2026 ICD-10-CM Diagnosis Code I48.4Atypical atrial flutter

ICD-10-CM Codes›I00–I99›I30-I5A›I48

ICD-10-CM I48.4
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

I48.4 is a billable ICD-10-CM diagnosis code for atypical atrial flutter. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 308 through 310. Coders also document this condition as atrial flutter. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cardiac dysrhythmias.

This medical diagnosis code is frequently used in Cardiology medical specialties to designate conditions such atrial fibrillation and flutter.

Code Identity

ICD-10-CM Code
I48.4
Billable Status
Yes — Valid for Submission
Code Describes
Atypical atrial flutter
Short Description
Atypical atrial flutter
Same as the full description in the CMS dataset.
Parent Code
I48
Atrial fibrillation and flutter

Code Classification

ChapterI00–I99Diseases of the circulatory system
SectionI30-I5AOther forms of heart disease
CategoryI48Atrial fibrillation and flutter
This CodeI48.4Atypical atrial flutter

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Atrial flutter
  • Atypical atrial flutter

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

Inclusion Terms

  • Type II atrial flutter

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Flutter
      • atrial or auricular
        • atypical
    • Flutter
      • atrial or auricular
        • type II
    • Flutter
      • heart
        • atrial or auricular
          • atypical
    • Flutter
      • heart
        • atrial or auricular
          • type II

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR CIR017
Cardiac dysrhythmias
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Atrial Flutter

    rapid, irregular atrial contractions caused by a block of electrical impulse conduction in the right atrium and a reentrant wave front traveling up the inter-atrial septum and down the right atrial free wall or vice versa. unlike atrial fibrillation which is caused by abnormal impulse generation, typical atrial flutter is caused by abnormal impulse conduction. as in atrial fibrillation, patients with atrial flutter cannot effectively pump blood into the lower chambers of the heart (heart ventricles).

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.

ICD-9-CM
427.32 Atrial flutter
Approximate The match is approximate rather than exact.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About I48.4Overview

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, 2025 through September 30, 2026.

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 308, 309, 310, with relative weights from 0.5661 to 1.2040 depending on complications. Higher weights mean higher Medicare reimbursement.

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.

Footnotes

[1] Chronic - a chronic condition code indicates a condition lasting 12 months or longer and its effect on the patient based on one or both of the following criteria:

  • The condition results in the need for ongoing intervention with medical products,treatment, services, and special equipment
  • The condition places limitations on self-care, independent living, and social interactions.