I21.21

HCC Category Mapping

What This Code Means

A heart attack caused by a blood clot blocking the left circumflex coronary artery, with characteristic ST segment elevation visible on an EKG.

Coding Tips

• •Left circumflex STEMI may present with lateral or posterior wall involvement; verify documentation identifies the circumflex as the culprit vessel
• •Include the appropriate 7th character to indicate whether this is the initial episode or a subsequent episode

Clinical Significance

STEMI involving the left circumflex coronary artery typically affects the lateral or posterior wall of the heart. Left circumflex STEMIs can be particularly challenging to diagnose because standard 12-lead electrocardiogram may show only subtle changes, and posterior involvement may require posterior leads (V7-V9). This code is clinically important for capturing these sometimes-missed presentations that carry significant morbidity.

Documentation Requirements

• ✓Explicit documentation of STEMI with left circumflex artery involvement
• ✓Electrocardiogram findings (may show lateral ST elevation in leads I, aVL, V5, V6 or posterior changes)
• ✓Cardiac catheterization or angiography confirming left circumflex occlusion
• ✓Cardiac biomarker elevation
• ✓Timing of the acute event within the 4-week window
• ✓Documentation of any lateral or posterior wall involvement

Commonly Confused Codes