Myocardial Infarction

Myocardial infarction is the death (necrosis) of heart muscle caused by prolonged ischemia, most often when an atherosclerotic plaque disrupts and a thrombus interrupts coronary blood flow. It is detected by a characteristic rise and fall in cardiac troponin together with clinical, electrocardiographic, or imaging evidence of ischemia.

Definition

Myocardial infarction is defined as myocardial cell death due to prolonged ischemia, recognised clinically by a rise and/or fall of cardiac troponin with at least one value above the upper reference limit, accompanied by evidence of ischemia such as symptoms, ischemic electrocardiographic changes, new wall-motion abnormality, or identification of a coronary thrombus.

Scope

This topic covers the definition and types of myocardial infarction, its pathophysiology, the role of cardiac biomarkers and the electrocardiogram in its recognition, and the conceptual distinction between infarction and reversible ischemia. It is a reference entry that explains how the condition is defined and classified, not a guide to its management.

Key concepts

• Ischemic myocardial necrosis
• Cardiac troponin rise and fall
• Type 1 (plaque-mediated) versus type 2 (supply-demand) infarction
• ST-elevation versus non-ST-elevation MI
• Universal definition of myocardial infarction
• Infarct size and time-dependent injury
• Reperfusion concept

Mechanisms

In the most common (type 1) infarction, an atherosclerotic plaque ruptures or erodes, exposing thrombogenic material and provoking thrombus formation that abruptly limits or stops coronary flow. The undersupplied myocardium becomes ischemic, and if flow is not restored, a wavefront of necrosis spreads from the inner (subendocardial) layer outward over time, so that infarct size depends on the artery involved, the duration of occlusion, and collateral supply. Type 2 infarction reflects a mismatch between oxygen supply and demand without acute plaque thrombosis. Necrosis releases structural proteins such as troponin into the circulation, providing the biochemical signature used to detect infarction.

Clinical relevance

Myocardial infarction is a leading cause of death and disability and a defining endpoint in cardiovascular research and classification. This entry explains how infarction is conceptualised, typed, and biochemically detected for educational reference; it does not provide diagnostic cut-offs for individuals or any treatment guidance.

Epidemiology

Myocardial infarction is a major contributor to global cardiovascular mortality. Its incidence rises with age and with the burden of modifiable risk factors, and the introduction of sensitive troponin assays has influenced how cases are detected and counted over time.

Evidence & guidelines

The Fourth Universal Definition of Myocardial Infarction provides the internationally used framework that distinguishes infarction from other causes of troponin elevation and defines its clinical types. It is referenced here to convey how the entity is defined rather than as a source of management recommendations.

History

For much of the twentieth century myocardial infarction was recognised mainly by symptoms and the electrocardiogram. The advent of cardiac enzymes and then of highly specific troponin assays sharpened detection, and successive international consensus documents — culminating in the universal definition series — standardised what counts as an infarction and separated it into mechanistic types.

Debates

How should type 2 myocardial infarction be defined and distinguished?

With sensitive troponin assays, many patients show myocardial injury from supply-demand imbalance without acute plaque thrombosis; defining the boundary between type 2 infarction and non-ischemic myocardial injury, and how to act on it, remains an area of discussion.

Key figures

• Kristian Thygesen
• Joseph S. Alpert
• Allan S. Jaffe
• Peter Libby

Seminal works

• thygesen-2018
• libby-2013

Frequently asked questions

What is the difference between myocardial ischemia and myocardial infarction?

Ischemia is reduced blood supply to the heart muscle that can be reversible if flow is restored, whereas infarction is the actual death of heart-muscle cells that results when severe ischemia is prolonged.

Why is troponin central to the definition of myocardial infarction?

Troponin is a protein released when heart-muscle cells are injured, and a characteristic rise and fall of troponin is the biochemical marker the universal definition uses, together with evidence of ischemia, to identify infarction.