cardiac Events (MACE). MACE was defined as a composite of cardiogenic shock (systolic BP <90 mmHg with signs of hypoperfusion), new-onset malignant arrhythmias (VT/VF), re-infarction, or all-cause mortality during the hospital stay.

Statistical Analysis
Data were analyzed using SPSS software (Version 26.0, IBM Corp). Continuous variables were expressed as mean ± standard deviation (SD) and categorical variables as frequencies and percentages. The Kolmogorov-Smirnov test was used to check for normality. Independent Student’s t-test was used to compare means between two groups (AMI vs. Control; MACE vs. No-MACE). Chi-square tests were used for categorical variables. Pearson’s correlation coefficient () was calculated to assess the relationship between CHE and other continuous variables (CRP, LVEF, Troponin). Receiver Operating Characteristic (ROC) curve analysis was performed to determine the optimal cutoff value of CHE for predicting mortality. A two-tailed -value < 0.05 was considered statistically significant

Demographic and Clinical Characteristics
The study included 240 participants. The mean age of the AMI group was  years, which was statistically similar to the control group ( years, ). As expected, the AMI group had a significantly higher prevalence of traditional cardiovascular risk factors, including diabetes mellitus ( vs. ) and hypertension ( vs. ). Baseline characteristics are summarized in Table 1.

Table 1: Baseline Demographic and Clinical Characteristics of the Study Population

Comparison of Serum Cholinesterase and Inflammatory Markers
There was a marked difference in serum CHE levels between the groups. The AMI group exhibited significantly lower CHE activity compared to the control group ( U/L vs.  U/L, ). Conversely, inflammatory markers such as WBC count and CRP were significantly elevated in the AMI group. Notably, CHE levels in the AMI group showed a significant inverse correlation with CRP () and peak Troponin I (). Table 2 details the biochemical comparisons.

Table 2: Comparison of Biochemical Parameters

Note: Liver enzymes (ALT) and Albumin were comparable, ruling out hepatic failure as a cause for low CHE.

Prognostic Significance of CHE in AMI
Within the AMI group, 38 patients (31.7%) developed MACE during their hospital stay, including 12 deaths. We compared the admission CHE levels between patients who developed MACE and those with an uncomplicated course. Patients with adverse events had significantly lower admission CHE levels ( U/L) compared to those without events ( U/L). Furthermore, non-survivors had the lowest recorded mean CHE levels ( U/L). Table 3 illustrates the relationship between CHE levels and clinical outcomes.

Table 3: Serum Cholinesterase Levels Stratified by In-Hospital Outcomes (AMI Group)

Compared to No MACE group.

ROC analysis for the prediction of in-hospital mortality revealed an Area Under the Curve (AUC) of 0.89 (95% CI: 0.82–0.96, ). A cutoff value of  U/L was identified as having the optimal balance of sensitivity () and specificity ().

The present study establishes a robust association between reduced serum cholinesterase (CHE) levels and the presence of Acute Myocardial Infarction (AMI), as well as its short-term prognosis. Our findings demonstrate that CHE levels are nearly 50% lower in AMI patients compared to healthy controls, and that profound reductions are predictive of Major Adverse Cardiac Events (MACE) and mortality.

The significant reduction of CHE in AMI patients observed in our study aligns with the findings of Goliasch et al., who first highlighted BChE as a strong predictor of cardiac mortality [11]. The mechanism behind this reduction is likely multifactorial. First, the "cholinergic anti-inflammatory pathway" hypothesis suggests that the autonomic nervous system interacts directly with the immune system. In the setting of AMI, the massive release of pro-inflammatory cytokines, particularly IL-6 and TNF-, inhibits the hepatic synthesis of negative acute-phase reactants, including albumin and CHE [12]. Since our study excluded patients with chronic liver disease and showed comparable albumin levels between groups, the acute drop in CHE is likely a specific response to the systemic stress of infarction rather than baseline hepatic insufficiency.

Secondly, the reduction in CHE may reflect a desperate physiological attempt to preserve acetylcholine. Acetylcholine acts as a "brake" on the inflammatory cascade; therefore, downregulating the enzyme that destroys it (CHE) theoretically increases vagal tone and anti-inflammatory activity [13]. However, paradoxically, persistently low CHE in our "MACE" group correlated with poor outcomes. This supports the theory proposed by Arbel et al., which posits that low CHE is a marker of exhausted parasympathetic reserve [14]. Patients who cannot maintain autonomic homeostasis—reflected by low CHE—are more susceptible to catecholamine toxicity, leading to malignant arrhythmias and cardiogenic shock, as observed in our cohort.

Our data indicated a strong inverse correlation between CHE and CRP, a marker of inflammation. This corroborates the work of Lamprecht et al., who found similar associations in critically ill surgical patients [15]. The high inflammatory burden in severe AMI suppresses CHE synthesis. Consequently, CHE serves as an integrative marker combining information about both the autonomic status and the inflammatory severity.

Comparing survivors vs. non-survivors, the difference in CHE was stark ( vs.  U/L). This distinction is clinically relevant. Current risk scores like GRACE or TIMI rely heavily on age, hemodynamics, and creatinine [16]. CHE offers a glimpse into a different pathophysiological axis—the neuro-immune axis. Previous studies have suggested that adding CHE to established risk models improves their predictive power [17]. Our ROC analysis supports this, showing a high AUC (0.89) for mortality prediction. A cutoff of 4,200 U/L provided excellent sensitivity, suggesting that patients presenting with levels below this threshold warrant aggressive monitoring and potentially earlier invasive management.

It is also worth noting the association with arrhythmias. The vague nerve stabilizes the myocardium electrically. The significantly lower CHE in patients with VT/VF suggests that low enzyme activity might correlate with vagal withdrawal and sympathetic dominance, lowering the threshold for fibrillation [18-20].

Limitations
This study has several limitations. It was a single-center study, which may limit generalizability. While we excluded overt liver disease, subclinical hepatic dysfunction (e.g., fatty liver) could not be ruled out entirely without biopsy or elastography, though normal ALT levels mitigate this concern. Additionally, we did not measure serial CHE levels, which would have provided insight into the kinetics of the enzyme during recovery. Finally, we measured total butyrylcholinesterase activity, not the specific isoenzymes, which might vary genetically.

In conclusion, serum cholinesterase is a valuable, widely available, and cost-effective biomarker in the setting of acute myocardial infarction. This study confirms that CHE levels are significantly suppressed in AMI patients compared to healthy controls. Furthermore, the degree of suppression correlates strongly with the severity of inflammation and the risk of major in-hospital complications, including shock, arrhythmia, and death.

A serum CHE level of  U/L on admission should be considered a "red flag" for high risk. We propose that CHE assessment be integrated into the routine biochemical profile for AMI patients to enhance risk stratification and guide therapeutic decision-making. Future multicenter studies should investigate whether therapeutic modulation of the cholinergic pathway can improve outcomes in patients identified as high-risk by this biomarker.

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