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Bradycardia

ABCs

ABCs, full vitals, cardiac monitor
definition → HR < 60 bpm; clinically significant often < 50 bpm; treat by symptoms, perfusion and rhythm
confirm → recheck HR, exclude monitor artifact (cold hands, poor probe contact, motion), confirm on ECG
correct hypoxemia immediately (common trigger)
pacing pads early if unstable or high-grade AV block
categorize → stable · symptomatic but stable · unstable

unstable, attributable to bradycardia (any of)

symptoms: lightheadedness, syncope, chest pain, exercise intolerance
drug history: beta blockers, verapamil / diltiazem, digoxin, amiodarone, sotalol, clonidine; recent dose change, new interacting drug, or possible overdose

common and reversible, check first
- hypoxia
- myocardial ischemia / infarction
- hyperkalemia / electrolyte disturbance
- hypothermia
- drugs / toxins → beta blockers, CCBs (verapamil, diltiazem), amiodarone, sotalol, digoxin, clonidine, methyldopa, lithium, antipsychotics, TCAs
- increased vagal tone (vasovagal episodes)
- hypothyroidism
- myocarditis / infection
- raised ICP
- intrinsic conduction disease (degenerative, ischemic, post-surgical)
rarer
- infiltrative / rheumatologic disease, Lyme disease
- carotid sinus hypersensitivity
- neuromuscular / genetic → Friedreich ataxia, muscular dystrophy
- anorexia nervosa

ECG analysis, key patterns:

rhythm	features
Sinus bradycardia	common in athletes, sleep, increased vagal tone
1° AV block	PR > 200 ms
2° AV block Type I (Wenckebach)	progressive PR lengthening with dropped beat
2° AV block Type II	dropped beat with constant PR; high-risk, usually infranodal
3° AV block	AV dissociation; pacing often needed

high-risk features in AV block

stable or asymptomatic

monitor; find and treat reversible causes: hypoxia, hyperkalemia, ACS, drug toxicity
no emergency drugs for an incidental low rate with good perfusion and no high-grade block

unstable bradycardia

call and prepare
- senior / resuscitation team; continuous cardiac monitoring
- pacing / defibrillation pads; IV / IO access
- oxygen only if hypoxemic; 12-lead ECG if it does not delay treatment
- correct reversible causes in parallel
atropine 1 mg IV, repeat every 3–5 min, maximum total 3 mg
- do not delay pacing for repeated atropine in Mobitz II, complete / high-grade or likely infranodal block
- usually ineffective after cardiac transplant
atropine ineffective or unlikely to work → either or both while preparing definitive pacing
- transcutaneous pacing
- epinephrine infusion 2–10 mcg/min
- dopamine infusion 5–20 mcg/kg/min
if pacing
- increase current until electrical capture; confirm mechanical capture (pulse, BP or arterial waveform)
- analgesia / sedation if conscious and hemodynamically tolerant; do not delay pacing for sedation
- no IV / IO access yet → pace transcutaneously while access is obtained
escalate: Cardiology and ICU early; transvenous pacing if instability persists

cause-specific note

heart-transplant patient: atropine may be ineffective or harmful → immediate specialist support; pacing / catecholamines per protocol; no repeated atropine
suspected beta-blocker or calcium-channel-blocker toxicity: immediate toxicology / ICU → local poisoning protocol (may include calcium and high-dose insulin); glucagon is an option, not definitive alone

source	type
2025 AHA Adult Advanced Life Support	international guideline
2025 ERC guidance	international guideline

Verify indication, dose, allergies, interactions, renal/hepatic function and local protocols before prescribing.

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Last clinically reviewed · 17 August 2026 · Last updated · September 2026