What Is Myocardial Infarction?

Myocardial infarction, known outside clinical settings as a heart attack, is the death of heart muscle caused by prolonged loss of blood supply. Coronary arteries deliver oxygen to the myocardium, and when flow through one of them falls far enough for long enough, the cells it feeds begin to die within minutes and the damage becomes irreversible over the following hours. The condition is the most consequential form of ischemic heart disease and remains among the leading causes of death worldwide.

The term is defined precisely rather than loosely, because treatment decisions and epidemiological statistics both depend on a consistent threshold. The Fifth Universal Definition of Myocardial Infarction, issued in 2026 by a joint task force of the European Society of Cardiology, the American College of Cardiology, the American Heart Association, and the World Heart Federation, keeps the distinction between myocardial injury, meaning any detectable cell death, and myocardial infarction, which additionally requires clinical evidence of ischemia. That distinction matters because troponin can rise from sepsis, kidney disease, or heart failure without any coronary blockage.

Mechanism and Classification

The classic mechanism is atherothrombosis: an atherosclerotic plaque in a coronary artery ruptures or erodes, exposing material that triggers clot formation, and the resulting thrombus occludes the vessel. The 2026 definition designates this a primary infarction, having replaced the numbered type 1 through type 5 scheme introduced in 2007 with three clinical categories. Secondary infarction covers an oxygen supply and demand mismatch without a primary coronary event, as in severe anemia, sustained tachycardia, or profound hypotension. Procedure-related infarction covers events arising from percutaneous coronary intervention, bypass surgery, and structural cardiac procedures. A parallel and more immediately operational split divides presentations by the electrocardiogram into ST-elevation infarction, which usually reflects complete occlusion and calls for urgent reperfusion, and non-ST-elevation infarction, which is managed on a different pathway.

Biomarkers and Diagnostic Thresholds

Cardiac troponin I and T are the preferred biomarkers because they are expressed almost exclusively in cardiac muscle and appear in blood soon after injury. The diagnostic threshold is the 99th percentile upper reference limit measured in a healthy reference population, now specified separately for men and women, and a rising or falling pattern across serial samples distinguishes acute injury from a chronic elevation. High-sensitivity assays detect concentrations an order of magnitude lower than earlier generations, which shortened rule-out protocols from many hours to one or two, and the analytical and interpretive consequences of that shift have been examined extensively. The tradeoff is a larger population of patients with detectable troponin who do not have an infarction, placing more weight on clinical context and imaging.

Electrocardiographic Detection and Automated Analysis

The 12-lead electrocardiogram remains the first test performed, because it is fast, inexpensive, and localizes the affected territory through the pattern of ST-segment deviation across leads. Automated interpretation has been built into ECG machines for decades using rule-based criteria on measured intervals and amplitudes. More recent work applies convolutional and recurrent neural networks directly to the raw waveform, and a review of deep learning methods for detecting and locating myocardial infarction on the ECG surveys several dozen such studies. Reported accuracies are high on public databases, though generalization across recording equipment, patient populations, and lead subsets is the recurring limitation. Wearable and single-lead devices extend the same signal processing problem to ambulatory monitoring, where noise and electrode placement vary far more than in a hospital.

Applications

Work on myocardial infarction connects to several engineering and technology areas, including:

• Biosensor and assay design for high-sensitivity cardiac troponin measurement
• Electrocardiograph instrumentation and automated waveform interpretation
• Machine learning for triage, risk scoring, and clinical decision support
• Cardiac imaging, including echocardiography, CT angiography, and cardiac MRI
• Catheter, guidewire, and drug-eluting stent design for reperfusion procedures
• Wearable and remote monitoring systems for post-infarction follow-up
• Emergency medical service telemetry for prehospital ECG transmission