Prognostic implications of calculated Apo‐lipoprotein B in patients with ST‐segment elevation myocardial infarction undergoing primary percutaneous coronary intervention: Outcome is tied to lower cut‐points

Abstract Background Debates still surround using lipoproteins including Apo‐B in risk assessment, management, and prognosis of patients with coronary artery disease. During an acute ST‐segment elevation myocardial infarction, Apo‐B might help to achieve incremental prognostic information. Objective We sought to determine the potential prognostic utility of calculated Apo‐B in a cohort of patients with STEMI undergoing primary PCI. Methods A retrospective cohort study was conducted enrolling 2,259 patients with a diagnosis of acute STEMI who underwent primary PCI. Apo‐B was obtained using a valid equation based on initial lipid measurements. High Apo‐B was defined as a level of 65 or higher. Primary endpoint of the study was major adverse cardiovascular events (MACE). Results Mean age of the participants was 59.54 years and 77.9% of them were male. After a Median follow up of 15 (6.2) months, high Apo‐B was associated with MACE and the OR (95% CI) was 3.02 (1.07–8.47), p = .036. Odds ratios for prediction of MACE pertaining to LVEF, and smoking were 0.97 (p = .044), and 1.07 (p = .033), respectively. However, High Apo‐B was not able to predict suboptimal TIMI flow. Accordingly, the Odds ratio was 0.56 (0.17–1.87), p = 0.349. The power of High LDL‐C and Non‐HDLC for prediction of MACE were assessed in distinct models. Attained odds ratios were [2.40 (0.90–6.36), p = .077] and [1.80 (0.75–4.35), p = 0.191], respectively. Conclusion Calculated Apo‐B appears to be a simple tool applicable for prediction of cardiovascular events in patients with STEMI superior to both Non‐HDLC and LDL‐C.

Accordingly, the Odds ratio was 0.56 (0.17-1.87), p = 0.349. The power of High LDL-C and Non-HDLC for prediction of MACE were assessed in distinct models.
Attained odds ratios were [2.40 (0.90-6.36 with an equation appears more feasible than direct measurement providing a relatively simple tool for risk stratification. Lipoprotein fractions such as VLDL-C, IDL, and LDL-C are comprised of structural proteins like Apo-B. These pro-atherogenic lipid particles contain one Apo-B component. Apo-B that is synthesized in the liver facilitates and amplifies cholesterol transfer in a cycle streaming from the liver to peripheral tissues. 4 Hence, precise estimation of serum Apo-B concentration indicates to burden of atherogenic lipoprotein particles. 5 Despite the utility of Apo-B in prediction of future cardiovascular events among general population and patients with stable CAD, 6,7 its clinical implications in STEMI remains to be determined. Measured Apo-B has shown incremental prognostic value in post-MI patients in few clinical studies which was superior to both LDL-C and Non-HDLC. 8,9 Nevertheless, Calculation of Apo-B has not been validated to enter the routine practice, particularly in the setting of STEMI. Furthermore, multiple large-scale studies are required to confirm the clinical relevance of an equation. In the present research, we aimed to investigate potential association of calculated Apo-B with cardiovascular events following primary PCI in high-risk STEMI patients. Furthermore, we assessed the power of high LDL-C and Non-HDLC in prediction of major adverse cardiovascular events (MACE).

| Study design and participants
We performed a thorough review of Tehran Heart Center (THC) registry for CAD. Patients with the diagnosis of STEMI (ST-elevation myocardial infarction) since March 2016 up to Juli 2019 were enrolled. We arranged a retrospective cohort design. All individuals with acute STEMI who underwent primary PCI or rescue PCI within 24 h since the onset of symptoms were included. Subjects in whom the initial presentation of MI was unclear or those with failed wire passage were excluded. All demographic characteristics, biochemical parameters, variables of clinical history, and physical examination were obtained from the database. Baseline Left ventricular Ejection fractions (LVEF) were used in the current study, which were determined at least 7 days post-MI. Cardiac Troponin-T was measured at baseline and 12 and 24 h following primary PCI denoting the extent of myocardial damage. In the current study, we applied the maximum level of Troponin-T in analyses.
All patients received the standard optimal guideline-directed medical treatment in combination with angioplasty. Either an ACEI or ARB agent, an appropriate beta-blocker, Aspirin (80 mg daily) and high-dose statin were administered for all participants. Aldosterone receptor antagonist had been prescribed for those with an LVEF under 40% or diabetics. All patients received a P2Y12 inhibitor drug including clopidogrel and ticagrelor. Loading dose of clopidogrel and ticagrelor were 600 mg and 180 mg, respectively. Then maintenance dose of the former (75 mg once daily) and the latter (90 mg twice a day) were continued for at least 12 months, thereafter. Unfractionated heparin (70-to 100-unit /kg) was used routinely during primary PCI. The choice of using thrombus aspiration and/ or glycoprotein IIb-IIIa inhibitors were optional depending on the opinion of the interventional cardiologist.

| Definitions
STEMI was diagnosed according to the fourth universal definition of myocardial infarction. 10 In brief, ischemic symptoms such as chest pain or its equivalents accompanied with ECG changes in two or more contiguous leads led to definite diagnosis. ST-segment elevation of 1 mm or more in at least two related leads except for V2 and V3 fulfills the criteria. In these two leads, a value of 2 mm or more is needed to confirm STEMI for men older than 40 years. In younger men (under 40) the cut-point of ST elevation in V2 and V3 is 2.5 mm while for women at any age, this measure is expected to reach 15 mm or more.
TIMI flow grade is a surrogate measure of myocardial perfusion, which is detected via inspection of angiography movies. Operators had recorded TIMI flow of the coronary arteries before and after PCI. This visual classification also helps to determine apparent success of the procedure. 11 Absence of any forward coronary flow is reported as TIMI grade zero whereas TIMI-1 addresses minimal presence of dye just beyond the stenosis. TIMI-2 characterizes a delayed slow filling of the distal segment in the culprit territory. Optimal antegrade stream is known as TIMI-3.  12 We used the target of Apo-B in very-high risk patients as the cut-off for determining high level according to 2019 ESC/EAS Guidelines for the management of dyslipidemias. 13 Thus, Apo-B values above 65 were defined as high. Elevated LDL-C and Non-HDLC were determined by levels ≥ 70, and ≥ 100, respectively.

| Endpoints
Primary endpoint of the study was Major Averse Cardiovascular Events (MACE), which was a composite of all-cause mortality, repeat

| Statistical analysis
Continuous variables were shown as mean ± SD or median

| RESULTS
A total of 2259 participants were eligible for analysis in this study.  Table 2 shows the association of dichotomized Apo-B and subsequent MACE in patients following primary PCI in multivariate models.
In Table 3  Besides, Non-HDLC also did not show the ability to predict the outcomes. As the main finding, results suggest that calculated Apo-B  We have also found the same results regarding the utility of Apo-B in patients with STEMI following primary PCI.
Since measurement of Apo-B is time consuming and not available as a routine test, we recruited an equation, which serves as a simple surrogate of this biomarker. Using only one baseline blood sample and the patient's conventional lipid profile, we are able to determine a modestly strong predictor of MACE in acute STEMI. We applied different cut-off levels of Apo-B to achieve considerable clinical and statistical significance because it was the first time for validation of prognostic utility of calculated Apo-B in STEMI. Ultimately, we found that the lowest level (65 mg/dl), which is, defined as the goal of therapy in very high-risk patients 13  Furthermore, a patient might be at increased risk of future MACE due to high Apo-B despite achieving an optimal LDL-C level. Hence considering tighter Apo-B control (lower cut-points like 65 mg/dL), may lead to better outcomes.
A recent case-control study with 10-year follow-up revealed that increased Apo-B concentrations (> 100 mg/dl) were associated with first STEMI in asymptomatic controls. However, they declared that neither Apo-B nor other plasma lipids did not predict MACE in patients with STEMI. These results are relatively in discordance with our findings. 26 Therefore, we should note that length of follow-up as well as Apo-B cutoff level influence on the subsequent risk. Thus the effects of baseline Apo lipoproteins on magnitude of the residual risk blunts over a long period. Only one study in a diabetic population has applied the cut-point of 63 mg/dl that is similar to our level. 27 They found that high Apo-B was associated with MACE and particularly subsequent non-fatal MI after index ACS. However, in our study, repeat revascularization was the main cause of difference but non-fatal MI just showed a trend toward significance.
We found no reports about the correlation of high Apo-B and suboptimal reperfusion, which is in agreement with the present analysis.
The stability, synthesis, and transportation of lipoproteins are regulated via various Apo lipoprotein components. Atherogenic lipoproteins such as very low-density lipoproteins (VLDL), intermediatedensity lipoproteins (IDL), lipoprotein (a), and LDL-C contain one molecule of Apo-B. Thus, serum Apo-B represents for total number of atherogenic particles and TG-rich lipoprotein remnants. The higher serum Apo-B concentration, the greater circulating cholesterol content and ultimately higher risk of atherosclerotic plaque deposition. 28 Variations in size of LDL-C particles accompanied with greater atherogenic capacity of small dense LDL-C as well as TG-rich remnants should also be addressed. With these in mind, using Apo-B prevents underestimation of cardiovascular risk. 29 Moreover, the calculated Apo-B incorporates TG with logarithmic scale in order to modify the impact of extreme values particularly those over 400 mg/dl. In the present study, it was also depicted that a strong relation exists between increased TG levels and subsequent MACE. This might signify the controversial role of TG-rich particles and turn the lights on the dark side of the scene. Although hypertriglyceridemia is a wellestablished risk factor of coronary artery disease and mortality, a paradoxical effect on prognosis of ACS patients have been suggested. 30 Albeit, these reports often did not differentiate between the subgroups with STEMI and Non-STEMI. Conversely, a recent large study postulate that the paradoxical correlation of baseline lipid profile with MACE is limited to serum LDL-C. 31 Increased TG-rich lipoproteins, low HDL-C and usually normal LDL-C levels characterize lipid profile of subjects with metabolic syndrome and insulin resistance. However, frequency of atherogenic particles including small dense LDL-C increases that tend to get oxidized. 32 Hence, Apo-B might be an appropriate marker to detect and optimize the true residual risk of STEMI patients who have underlying metabolic syndrome. Estimated Apo-B is thought to be associated with hs-CRP, microalbuminuria, Agatston calcium score 33 as well as SYNTAX score. 20 Furthermore, a robust correlation was found between Apo-B reduction and regression of atherosclerotic plaques (coronary plaque volume). 34 Accordingly, Apo-B serves as a useful biomarker providing incremental risk assessment through linking with multiple potential risk indicators. In addition, it addresses the severity of coronary artery disease, which is likely to occur in the setting of acute coronary syndrome. 17

| Study limitations
Several limitations might be considered in the present research. First, we have performed a retrospective cohort study, which encompasses known inherent biases. Second, phone call follow-up might potentially affect the reliability of event records. Pain-to-door time was relatively prolonged in this cohort, which elevates the underlying risk and diminishes the myocardial salvage for both groups. Third, we did not have repeated measurements of lipid markers in order to determine the efficacy of statin treatment. Fourth, despite finding a significant relationship between high Apo-B and poor STEMI outcome, we cannot strongly extrapolate the results. This caution should be considered due to several reasons including relatively broad confidence intervals, and lacking patients with other types of CAD.

| CONCLUSION
The present study helped to validate the efficacy of a simple equation for estimation of Apo-B in patients with STEMI. Clinical implications of calculated Apo-B was shown as evidenced for measured Apo-B previously. High Apo-B predicted subsequent MACE following primary PCI whereas, elevated Non-HDLC and LDL-C failed to have a significant association.

ACKNOWLEDGMENTS
The authors are pleased to show their gratitude for nursing and technical staff of Tehran Heart Center who participated in angiography, and all levels of medical care.