Myocardial Infarction w/ ST-Segment Elevation Disease Background

Last updated: 08 July 2025

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Introduction

Content on this page:

Introduction

Introduction

Myocardial infarction (MI) is death of cardiac myocytes (irreversible necrosis) caused by prolonged or severe myocardial ischemia. The term “acute” usually refers to the time 6 hours to 7 days following the pathologic appearance of the infarct. A recurrent MI is an MI occurring 28 days after an incident MI, while a re-infarction is an acute MI occurring within 28 days of an incident or recurrent MI.  

Acute coronary syndrome is any constellation of symptoms compatible with acute myocardial ischemia, usually caused by sudden reduction in coronary blood flow from atherosclerotic plaque rupture or erosion and subsequent thrombosis.

Epidemiology

Cardiovascular disease remains the number one cause of mortality in Western countries, with acute coronary disease being the leading cause.  Myocardial infarction with ST-segment elevation constitutes approximately 25% of acute coronary syndromes.  

The incidence rate of myocardial infarction among Asians was lower than other races. The reason for this may be due to lower prevalence of major risk factors (eg hypertension, smoking, obesity) among Asian people. In Asian countries such as Japan and Korea, the incidence rate is higher in men than in women. 

Pathophysiology

The initial mechanism in acute myocardial infarction is the rupture of vulnerable, lipid-laden atherosclerotic coronary plaque, resulting in a highly thrombogenic plaque core and matrix material circulation in the blood. Platelets then activate and aggregate at the site of the injury. Thrombin is generated, which accelerates platelet activation, resulting in fibrin trapping of red blood cells and leading to thrombus formation. A totally occluding thrombus leads to ST-elevation myocardial infarction. Reduced blood flow results in ischemia, leading to myocardial cell injury/death, ventricular dysfunction, and cardiac arrhythmias. Myocardial necrosis begins 20 minutes after coronary occlusion. 

Etiology

The etiologies of myocardial infarction are:

  • Coronary artery spasm
  • Coronary atherosclerosis and plaque rupture
  • Coronary embolism from atrial fibrillation, rheumatic heart disease, infective endocarditis, or intracavitary thrombus
  • Dissection into coronary arteries (aneurysmal, iatrogenic or spontaneous)
  • Periarteritis and other coronary artery inflammatory diseases
  • Anomalous origin of coronary artery (eg interarterial [aorta and pulmonary artery] course of coronary artery)
  • Increased blood viscosity or hypercoagulable states (eg polycythemia vera, systemic lupus, antiphospholipid syndrome)
  • Myocardial infarction with normal coronaries frequently seen in younger patients and cocaine users

Risk Factors

The risk factors for ST-elevation myocardial infarction are: 

  • Age
  • Sex
  • Family history of heart disease
  • Modifiable risk factors include:
    • Hyperlipidemia
    • Hypertension
    • Diabetes
    • Chronic Kidney Disease
    • Obesity
    • Psychosocial factors (eg stress)
  • Lifestyle risk factors include:
    • Smoking
    • Diet
    • Lack of exercise
    • Alcohol intake

Classification

An acute myocardial infarction is classified clinically as:

  • Type 1: Acute atherothrombosis usually caused by atherosclerotic plaque rupture or erosion and associated with partial or complete vessel thrombosis
  • Type 2: Myocardial O2 supply and demand imbalance not related to acute atherothrombosis
  • Type 3: Cardiac death in patients with symptoms suggestive of myocardial ischemia and presumed new ischemic changes on electrocardiogram (ECG) prior to cardiac troponin (cTn) values becoming available or abnormal
  • Type 4a: Percutaneous coronary intervention (PCI)-related MI detected ≤48 hours after the procedure
  • Type 4b: Coronary stent or stent scaffold thrombosis associated with PCI
  • Type 4c: Coronary stent restenosis associated with PCI
  • Type 5: Coronary artery bypass grafting (CABG)-related MI detected ≤48 hours after the procedure
  • Myocardial infarction with non-obstructive coronary arteries (MINOCA): MI with no significant coronary artery stenosis (ie <50%) on coronary angiography and includes coronary artery spasm, spontaneous coronary artery dissection, microvascular dysfunction, Takotsubo cardiomyopathy and pulmonary/coronary embolism


A prior or unrecognized/silent myocardial infarction is a condition that has the following criteria:

  • Abnormal Q waves with or without symptoms in the absence of non-ischemic causes
  • Loss of viable myocardium on imaging consistent with an ischemic cause
  • Patho-anatomical findings of a previous MI