ICD-10 Code I21.21 – ST elevation (STEMI) myocardial infarction involving left circumflex coronary artery (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code I21.21 – ST elevation (STEMI) myocardial infarction involving left circumflex coronary artery
What it is
This code identifies an acute ST-elevation myocardial infarction caused by blockage of the left circumflex coronary artery. Use it when documentation specifically links the STEMI to that vessel.
Clinical signs
Clinical features vary; refer to documentation. Typical STEMI findings include ischemic chest pain, ECG evidence of ST elevation, and confirmation that the left circumflex artery is involved.
When to use this code
Use I21.21 when the provider documents an acute STEMI and names the left circumflex coronary artery as the affected vessel. It is appropriate in emergency, inpatient, or catheterization reports when the infarct location is clearly stated. Check documentation if the artery is not specified.
Do not use for
Do not use this code for NSTEMI, old myocardial infarction, or unspecified acute MI. If the record does not identify the left circumflex artery, code the documented infarct type and location instead.
Coding tip
Assign this code only when STEMI and left circumflex involvement are both clearly documented.