Why do physicians monitor a patient's enzyme levels if they suspect that a heart attack has occured?

A heart attack can be caused by a build up of fat around it or a clot, this means that the enzymes did not work properly. they need to record amount immediately after to see if it's low and or a risk for the patient afterwards. and determine what treatment they will need

Changes over time in blood levels of heart enzymes indicate heart muscle health

They are all in a iving organism.

Are you asking about a street map usage  if so here is your answer  a street map for a very limited area could simply be a bit map or a .jpg image.  but a more general map would probably store the streets as vectors.  but you shouldn't assume that there is one way to do it