Ethics statement
The experiments were authorized by the Third Affiliated Hospital of Jinzhou Medical University (Approval No. KX2024024). All procedures strictly adhered to the Declaration of Helsinki. All subjects involved were fully informed of the study objectives and provided written informed consent before sampling.
Study Design and Participants
This post hoc analysis of the MPCS-ACS study (ClinicalTrials.gov NCT05164601, 01/6/2016) analyzed data from a large, multi-center cohort of ACS patients aged 18 to 79, hospitalized across three Chinese research centers from June 2016 to May 2021. From the study's inception, participants underwent regular follow-ups every 6 to 12 months. The inclusion criteria were consistent with those of the MPCS-ACS study: 1) Individuals aged 18 to 79. 2) A diagnosis of ACS, including Unstable Angina and Acute Myocardial Infarction, based on clinical symptoms, ECG changes, and elevated cardiac biomarkers. 3) Admission for ACS treatment at participating hospitals from June 1, 2016, to May 31, 2021. To examine the impact of LDL-C and RC levels on cardiovascular outcomes, 17,500 patients were initially screened. The exclusion criteria included: 1) Refusal of recommended treatment at admission. 2) LDL-C levels ≥ 1.8 mmol/L at admission. 3) LDL-C levels ≥ 1.8 mmol/L during two subsequent follow-ups. After screening, 4,329 ACS patients were included. The study's flow chart is depicted in Fig. 1.
Data collection
Basic characteristics and medical histories of ACS patients were collected, including gender, age, smoking status, alcohol consumption, hypertension, diabetes, stroke history, ACS types, and family history of cardiovascular disease (CVD). After fasting for at least 12 hours after admission, morning venous blood was drawn for biochemical indicator testing using equipment for chemical analysis (Dimension AR/AVL Clinical Chemistry System, Newark, NJ, USA), which included Blood Urea Nitrogen (BUN), Uric Acid, Serum Creatinine (SCr), Aspartate Aminotransferase (AST), Alanine Aminotransferase (ALT), Triglycerides (TG), Total Cholesterol (TC); High-Density Lipoprotein-C (HDL-C) and LDL-C. Echocardiography was performed on all participants during their hospitalization, and the measurements of the Right Atrial Diameter (RAD), Left Ventricular Diastolic Dimension (LVDD), Interventricular Septal Thickness (IVST), and Left Ventricular Ejection Fraction (LVEF) were recorded. Medication data were obtained from medical records and self-reports, while smoking and alcohol consumption statuses were assessed via self-report.
Smoking status referred to individuals who had smoked for six months or more, either continuously or cumulatively, classifying them as smokers. Alcohol consumption was classified based on drinking frequency, with individuals drinking more than three times weekly considered as alcohol consumers [16–18]. Diabetes Mellitus was defined by a glycosylated hemoglobin level over 6.5%, treated with oral drugs or insulin [19]. Hypertension was identified by blood pressure exceeding 140/90 mmHg or antihypertensive drug use [19]. Stroke was confirmed by brain imaging (CT or MRI) indicating tissue damage from vascular occlusion (ischemic) or rupture (hemorrhagic) [20]. Family history of CVD involved cardiovascular diseases in direct relatives before age 60 [21].
Remnant Cholesterol measurement
Levels of RC were estimated as TC minus HDL-C minus calculated LDL-C [13]. Participants were categorized into four groups based on baseline RC levels: Q1: < 0.29 mmol/L, Q2: 0.29–0.45 mmol/L, Q3: 0.46–0.71 mmol/L, Q4: > 0.71 mmol/L.
Endpoints
This study tracked CAD patients over periods ranging from 6 to 90 months, using clinic visits, calls, and surveys conducted by trained investigators for evaluations. Key evaluations encompassed lipid profiles, medication adherence, and recording of adverse events. The primary objective was to study long-term mortality, specifically all-cause mortality (ACM) and cardiac mortality (CM), with the latter arising from coronary heart disease, cardiogenic shock, or sudden cardiac events.
Secondary objectives included evaluating the incidence of major adverse cardiovascular and cerebrovascular events (MACCE) and major adverse cardiovascular events (MACE). MACE comprised cardiac death, non-fatal myocardial infarction, major aortic pathologies (aortic dissection, aortic aneurysm rupture), unstable angina needing medical treatment, acute heart failure requiring hospitalization (Killip Class IV), and target vessel revascularization. MACCE expanded on MACE to include cerebrovascular complications: ischemic stroke, hemorrhagic stroke, transient ischemic attacks (TIAs), and subarachnoid hemorrhage.
Statistical analyses
Statistical analyses were performed using SPSS 29.0 for Windows (SPSS Inc., Chicago, IL, USA) and R version 4.1.2. RC levels were treated as continuous data and divided into four categories. Continuous variables were reported as mean or median, and categorical variables as percentages. Differences in normally distributed variables were analyzed using a t-test, and non-normally distributed variables with the Mann–Whitney U test. Categorical variables were compared using a χ2 test. Kaplan–Meier analysis was employed to calculate the cumulative incidence rates of long-term events, with group comparisons made via a log-rank test. The models were adjusted for the following variables: basic characteristics (sex, age, smoking status, drinking status), medical history (hypertension, diabetes, stroke, type of acute coronary syndrome, family history of cardiovascular disease), medication history (ACEI/ARBs, β-blockers, CCBs, and nitrates use), biochemical indicators (BUN, uric acid, SCr, AST, ALT, TG, TC, HDL-C, LDL-C), and echocardiogram indices (RAD, LVDD, IVST, LVEF). Cox proportional hazards models calculated hazard ratios (HR) and 95% confidence intervals for adverse outcomes. The R package 'smoothHR' was utilized for this analysis. HR curves, allowing for non-linear associations, examined the relationship between RC and adverse outcomes, with Q2 as the reference category and adjustments for covariates.