myocardial infarction
Meaning of myocardial infarction: The formal name pins down what the everyday phrase leaves vague: a patch of heart muscle killed by blood flow that stopped.
Definition of myocardial infarction
Myocardial infarction is death of heart muscle caused by a loss of its blood supply. Myocardium is the muscular wall of the heart, and an infarction is an area of tissue killed by lack of circulation. It is the technical name for what is usually called a heart attack, and it is recognized from evidence of muscle injury together with signs that the muscle was starved of blood.
What do the two words mean?
Myocardium is the muscular wall of the heart, the layer that does the pumping. An infarct is a patch of tissue that has died because its blood supply was cut off, and infarction is the process that produces it. Put together, the phrase states exactly what happened and where, without borrowing the vague word attack. The same construction names the same event elsewhere in the body, as in cerebral infarction for the dead tissue left behind by a stroke, or bowel infarction when the gut loses its supply.
Why is it not one single condition?
| Form | What lies behind it |
|---|---|
| Type 1 | A deposit in a coronary artery ruptures and a clot forms on it |
| Type 2 | Demand outruns supply with no new blockage, as in heavy bleeding, a very fast rhythm or overwhelming infection |
| With ST elevation | The tracing indicates a coronary artery blocked through its full thickness |
| Without ST elevation | Muscle injury with a tracing that does not show complete blockage |
The first split concerns the mechanism and the second concerns what the electrical tracing shows, so the two run alongside each other rather than in sequence. The difference is not academic. A vessel blocked through its full thickness means muscle is dying at that moment, and the urgency attached to it is not the urgency attached to injury found on a blood test alone.
How is the diagnosis reached?
The definition rests on two elements together: evidence that heart muscle has been injured, and evidence that the injury came from a shortage of blood. Injury is measured by troponin, a protein that leaks from damaged heart muscle into the bloodstream. Evidence of ischemia comes from symptoms, from the electrical tracing, or from imaging showing a segment of wall that no longer moves. Troponin alone is not enough, because the protein also rises in kidney failure, in severe infection, in heart failure and after a clot lodges in the lungs. Telling an injured heart muscle from a starved one is the everyday work behind the label.
Also known as
Used in a sentence
The discharge summary recorded a non-ST-elevation myocardial infarction managed medically.
Good to know
A raised troponin shows that heart muscle has been injured but not why, and the level also climbs in kidney failure, sepsis, heart failure and pulmonary embolism, so the label rests on the whole picture rather than on the blood test alone.
Word origin
Where “myocardial infarction” comes from
Myocardial joins the Greek mys, muscle, with kardia, heart. Infarction comes from the Latin infarcire, to stuff or cram, describing tissue plugged by a blockage.