2027 ICD-10-CM Diagnosis Code I44.4Left anterior fascicular block

ICD-10-CM Codes›I00–I99›I30-I5A›I44

ICD-10-CM I44.4
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

I44.4 is a billable ICD-10-CM diagnosis code for left anterior fascicular block. 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. The code is flagged as a questionable admission, since it rarely justifies inpatient admission on its own. Coders also document this condition as bifascicular block. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Conduction disorders.

Code Identity

ICD-10-CM Code
I44.4
Billable Status
Yes — Valid for Submission
Code Describes
Left anterior fascicular block
Short Description
Left anterior 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 CodeI44.4Left anterior fascicular block

Code EditsBilling

Medicare Code Editor checks that affect claim validity for I44.4.

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.

  • Bifascicular block
  • Bifascicular block on electrocardiogram
  • EKG: left bundle branch block
  • EKG: right bundle branch block
  • Left anterior fascicular block
  • Left anterior fascicular block on electrocardiogram
  • Monofascicular block
  • Right bundle branch block AND left anterior fascicular block
  • Right bundle branch block and left anterior fascicular block on electrocardiogram
  • Right bundle branch block with left bundle branch block

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to I44.4: its own notes plus those printed at Chapter 9. A note printed at a category, block or chapter applies to every code under it.

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.

From Chapter 9 (I00-I99) Diseases of the circulatory system applies to 1,433 codes
  • 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.

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

Clinical ClassificationClinical

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

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

Clinical InformationClinical

  • Left Anterior Fascicular Block by ECG Finding

    an electrocardiographic finding of a slightly widened qrs duration (typically less than 120 ms) with leftward frontal plane qrs axis and typically small q waves in leads i and avl. (cdisc)

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 I44.4 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 2017–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About I44.4Overview

What is the ICD-10 code for left anterior fascicular block?

The ICD-10-CM code for left anterior fascicular block is I44.4 (sometimes written as I444). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is I44.4 (Atrioventricular and left bundle-branch block) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report left anterior fascicular block on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

What MS-DRG does I44.4 group to?

When left anterior fascicular block is the principal diagnosis on an inpatient stay, it groups to MS-DRG 309, 310, 308, with relative weights from 0.5686 to 1.1809 depending on complications. Higher weights mean higher Medicare reimbursement.

Does I44.4 justify an inpatient admission?

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

What is the ICD-9 equivalent of I44.4?

Under the General Equivalence Mappings, left anterior fascicular block converts to ICD-9-CM 426.2 (left bb hemiblock). The mapping is approximate, so confirm the match fits the documentation.