Bedside Rounds

Symptomatic bradycardia and heart block: workup and management

Bradycardia (HR <50) matters when it causes symptoms or instability, or reflects high-grade AV block. Treat instability with atropine, chronotropes or pacing, look for reversible causes (drugs, ischemia, hyperkalemia, hypothyroidism, Lyme), and decide on permanent pacing.

Working diagnosis Adult · US guidelines Draft · awaiting physician review
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01Orient

What's new in the evidence

  • 2025 AHA adult ALS guideline: atropine 1 mg IV every 3–5 min (max 3 mg); transcutaneous pacing or epinephrine/dopamine infusion if ineffective
  • 2018 ACC/AHA/HRS bradycardia guideline remains current: treat reversible causes before permanent pacing
  • If a needed beta-blocker or antiarrhythmic is causing bradycardia, proceeding to pacing without a washout is reasonable

Differential diagnoses

  1. Sinus node dysfunction (sick sinus, tachy-brady syndrome)
  2. Second-degree Mobitz II or third-degree AV block (can't miss)
  3. Drugs: beta-blockers, nondihydropyridine CCBs, digoxin, amiodarone, ivabradine, clonidine
  4. Hyperkalemia (can't miss)
  5. Inferior MI (can't miss)
  6. Hypothyroidism, hypothermia, raised ICP, Lyme carditis, infiltrative disease (sarcoid, amyloid)

02Assess

Risk scores and decision tools

  • Instability: hypotension, altered mental status, ischemic chest pain, acute heart failure, shock
  • Level of block: narrow QRS escape (nodal, atropine-responsive) vs wide QRS (infranodal, needs pacing)
  • Lyme carditis risk (Suspicious Index in Lyme Carditis)

Key history questions

  • Syncope, presyncope, fatigue, dyspnea, chest pain
  • Medication list and recent changes, overdose
  • Tick exposure, rash; recent travel
  • Thyroid, kidney disease; sleep apnea
  • Prior cardiac surgery or TAVR

Examination findings

  • Hemodynamics, perfusion, mental status
  • Cannon a waves, variable S1 (AV dissociation)
  • Signs of heart failure
  • Hypothermia, signs of hypothyroidism

03Investigate

Initial investigations

  • 12-lead ECG and continuous telemetry
  • BMP (potassium), magnesium, troponin, TSH
  • Digoxin level if applicable; glucose

Advanced investigations

  • Echocardiogram
  • Lyme serology in endemic areas
  • Ambulatory monitoring or EP study for intermittent symptoms
  • Cardiac MRI or PET for suspected infiltrative disease in younger patients

04Treat

Immediate management

  • Unstable: atropine 1 mg IV every 3–5 minutes (max 3 mg); less effective in infranodal block
  • Transcutaneous pacing with analgesia/sedation if atropine fails
  • Epinephrine 2–10 mcg/min or dopamine 5–20 mcg/kg/min infusion as a bridge
  • Treat hyperkalemia urgently; antidotes for drug toxicity (glucagon for beta-blocker, calcium/high-dose insulin for CCB, digoxin immune Fab)

First-line treatment

  • Stop or reduce culprit drugs
  • Transvenous temporary pacing for persistent high-grade block
  • Lyme carditis: IV ceftriaxone and temporary pacing; block usually resolves

Second-line treatment

  • Permanent pacemaker for symptomatic sinus node dysfunction or Mobitz II/third-degree block without a reversible cause
  • Isoproterenol infusion as a bridge when ischemia is unlikely

Specialist referrals

  • Cardiology/electrophysiology for pacing
  • ICU or CCU for unstable patients or temporary pacing

05Disposition

Admission criteria

  • Mobitz II or third-degree block
  • Syncope with bradycardia
  • Hemodynamic compromise or need for chronotropes or pacing

Safe discharge criteria

  • Asymptomatic sinus bradycardia or first-degree/Mobitz I block with reversible cause addressed
  • Outpatient monitoring arranged

Follow-up timing

  • Device clinic 1–2 weeks after pacemaker
  • Cardiology within 2–4 weeks if monitored outpatient

Patient instructions

  • Do not restart rate-slowing drugs without review
  • Return for fainting or breathlessness

Monitoring

  • Continuous telemetry
  • Pacing threshold checks if temporary wire

Clinical pearls and pitfalls

  • Asymptomatic sinus bradycardia during sleep or in athletes needs no treatment
  • Inferior MI often causes transient nodal block; anterior MI with block suggests extensive infarction
  • Bradycardia, renal failure, AV nodal blocker and hyperkalemia together (BRASH syndrome) need correction of all components

RefGuidelines and landmark evidence

For education only. Typical adult starting points; confirm doses against renal function, allergies, interactions and your institution's protocols. Not a substitute for clinical judgment or senior review.

Calculators for this workup

Canadian Syncope Risk Score
Acetaminophen overdoseAcute abdominal painAcute aortic dissectionAcute cholangitis and choledocholithiasisAcute decompensated heart failureAcute diverticulitisAcute dizziness and vertigoAcute ischemic stroke and TIAAcute kidney injuryAcute pancreatitisAcute pericarditisAdrenal crisisAlcohol withdrawalAlcohol-associated hepatitisAnaphylaxisAnemia in hospitalized adultsAsthma exacerbationAtrial fibrillation with rapid ventricular responseBacterial meningitisCellulitisChest painClostridioides difficile infectionCommunity-acquired pneumoniaCOPD exacerbationDecompensated cirrhosis (ascites, SBP, hepatic encephalopathy)Deep vein thrombosisDelirium / acute confusionDiabetic foot infection and osteomyelitisDiabetic ketoacidosisFebrile neutropeniaFirst seizure and status epilepticusHypercalcemiaHyperglycemia in hospitalized adultsHyperkalemiaHypernatremiaHyperosmolar hyperglycemic state (HHS)Hypertensive emergencyHypoglycemiaHypokalemiaHyponatremiaInfective endocarditisLower GI bleedMajor bleeding on anticoagulants (reversal)Malignant spinal cord compressionNSTEMI and non-ST-elevation ACSOpioid overdose and opioid use disorderPulmonary embolismPyelonephritis and complicated UTIRhabdomyolysisSepsisShortness of breathSickle cell vaso-occlusive crisisStaphylococcus aureus bacteremiaSyncopeThrombocytopenia (including TTP, HIT and ITP)Thunderclap headache (rule out subarachnoid hemorrhage)Thyroid stormTumor lysis syndromeUpper GI bleed