What is the initial management for symptomatic bradycardia (abnormally slow heart rate) with arrhythmia (irregular heart rhythm)?

Management of Bradycardia with Arrhythmia

For symptomatic bradycardia with arrhythmia, atropine 0.5-1 mg IV (repeated every 3-5 minutes to maximum 3 mg) is the first-line treatment, followed by transcutaneous pacing or beta-agonist infusions (dopamine, epinephrine) if atropine fails, while simultaneously identifying and treating reversible causes. 1, 2

Initial Assessment and Stabilization

Determine if the bradycardia is causing the symptoms by identifying signs of hemodynamic instability: 2, 3

• Altered mental status or confusion 2, 3
• Ischemic chest discomfort or angina 1, 2, 3
• Acute heart failure (dyspnea, pulmonary edema) 1, 2, 3
• Hypotension (systolic BP <90 mmHg, cool extremities) 1, 2, 3
• Signs of shock (end-organ hypoperfusion) 2, 3

Immediately secure airway and breathing, provide supplemental oxygen if hypoxemic, establish IV access, attach cardiac monitor, and obtain 12-lead ECG without delaying treatment. 2

Identify and Treat Reversible Causes

Before pharmacologic intervention, rapidly assess for reversible etiologies: 1, 2

• Medications: Beta-blockers, calcium channel blockers, digoxin, antiarrhythmics 1, 2
• Electrolyte abnormalities: Hyperkalemia, hypokalemia 2
• Metabolic: Hypothyroidism, hypothermia 1, 2
• Cardiac: Acute myocardial infarction or ischemia 1, 2
• Other: Increased intracranial pressure, infections, sleep apnea 1, 2

Special Overdose Management

For calcium channel blocker overdose: Administer IV calcium chloride 1-2 g every 10-20 minutes or calcium gluconate 3-6 g every 10-20 minutes. 1, 4

For beta-blocker or calcium channel blocker overdose: Glucagon 3-10 mg IV bolus followed by 3-5 mg/h infusion, or high-dose insulin therapy (1 unit/kg bolus, then 0.5 units/kg/h infusion with glucose monitoring). 1, 4

For digoxin toxicity: Administer digoxin-specific antibody fragments (dose dependent on amount ingested or serum digoxin level; one vial binds approximately 0.5 mg digoxin). 1

Pharmacologic Management Algorithm

First-Line: Atropine

Administer atropine 0.5-1 mg IV, repeat every 3-5 minutes to maximum total dose of 3 mg. 1, 2

• Atropine is most effective for sinus bradycardia and AV nodal-level blocks (second-degree type I, third-degree with narrow-complex escape rhythm) 1, 3
• Doses less than 0.5 mg may paradoxically slow heart rate 1, 3
• Atropine is less effective for infranodal blocks (typically presenting with wide-complex escape rhythms) 3
• Do NOT use atropine in post-heart transplant patients without autonomic reinnervation (Class III: Harm) 1

Second-Line: Beta-Agonists (if atropine fails or is contraindicated)

If bradycardia persists despite atropine or patient has hypotension, initiate chronotropic infusions: 1, 2

• Dopamine: 5-20 mcg/kg/min IV, starting at 5 mcg/kg/min and increasing by 5 mcg/kg/min every 2 minutes (particularly useful if hypotension present; doses >20 mcg/kg/min may cause vasoconstriction or arrhythmias) 1
• Epinephrine: 2-10 mcg/min IV or 0.1-0.5 mcg/kg/min IV titrated to effect 1
• Isoproterenol: 20-60 mcg IV bolus followed by 10-20 mcg doses, or infusion of 1-20 mcg/min based on heart rate response (monitor for ischemic chest pain) 1

These agents carry Class IIb, LOE B recommendation for patients at low likelihood of coronary ischemia. 1

Third-Line: Transcutaneous Pacing

Initiate transcutaneous pacing in unstable patients who do not respond to atropine (Class IIa, LOE B). 1, 2

• Transcutaneous pacing serves as a bridge to transvenous pacing if needed 3
• Immediate pacing may be considered in unstable patients with high-degree AV block when IV access is not available (Class IIb, LOE C) 1

Progression to Definitive Management

If temporary measures (atropine, chronotropes, transcutaneous pacing) are ineffective, prepare for transvenous pacing. 1, 2

Permanent pacemaker implantation is indicated for: 1, 2, 3

• Acquired second-degree Mobitz type II AV block, high-grade AV block, or third-degree AV block not caused by reversible causes (recommended regardless of symptoms) 1
• Chronic symptomatic bradycardia after excluding reversible causes 2, 3
• Symptomatic sinus node dysfunction with documented symptom-rhythm correlation 1

Critical Pitfalls to Avoid

Do NOT treat asymptomatic bradycardia (even with heart rates <40 bpm in athletes, during sleep, or in young healthy individuals with elevated parasympathetic tone). 1, 5

Do NOT use adenosine for irregular or polymorphic wide-complex tachycardias, as it may cause degeneration to ventricular fibrillation (Class III, LOE C). 1

Atropine should be used cautiously in acute MI due to the protective effect of parasympathetic tone against ventricular fibrillation and infarct extension; titrate to minimally effective heart rate (approximately 60 bpm). 1

There is no established minimum heart rate threshold for pacing—establishing temporal correlation between symptoms and bradycardia is essential before considering permanent pacing. 1, 3