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Acute Myocardial Infarction (AMI)

Despite being one of the most common conditions treated in the hospital, the diagnosis of acute myocardial infarction is often misunderstood.  The 4th universal definition provides some clarity, but the application remains challenging.

The most common types of myocardial infarctions are type 1 and type 2 events.  Type 1 myocardial infarctions are atherothrombotic, and these can be STEMIs or NSTEMIs.  Type 2 myocardial infarctions are caused by supply-demand mismatch, and these are always due to something else.

There are two steps to diagnosing a type 1 or type 2 MI.  First, look for an acute troponin elevation.  You need to see a rise and/or fall in the troponin, and at least one level must be elevated (above the 99th percentile). Remember, a troponin can get you started toward making the diagnosis of MI, but you need more.

Next, look for at least one other finding of ischemia.  Options include anginal symptoms such as chest pain, new ischemic EKG changes, new Q waves on EKG, imaging evidence of new wall motion abnormality, or coronary thrombus on cardiac catheterization (the latter only applies to type 1 NSTEMIs).

In terms of coding, an acute MI may be reported as an additional diagnosis for up to 28 days after the index event, provided that it meets reportability guidelines.  Also, remember that type 2 Mis are always caused by something else, and instructional notes mandate first coding the underlying cause.

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