# Myocardial Infarction Pathology

> Myocardial infarction in MBBS Pathology: coagulative necrosis timeline, troponin kinetics, day 3-7 ruptures and Dressler syndrome.

- Canonical URL: https://prepelephant.com/topics/mbbs/pathology/myocardial-infarction-pathology
- Exam / course: MBBS · Subject: Pathology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Myocardial Infarction Pathology", PrepElephant, https://prepelephant.com/topics/mbbs/pathology/myocardial-infarction-pathology

## Direct answer

Coagulative necrosis of myocytes in a coronary territory, triggered by an occluding thrombus over a ruptured atherosclerotic plaque, defines myocardial infarction. Irreversible injury begins after roughly twenty to thirty minutes of total ischaemia and spreads as a wavefront from subendocardium to epicardium over the next three to six hours, which is why door-to-balloon time decides salvage. Cardiac troponin I rises within three to four hours and stays raised for seven to ten days; CK-MB clears within two to three days and marks re-infarction. Half of all deaths occur within the first hour from ventricular arrhythmia, before the patient reaches hospital — the statistic behind community defibrillation.

## What you must remember

- **Tissue clock:** wavy fibres and coagulative necrosis by 12-24 hours; neutrophils peak days one to three (grossly a yellow-tan soft myocardium); macrophages and granulation tissue days three to seven; collagen from week two; a grey-white scar by four to six weeks.
- **Serological clock:** troponin I up at 3-4 hours, peak at 18-24 hours, elevated 7-10 days (troponin T even longer); CK-MB rises 4-6 hours, peaks near 24 hours, normalises by 48-72 hours — the re-infarction marker.
- **Territory map:** left anterior descending artery in roughly 40-50% (anterior wall, apex, anterior septum), right coronary in 30-40% (inferior wall, posterior descending branch), left circumflex in 15-20% (lateral wall).
- **Rupture window:** days three to seven, when neutrophil-laden tissue is softest — papillary muscle, interventricular septum or free wall; free wall rupture causes haemopericardium and tamponade.
- **Papillary muscle rule:** the posteromedial papillary muscle, supplied by the posterior descending artery alone, ruptures far more often than the dual-supplied anterolateral one.
- **Late complications:** true ventricular aneurysm (apical, after LAD occlusion, dyskinetic bulge with thrombus), mural thrombus with embolism, and Dressler syndrome — immune pericarditis two to ten weeks after infarction.
- **Type 1 versus type 2:** plaque rupture with thrombosis versus supply-demand mismatch (anaemia, tachyarrhythmia, shock, sepsis); the pathology and the treatment differ.

## A five-day deterioration, worked through

On day five after an anterior infarction, a monitored patient suddenly develops a loud new pansystolic murmur and shock. Reason anatomically. If the septum has ruptured, a step-up in oxygen saturation occurs in the right ventricle; if the posteromedial papillary muscle has given way, acute mitral regurgitation floods the lungs with a murmur radiating to the axilla; if the free wall has split, the jugular veins distend, the pressure equalises and electromechanical dissociation arrests the patient within minutes. All three belong to the same day-three-to-seven window, when the infarct is a soft neutrophil soup with no collagen yet laid down. Weeks later a different complication appears: a bulging apical aneurysm with a haemodynamically stable but persistently raised ST segment, or Dressler's fever, pleuritic chest pain and friction rub responding to non-steroidal drugs. The timeline is the diagnosis.

## Troponin without infarction

A raised troponin means myocyte injury, not necessarily atherosclerotic occlusion — the commonest exam trap in the modern era. Renal failure slows clearance, myocarditis lyses myocytes diffusely, pulmonary embolism strains the right ventricle, sepsis and tachyarrhythmias create supply-demand mismatch, and all produce positive assays. The delta matters: a rising pattern with chest pain and electrocardiographic change argues for type 1 infarction, demanding antiplatelet therapy and angiography; a flat, low-level elevation in a dialysis patient does not. Indian experience adds another twist — patients frequently present a day or more after symptom onset, so troponin has peaked and the history, not the curve, dates the event and governs reperfusion decisions.

## Frequently asked questions

### When does ventricular free wall rupture typically occur after infarction?

Between days three and seven, when the neutrophil-rich infarct is softest; it produces haemopericardium, tamponade and often electromechanical dissociation.

### Why does the posteromedial papillary muscle rupture more often?

It receives blood from the posterior descending artery alone, whereas the anterolateral papillary muscle has a dual supply.

### Which cardiac marker is most specific for myocardial necrosis?

Cardiac troponin I and T; troponin I rises within 3-4 hours and remains elevated for 7-10 days.

### What is Dressler syndrome?

An immune-mediated pericarditis with fever, pleuritic pain and a friction rub appearing two to ten weeks after infarction, treated with non-steroidal anti-inflammatory drugs.

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

The left anterior descending artery, accounting for roughly 40-50% of cases and supplying the anterior wall, apex and anterior two-thirds of the septum.