2027 ICD-10-CM Diagnosis Code I49.5Sick sinus syndrome

ICD-10-CM Codes›I00–I99›I30-I5A›I49

ICD-10-CM I49.5
CMSSource: CMS FY 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

I49.5 is a billable ICD-10-CM diagnosis code for sick sinus syndrome. 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. Coders also document this condition as autosomal recessive sick sinus syndrome. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Cardiac dysrhythmias.

For Medicare Advantage risk adjustment, I49.5 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 cardiac arrhythmias (other).

Code Identity

ICD-10-CM Code
I49.5
Billable Status
Yes — Valid for Submission
Code Describes
Sick sinus syndrome
Short Description
Sick sinus syndrome
Same as the full description in the CMS dataset.
Parent Code
I49
Other cardiac arrhythmias

Code Classification

ChapterI00–I99Diseases of the circulatory system
SectionI30-I5AOther forms of heart disease
CategoryI49Other cardiac arrhythmias
This CodeI49.5Sick sinus syndrome

Medicare Risk Adjustment (HCC)Billing

I49.5 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.

CMS-HCC V28 Category (Payment Model)
HCC 238— Specified Heart Arrhythmias
Payment HCC · PY 2027 one of 17 ICD-10-CM codes in this category
Risk Adjustment Factor (RAF) Weight
+0.299
community, non-dual, aged · ranges 0.245–0.407 across segments
Hierarchy
Top of its hierarchy
HCC 238 is not superseded by any other condition category
Prior Model (CMS-HCC V24)
HCC 96
V24 retired V28 pays 100% of MA risk scores since PY 2026
Other CMS Models
PACE (CMS-HCC V22): HCC 96 · ESRD (V21): HCC 96 · ESRD (V24): HCC 96
ESRD V21 weights: 0.093 dialysis, 0.247–0.303 functioning graft · ESRD V24 weights: 0.049 dialysis, 0.227–0.346 functioning graft
Part D (RxHCC)
Not mapped
I49.5 does not risk-adjust in the RxHCC prescription drug model

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.

  • Autosomal recessive sick sinus syndrome
  • Complete deafness
  • Congenital deafness
  • Familial sick sinus syndrome
  • Postoperative cardiac arrhythmia
  • Postoperative sinus node dysfunction
  • Sick sinus syndrome
  • Sinoatrial node dysfunction and deafness
  • Tachycardia-bradycardia

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to I49.5: its own notes plus those printed at I49 and 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.

  • Tachycardia-bradycardia syndrome

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 I49 Other cardiac arrhythmias applies to 12 codes
  • bradycardia NOS (R00.1)
  • neonatal dysrhythmia (P29.1-)
  • sinoatrial bradycardia (R00.1)
  • sinus bradycardia (R00.1)
  • vagal bradycardia (R00.1)
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.-)

Code First

The underlying condition named in the note is sequenced before this code.

From I49 Other cardiac arrhythmias applies to 12 codes
  • cardiac arrhythmia complicating:
  • abortion or ectopic or molar pregnancy (O00-O07, O08.8)
  • obstetric surgery and procedures (O75.4)

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name I49.5, its category, or a range that includes it.

Excludes2 1

These codes carry an Excludes2 note naming I49.5: its condition is not part of those codes, and both may be reported when the patient has both.

  • R00 Abnormalities of heart beat
    specified arrhythmias (I47-I49) names I47-I49, which includes this code

Code Also 1

These codes say I49.5 may also be needed to fully describe the condition. The note gives no sequencing direction.

  • M35.81 Multisystem inflammatory syndrome
    cardiac arrhythmia (I47-I49.-) names I47-I49, which includes this code

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

Clinical InformationClinical

  • Sick Sinus Syndrome

    a condition caused by dysfunctions related to the sinoatrial node including impulse generation (cardiac sinus arrest) and impulse conduction (sinoatrial exit block). it is characterized by persistent bradycardia, chronic atrial fibrillation, and failure to resume sinus rhythm following cardioversion. this syndrome can be congenital or acquired, particularly after surgical correction for heart defects.

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 I49.5 to ICD-9-CMHistory

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

ICD-9-CM
427.81 Sinoatrial node dysfunct
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 I49.5Overview

What is the ICD-10 code for sick sinus syndrome?

The ICD-10-CM code for sick sinus syndrome is I49.5 (sometimes written as I495). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

Is I49.5 (Other cardiac arrhythmias) a billable code?

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

What MS-DRG does I49.5 group to?

When sick sinus syndrome 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.

What is coded first with I49.5?

The Code First note at I49, which applies to I49.5, reads: cardiac arrhythmia complicating: abortion or ectopic or molar pregnancy (O00-O07, O08.8); obstetric surgery and procedures (O75.4). When one of these applies, it is sequenced before I49.5.

What is the ICD-9 equivalent of I49.5?

Under the General Equivalence Mappings, sick sinus syndrome converts to ICD-9-CM 427.81 (sinoatrial node dysfunct). The mapping is approximate, so confirm the match fits the documentation.

What HCC is I49.5?

I49.5 (sick sinus syndrome) 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. It does not map to any RxHCC in the Part D prescription drug model.

Does I49.5 risk-adjust for Medicare Advantage payment?

Yes. When documented and reported on a Medicare Advantage encounter, I49.5 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.