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# Myocardial infarction: pathogenesis

- Lesion

A heart attack is the death of heart muscle when a clot blocks a coronary artery. Which artery is blocked decides which wall dies.

Updated Nov 12, 2026

## Key points

- Left anterior descending: about 40 to 50 %, anterior wall, apex and anterior two-thirds of the septum.
- Right coronary: about 30 to 40 %, inferior (posterior) wall, posterior third of the septum, right ventricle in right-dominant hearts.
- Left circumflex: about 15 to 20 %, lateral wall.
- Subendocardium is the most vulnerable zone: last to be perfused, under the highest pressure.
- Troponin I and T are the most sensitive and specific markers: rise within hours, peak around a day or two, stay up about a week or more.
- Reperfusion: hemorrhagic infarct, contraction bands, stunning; the earlier, the more muscle saved.

## What it is

Most myocardial infarctions follow acute plaque change and thrombosis in a coronary artery. Within a minute of severe ischemia, contraction stops; after about 20 to 40 minutes, injury becomes irreversible, beginning in the subendocardium and spreading as a wavefront toward the epicardium over about 3 to 6 hours. Transmural infarcts usually come from an occlusive thrombus (ST-elevation MI); subendocardial infarcts from partial occlusion, global hypoperfusion or reperfused occlusion (often non-ST-elevation). Reperfusion saves tissue but adds reperfusion injury, haemorrhage and contraction-band necrosis.

## Structure

- Gross and microscopic evolution over hours to months: see the infarct timeline page.
- Reperfused infarct: haemorrhagic, with contraction-band necrosis (hypercontracted sarcomeres) at the borders.
- Subendocardial infarct: necrosis of the inner third to half of the wall, often circumferential in global hypoperfusion.

## Step by step

- A plaque ruptures and platelets adhere, aggregate and release mediators; the coagulation cascade forms a thrombus.
- The thrombus occludes the artery; within seconds the myocardium switches to anaerobic glycolysis and stops contracting.
- ATP falls and lactate rises; after 20 to 40 minutes injury becomes irreversible in the subendocardium.
- Necrosis advances toward the epicardium; most of the final infarct is complete within about 6 hours.
- Damaged membranes leak troponin and CK-MB into the blood.
- Reperfusion limits the infarct but can cause haemorrhage, calcium overload with contraction bands and oxidative injury.

## Which artery infarcts which wall

| Artery | Share of infarcts | Territory |
| --- | --- | --- |
| Left anterior descending | About 40–50 % | Anterior LV wall, apex, anterior two-thirds of septum |
| Right coronary | About 30–40 % | Inferior/posterior LV wall, posterior septum, RV (right-dominant) |
| Left circumflex | About 15–20 % | Lateral LV wall |

## Clinical notes

- Typical presentation: crushing chest pain over 30 minutes radiating to the left arm or jaw, sweating, dyspnea; diabetics and older adults may have silent infarcts.
- Type 2 MI: supply–demand mismatch without plaque rupture (anemia, shock, tachyarrhythmia).

## Memory aid

Time is muscle: the wave of death travels from the inner wall outward, and the artery decides the wall.

## Test yourself

Think of the answer, then tap the question to see it.

## Which coronary artery is most often occluded in myocardial infarction?

The left anterior descending artery (about 40 to 50 % of infarcts).

## Why is the subendocardium the first zone to die?

It is the farthest from the epicardial arteries and is compressed by the high intraventricular pressure, so it is perfused last.

## What is contraction-band necrosis, and when is it seen?

Eosinophilic transverse bands of hypercontracted sarcomeres from calcium influx, typical of reperfused infarcts.

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## Elsewhere in DurgiPedia

- [The ECG in ischemia and infarction](https://durgical.com/en/physiology/the-ecg-in-ischemia-and-infarction/)
- [Coronary circulation and myocardial ischemia](https://durgical.com/en/physiology/coronary-circulation-and-myocardial-ischemia/)
- [Cardiac muscle: intercalated discs](https://durgical.com/en/histology/cardiac-muscle-intercalated-discs/)

## Connections

## Related 6

- [The myocardial infarct over time: what the pathologist sees from hours to months](https://durgical.com/en/general-pathology/the-myocardial-infarct-over-time-what-the-pathologist-sees-from-hours-to-months/)
- [Hypoxia, ischemia and reperfusion injury](https://durgical.com/en/general-pathology/hypoxia-ischemia-and-reperfusion-injury/)
- [Patterns of necrosis: coagulative, liquefactive, caseous, fat, fibrinoid, gangrenous](https://durgical.com/en/general-pathology/patterns-of-necrosis-coagulative-liquefactive-caseous-fat-fibrinoid-gangrenous/)
- [Infarction: red vs white, and what decides the damage](https://durgical.com/en/general-pathology/infarction-red-vs-white-and-what-decides-the-damage/)
- [Complications of myocardial infarction](https://durgical.com/en/general-pathology/complications-of-myocardial-infarction/)
- [Ischaemic heart disease](https://durgical.com/en/general-pathology/ischaemic-heart-disease/)

## Related conditions 3

- [Myocardial Infarction (Heart Attack)](https://durgical.com/en/conditions/myocardial-infarction/)
- [Cardiogenic shock](https://durgical.com/en/conditions/cardiogenic-shock/)
- [Stable angina](https://durgical.com/en/conditions/stable-angina/)

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Heart Attack | Myocardial Infarction | MedlinePlus](https://medlineplus.gov/heartattack.html) (MedlinePlus, US National Library of Medicine, 2025); [Hospital Mortality from Myocardial Infarction in Latin America and the Caribbean: Systematic Review and Meta-Analysis](https://europepmc.org/article/PMC/PMC9814809/) (Arquivos brasileiros de cardiologia, 2023).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/myocardial-infarction-pathogenesis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/myocardial-infarction-pathogenesis/