2027 ICD-10-CM Diagnosis Code I48.4Atypical atrial flutter
ICD-10-CM Codes›I00–I99›I30-I5A›I48
- Billable — Valid for Submission
- CC — Complication or Comorbidity
- Risk Adjusts — HCC 238
- Chronic Condition
I48.4 is a billable ICD-10-CM diagnosis code for atypical atrial flutter. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 308 through 310, 791, 793. 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 54 closely related codes. Coders also document this condition as atrial flutter. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cardiac dysrhythmias.
For Medicare Advantage risk adjustment, I48.4 maps to CMS-HCC Category 238 (Specified Heart Arrhythmias) under the V28 model, adding a risk factor of about 0.299 for a community, non-dual, aged beneficiary in payment year 2027.
This medical diagnosis code is frequently used in Cardiology medical specialties to designate conditions such atrial fibrillation and flutter.
Code Identity
Code Classification
Medicare Risk Adjustment (HCC)Billing
I48.4 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 2027.
Source: CMS Payment Year 2027 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 flutter
- Atypical atrial flutter
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to I48.4: its own notes plus those printed at Chapter 9. A note printed at a category, block or chapter applies to every code under it.
Applicable To
Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.
- Type II atrial flutter
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
- certain conditions originating in the perinatal period (P04-P96)
- certain infectious and parasitic diseases (A00-B99)
- complications of pregnancy, childbirth and the puerperium (O00-O9A)
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
- endocrine, nutritional and metabolic diseases (E00-E88)
- injury, poisoning and certain other consequences of external causes (S00-T88)
- neoplasms (C00-D49)
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
- systemic connective tissue disorders (M30-M36)
- transient cerebral ischemic attacks and related syndromes (G45.-)
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Index to Diseases and InjuriesGuidance
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Patient EducationClinical
Arrhythmia
An arrhythmia is a problem with the rate or rhythm of your heartbeat. Your heart beats too quickly, too slowly, or with an irregular pattern. Changes in the electrical signals that control your heartbeat cause arrhythmias.
The full article covers:
- What is an arrhythmia?
- What causes an arrhythmia?
- What are the symptoms of an arrhythmia?
- How is an arrhythmia diagnosed?
- What are the treatments for an arrhythmia?
- Can arrhythmias be prevented?
Read the full article at MedlinePlus
Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.
Convert I48.4 to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About I48.4Overview
What is the ICD-10 code for atypical atrial flutter?
The ICD-10-CM code for atypical atrial flutter is I48.4 (sometimes written as I484). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is I48.4 (Atrial fibrillation and flutter) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report atypical atrial flutter on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does I48.4 group to?
When atypical atrial flutter is the principal diagnosis on an inpatient stay, it groups to MS-DRG 793, 791, 309, 310, 308, with relative weights from 0.5686 to 4.2192 depending on complications. Higher weights mean higher Medicare reimbursement.
Is I48.4 a CC or MCC?
CMS lists I48.4 as a CC (complication or comorbidity) for FY 2027. 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 54 closely related codes in its exclusion list.
What is the ICD-9 equivalent of I48.4?
Under the General Equivalence Mappings, atypical atrial flutter converts to ICD-9-CM 427.32 (atrial flutter). The mapping is approximate, so confirm the match fits the documentation.
What HCC is I48.4?
I48.4 (atypical atrial flutter) maps to CMS-HCC Category 238 (Specified Heart Arrhythmias), commonly written as HCC 238, in the CMS-HCC V28 model used for Medicare Advantage risk adjustment in payment year 2027. It mapped to HCC 96 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 193.
Does I48.4 risk-adjust for Medicare Advantage payment?
Yes. When documented and reported on a Medicare Advantage encounter, I48.4 adds a risk adjustment factor of about 0.299 to the beneficiary's RAF score for a community, non-dual, aged enrollee (published V28 weights range from 0.245 to 0.407 depending on the payment segment). HCC 238 sits at the top of its hierarchy, so no other condition category supersedes it. See the full factor table on the HCC 238 category page.
