Overview
Bradycardia
Topic Overview
Summary
Bradycardia is a heart rate below 60 bpm. It may be physiological (athletes, sleep) or pathological (sinus node dysfunction, heart block, drugs, hypothyroidism). Clinical significance depends on symptoms and haemodynamic status. Unstable bradycardia (hypotension, altered consciousness, heart failure) requires urgent treatment: atropine, pacing, and addressing the underlying cause. Stable bradycardia may need investigation but not emergency treatment.
Key Facts
- Definition: Heart rate under 60 bpm
- Causes: Physiological, drugs, sinus node disease, heart block, MI, hypothyroidism
- Unstable features: Hypotension, syncope, heart failure, altered consciousness
- First-line treatment: Atropine 500mcg IV (up to 3mg)
- If atropine fails: Pacing (transcutaneous or transvenous)
Clinical Pearls
Atropine may not work in complete heart block (infra-nodal) — prepare for pacing
Beta-blockers and calcium channel blockers are common causes of symptomatic bradycardia
Inferior MI commonly causes bradycardia (vagal tone, RCA supplies SA/AV node)
Why This Matters Clinically
Bradycardia with adverse features is life-threatening. Rapid recognition and treatment with atropine or pacing can be life-saving. Identifying the underlying cause determines long-term management.
Visual Summary
Visual assets to be added:
- Bradycardia algorithm (ALS)
- ECG examples of sinus bradycardia, heart blocks
- Pacing thresholds
- Causes of bradycardia diagram
Epidemiology
Incidence
- Common finding
- Often physiological in young, fit patients
- Pathological more common in elderly
Demographics
- Athletes (physiological)
- Elderly (sinus node disease)
- Patients on rate-limiting drugs
Causes
| Category | Examples |
|---|---|
| Physiological | Athletes, sleep, vasovagal |
| Drugs | Beta-blockers, calcium channel blockers, digoxin, amiodarone |
| Cardiac | Sinus node disease, heart block, MI (especially inferior) |
| Metabolic | Hypothyroidism, hyperkalaemia, hypothermia |
| Autonomic | Carotid sinus hypersensitivity, vasovagal |
| Infection | Lyme disease, endocarditis |
Pathophysiology
Normal Conduction
- SA node → atria → AV node → His bundle → bundle branches → Purkinje fibres
Mechanisms of Bradycardia
| Type | Mechanism |
|---|---|
| Sinus bradycardia | SA node fires slowly |
| Sinus node dysfunction (sick sinus) | SA node failure; may alternate with tachycardia |
| 1st degree AV block | Prolonged PR interval (over 200ms) |
| 2nd degree AV block (Mobitz I/Wenckebach) | Progressive PR prolongation then dropped beat |
| 2nd degree AV block (Mobitz II) | Intermittent non-conducted P waves (fixed PR) |
| 3rd degree (complete) AV block | No conduction from atria to ventricles |
Blood Supply
- SA node: Usually RCA (60%) or LCx (40%)
- AV node: Usually RCA (90%)
- Inferior MI → SA/AV node ischaemia → bradycardia
Clinical Presentation
Symptoms
Signs
Adverse (Unstable) Features — Resuscitation Council UK
| Feature | Significance |
|---|---|
| Shock | Hypotension, pallor, sweating |
| Syncope | Reduced cerebral perfusion |
| Myocardial ischaemia | Chest pain, ECG changes |
| Heart failure | Pulmonary oedema |
Red Flags
| Finding | Significance |
|---|---|
| Complete heart block | Usually needs pacing |
| Mobitz II | High risk of progression to complete block |
| Recent MI | May need temporary pacing |
| Drug toxicity | Identify and treat |
Asymptomatic (if physiological)
Common presentation.
Fatigue
Common presentation.
Dizziness, lightheadedness
Common presentation.
Pre-syncope or syncope
Common presentation.
Dyspnoea
Common presentation.
Chest pain
Common presentation.
Clinical Examination
Vital Signs
- Heart rate under 60 bpm
- Blood pressure (may be low or normal)
Cardiovascular
- Slow, regular or irregular pulse
- Cannon A waves in JVP (AV dissociation)
- Variable S1 intensity (AV dissociation)
- Signs of heart failure
General
- Signs of hypothyroidism
- Signs of shock
Investigations
ECG — Essential
| Finding | Diagnosis |
|---|---|
| Slow regular rhythm, normal P waves | Sinus bradycardia |
| PR over 200ms | 1st degree AV block |
| Progressive PR prolongation, dropped beat | Mobitz I (Wenckebach) |
| Fixed PR, intermittent dropped beat | Mobitz II |
| No relationship between P and QRS | 3rd degree (complete) heart block |
Blood Tests
| Test | Purpose |
|---|---|
| U&E | Hyperkalaemia |
| TFTs | Hypothyroidism |
| Digoxin level | If on digoxin |
| Troponin | If MI suspected |
| Magnesium, calcium | Electrolyte abnormalities |
Other
- Holter monitor: Intermittent symptoms
- Echo: Structural heart disease
- Coronary angiogram: If ischaemia suspected
Classification & Staging
By ECG
| Type | PR Interval | Conduction |
|---|---|---|
| 1st degree AV block | Prolonged (over 200ms) | All conducted |
| 2nd degree Mobitz I | Progressive prolongation | Periodic dropped beat |
| 2nd degree Mobitz II | Fixed | Intermittent dropped beats |
| 3rd degree | No relationship | Complete dissociation |
By Haemodynamic Status
- Stable: No adverse features
- Unstable: Adverse features present
Management
Unstable Bradycardia (Adverse Features Present)
Follow ALS Bradycardia Algorithm:
| Step | Action |
|---|---|
| 1. Atropine | 500mcg IV; repeat every 3-5 min; max 3mg |
| 2. If atropine fails | Transcutaneous pacing (may need analgesia/sedation) |
| 3. Interim measures | Adrenaline 2-10mcg/min infusion; isoprenaline |
| 4. Expert help | Consider transvenous pacing |
Transcutaneous Pacing
- Apply pads (anterior-posterior or apex-sternum)
- Set rate 60-90 bpm
- Increase current until capture (usually 50-100 mA)
- Confirm mechanical capture (palpable pulse)
Transvenous Pacing
- Temporary pacing wire via central vein
- Bridge to permanent pacemaker
Stable Bradycardia (No Adverse Features)
| Action | Details |
|---|---|
| Observe | Monitor for deterioration |
| Identify cause | Review medications, check bloods |
| Treat underlying cause | Stop offending drugs; treat hypothyroidism |
| Consider referral | For pacemaker if symptomatic sinus node disease or high-grade block |
Drug-Induced Bradycardia
- Stop offending drug
- May need specific antidotes (e.g., glucagon for beta-blockers)
Indications for Permanent Pacemaker
- Symptomatic sinus node dysfunction
- Mobitz II 2nd degree AV block
- Complete (3rd degree) heart block
- Symptomatic bifascicular/trifascicular block
Complications
Of Bradycardia
- Syncope and falls
- Heart failure
- Cardiogenic shock
- Cardiac arrest (asystole)
Of Pacing
- Local complications (haematoma, infection)
- Pneumothorax (transvenous)
- Lead displacement
- Pacemaker malfunction
Prognosis & Outcomes
Prognosis
- Physiological bradycardia: Excellent
- Sinus node disease with pacemaker: Good
- Complete heart block with pacemaker: Good
Without Treatment
- Mobitz II and complete heart block: Risk of sudden death without pacing
Evidence & Guidelines
Key Guidelines
- Resuscitation Council UK ALS Guidelines
- ESC Guidelines on Cardiac Pacing
Key Evidence
- Atropine is first-line for symptomatic bradycardia
- Permanent pacing improves outcomes in symptomatic heart block
Patient & Family Information
What is Bradycardia?
Bradycardia means your heart is beating slower than normal (under 60 beats per minute). This can be normal in fit people but may cause problems in others.
Symptoms
- Feeling tired or weak
- Dizziness or fainting
- Shortness of breath
Causes
- Medications
- Heart problems
- Thyroid problems
Treatment
- Treating the underlying cause
- Medication adjustments
- Sometimes a pacemaker is needed
Resources
References
Primary Guidelines
- Resuscitation Council UK. Advanced Life Support Guidelines. 2021.
- Glikson M, et al. 2021 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy. Eur Heart J. 2021;42(35):3427-3520. PMID: 34455427
Key Reviews
- Kusumoto FM, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay. Circulation. 2019;140(13):e506-e522. PMID: 30586772