I21.A9 — Other myocardial infarction type
I21.A9 is a billable, specific ICD-10-CM code for other myocardial infarction type. It is valid for submission on a claim.
Code first
The underlying condition must be sequenced before this code.
Code also
Both codes may be needed to describe the encounter fully. Sequencing depends on the reason for the visit.
- complication, if known and applicable, such as:
- (acute) stent occlusion (T82.897-)
- (acute) stent stenosis (T82.855-)
- (acute) stent thrombosis (T82.867-)
- cardiac arrest due to underlying cardiac condition (I46.2)
- complication of percutaneous coronary intervention (PCI) (I97.89)
- occlusion of coronary artery bypass graft (T82.218-)
Inclusion terms
Alternative wordings a physician may use in the chart for this same code.
- Myocardial infarction associated with revascularization procedure
- Myocardial infarction type 3
- Myocardial infarction type 4a
- Myocardial infarction type 4b
- Myocardial infarction type 4c
- Myocardial infarction type 5
Other codes that can never be billed with I21.A9
These codes carry an Excludes1 note pointing at I21.A9. The conflict binds both ways, but ICD-10-CM only writes it down on one side — so you would not find this by reading I21.A9 alone.
- I22Subsequent ST elevation (STEMI) and non-ST elevation (NSTEMI) myocardial infarction
Risk adjustment
I21.A9 risk-adjusts. Under the CMS-HCC V28 model it maps to this category:
- HCC 228 Acute Myocardial Infarction0.252 RAF
Coefficient shown for the Community Non-dual Aged segment. A higher HCC in the same hierarchy will suppress this one, so capturing it does not always add score.
Medicare coverage
I21.A9 is named in 50 Medicare coverage policies — 50 listing it as supporting medical necessity. Which of them applies to you depends on your Medicare contractor, and coverage genuinely differs by state.
- A52850Billing and Coding: Cardiac Catheterization and Coronary Angiography
- A52850Billing and Coding: Cardiac Catheterization and Coronary Angiography
- A56423Billing and Coding: Cardiology Non-emergent Outpatient Stress Testing
- A56423Billing and Coding: Cardiology Non-emergent Outpatient Stress Testing
How I21.A9 is indexed
Coders do not find codes by browsing the tabular list — they look them up in the alphabetic index, under the word the physician wrote. These are the index entries that lead here, so you can see which chart wordings map to I21.A9.
- Infarct, infarction›myocardium, myocardial›associated with revascularization procedure
- Infarct, infarction›myocardium, myocardial›type 3
- Infarct, infarction›myocardium, myocardial›type 4(a) (b) (c)
- Infarct, infarction›myocardium, myocardial›type 5
- Infarct, infarction›myocardium, myocardial›subsequent›type 3
- Infarct, infarction›myocardium, myocardial›subsequent›type 4
- Infarct, infarction›myocardium, myocardial›subsequent›type 5
Related codes at this level
Codes that share I21.A. If I21.A9 is not quite right, the correct code is usually one of these.
Questions about I21.A9
- Is I21.A9 a billable ICD-10-CM code?
- Yes. I21.A9 is a billable, specific ICD-10-CM code and is valid for submission on a claim.
- Where does I21.A9 sit in the tabular list?
- Diseases of the circulatory system (I00-I99), in the block Ischemic heart diseases (I20-I25).