2026 ICD-10-CM Diagnosis Code I44.5Left posterior fascicular block

ICD-10-CM Codes›I00–I99›I30-I5A›I44

ICD-10-CM I44.5
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

I44.5 is a billable ICD-10-CM diagnosis code for left posterior fascicular block. 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. The code is flagged as a questionable admission, since it rarely justifies inpatient admission on its own. Coders also document this condition as EKG: left bundle branch block. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Conduction disorders.

Code Identity

ICD-10-CM Code
I44.5
Billable Status
Yes — Valid for Submission
Code Describes
Left posterior fascicular block
Short Description
Left posterior fascicular block
Same as the full description in the CMS dataset.
Parent Code
I44
Atrioventricular and left bundle-branch block

Code Classification

ChapterI00–I99Diseases of the circulatory system
SectionI30-I5AOther forms of heart disease
CategoryI44Atrioventricular and left bundle-branch block
This CodeI44.5Left posterior fascicular block

Code EditsBilling

Medicare Code Editor checks that affect claim validity for I44.5.

Questionable admission codes
Some diagnoses are not usually sufficient justification for admission to an acute care hospital. For example, if a patient is given code R030 for elevated blood pressure reading, without diagnosis of hypertension, then the patient would have a questionable admission, since elevated blood pressure reading is not normally sufficient justification for admission to a hospital. The following list contains diagnosis codes identified as questionable admission when used.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • EKG: left bundle branch block
  • Left posterior fascicular block
  • Left posterior fascicular block on electrocardiogram
  • Monofascicular block

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.

    • Block, blocked
      • bundle-branch (complete) (false) (incomplete)
        • left
          • hemiblock
            • posterior
    • Block, blocked
      • fascicular (left)
        • posterior

Clinical ClassificationClinical

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

CCSR CIR016
Conduction disorders
Default principal diagnosis: inpatient Yes · outpatient Yes

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 I44.5 to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
426.2 Left bb hemiblock
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 I44.5Overview

Is I44.5 (Atrioventricular and left bundle-branch block) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report left posterior fascicular block on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does I44.5 group to?

When left posterior fascicular block 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.

Does I44.5 justify an inpatient admission?

Not on its own. The Medicare Code Editor lists this code as a questionable admission because left posterior fascicular block is not usually sufficient justification for admission to an acute care hospital.

What is the ICD-9 equivalent of I44.5?

Under the General Equivalence Mappings, left posterior fascicular block converts to ICD-9-CM 426.2 (left bb hemiblock). 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.