What is the management approach for bradycardia (abnormally slow heart rate)?

Management of Bradycardia

For symptomatic bradycardia causing hemodynamic compromise, immediately administer atropine 0.5-1 mg IV (may repeat every 3-5 minutes to maximum 3 mg) while simultaneously identifying and treating reversible causes, and prepare for temporary pacing if medical therapy fails. 1

Initial Assessment and Stabilization

Clinically significant bradycardia is defined as heart rate <50 beats per minute with associated symptoms or hemodynamic compromise. 1

Immediate Actions:

• Assess airway, breathing, and oxygenation status - hypoxemia is a common reversible cause requiring supplementary oxygen 1
• Establish IV access and continuous cardiac monitoring with blood pressure monitoring 1
• Obtain 12-lead ECG to identify the specific bradyarrhythmia mechanism (sinus node dysfunction vs. AV block), but do not delay treatment 1
• Determine if symptoms (acute altered mental status, chest pain, heart failure, hypotension, shock) are caused by the bradycardia rather than the bradycardia being a response to another condition 1

Identify and Treat Reversible Causes

Before considering permanent pacing, aggressively evaluate and treat potentially reversible causes - this is a Class I recommendation. 1, 2

Common Reversible Causes to Address:

Medications: 1, 2

• Beta-blockers, non-dihydropyridine calcium channel blockers, digoxin, antiarrhythmic drugs
• Discontinue or reduce dosage of offending agents
• Note: If bradycardia persists despite stopping necessary guideline-directed medical therapy (e.g., beta-blockers for heart failure), proceed to permanent pacing without prolonged observation for drug washout 1

Metabolic/Endocrine: 1, 2

• Hypothyroidism (treat with thyroxine replacement)
• Hyperkalemia, hypokalemia, hypoglycemia
• Severe acidosis

Cardiac Conditions: 1, 2

• Acute myocardial ischemia/infarction
• Cardiac surgery (valve replacement, CABG, Maze procedure)

Other Reversible Causes: 1, 2

• Hypothermia (therapeutic or environmental)
• Elevated intracranial pressure
• Obstructive sleep apnea
• Infections (Lyme disease, viral illnesses)
• Hypervagotonia (including acute abdominal pain causing reflex bradycardia) 3

Acute Medical Management

For Sinus Node Dysfunction:

First-line: Atropine 0.5-1 mg IV (Class IIa recommendation) 1

• Repeat every 3-5 minutes to maximum total dose of 3 mg 1
• Mechanism: Blocks vagal effects by antagonizing muscarinic acetylcholine receptors 4
• Critical exception: Do NOT use atropine in heart transplant patients without autonomic reinnervation (Class III: Harm) - it is ineffective and potentially harmful 1

Second-line Beta-Adrenergic Agonists (Class IIb recommendation) - use when atropine fails or in patients with low likelihood of coronary ischemia: 1

• Dopamine: 5-20 mcg/kg/min IV, starting at 5 mcg/kg/min, increase by 5 mcg/kg/min every 2 minutes 1
• Isoproterenol: 20-60 mcg IV bolus or infusion 1-20 mcg/min titrated to heart rate response 1
• Epinephrine: 2-10 mcg/min IV or 0.1-0.5 mcg/kg/min IV 1
• Dobutamine: Similar dosing to dopamine 1

For Atrioventricular Block:

Atropine is reasonable for AV nodal-level block (second-degree or third-degree) with symptoms (Class IIa) 1

• Most effective for AV nodal block; less effective for infranodal block 1

Beta-adrenergic agonists may be considered for symptomatic second- or third-degree AV block in patients with low coronary ischemia risk (Class IIb) 1

Special situation - Acute inferior MI with AV block: 1

• Aminophylline 250 mg IV bolus may be considered (Class IIb) 1

For Specific Overdoses:

Calcium channel blocker overdose: 1

• 10% calcium chloride: 1-2 g IV every 10-20 minutes or infusion 0.2-0.4 mL/kg/h
• 10% calcium gluconate: 3-6 g IV every 10-20 minutes or infusion 0.6-1.2 mL/kg/h

Beta-blocker or calcium channel blocker overdose: 1

• Glucagon: 3-10 mg IV bolus, then infusion 3-5 mg/h
• High-dose insulin: 1 unit/kg IV bolus, then 0.5 units/kg/h infusion

Digoxin overdose: 1

• Digoxin-specific antibody fragments (dose depends on amount ingested or serum level)

Temporary Pacing

Temporary transvenous pacing is reasonable (Class IIa) for symptomatic bradycardia with hemodynamic compromise refractory to medical therapy. 1

Transcutaneous pacing may be considered (Class IIb) as a bridge to transvenous or permanent pacing, but is painful and less reliable. 1

Key Points About Temporary Pacing:

• Use externalized permanent active fixation leads rather than passive fixation temporary leads if prolonged temporary pacing is needed (Class IIa) 1
• Complications occur in 14-40% of cases: venous thrombosis, pulmonary emboli, arrhythmias, loss of capture 1
• Do NOT use temporary pacing for minimal/infrequent symptoms without hemodynamic compromise (Class III: Harm) 1

Indications for Permanent Pacemaker

Permanent pacing is indicated when: 2, 5

• Symptomatic bradycardia persists despite treatment of reversible causes (Class I) 1
• Bradycardia is due to necessary guideline-directed medical therapy with no alternative treatment 2
• Second-degree Mobitz II or third-degree AV block, even if asymptomatic (for prognostic reasons) 6
• Cardiac sarcoidosis with second- or third-degree AV block (proceed without waiting for reversibility) 1

Permanent pacing is NOT indicated for: 2

• Asymptomatic bradycardia (especially in athletes, young individuals, or during sleep)
• Bradycardia clearly attributable to reversible causes that resolve with treatment

Critical Pitfalls to Avoid

Do not implant permanent pacemakers for reversible bradycardia - particularly medication-induced, hypothyroidism, or reflex bradycardia from acute abdominal pain 2, 3

Do not use atropine in heart transplant recipients - it is ineffective due to denervation and may cause paradoxical effects 1

Do not assume all bradycardia requires treatment - asymptomatic bradycardia, particularly in athletes or during sleep, is physiologic and requires no intervention 2, 5

Recognize that beta-adrenergic agonists can precipitate myocardial ischemia - use cautiously in patients with coronary artery disease 1

Temporary pacing has significant complications - reserve for truly unstable patients and transition to permanent pacing or resolution of reversible cause as quickly as possible 1