2026 ICD-10-CM Diagnosis Code I23.6Thrombosis of atrium, auricular appendage, and ventricle as current complications following acute myocardial infarction
ICD-10-CM Codes›I00–I99›I20-I25›STEMI
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 229
- Chronic Condition
I23.6 is a billable ICD-10-CM diagnosis code for thrombosis of atrium, auricular appendage, and ventricle as current complications following acute myocardial infarction. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 314 through 316. As a secondary diagnosis, it counts as a complication or comorbidity (CC) and moves an inpatient stay to a higher severity level within its MS-DRG family. It does not count, however, when the principal diagnosis is one of 115 closely related codes. The code is restricted by the Medicare Code Editor to adult patients (age 15 through 124). In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Complications of acute myocardial infarction.
For Medicare Advantage risk adjustment, I23.6 maps to CMS-HCC Category 229 (Unstable Angina and Other Acute Ischemic Heart Disease) under the V28 model, adding a risk factor of about 0.240 for a community, non-dual, aged beneficiary in payment year 2026.
This medical diagnosis code is frequently used in Cardiology medical specialties to designate conditions such selected atherosclerosis, ischemia, and infarction.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for I23.6.
Medicare Risk Adjustment (HCC)Billing
I23.6 maps to a payment category in the CMS-HCC model used to risk-adjust Medicare Advantage payments. Weights are the published community factors for payment year 2026.
Source: CMS Payment Year 2026 risk adjustment mappings and model software. Weights are relative factors, not dollar amounts; a beneficiary's total RAF also includes demographics and interactions. Browse all CMS-HCC categories.
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Atrial thrombosis
- Left ventricular thrombus
- Mural thrombus of heart
- Mural thrombus of left ventricle
- Mural thrombus of left ventricle following acute myocardial infarction
- Mural thrombus of right ventricle
- Mural thrombus of right ventricle following acute myocardial infarction
- Mural thrombus of ventricle of heart
- Post-infarction mural thrombus
- Right ventricular thrombus
- Thrombosis of atrium, auricular appendage, and ventricle due to and following acute myocardial infarction
- Ventricular thrombus following acute myocardial infarction
Tabular List NotesGuidance
Coding notes and annotation back-references applicable to this code.
Type 1 Excludes
- thrombosis of atrium, auricular appendage, and ventricle not specified as current complication following acute myocardial infarction I51.3
A type 1 excludes note is a pure excludes note. It means "NOT CODED HERE!" An Excludes1 note indicates that the code excluded should never be used at the same time as the code above the Excludes1 note. An Excludes1 is used when two conditions cannot occur together, such as a congenital form versus an acquired form of the same condition.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
acute myocardial infarction NEC I23.8
thrombosis I23.6
atrium I23.6
auricular appendage I23.6
ventricle (heart) I23.6
thrombosis I23.6
Thrombosis, thrombotic (bland) (multiple) (progressive) (silent) (vessel) I82.90
atrium, auricular See Also: Infarct, myocardium;
ventricle See Also: Infarct, myocardium;
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Heart Attack
Each year almost 800,000 Americans have a heart attack. A heart attack happens when blood flow to the heart suddenly becomes blocked. Without the blood coming in, the heart can't get oxygen. If not treated quickly, the heart muscle begins to die.
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert I23.6 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About I23.6Overview
Is I23.6 a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report thrombosis of atrium, auricular appendage, and ventricle as current complications following acute myocardial infarction on HIPAA-covered claims from October 1, 2025 through September 30, 2026.
What MS-DRG does I23.6 group to?
When thrombosis of atrium, auricular appendage, and ventricle as current complications following acute myocardial infarction is the principal diagnosis on an inpatient stay, it groups to MS-DRG 314, 315, 316, with relative weights from 0.6821 to 2.0852 depending on complications. Higher weights mean higher Medicare reimbursement.
Is I23.6 a CC or MCC?
CMS lists I23.6 as a CC (complication or comorbidity) for FY 2026. Reported as a secondary diagnosis, it moves the inpatient stay to a higher-weighted DRG within its severity family. It does not count when the principal diagnosis is one of the 115 closely related codes in its exclusion list.
Who can I23.6 be reported for?
The Medicare Code Editor checks thrombosis of atrium, auricular appendage, and ventricle as current complications following acute myocardial infarction against patient demographics: this code is intended for adult patients (age 15 through 124). Claims outside these limits are flagged as inconsistent.
What is the ICD-9 equivalent of I23.6?
Under the General Equivalence Mappings, thrombosis of atrium, auricular appendage, and ventricle as current complications following acute myocardial infarction converts to ICD-9-CM 429.79 (other sequelae of MI NEC). The mapping is approximate, so confirm the match fits the documentation.
What HCC is I23.6?
I23.6 (thrombosis of atrium, auricular appendage, and ventricle as current complications following acute myocardial infarction) maps to CMS-HCC Category 229 (Unstable Angina and Other Acute Ischemic Heart Disease), commonly written as HCC 229, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2026. It mapped to HCC 87 under the retired V24 model. It also maps in the PACE (CMS-HCC V22), ESRD (V21), and ESRD (V24) models. In the Part D prescription drug model it maps to RxHCC 188.
Does I23.6 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, I23.6 adds a risk adjustment factor of about 0.240 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.240 to 0.458 depending on the payment segment). A more severe related category (HCC 228) supersedes it when both are reported. See the full factor table on the HCC 229 category page.
