Myocardial infarction
How a blocked coronary artery starves a territory of heart muscle, why the inner wall dies first, and how lost muscle, healing and scarring explain the symptoms and the complications that can follow.
By the end, you can
- Relate each main coronary artery to the territory of heart muscle it supplies.
- Explain how ischaemia moves from reversible to irreversible injury in a cardiac muscle cell.
- Distinguish subendocardial from transmural infarction, and explain what STEMI and NSTEMI describe.
- Explain how loss of contracting muscle changes the heart’s output and filling pressure.
- Relate the main complications to the timeline of healing.
- Recognise how an infarct is dated and classified and which tests confirm it, and explain how reperfusion and the main drug classes act on the mechanism.
What it is
Myocardial infarction is death of heart muscle caused by prolonged ischaemia, recognised by a rise in cardiac troponin together with evidence of ischaemia. Most infarcts follow thrombosis on a disrupted coronary plaque. They are described by depth (subendocardial or transmural) and, while they happen, by the ECG (STEMI or NSTEMI).
3 types to tell apart
- STEMI
- Troponin rises with persistent ST elevation on the ECG, usually from complete occlusion of a coronary artery with injury extending through the full thickness of the wall.
- NSTEMI
- Troponin rises without ST elevation (often with ST depression or T-wave inversion), usually from incomplete or intermittent blockage, with injury mainly in the inner wall.
- Supply–demand (type 2) infarction
- Infarction from an imbalance between supply and demand, such as severe anaemia, a fast arrhythmia or low blood pressure, without a new coronary thrombus.
US spelling: ischaemia → ischemia.
Normal function
How the heart muscle is supplied
Two coronary arteries leave the aorta just above the aortic valve. The soon divides into the (the left anterior descending artery, LAD), which runs down the front of the septum towards the apex, and the , which follows the groove round to the left side. The supplies the right ventricle and, in most people, the inferior wall of the left ventricle.
Each artery has a territory: the block of muscle it supplies. Branches run on the surface and dive inwards, so the innermost layer of muscle, the subendocardium, is the last to be reached. It is also squeezed hardest during contraction, so it fills with blood mainly in diastole.
Heart muscle already extracts most of the oxygen from coronary blood at rest, so it can only meet a rise in demand by increasing flow. It has almost no reserve of oxygen or energy.
Underlying change · Step 1 of 5
A coronary artery is blocked
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Underlying change · Step 2 of 5
Ischaemia: from reversible to irreversible injury
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 5
Subendocardial or transmural
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 4 of 5
The ventricle pumps less well
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 5 of 5
Healing, and complications by timing
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .