What is the appropriate treatment for symptomatic bradycardia in an adult?

Treatment for Bradycardia

Administer atropine 0.5-1 mg IV immediately for symptomatic bradycardia, repeating every 3-5 minutes up to a maximum total dose of 3 mg, and if the patient remains unstable despite atropine, initiate transcutaneous pacing without delay while preparing dopamine or epinephrine infusions as second-line therapy. 1

Identifying When Treatment Is Required

• Symptomatic bradycardia requires treatment when heart rate is typically <50 beats/min accompanied by signs of poor perfusion: altered mental status, ischemic chest discomfort, acute heart failure, hypotension (systolic BP <80-90 mmHg), syncope, dizziness, dyspnea, or other signs of shock. 1, 2

• Asymptomatic bradycardia does not require treatment, even with heart rates <40 bpm—this is common in athletes and during sleep. 1

Initial Stabilization Steps

• Maintain a patent airway and assist breathing as necessary, providing supplemental oxygen if the patient is hypoxemic or shows increased work of breathing. 1

• Establish cardiac monitoring to identify rhythm, monitor blood pressure, and measure oxygen saturation. 1

• Obtain IV access immediately for medication administration. 1

• Obtain a 12-lead ECG if available to identify the type of bradycardia, but do not delay therapy. 1

First-Line Pharmacologic Treatment: Atropine

• Dosing protocol: Give atropine 0.5-1 mg IV push immediately upon recognition of symptomatic bradycardia. 1, 2

• Repeat dosing: Administer every 3-5 minutes as needed, up to a maximum cumulative dose of 3 mg (approximately 3-4 total doses). 1, 2

• Critical warning: Never give doses <0.5 mg, as sub-therapeutic amounts may paradoxically worsen bradycardia through a parasympathomimetic response. 1, 2, 3

• Mechanism: Atropine blocks muscarinic acetylcholine receptors, abolishing vagal cardiac slowing and preventing or reversing bradycardia or asystole produced by vagal activity. 3

When Atropine Will Be Effective

• Nodal-level blocks likely to respond: Sinus bradycardia, first-degree AV block, Mobitz I (Wenckebach) second-degree AV block, sinus arrest, and vagally-mediated bradycardia. 1, 2

When Atropine Will Fail

• Infranodal blocks unlikely to respond: Mobitz II second-degree AV block, third-degree (complete) heart block with wide QRS complex, and new bundle-branch block patterns—atropine is ineffective and potentially harmful in these situations. 1, 2

• Special populations: Heart transplant patients without autonomic reinnervation may develop paradoxical high-degree AV block with atropine; use epinephrine instead. 1

Second-Line Treatment When Atropine Fails

Transcutaneous Pacing (TCP)

• Initiate TCP immediately in unstable patients who do not respond to atropine—do not delay pacing while giving multiple atropine doses. 1, 2

• Prophylactic pad placement: In high-risk patients (elderly, known cardiac disease, severe hypoxia), place TCP pads before the heart rate drops further to enable instant pacing if needed. 2

• Limitation: TCP is a temporizing measure only and may require sedation/analgesia due to pain in conscious patients. 1

Chronotropic Infusions

• Dopamine: Start at 5-10 mcg/kg/min IV infusion, titrating to hemodynamic response up to a maximum of 20 mcg/kg/min. 1, 2

  • At 5-20 mcg/kg/min, dopamine provides both chronotropic (heart rate) and inotropic (contractility) effects through beta-1 adrenergic stimulation. 1
  • Higher doses (>10 mcg/kg/min) cause excessive vasoconstriction and increase arrhythmia risk. 1

• Epinephrine: Start at 2-10 mcg/min IV infusion, preferred when severe hypotension requires combined chronotropic and inotropic support. 1, 2

  • Epinephrine has stronger alpha-adrenergic effects causing more profound vasoconstriction than dopamine. 1

• Isoproterenol: Consider 20-60 mcg IV bolus or infusion of 1-20 mcg/min based on heart rate response—provides chronotropic and inotropic effects without vasopressor effects, making it preferable in some scenarios. 1

Special Clinical Scenarios

Acute Coronary Syndrome

• Use atropine cautiously in acute MI or ongoing ischemia, as increasing heart rate may worsen ischemia or enlarge infarct size. 1, 2

• Limit total dose to 0.03-0.04 mg/kg (approximately 2 mg in a 70 kg patient) in patients with known coronary artery disease. 2

• Atropine is indicated for symptomatic bradycardia with hypotension, altered mental status, worsening chest pain, acute heart failure, or frequent ventricular ectopy in the ACS setting. 2

• Atropine is contraindicated for asymptomatic bradycardia in ACS—preserving parasympathetic tone may protect against ventricular fibrillation. 2

Neurogenic Shock (Spinal Cord Injury)

• Atropine often fails in neurogenic shock due to the unique pathophysiology of spinal cord injury. 1

• Aminophylline alternative: Consider aminophylline 6 mg/kg in 100-200 mL IV over 20-30 minutes or theophylline 100-200 mg slow IV injection (maximum 250 mg) for atropine-refractory bradycardia in spinal cord injury. 1, 4

  • Aminophylline works by increasing cyclic AMP and activating the sympathoadrenal system. 4

• Vasopressor therapy: If bradycardia persists, initiate dopamine 5-20 mcg/kg/min or epinephrine 2-10 mcg/min IV infusion. 1

Medication-Induced Bradycardia

• Identify and discontinue the offending agent: atypical antipsychotics (quetiapine), beta-blockers, non-dihydropyridine calcium-channel blockers (diltiazem, verapamil), digoxin, or amiodarone. 1

• Taper quetiapine as the most reversible cause when present. 1

• Reduce or substitute beta-blockers and calcium-channel blockers unless essential for heart failure or post-MI therapy. 1

Definitive Management: Permanent Pacemaker

• Permanent pacemaker implantation is indicated when symptomatic bradycardia persists after excluding and treating all reversible causes, particularly in high-grade AV block, sinus node dysfunction with documented symptomatic bradycardia, or bifascicular block with intermittent complete heart block. 1

• Delayed pacemaker implantation (≥3 days) is not associated with increased adverse events compared to early implantation (≤2 days), but temporary transvenous pacing increases complications (19.1% vs 3.4%, P<.001). 5

• Weekend admissions prolong time to pacemaker by 1 day and length of stay by 2 days—consider weekend pacemaker implantation to reduce temporary pacing needs. 5

Critical Pitfalls to Avoid

• Never give atropine <0.5 mg—paradoxical worsening of bradycardia may occur. 1, 2, 3

• Do not exceed 3 mg total atropine—excessive doses may cause central anticholinergic syndrome (confusion, agitation, hallucinations). 1

• Do not delay transcutaneous pacing in unstable patients while repeatedly dosing atropine. 1, 2

• Avoid atropine in wide-complex escape rhythms or Type II/third-degree AV block—the drug is ineffective and may be harmful in infranodal disease. 1, 2

• Do not use temporary transvenous pacing routinely—it significantly increases complications compared to early permanent pacemaker placement. 5