I21Acute myocardial infarction

I21 is the ICD-10-CM diagnosis code for acute myocardial infarction. It belongs to block I20-I25 (ischemic heart diseases) and chapter 9 (diseases of the circulatory system). It is a header code, so it can't be reported by itself; one of its 8 subcodes must be used instead.

To report this condition, pick the subcode that matches the documentation: I21.0 (wall), I21.1 (wall), I21.2 (sites), I21.3 (site), I21.4 (infarction), I21.9 (unspecified), I21.A (infarction) and I21.B (dysfunction).

The conditions in its Excludes2 note aren't part of I21, but may be coded alongside it if the patient has both: old myocardial infarction (I25.2), postmyocardial infarction syndrome (I24.1) and subsequent type 1 myocardial infarction (I22.-).

Use an additional code, if applicable, to identify: exposure to environmental tobacco smoke (Z77.22), history of tobacco dependence (Z87.891), occupational exposure to environmental tobacco smoke (Z57.31), status post administration of tPA (rtPA) in a different facility within the last 24 hours prior to admission to current facility (Z92.82), tobacco dependence (F17.-) and 1 more.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015, and changed in FY2018 (title revised).