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I49.5
I49.5

I49.5: Sick sinus syndrome

The ICD-10-CM code for sick sinus syndrome, covering the tachycardia-bradycardia syndrome that the FY2027 tabular carries as an inclusion term under the same code.

Billable
FY2027

TABLE OF CONTENTS

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TABLE OF CONTENTS

At a glance

Code Family

I49: Other cardiac arrhythmias.

DRG Grouping

MDC 05, Diseases and Disorders of the Circulatory System, under the FY2027 MS-DRG v44 grouper: MS-DRG 308 with MCC, MS-DRG 309 with CC, or MS-DRG 310 without CC or MCC.

HCC Mapping (v28)

HCC 238: Specified Heart Arrhythmias.

Condition

Sick sinus syndrome

Family Specificity

Twelve billable codes in category I49 in FY2027, each naming a different arrhythmia rather than grading one condition. I49.5 is the entry for sick sinus syndrome, and it carries Tachycardia-bradycardia syndrome as its inclusion term.

Billable

Yes, a valid four character code. Its parent I49 is a category header and cannot be reported.

Which I49 code do I assign?

Category I49 does not grade one condition across a severity ladder. Each code names a different arrhythmia. The selection turns on which rhythm the provider documents. Several codes that compete with I49.5 sit outside category I49 altogether.

When documentation says…
Code
Tachycardia-bradycardia syndrome
I49.5
The FY2027 tabular lists Tachycardia-bradycardia syndrome as the inclusion term under I49.5. A note reading tachy-brady syndrome is coded here with no further qualification. The alphabetic index routes Syndrome, bradycardia-tachycardia to the same code. There is no separate ICD-10-CM code for the tachy-brady pattern, and the tachycardia half does not move the case out of I49.5.
Sinus bradycardia at 46, no symptoms, no sinus node diagnosis
R00.1
Bradycardia, unspecified. The FY2027 tabular lists Sinoatrial bradycardia, Sinus bradycardia, Slow heart beat and Vagal bradycardia as inclusion terms under R00.1. Category I49 carries Excludes2 notes for bradycardia NOS, sinoatrial bradycardia, sinus bradycardia and vagal bradycardia (R00.1). A slow sinus rate on its own is a rhythm finding, not a diagnosis of sinus node disease, and R00.1 maps to no HCC under CMS-HCC v28.
Complete heart block
I44.2
Atrioventricular block, complete. Atrioventricular conduction disease is classified in category I44, which describes a block below the sinus node rather than failure of the sinus node itself. Second degree block goes to I44.1 and first degree to I44.0. Sick sinus syndrome and AV block are distinct lesions, and a record documenting both supports a code from category I44 alongside I49.5.
Sinoatrial block on the tracing
I45.5
Other specified heart block. The FY2027 tabular lists Sinoatrial block and Sinoauricular block as inclusion terms under I45.5. Exit block at the sinus node is classified as a conduction disorder in category I45, not as sick sinus syndrome, even though the lesion sits at the same anatomical site. Assign I49.5 only where the provider names the syndrome.
A nodal, ectopic or coronary sinus rhythm disorder
I49.89
Other specified cardiac arrhythmias not elsewhere classified. In FY2027, I49.8 became a subcategory. Its inclusion terms Coronary sinus rhythm disorder, Ectopic rhythm disorder and Nodal rhythm disorder moved to I49.89, and Brugada syndrome gained its own code, I49.81. A documented sick sinus syndrome belongs in I49.5 instead.
Arrhythmia, no further detail in the record
I49.9
Cardiac arrhythmia, unspecified, which carries Arrhythmia (cardiac) NOS as its inclusion term. Assign it only after the record has been reviewed for a named rhythm. Where the chart elsewhere documents sick sinus syndrome, query for confirmation rather than defaulting to I49.9.
Tachy-brady syndrome with atrial fibrillation
I48.91
Unspecified atrial fibrillation, reported alongside I49.5 rather than in place of it. Neither category carries an Excludes1 note against the other. Where the fibrillation subtype is documented, assign the specific I48 code, such as I48.0 for paroxysmal atrial fibrillation.

Tabular notes

INCLUSION TERM

The FY2027 tabular lists one inclusion term under I49.5: Tachycardia-bradycardia syndrome. That term is the reason this code absorbs tachy-brady documentation without a second code for the tachycardia. The ICD-10-CM alphabetic index routes Syndrome, bradycardia-tachycardia to I49.5. The reversed word order lands in the same place. The Index also sends Dysfunction, sinoatrial node to I49.5.

EXCLUDES2

Category I49 carries five Excludes2 notes, and they propagate to I49.5: bradycardia NOS (R00.1), sinoatrial bradycardia (R00.1), sinus bradycardia (R00.1), vagal bradycardia (R00.1) and neonatal dysrhythmia (the P29.1- codes). An Excludes2 note means the excluded condition is not part of I49.5. The patient may carry both, and both codes may be reported where both are separately documented. The bradycardia that defines sick sinus syndrome is not separately documented in that sense. Guideline I.B.5 of the FY2027 ICD-10-CM Official Guidelines states that signs and symptoms associated routinely with a disease process should not be assigned as additional codes. The slow sinus rate that is the syndrome stays inside I49.5.

CODE FIRST

Category I49 carries a Code first instruction that propagates to I49.5, for cardiac arrhythmia complicating abortion or ectopic or molar pregnancy (O00–O07, O08.8) and for cardiac arrhythmia complicating obstetric surgery and procedures (O75.4). Where the arrhythmia arises in one of those settings, the obstetric code is sequenced first and I49.5 follows it. This is the only sequencing instruction the tabular attaches to the code.

FY2027: EFFECTIVE 1 OCTOBER 2026

Code I49.5 carries no Excludes1 note, no Use additional instruction and no Code also instruction at the code level. The FY2027 update makes no change to I49.5, its inclusion term or the category I49 notes. Elsewhere in category I49, FY2027 deletes I49.8 as a billable code and adds I49.81: Brugada syndrome, I49.82: Ventricular bigeminy and I49.89: Other specified cardiac arrhythmias not elsewhere classified.

Operational & financial impact

Why specificity matters beyond the chart: risk adjustment, DRG assignment and denial exposure all follow from which code is selected.

CMS-HCC v28 (PY2024+)

HCC 238: Specified Heart Arrhythmias.

Code I49.5 maps to HCC 238 in the CMS-HCC v28 ICD-10-CM mapping.

Under CMS-HCC v24 the same code mapped to HCC 96, also named Specified Heart Arrhythmias.

Code I48.91, unspecified atrial fibrillation, maps to the same HCC 238. Where tachy-brady syndrome and atrial fibrillation are both documented, the second code adds no further risk adjustment weight. It still belongs on the claim as a separate condition.

Code Z95.0, presence of cardiac pacemaker, maps to no HCC. A device carries no risk adjustment weight of its own, and it does not retire the diagnosis that prompted it.

Code R00.1, bradycardia unspecified, maps to no HCC. Selecting the symptom code in place of the diagnosis removes the encounter from HCC 238 entirely.

Capture is annual. Code I49.5 must appear on a dated encounter note from the data collection year rather than only on a problem list.

MS-DRG v44 (FY2027)

MS-DRG 308: Cardiac arrhythmia and conduction disorders with MCC.

MS-DRG 309: Cardiac arrhythmia and conduction disorders with CC.

MS-DRG 310: Cardiac arrhythmia and conduction disorders without CC/MCC.

All three sit in MDC 05, Diseases and Disorders of the Circulatory System.

Code I49.5 appears on the principal diagnosis list for this triplet. Where the sick sinus syndrome is the condition chiefly responsible for the admission, the case groups to MS-DRG 308, 309 or 310 according to the complications and comorbidities reported alongside it.

Where a permanent pacemaker is implanted during the stay, the procedure moves the case out of the medical triplet and into MS-DRG 242, 243 or 244. In v44 these are MS-DRG 242, Permanent cardiac pacemaker implant with MCC; MS-DRG 243, Permanent cardiac pacemaker implant with CC; and MS-DRG 244, Permanent cardiac pacemaker implant without CC/MCC. Those DRGs sit in MDC 05 as well.

Version 44.0 of the grouper applies to discharges on or after 1 October 2026.

Medicare and commercial payers

Medicare NCD 20.8.3, Single Chamber and Dual Chamber Permanent Cardiac Pacemakers, effective 13 August 2013, covers implantation for documented non reversible symptomatic bradycardia due to sinus node dysfunction. It also covers documented non reversible symptomatic bradycardia due to second degree or third degree atrioventricular block.

The record must show symptoms directly attributable to the bradycardia, and must show that reversible causes such as electrolyte abnormalities, medications or drugs and hypothermia were excluded.

The MS-DRG rules apply to Medicare Fee for Service inpatient claims. The CMS-HCC v28 rules apply to Medicare Advantage plans for payment year 2026.

WHERE SPECIFICITY IS LOST

Where the provider documented sick sinus syndrome and R00.1 was assigned, the claim reports a rhythm finding in place of a diagnosis. Code R00.1 maps to no HCC. Code I49.5 maps to HCC 238.

Where a pacemaker is in place and only Z95.0 was reported, the sick sinus syndrome drops off the claim. Code Z95.0 maps to no HCC. Pacing does not cure sinus node disease, and I49.5 remains reportable for as long as the condition is documented and assessed at the encounter.

Where tachy-brady syndrome is documented and only the atrial fibrillation was coded, the record loses I49.5. Both codes map to HCC 238. The risk adjustment total is unchanged. The clinical picture on the claim is not, and the pacing indication disappears from the record.

Where the note reads sinoatrial block and I49.5 was assigned, the claim misses I45.5. Where it reads complete heart block, the claim misses a code from category I44.

Where a device interrogation encounter was coded Z95.0, the encounter reason is misstated. Code Z95.0 carries an Excludes1 note against the Z45.0- codes, which means the two are not reported together for the same device.

SEVERITY DESIGNATION (MS-DRG V44.0)

I49.5 carries no severity designation. It appears in neither Appendix G, the CC list, nor Appendix H, the MCC list, of the ICD-10 MS-DRG Definitions Manual Version 44.0. A case reaches a higher tier of its DRG family only on a designation carried by another diagnosis.

Documentation checklist to support I49.5

Chart elements that support code selection and reduce specificity-driven denials.

FAQ

What ICD-10 code covers tachy-brady syndrome?

Tachy-brady syndrome is coded I49.5. The FY2027 tabular lists Tachycardia-bradycardia syndrome as the inclusion term under I49.5, sick sinus syndrome, and the alphabetic index routes Syndrome, bradycardia-tachycardia to the same code. There is no separate code for the tachy-brady pattern and no requirement to add a tachycardia code for the fast phase. Where a named tachyarrhythmia such as atrial fibrillation is separately documented, that code is reported in addition to I49.5.

Is I49.5 a billable code?

Yes. Code I49.5 is a valid four character billable code in the FY2027 code set, effective 1 October 2026. Its parent I49, other cardiac arrhythmias, is a category header and cannot be reported on a claim. No fifth character exists and none is needed.

When do I use R00.1 instead of I49.5?

Use R00.1, bradycardia unspecified, when the record documents a slow heart rate without a diagnosis of sinus node disease. The FY2027 tabular lists Sinoatrial bradycardia, Sinus bradycardia, Slow heart beat and Vagal bradycardia as inclusion terms under R00.1. Category I49 carries Excludes2 notes for bradycardia NOS, sinoatrial bradycardia, sinus bradycardia and vagal bradycardia (R00.1). Use I49.5 once the provider names sick sinus syndrome, sinus node dysfunction or tachy-brady syndrome. The distinction matters financially: I49.5 maps to HCC 238 under CMS-HCC v28 and R00.1 maps to no HCC.

Do I still code I49.5 after a pacemaker is implanted?

Yes, I49.5 is still coded for as long as the condition is documented and assessed at the encounter. Sick sinus syndrome is a chronic sinus node disorder, and pacing treats the bradycardia rather than resolving the disease. Report Z95.0, presence of cardiac pacemaker, as a companion status code under guideline I.C.21.c.3. Code Z95.0 maps to no HCC on its own. Reporting it in place of I49.5 removes the encounter from HCC 238.

Which code do I use for a pacemaker check?

Use a code from the Z45.0- group rather than Z95.0. Assign Z45.010 for checking and testing of the cardiac pacemaker pulse generator, which also carries generator replacement as an inclusion term. Assign Z45.018 for adjustment and management of another part of the pacemaker, including lead reprogramming. Code Z95.0 carries an Excludes1 note against the Z45.0- codes. The status code and the management code are not reported together for the same device. Code I49.5 is still reported alongside the device encounter code where the syndrome is assessed.

How do I code sick sinus syndrome with atrial fibrillation?

Report both. Assign I49.5 for the sinus node disorder and a code from category I48 for the fibrillation, using the documented subtype where it is available and I48.91 where it is not. Neither category carries an Excludes1 note against the other. Both codes map to HCC 238 under CMS-HCC v28. The pairing adds no further risk adjustment weight while keeping the clinical record accurate on the claim.

How is I49.5 sequenced, and does the rule differ for outpatient encounters?

Under Section II of the FY2027 ICD-10-CM Official Guidelines, the principal diagnosis is the condition established after study to be chiefly responsible for the admission. Where the sick sinus syndrome is the reason for admission, I49.5 is sequenced first and the case groups to MS-DRG 308, 309 or 310. Category I49 carries one Code first instruction, for arrhythmia complicating abortion, ectopic or molar pregnancy and for arrhythmia complicating obstetric surgery, where the obstetric code is sequenced ahead of I49.5. In the outpatient setting a probable or suspected sick sinus syndrome is not coded as confirmed. On the inpatient side a diagnosis documented as probable or suspected at the time of discharge is coded as confirmed under the UHDDS rules.

What changed for I49.5 in FY2027?

I49.5 is unchanged in the FY2027 update. The update, effective 1 October 2026, leaves I49.5, its inclusion term and the category I49 notes unchanged. It does change the category: I49.8 is no longer billable, and Brugada syndrome (I49.81), ventricular bigeminy (I49.82) and other specified cardiac arrhythmias not elsewhere classified (I49.89) take its place.

Related codes

Codes in the same family as I49.5. Only codes with a published page render as links.

Sibling codes in the I49 family

  • I49.01: Ventricular fibrillation.
  • I49.02: Ventricular flutter.
  • I49.1: Atrial premature depolarization.
  • I49.2: Junctional premature depolarization.
  • I49.3: Ventricular premature depolarization.
  • I49.40: Unspecified premature depolarization.
  • I49.49: Other premature depolarization.
  • I49.81: Brugada syndrome.
  • I49.82: Ventricular bigeminy.
  • I49.89: Other specified cardiac arrhythmias not elsewhere classified.
  • I49.9: Cardiac arrhythmia, unspecified.

Additional codes to consider

Codes outside the I49 family considered alongside I49.5.

Companion: code alongside when documented

  • Z95.0: Presence of cardiac pacemaker. The standard status companion to I49.5 once a device is implanted, and the inclusion term covers a cardiac resynchronization therapy pacemaker.
  • Z45.010: Encounter for checking and testing of cardiac pacemaker pulse generator [battery]. Assign for a device check or generator replacement encounter in place of Z95.0, which carries an Excludes1 note against the Z45.0- codes.
  • Z45.018: Encounter for adjustment and management of other part of cardiac pacemaker. Assign for reprogramming or lead management, again in place of Z95.0.
  • Z95.810: Presence of automatic (implantable) cardiac defibrillator. Assign instead of Z95.0 where the device is a defibrillator with synchronous pacing, which Z95.0 excludes.

Consider instead

  • R00.1: Bradycardia, unspecified. Use for a slow sinus rate with no diagnosis of sinus node disease, carrying Sinus bradycardia and Vagal bradycardia as inclusion terms.
  • I44.2: Atrioventricular block, complete. Use where the documented block is at the AV node rather than the sinus node.
  • I44.1: Atrioventricular block, second degree. Use where second degree AV block is the documented lesion.
  • I45.5: Other specified heart block. Carries Sinoatrial block and Sinoauricular block as inclusion terms. SA exit block is classified here rather than under I49.5.
  • I49.89: Other specified cardiac arrhythmias not elsewhere classified. Use for a named arrhythmia with no code of its own, such as a nodal rhythm disorder. Brugada syndrome takes I49.81 from FY2027.
  • I49.9: Cardiac arrhythmia, unspecified. Use only where the record names no rhythm at all.
  • I45.9: Conduction disorder, unspecified. Use where a conduction disorder is documented without a named site or degree.
  • P29.12: Neonatal bradycardia. The Excludes2 note at category I49 sends neonatal dysrhythmia to the P29.1- codes.
  • R94.31: Abnormal electrocardiogram [ECG] [EKG]. Use where the tracing is reported as abnormal and no rhythm diagnosis has been made.

Sources

All claims on this page derive from government and professional-standards sources.

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