2025 ICD-10-CM Diagnosis Code I44.5

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Left posterior fascicular block

  • I44.5 is a billable/specific ICD-10-CM code that can be used to indicate a diagnosis for reimbursement purposes.
  • The 2025 edition of ICD-10-CM I44.5 became effective on October 1, 2024.
  • This is the American ICD-10-CM version of I44.5 – other international versions of ICD-10 I44.5 may differ.

ICD-10-CM Coding Rules

  • I44.5 is not usually sufficient justification for admission to an acute care hospital when used a principal diagnosis.

The following code(s) above I44.5 contain annotation back-references

 that may be applicable to I44.5:

  • I00-I99  Diseases of the circulatory system

Approximate Synonyms

  • Left posterial fascicular hemiblock (heart rhythm)
  • Left posterior hemiblock

Clinical Information

  • An impairment of transmission of the cardiac electrical impulse along the fibers of the left posterior fascicle. In pure left posterior fascicular block (lpfb), the impulse emerges from the unblocked anterosuperior division, thus producing small q waves in leads ii, iii, and avf. Thereafter, the impulse moves through the electrically predominant left ventricle in an inferior and rightward direction, thus explaining the s waves in leads i and avl as well as the r waves in leads ii, iii, and avf.
  • An impairment of transmission of the cardiac electrical impulse along the fibers of the left posterior fascicle. In pure left posterior fascicular block (lpfb), the impulse emerges from the unblocked anterosuperior division, thus producing small q waves in leads ii, iii, and avf. Thereafter, the impulse moves through the electrically predominant left ventricle in an inferior and rightward direction, thus explaining the s waves in leads i and avl as well as the r waves in leads ii, iii, and avf. Left posterior fascicular block is characterized by all of the following: right-axis deviation with frontal qrs axis between +90 degrees and +180 degrees; rs in leads i and avl and qr in inferior leads (q waves 40 ms) qrs duration <120 ms.

ICD-10-CM I44.5 is grouped within Diagnostic Related Group(s) (MS-DRG v42.0):

  • 308 Cardiac arrhythmia and conduction disorders with mcc
  • 309 Cardiac arrhythmia and conduction disorders with cc
  • 310 Cardiac arrhythmia and conduction disorders without cc/mcc

Convert I44.5 to ICD-9-CMCode History

  • 2016 (effective 10/1/2015): New code (first year of non-draft ICD-10-CM)
  • 2017 (effective 10/1/2016): No change
  • 2018 (effective 10/1/2017): No change
  • 2019 (effective 10/1/2018): No change
  • 2020 (effective 10/1/2019): No change
  • 2021 (effective 10/1/2020): No change
  • 2022 (effective 10/1/2021): No change
  • 2023 (effective 10/1/2022): No change
  • 2024 (effective 10/1/2023): No change
  • 2025 (effective 10/1/2024): No change

Diagnosis Index entries containing back-references to I44.5:

  • Block, blocked
    • bundle-branch (complete) (false) (incomplete) I45.4
      • leftI44.7
        • hemiblockI44.60
          • posterior I44.5
    • fascicular (left) I44.60
      • posterior I44.5
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