Type 1 ST elevation myocardial infarction (STEMI) and non-ST elevation myocardial infarction (NSTEMI)

The ICD-10-CM codes for type 1 acute myocardial infarction (AMI) identify the site, such as 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). Code I21.4, Non-ST elevation (NSTEMI) myocardial infarction, is used for type 1 non-ST elevation myocardial infarction (NSTEMI) and nontransmural MIs.

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. For encounters occurring while the myocardial infarction is equal to, or less than, four weeks old, including transfers to another acute setting or a postacute setting, and the myocardial infarction meets the definition for “other diagnoses” (see Section III, Reporting Additional Diagnoses), codes from category I21 may continue to be reported.

For encounters after the 4-week time frame and the patient is still receiving care related to the myocardial infarction, the appropriate aftercare code should be assigned, rather than a code from category I21. For old or healed myocardial infarctions not requiring further care, code I25.2, Old myocardial infarction, may be assigned.