The atherosclerotic plaque narrows the lumen of the coronary artery leading to reduced blood supply to a specific segment in the heart’s muscle. Gradual narrowing of the affected artery does not usually lead to infarction because of development of collateral vessels. But, when the plaque ruptures or ulcerates, it creates aggregation of platelets that leads to development of clot (thrombus) formation and occlusion (blockage) of the artery. This occlusion abruptly decreases the blood supply resulting in deadening of the affected area (leading to infarction).
The extent of damage depends on the area supplied by the involved artery, extent of occlusion, presence or absence of collateral vessels, spontaneous lysis (dissolution) of thrombus (or clot).