Acute coronary syndrome (ACS) is a major cause of mortality worldwide. There are several protocols for the diagnosis and triaging of ACS, including ST-elevation myocardial infarction (STEMI), non-ST-elevation myocardial infarction (NSTEMI), and unstable angina, all aimed at timely diagnosis and early referral if indicated, which is essential for a favorable outcome. ¹

The preferred biomarkers for assessing myocardial damage in ACS are cardiac troponin T (cTnT) and cardiac troponin I (cTnI). It is recommended that high-sensitivity cardiac troponin assays should be used in clinical practice. ^{2 – 5} Other biomarkers such as CK-MB have lower sensitivity and specificity. ⁶ Platelets play a major role in thrombosis, which is a causative factor for most acute coronary syndromes.

Enzyme markers with good specificity have a few disadvantages, such as being negative during the window period and may not be available at all centers. ⁷ Therefore in our study, we attempted to determine how effective platelet indices (mean platelet volume, platelet count, and platelet distribution width) are diagnostic markers in acute coronary syndromes. Additionally, we attempted to assess their prognostic ability among cases of ACS.

A total of 145 patients and 145 controls were included in this study [ Table 1]. Among the cases, the majority had STEMI, followed by NSTEMI, and unstable angina [ Table 2]. On comparing platelet indices between cases and controls, all of them (MPV, plateletcrit, and PDW) were found to be higher among the cases. However, only the MPV was statistically significant [ Table 3].

When platelet indices were compared to the laboratory markers, Troponin T, pro-BNP, MPV, and plateletcrit correlated with both troponin T and pro-BNP, while PDW showed a positive correlation only with troponin T. The only significant correlations were between plateletcrits and pro-BNP [ Table 4]. The degree of ventricular dysfunction, severity of coronary artery disease, and existence or absence of arrhythmias were among the other criteria whose relation with the platelet indices were studied. Plateletcrit showed a positive relationship with all the mentioned parameters [ Tables 5, 6].

Analysis of the relationship between platelet indices and other risk factors of coronary artery disease, such as diabetes mellitus (represented by HbA1c) and dyslipidemia (lipid profile), showed that MPV had a positive relationship with HbA1C and the entire lipid profile, while PDW showed a positive relationship with only Hba1C and triglycerides. Plateletcrits had a positive relation with Hba1C and total cholesterol [ Table 7].

Acute coronary syndrome refers to STEMI, NSTEMI, and unstable angina. Myocardial infarction is defined as “myocardial cell death due to prolonged ischemia.” ⁹

The first ultrastructural alterations include reduced cellular glycogen, loosened myofibrils, and sarcolemmal disruption, which can occur within 10–15 min after the onset of ischemia. ¹⁰ Mitochondrial anomalies can be observed by electron microscopy as soon as 10 min after cardiac blockage and are progressive. ¹¹ Necrosis proceeds from the subendocardium to the subepicardium over several hours in an experimental setting. An increase in collateral flow, decreased drivers of cardiac oxygen demand, and intermittent occlusion or reperfusion that may prepare the heart can all add to the length of time.

Significance is that when reperfusion therapy is administered promptly, it helps to prevent myocardial ischemia. ^{12 – 14} Cardiac troponins I (cTnI) and T (cTnT) are components of the contractile machinery of myocardial cells and are found virtually exclusively in the heart. ^{2 , 3}

Injuries to non-cardiac tissues have not been linked to an increase in cTnI levels. This situation is more complicated for cTnTs. Biochemical evidence suggests that the cardiac troponin T assay detects proteins expressed by damaged skeletal muscle, implying that cTnT increases could come from skeletal muscle in some cases. ^{14 – 21} The preferred biomarkers for assessing myocardial damage are cTnI and cTnT, and it is recommended that high-sensitivity cardiac troponin assays be used in clinical practice. ^{2 – 5} Other biomarkers, such as CK-MB, have lower sensitivity and specificity. ⁶ Myocardial injury is said to be present when the levels of cardiac troponin in the blood are above the 99th percentile of the upper reference limit. Injury may be acute, as demonstrated by a “newly found dynamic rising and/or falling level of cTn values above the 99th percentile URL, or chronic, as evidenced by continuously elevated cTn levels”. ^{2 – 5}

The commonly measured platelet indices are the mean platelet volume (MPV), plateletcrit (PCT), and platelet distribution width (PDW). The mean platelet volume is a measure of the platelet volume measured in femtolitres, whereas PDW and PCT are presented as percentages. Plateletcrit refers to the volume occupied by platelets in blood. PDW is an indicator of volume variability in platelet size.

Regarding the role of platelet indices in acute coronary syndrome, larger and hyperactive platelets play a pivotal role in accelerating the formation and propagation of intracoronary thrombi, leading to acute thrombotic events. Larger platelets are enzymatically and metabolically active and have higher thrombotic ability than smaller platelets. ^{7 , 22 , 23}

We evaluated the diagnostic and prognostic significance of platelet indices in ACS, considering the function of platelets in the pathophysiology of the disease.

We suggest that platelet indices be applied in the following clinical practice methods. In an outpatient setting where an individual with risk factors is presented for routine evaluation, if platelet indices are grossly deranged, then they may be candidates for further evaluation in the form of coronary CT or coronary angiography to rule out underlying coronary artery disease.

In case of an emergency setting with a patient presenting with acute onset symptoms and if ACS is suspected, deranged platelet indices can be used in the periphery where cardiac biomarkers are not available to decide on referral to a higher center. In other words, platelet indices can be used to triage suspected ACS patients. If ACS is confirmed, platelet indices can be used to prognosticate.

The study was approved by our Institutional Review Board (IRB) known as Kasturba Medical College and Kasturba Hospital Institutional Ethics Committee (reference number: 954/2019) on 19th November, 2019. This study was conducted in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all participants.