Cracking the Code

Coding Myocardial Infarction

Myocardial infarction (heart attack) occurs when blood flow to the heart is blocked. MIs are classified as acute if the duration is four weeks or less. When a provider documents Acute MI with no further specification, I21.9 is reported. Type 1 MI’s also can be classified by whether there is an ST-segment elevation. The ST refers to the S-T segment or wave on an ECG. The ICD-10-CM codes for type 1 acute myocardial infarction (AMI) identify the site, such as the anterolateral wall or true posterior wall. Subcategories I21.0-I21.2 and code I21.3 are used for type 1 ST elevation myocardial infarction (STEMI). A non-ST elevation myocardial infarction (NSTEMI) describes when the blood clot only partly occludes the artery, and only a portion of the heart muscle being supplied by the affected artery dies. Code I21.4, non-ST elevation (NSTEMI) myocardial infarction, is used for type 1 non-ST elevation myocardial infarction (NSTEMI) and nontransmural MI’s.

If a type 1 NSTEMI evolves to STEMI, assign the STEMI code. If a type 1 STEMI converts to NSTEMI due to thrombolytic therapy, it is still coded as STEMI.

Q: Mrs. Jones is evaluated by a cardiologist and admitted with an inferolateral wall acute STEMI. The patient’s symptoms started three days prior to her presentation to the emergency department. What is the ICD-10-CM code?
A: I21.19, ST elevation (STEMI) myocardial infarction involving other coronary artery of inferior wall. Rationale: Referencing our ICD-10-CM Alphabetic Index for Infarct, infarction/myocardium, myocardial/ST elevation/inferior, it brings us to I21.19. In ICD-10-CM, myocardial infarctions are classified as acute if the duration is four weeks or less. As always, we want to verify the code selection in the Tabular List.
Reference: FY 2024 ICD-10-CM guidelines and code book
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