---
title: Sick sinus syndrome
description: What sick sinus syndrome is, why it happens, how it is diagnosed, which treatment approaches clinical guidelines describe and when urgent help is needed.
type: disease
preset: sick-sinus-syndrome
aliases:
  - SSS
  - sinus node dysfunction
  - SND
  - tachy-brady syndrome
  - bradycardia-tachycardia syndrome
sources:
  - tier: guideline
    org: minzdrav-rf
    title: Брадиаритмии и нарушения проводимости
    year: 2025
    doi: 10.15829/1560-4071-2025-6669
    url: https://cr.minzdrav.gov.ru/view-cr/160_2
  - tier: guideline
    org: esc
    title: 2021 Рекомендации ESC по электрокардиостимуляции и сердечной ресинхронизирующей терапии
    year: 2022
    doi: 10.15829/1560-4071-2022-5159
    url: https://doi.org/10.15829/1560-4071-2022-5159
  - tier: reference
    org: msd-manuals
    title: Sick Sinus Syndrome (Sinus Node Dysfunction)
    year: 2024
    url: https://www.msdmanuals.com/professional/cardiovascular-disorders/specific-cardiac-arrhythmias/sinus-node-dysfunction
  - tier: guideline
    org: nice
    title: Dual-chamber pacemakers for symptomatic bradycardia due to sick sinus syndrome and/or atrioventricular block (TA88)
    year: 2014
    url: https://www.nice.org.uk/guidance/ta88
  - tier: guideline
    org: nice
    title: Transient loss of consciousness ('blackouts') in over 16s (CG109)
    year: 2023
    url: https://www.nice.org.uk/guidance/cg109
sources_checked: 2026-10-12
review: null
---

Sick sinus syndrome (SSS) is a disorder of the sinus node in which the heart beats too slowly for the body's needs.<Cite n={[1, 3]} /> The Russian Ministry of Health guideline calls the disorder itself sinus node dysfunction (SND) and uses "sick sinus syndrome" for SND that causes symptoms of a slow rhythm; the ESC guideline uses the two names as synonyms.<Cite n={[1, 2]} /> The sinus node is a small area of the right atrium that acts as the heart's natural pacemaker: its cells produce electrical impulses on their own.<Cite n={4} /> How the impulse travels on through the heart is explained in the article on the [conduction system of the heart](../../anatomy/conduction-system/).

<Diagram name="sick-sinus-syndrome">
  <p slot="normal">
    Normally the <Structure id="sa-node">sinus node</Structure> produces impulses regularly, and
    each one is conducted to the atria.<Cite n={1} /> The impulse then reaches the ventricles
    through the <Structure id="av-node">AV node</Structure> and the <Structure id="bundle-of-his">bundle of His</Structure>.<Cite n={4} />
  </p>
  <p slot="disease">
    The diagram shows a sinus pause (sinus arrest): the sinus node stops working for a while, and
    the P waves disappear from the ECG — no impulses reach the atria from the sinus node.<Cite n={3} />
    During a pause, lower pacemakers usually take over and keep the heart beating<Cite n={3} />;
    they are not drawn, so the ventricles are not activated either. Long pauses cause dizziness and
    fainting.<Cite n={3} />
  </p>
</Diagram>

## Why it happens

<Patient>

The main cause is that, with age, the tissue of the sinus node is replaced by fibrous (scar) and fatty tissue.<Cite n={[1, 4]} /> This process often spreads to nearby parts of the conduction system, so sick sinus syndrome can occur together with [atrioventricular block](../../disease/av-block/).<Cite n={[1, 3]} />

The work of the sinus node is regulated by the autonomic nervous system: parasympathetic influences slow it down, sympathetic ones speed it up.<Cite n={1} /> A slow rhythm can also have outside causes: medicines that slow the heart rate, excessive vagal tone, abnormal potassium levels, an underactive thyroid (hypothyroidism) and sleep apnoea.<Cite n={[1, 3]} /> Other causes are coronary heart disease and inflammatory and infiltrative diseases.<Cite n={3} />

It mainly affects older people, especially those with another heart condition or diabetes.<Cite n={3} /> How common sinus node dysfunction is cannot be estimated accurately, because cases without symptoms cannot be counted.<Cite n={1} />

A slow pulse on its own is not a disease. In healthy people the heart normally beats more slowly during sleep, and in highly trained athletes, people doing heavy physical work and young men the pulse can be very slow. This counts as normal only if there are no symptoms and the pulse rises enough with physical exertion.<Cite n={1} />

</Patient>

<Student>

SND covers a range of arrhythmias: sinus bradycardia, sinus arrest, sinoatrial (SA) block, tachy-brady syndrome and chronotropic incompetence.<Cite n={[1, 2, 3]} />

- Sinus pause (sinus arrest) is a temporary cessation of sinus node activity; on the ECG the P waves disappear for seconds to minutes.<Cite n={3} />
- Sinoatrial (SA) exit block: the sinus node produces an impulse, but conduction of the impulse to the atria is impaired.<Cite n={3} /> It is divided into first, second (type I and type II) and third degree; in third-degree block conduction is completely blocked and the atria are not activated from the sinus node.<Cite n={1} />
- Tachy-brady syndrome is the alternation of paroxysms of supraventricular tachyarrhythmia (atrial fibrillation or atrial flutter) with episodes of slow rhythm and/or ventricular asystole.<Cite n={1} /> According to the ESC, it is the most common form of SND; it is characterised by progressive, age-related degenerative fibrosis of the sinus node and the atrial myocardium.<Cite n={2} />
- Chronotropic incompetence is an inadequate rise in heart rate with exercise.<Cite n={[2, 3]} />

External causes of bradyarrhythmias listed in the Russian Ministry of Health guideline: beta blockers, calcium channel blockers, cardiac glycosides, class I and III antiarrhythmic drugs, hypokalaemia and hyperkalaemia, hypothyroidism and sleep apnoea.<Cite n={1} />

The limits of normal differ between documents. The Russian Ministry of Health guideline takes 40 beats per minute during the day at rest and 35 beats per minute at night as the lowest normal rates and accepts sinus pauses of no longer than 2 seconds.<Cite n={1} /> The ESC states that sinus bradycardia of 40–50 beats per minute at rest and 30 beats per minute during sleep, particularly in professional athletes, can be physiological, and that pauses longer than 2.5 s are rare in healthy people but should not on their own be taken as a disease.<Cite n={2} />

According to the Russian Ministry of Health guideline, SND accounts for about half of all pacemaker implantations.<Cite n={1} />

</Student>

<HeartModel highlight={['sa-node']} />

## Symptoms

<Patient>

Many people with sick sinus syndrome have no symptoms.<Cite n={3} /> A persistently slow rhythm can cause tiredness, tiring easily, lethargy, apathy and reduced mental ability.<Cite n={1} /> A slow rhythm can show itself as dizziness, confusion, falls and fainting, palpitations, tiredness on exertion, breathlessness and chest pain.<Cite n={4} />

Fainting is common in sick sinus syndrome: according to the ESC, it occurs in half of the patients referred for a pacemaker.<Cite n={2} />

In tachy-brady syndrome there can also be symptoms of a fast rhythm.<Cite n={3} /> Fainting can happen when an episode of fast rhythm ends and the sinus node does not start working again straight away.<Cite n={3} /> Sinus node function usually gets worse over time.<Cite n={3} />

</Patient>

<Student>

Symptoms occur at rest, at the end of a tachyarrhythmia episode (the conversion, or pre-automatic, pause) or during exercise, and range from mild fatigue to dizziness, presyncope and syncope.<Cite n={2} /> Exertional dyspnoea may be related to chronotropic incompetence.<Cite n={2} />

In acute disturbances, bradyarrhythmias present with cerebral hypoperfusion: sudden dizziness, confusion and, in severe cases, presyncope and syncope up to full Morgagni–Adams–Stokes attacks.<Cite n={1} />

</Student>

## How it is diagnosed

<Patient>

The diagnosis is made when the rhythm disturbance is recorded on an [electrocardiogram](../../diagnostic/ecg/) (ECG) or on a long ECG recording and matches the symptoms.<Cite n={[1, 3, 4]} /> The disturbances often come and go, so the rhythm is recorded for a long time: with a [Holter monitor](../../diagnostic/holter-monitoring/) for a day or longer.<Cite n={1} /> If symptoms are very rare, an implantable heart rhythm recorder may be needed.<Cite n={[1, 3]} />

To check whether the pulse rises with exertion, an exercise ECG is done.<Cite n={[1, 3]} /> The doctor also looks for causes that can be removed: they check which medicines the person takes and order blood tests, including thyroid-stimulating hormone (TSH) and potassium.<Cite n={1} /> When indicated, an ultrasound scan of the heart (echocardiography) and tests for sleep apnoea are done.<Cite n={3} />

</Patient>

<Student>

Bradyarrhythmias are diagnosed on documented confirmation by ECG and/or prolonged ECG monitoring together with the clinical symptoms.<Cite n={1} /> A 12-lead ECG is recommended for all patients with suspected bradycardia (class I, level C).<Cite n={1} /> Holter monitoring usually lasts 24–48 hours; there are recorders that record for up to 7 days.<Cite n={1} /> Sometimes SND shows itself only as a post-conversion sinus pause after sinus rhythm is restored in a patient with atrial fibrillation.<Cite n={3} /> With infrequent symptoms (more than 30 days between them) and non-diagnostic non-invasive tests, an implantable loop recorder is recommended (class I, level A).<Cite n={1} />

Chronotropic function is assessed with an exercise ECG (class IIa, level B).<Cite n={1} /> The Russian Ministry of Health guideline calculates the chronotropic index and considers ≥80% normal.<Cite n={1} /> MSD most commonly defines chronotropic incompetence as reaching less than 80% of the maximum age-predicted heart rate (220 minus age) on an exercise tolerance test.<Cite n={3} />

Polysomnography is recommended for patients being considered for permanent pacing (class I, level C).<Cite n={1} /> An invasive electrophysiological study is recommended if non-invasive tests are non-diagnostic (class IIb, level B).<Cite n={1} />

</Student>

## How it is treated

<Patient>

Decisions about treatment are made by a doctor. If a slow rhythm causes no symptoms, or its cause can be removed, a pacemaker is not recommended.<Cite n={[1, 2]} />

First, reversible causes are looked for and treated.<Cite n={1} /> If the cause is a medicine, the doctor decides whether this person really needs to take it.<Cite n={1} /> When a pacemaker is not needed, doctors avoid medicines that suppress the sinus node or prescribe them with caution.<Cite n={1} />

The main treatment for sick sinus syndrome with symptoms is a permanent pacemaker.<Cite n={[1, 2, 3]} /> This is a small device placed under the skin, usually below the collarbone. Through a lead it sends an impulse to the heart when the heart's own rhythm slows down or pauses, and it does not interfere when the rhythm is normal.<Cite n={1} /> Fitting it does not need open-heart surgery.<Cite n={1} /> A pacemaker clearly improves quality of life.<Cite n={1} /> Unlike in AV block, there is no evidence that in SND a pacemaker improves the prognosis, that is, helps people live longer.<Cite n={2} />

If a slow rhythm has caused a dangerous circulatory problem, doctors use medicines that speed up the heart rate for a while and temporary pacing.<Cite n={1} /> People with a pacemaker need regular check-ups; remote monitoring can replace some of the visits.<Cite n={1} />

People with sick sinus syndrome can develop [atrial fibrillation](../../disease/atrial-fibrillation/), which raises the risk of heart failure and stroke.<Cite n={3} /> That is why the pacemaker's data are checked, including for episodes of atrial fibrillation: this decides whether medicines that reduce blood clotting are needed.<Cite n={1} />

</Patient>

<Student>

Pacemaker implantation is recommended for symptomatic bradycardia due to SND (class I, level B in the Russian Ministry of Health guideline and the ESC).<Cite n={[1, 2]} /> Pacing is not recommended for asymptomatic bradycardia or bradycardia with reversible causes (III C).<Cite n={[1, 2]} />

- Mode: in SND, dual-chamber (DDD) pacing with minimisation of unnecessary ventricular pacing is recommended (I A).<Cite n={[1, 2]} /> Systematic right ventricular pacing should be avoided: it is associated with AF and worsening heart failure.<Cite n={2} />
- Tachy-brady syndrome: pacing is indicated to correct the bradyarrhythmia and allow drug therapy when ablation of the tachyarrhythmia is not preferred (I B); AF ablation to avoid pacemaker implantation should be considered in patients with symptomatic pre-automatic pauses after AF conversion (IIa C).<Cite n={2} />
- Chronotropic incompetence with symptoms during exercise: DDD pacing with rate response should be considered (ESC IIa B); the benefit is uncertain and the decision is individual.<Cite n={2} />
- Syncope with a documented asymptomatic pause of more than 6 seconds due to sinus arrest: pacing may be considered (IIb C).<Cite n={[1, 2]} />
- In haemodynamically unstable SND refractory to drug therapy, temporary pacing is recommended until a permanent pacemaker is implanted or the bradycardia resolves (class I, level C).<Cite n={1} />

In patients with SND the prognosis is unpredictable, and there are no data that permanent pacing improves it.<Cite n={2} /> In the follow-up of patients with a pacemaker, monitoring of device data is recommended for early detection of AF, including asymptomatic AF, so that anticoagulant therapy can be started in time (class I, level A).<Cite n={1} />

</Student>

## When to call an ambulance

Emergency care for bradyarrhythmias with fainting is started by the ambulance crew.<Cite n={1} /> If someone has lost consciousness, they need an ambulance.<Cite n={1} /> Call your local emergency number (112 in the EU, 911 in the US and Canada, 999 in the UK). Sudden dizziness, confusion or feeling faint can also be signs of an acute rhythm disturbance.<Cite n={1} /> NICE treats a blackout together with inappropriate persistent bradycardia on the ECG, or a blackout during exertion, as a red flag: such a person is referred urgently for cardiovascular assessment, and a specialist reviews the referral within 24 hours (the guideline covers people over 16).<Cite n={5} />

If fainting, feeling faint, weakness or dizziness appear that may be linked to a slow rhythm, do not put off seeing a doctor: the Russian Ministry of Health guideline names such symptoms as a reason for planned hospital admission.<Cite n={1} /> If dizziness or feeling faint comes back in a person with a pacemaker, this is a reason for an unscheduled visit to the doctor, and if they lose consciousness, call an ambulance.<Cite n={1} />

Sick sinus syndrome can be complicated by atrial fibrillation, which raises the risk of stroke.<Cite n={3} /> If there are signs of a stroke, call your local emergency number straight away (112 in the EU, 911 in the US and Canada, 999 in the UK). As with any heart condition, call an ambulance for fainting, chest pain or severe shortness of breath: this is the site's general safety rule, repeated at the bottom of every page.

<Quiz />