Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Link symptoms to sinus bradycardia or pauses, remove reversible causes, stabilise adverse bradycardia and select permanent pacing on clinical rather than rate criteria alone.
Intrinsic degeneration or disease of the sinus node and surrounding atrium can impair impulse formation or exit. Extrinsic autonomic, metabolic and pharmacological influences can mimic it, so a reversible-cause review precedes a permanent-device decision whenever the patient is stable.
Symptoms range from fatigue and exercise intolerance to presyncope and syncope. Because asymptomatic nocturnal bradycardia and pauses can be physiological, the key evidence is temporal agreement between a symptom and clinically plausible bradycardia or failure to raise heart rate with activity.
Acute resuscitation and chronic therapy are separate. Atropine and temporary pacing restore perfusion during deterioration; a dual-chamber permanent pacemaker is an established option for symptomatic SND without AV block, selected after specialist assessment.
Progressive fibrosis around the sinus node and atrial conduction tissue reduces pacemaker cell function and impulse propagation, making intrinsic dysfunction more common with age.
Ischaemia, cardiomyopathy, infiltrative disease and prior cardiac surgery can injure the sinus node, its arterial supply or surrounding atrial tissue.
Beta-blockers, rate-limiting calcium-channel blockers, digoxin and antiarrhythmics suppress automaticity or conduction and may reveal latent dysfunction, particularly when several agents are combined.
Hypothyroidism, electrolyte disturbance, hypothermia, high vagal tone and sleep apnoea can produce reversible sinus slowing or pauses that mimic intrinsic disease.
Degeneration, ischaemia or extrinsic suppression can reduce spontaneous depolarisation within the sinus node or slow conduction from the node into surrounding atrial myocardium.
Impaired impulse formation produces inappropriate sinus bradycardia or arrest, while impaired impulse exit can create sinoatrial block despite continuing nodal activity.
The same atrial remodelling predisposes to atrial fibrillation or flutter. When the tachyarrhythmia terminates, delayed sinus-node recovery can expose a prolonged pause.
A slow resting rate, prolonged pause or failure to increase rate with exertion lowers cardiac output, causing fatigue, exercise intolerance, presyncope, syncope or haemodynamic compromise.
A sinus P wave precedes each QRS at an inappropriately slow rate for the clinical setting; athletic conditioning and sleep may be physiological alternatives.
A pause lacks a sinus P wave. A pause that is an exact multiple of the basic P-P interval suggests sinoatrial exit block; non-multiple timing favours sinus arrest.
Heart rate fails to rise appropriately with exertion, producing fatigue, breathlessness or exercise limitation despite an acceptable resting rate.
AF, flutter or atrial tachycardia alternates with bradycardia, and termination of the tachyarrhythmia may expose a prolonged pause.
Shock, syncope, myocardial ischaemia or severe heart failure attributable to bradycardia requires immediate treatment.
Recent asystole, Mobitz II block, complete heart block with broad QRS or a ventricular pause longer than 3 seconds increases concern and prompts pacing readiness, although these may represent AV rather than sinus-node disease.
Athletic conditioning, sleep and high vagal tone can cause marked slowing without symptoms; appropriate rate increase with activity and absence of daytime events are reassuring clues.
Continuing P waves that intermittently or completely fail to conduct, with diagnostic PR relationships, favour AV block rather than failure of sinus impulse formation. A broad-QRS escape suggests distal conduction disease but is not specific by itself.
An early non-conducted P wave hidden within the preceding T wave can reset the sinus node and mimic a pause from sinus arrest.
Absent organised P waves and an irregular ventricular rhythm identify atrial fibrillation; rate-limiting medicines or AV-node disease may explain the slow response.
A temporal medicine change, thyroid or electrolyte abnormality, hypothermia or sleep apnoea supports secondary suppression and should be addressed before permanent-device decisions when safe.
Long pauses or an inadequate rate can transiently reduce cerebral perfusion, causing unpredictable syncope, traumatic injury and loss of driving or occupational independence.
Persistent severe bradycardia lowers cardiac output and may reduce systemic and coronary perfusion pressure, potentially worsening congestion or angina, especially in people with limited ventricular reserve.
Tachy-brady syndrome commonly includes atrial fibrillation or flutter. The resulting thromboembolic risk requires separate assessment because pacing does not prevent atrial clot formation.
Prolonged failure of impulse formation without a reliable escape rhythm can cause profound hypotension, seizure-like syncope, cardiac arrest or death.
A long asymptomatic pause during sleep does not automatically equal clinically important SND; symptoms and context determine significance.
An early non-conducted P wave hidden in the T wave can reset the sinus node and imitate sinus arrest.
RCUK specifically advises against atropine after heart transplantation and in high-grade AV block with wide QRS.
A pacing spike followed by QRS proves electrical capture; an associated pulse or arterial waveform proves mechanical capture.
Device support can make tachyarrhythmia treatment safer, but it does not prevent embolic stroke from AF/flutter.
Implanting a pacemaker for asymptomatic sleep-related bradycardia without addressing sleep apnoea.
Diagnosing SND from a rate number without symptom correlation.
Giving repeated atropine while an unstable patient waits for pacing.
Using the 1 mg cardiac-arrest adrenaline bolus for bradycardia with a pulse instead of a titrated infusion.
Treating tachy-brady symptoms with more AV-nodal blocker before documenting the pauses.
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A patient has sinus bradycardia at 32/min with hypotension and pulmonary oedema. There is no transplant history. What is the initial RCUK atropine regimen?
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes
Do not use after cardiac transplantation; avoid high-grade AV block with wide QRS because it is ineffective and may worsen block. Do not delay pacing when response is poor.
Can provoke tachyarrhythmia and myocardial ischaemia; specialist monitored use.
Use a controlled infusion with continuous monitoring; avoid confusing this peri-arrest infusion with the 1 mg cardiac-arrest bolus.