Expansion
Perfusion falls, then metabolism, then diastolic and systolic function, then ECG changes, then pain
Expansion
In order:
- Perfusion mismatch between supply and demand
- Metabolic change: a switch to anaerobic metabolism, lactate production, falling ATP
- Diastolic dysfunction: impaired relaxation, since relaxation is ATP dependent
- Systolic dysfunction: regional wall motion abnormality
- ECG changes: ST depression or elevation, T wave change
- Angina
The order explains diagnostic sensitivity. Perfusion imaging and stress echocardiography detect steps 1 to 4 and are therefore more sensitive than the exercise ECG, which detects step 5.
It also explains silent ischaemia, common in diabetes and the elderly, where autonomic neuropathy blunts the final step while all the earlier ones proceed.
Irreversible injury begins after about 20 minutes of complete occlusion and spreads as a wavefront from subendocardium to epicardium, which is the rationale for rapid reperfusion.