Expansion
The left coronary artery fills in diastole, when the myocardium is relaxed
Expansion
During systole the contracting left ventricular myocardium compresses the intramyocardial vessels and left coronary flow almost stops. Filling therefore occurs in diastole.
Three consequences follow:
- Tachycardia shortens diastole disproportionately and reduces coronary filling time
- Aortic regurgitation lowers diastolic pressure and reduces perfusion pressure
- Left ventricular hypertrophy raises end-diastolic pressure and opposes perfusion
The subendocardium is the most compressed layer and sits at the end of the arterial tree, so it is the first region to become ischaemic. That is the anatomical basis of subendocardial infarction and of ST depression in demand ischaemia.
The right coronary artery is less affected, because right ventricular pressure is low and it continues to receive some flow during systole.