ICD-10 Code I21.09 – ST elevation (STEMI) myocardial infarction involving other coronary artery of anterior wall (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I21.09 – ST elevation (STEMI) myocardial infarction involving other coronary artery of anterior wall
What it is
This code identifies an acute ST-elevation myocardial infarction affecting an anterior-wall territory supplied by a coronary artery other than the main vessels named in separate codes. Use it when documentation specifies this exact location.
Clinical signs
Typical findings include acute chest pain or equivalent ischemic symptoms with ECG evidence of ST elevation. Clinical features vary; refer to documentation for the documented coronary artery and infarct location.
When to use this code
Use I21.09 when the provider documents STEMI involving the anterior wall and identifies another coronary artery, not one of the more specific anterior-wall STEMI codes. Apply it for the confirmed acute event, not a history of infarction. If the artery or wall location is unclear, check documentation.
Do not use for
Do not use this code for NSTEMI, old myocardial infarction, or unspecified acute MI. Also avoid it when the record names a more specific STEMI code for the culprit artery or another wall.
Coding tip
Match the infarct wall and named artery exactly; if the note is vague, query for clarification before assigning I21.09.