Bradycardia
ABCs
- ABCs and full vitals
- recheck HR; confirm with ECG
- identify and correct hypoxemia immediately (common trigger)
- cardiac monitor + prepare pacing pads
- rule out monitor artifacts (cold hands, poor probe contact, motion)
unstable bradycardia (any of)
- altered mental status
- ischemic chest pain
- acute heart failure
- hypotension
- shock despite adequate airway and oxygenation
HPI
- symptoms: lightheadedness, syncope, chest pain
- signs of unstable bradycardia (see ABCs box)
causes
- intrinsic
- idiopathic degeneration
- ischemic heart disease
- hypertensive heart disease
- cardiomyopathy
- post-surgical / transplant
- inflammatory or infectious → pericarditis, myocarditis, rheumatic fever, Lyme disease, collagen vascular disease
- vasovagal syncope
- carotid sinus hypersensitivity
- neuromuscular / genetic → Friedreich ataxia, muscular dystrophy, familial disorders
- extrinsic
- medications → beta blockers, CCBs (verapamil, diltiazem), amiodarone, sotalol, digoxin, clonidine, methyldopa, lithium, antipsychotics, TCAs
- hypothyroidism
- raised ICP
- trauma
- hypothermia
- hyperkalemia
- hypoxia
- anorexia nervosa
workup
- review medications (beta blockers, digoxin, CCBs, opioids, psychiatric meds)
- labs: electrolytes, TSH, cardiac enzymes
- imaging if neurological cause suspected
ECG rhythm analysis
| 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 |
| 3° AV block | atrial and ventricular dissociation; pacing often needed |
high-risk features in AV block
- pause > 3 sec with symptoms
- ventricular escape rhythm < 40 bpm
- syncope with documented bradyarrhythmia
- alternating bundle branch block
management
stable / asymptomatic with HR > 50 and no ECG changes
- monitor + treat reversible causes: hypoxia, hyperkalemia, ACS, drug toxicity
unstable or symptomatic
- call for assistance
- atropine 1 mg IV every 3–5 min (max 3 mg)
- not effective in heart transplant recipients or Mobitz II / 3° AV block
- if atropine fails → start a chronotrope while preparing pacing: dopamine 5–20 mcg/kg/min, or epinephrine 2–10 mcg/min
- escalate to temporary pacing (transcutaneous → transvenous)
- contact cardiology
studying for the IM exam? the IM Rapid Review covers bradyarrhythmias and pacing in the same format. see the sample chapter.
Last reviewed · June 2026