FY2027 ICD-10-CM reference
I21.29: ST elevation (STEMI) myocardial infarction involving other sites
By the HCC Buddy Coding Team
The official ICD-10-CM descriptor is ST elevation (STEMI) myocardial infarction involving other sites. The FY2027 annual edition starts October 1, 2026. Check the edition that applies to the encounter or inpatient discharge, including any April update.
Billable code. Verified against the official FY2027 order file.
FY2027 Tabular instructions
Instructions below include applicable chapter, section and parent-code notes. Each note identifies where it appears in the official source.
Excludes2
certain conditions originating in the perinatal period (P04-P96)
Source: I00-I99 (chapter, inherited).
Excludes2
certain infectious and parasitic diseases (A00-B99)
Source: I00-I99 (chapter, inherited).
Excludes2
complications of pregnancy, childbirth and the puerperium (O00-O9A)
Source: I00-I99 (chapter, inherited).
Excludes2
congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
Source: I00-I99 (chapter, inherited).
Excludes2
endocrine, nutritional and metabolic diseases (E00-E88)
Source: I00-I99 (chapter, inherited).
Excludes2
injury, poisoning and certain other consequences of external causes (S00-T88)
Source: I00-I99 (chapter, inherited).
Excludes2
neoplasms (C00-D49)
Source: I00-I99 (chapter, inherited).
Excludes2
symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
Source: I00-I99 (chapter, inherited).
Excludes2
systemic connective tissue disorders (M30-M36)
Source: I00-I99 (chapter, inherited).
Excludes2
transient cerebral ischemic attacks and related syndromes (G45.-)
Source: I00-I99 (chapter, inherited).
Code also
the presence of hypertension (I10-I1A)
Source: I20-I25 (section, inherited).
Includes
cardiac infarction
Source: I21 (category, inherited).
Includes
coronary (artery) embolism
Source: I21 (category, inherited).
Includes
coronary (artery) occlusion
Source: I21 (category, inherited).
Includes
coronary (artery) rupture
Source: I21 (category, inherited).
Includes
coronary (artery) thrombosis
Source: I21 (category, inherited).
Includes
infarction of heart, myocardium, or ventricle
Source: I21 (category, inherited).
Includes
myocardial infarction specified as acute or with a stated duration of 4 weeks (28 days) or less from onset
Source: I21 (category, inherited).
Instructional note
code, if applicable, to identify:
Source: I21 (category, inherited).
Instructional note
exposure to environmental tobacco smoke (Z77.22)
Source: I21 (category, inherited).
Instructional note
history of tobacco dependence (Z87.891)
Source: I21 (category, inherited).
Instructional note
occupational exposure to environmental tobacco smoke (Z57.31)
Source: I21 (category, inherited).
Instructional note
status post administration of tPA (rtPA) in a different facility within the last 24 hours prior to admission to current facility (Z92.82)
Source: I21 (category, inherited).
Instructional note
tobacco dependence (F17.-)
Source: I21 (category, inherited).
Instructional note
tobacco use (Z72.0)
Source: I21 (category, inherited).
Excludes2
old myocardial infarction (I25.2)
Source: I21 (category, inherited).
Excludes2
postmyocardial infarction syndrome (I24.1)
Source: I21 (category, inherited).
Excludes2
subsequent type 1 myocardial infarction (I22.-)
Source: I21 (category, inherited).
Instructional note
Type 1 ST elevation myocardial infarction of other sites
Source: I21.2 (self, inherited).
Instructional note
Acute transmural myocardial infarction of other sites
Source: I21.29 (self, direct).
Instructional note
Apical-lateral transmural (Q wave) infarction (acute)
Source: I21.29 (self, direct).
Instructional note
Basal-lateral transmural (Q wave) infarction (acute)
Source: I21.29 (self, direct).
Instructional note
High lateral transmural (Q wave) infarction (acute)
Source: I21.29 (self, direct).
Instructional note
Lateral (wall) NOS transmural (Q wave) infarction (acute)
Source: I21.29 (self, direct).
Instructional note
Posterior (true) transmural (Q wave) infarction (acute)
Source: I21.29 (self, direct).
Instructional note
Posterobasal transmural (Q wave) infarction (acute)
Source: I21.29 (self, direct).
Instructional note
Posterolateral transmural (Q wave) infarction (acute)
Source: I21.29 (self, direct).
Instructional note
Posteroseptal transmural (Q wave) infarction (acute)
Source: I21.29 (self, direct).
Instructional note
Septal transmural (Q wave) infarction (acute) NOS
Source: I21.29 (self, direct).
Compare the FY2027 additions, removals and billable-status changes
What does I21.29 mean in FY2027?
The official ICD-10-CM descriptor is ST elevation (STEMI) myocardial infarction involving other sites. The FY2027 annual edition starts October 1, 2026. Check the edition that applies to the encounter or inpatient discharge, including any April update.
Is I21.29 billable in FY2027?
The FY2027 order file marks I21.29 as billable. Check the complete Tabular instructions and documentation before assigning it.
Does I21.29 map to an HCC?
In the CMS 2027 Initial ICD-10-CM Mappings (payment year 2027, 2026 dates of service), I21.29 maps to CMS-HCC V28 HCC 228 (Acute Myocardial Infarction). For 2027 dates of service, CMS has not yet published the payment year 2028 mappings. Under the PY2026 CMS mapping; CMS 2027 initial file unchanged: ESRD HCC 86; RxHCC HCC 188. Coefficients for these models are pending verification for payment year 2027. HHS-HCC: HCC 131 under the HHS-HCC 2026 benefit year mapping (no RAF; HHS-HCC weights vary by metal level). CMS-HCC V24: not used for payment year 2027 Medicare Advantage payment (CMS CY 2027 Rate Announcement). The PACE mapping is still pending verification for FY2027.
Source: CMS FY2027 ICD-10-CM order file. Payment model: CMS CY 2027 Rate Announcement. Read the FY2027 Official Guidelines.
Review the FY2026 April edition