A marker of myocardial injury, not of myocardial infarction
Expansion
The universal definition: myocardial infarction requires a rise and/or fall of troponin with at least one value above the 99th centile, plus evidence of ischaemia, being symptoms, new ischaemic ECG changes, pathological Q waves, imaging evidence of new loss of viable myocardium, or thrombus on angiography.
Without that evidence, it is myocardial injury, not infarction.
Types of infarction
- Type 1: atherosclerotic plaque rupture with thrombus
- Type 2: supply and demand mismatch, from tachyarrhythmia, hypotension, sepsis, anaemia, hypoxia, hypertensive crisis or coronary spasm. Common in hospital, and treated by treating the cause rather than by antiplatelets and angiography
Non-coronary causes of a raised troponin
- Cardiac: myocarditis, Takotsubo, heart failure, arrhythmia, cardioversion, ablation, cardiac contusion, infiltration
- Non-cardiac: pulmonary embolism, sepsis, chronic kidney disease (a persistently raised baseline), stroke and subarachnoid haemorrhage, rhabdomyolysis, aortic dissection, extreme exertion, burns
High sensitivity assays detect very small amounts, so the emphasis has shifted from the absolute value to the delta change between two samples, typically at 0 and 3 hours. Algorithms use a low rule-out threshold and a high rule-in threshold with the change between.
A single very high troponin with no change on repeat suggests a chronic cause such as renal disease, not an acute event. Conversely a small but clearly rising value in the right clinical context is significant.