Final answer:
A completely blocked atherosclerotic blood vessel is referred to as occluded, which can lead to serious conditions like myocardial infarction if untreated.
Step-by-step explanation:
When a blood vessel is atherosclerotic and is completely blocked, the correct term is occluded. This means that there is a total obstruction preventing blood flow through the vessel. Atherosclerosis, a condition in which plaque builds up inside arteries, can cause the arteries to become so narrowed that they become occluded, resulting in decreased blood flow (ischemia) and insufficient oxygen (hypoxia) supplied to the tissues. If such occlusions occur in the coronary arteries and are not treated, they can lead to cardiac muscle death (myocardial infarction). Procedures like angioplasty and stent insertions can be used to treat these occlusions by mechanically widening the narrowed vessel.