In addition to EKG’s, we utilize cardiac biomarkers to determine extent of ischemia and infarction. There are a few main cardiac biomarkers, or also called cardiac enzymes, that we will monitor. As you’ll see, each one has a specific timeline of when it presents, peaks, and returns to normal. Therefore the most accurate way to determine the extent of the injury is to trend them over 12-24 hours.
The first one is myoglobin. Myoglobin is a protein which becomes elevated with any muscle damage. It begins to rise within 1-4 hours from damage, peaks at 6-12, and returns to normal within 1-2 days. However, myoglobin is not specific to the myocardium or cardiac muscle so it could be indicative of other muscle damage.
The second is CK-MB. This isoenzyme is released in the presence of ischemia within muscle tissue. It is not specific to cardiac muscle, but is more specific than myoglobin and highly likely to be elevated with cardiac ischemia. It begins to elevate within 6-10 hours, peaks at 12-24, and days a few days to return to normal.
Third is troponin I. Troponin I is an enzyme specific to cardiac muscle that is released with ischemia and damage. It is the most consistently specific to cardiac muscle and, due to it’s trend timing, is the most reliable. It begins to rise within 4-6 hours, peaks at 18, and takes a couple weeks to return fully to normal.
In addition to these three main cardiac enzymes, there is also an isoenzyme called LDH that can be monitored. There are 5 types of LDH, and each one will be elevated for different reasons, for example muscle or liver damage. It begins to elevate within 8-12 hours, peaks at 72, and begins to return to normal after a week or two. LDH1 is specific to cardiac muscle damage. However, it is difficult and expensive to test.
Understanding these enzymes will help you to follow lab trends for your MI patient.