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