What is the appropriate management for a patient with bradicardia?

Management of Bradycardia

For patients with symptomatic bradycardia causing hemodynamic compromise, atropine 0.5-1 mg IV every 3-5 minutes (maximum 3 mg) is the first-line treatment, followed by transcutaneous pacing if atropine fails, with permanent pacemaker placement indicated for persistent symptomatic bradycardia after reversible causes are excluded. 1, 2

Initial Assessment and Stabilization

The immediate priority is determining whether bradycardia is causing the patient's symptoms. Assess for signs of poor perfusion including altered mental status, ischemic chest discomfort, acute heart failure, hypotension, or shock 1, 2, 3. Obtain a 12-lead ECG immediately to document rhythm and identify conduction abnormalities, but do not delay treatment in unstable patients 1, 3.

Critical Distinction: Symptomatic vs Asymptomatic

Asymptomatic bradycardia requires no treatment, even with heart rates as low as 40-45 bpm 2, 4. This is physiologic in well-conditioned athletes, during sleep, and in young healthy individuals due to elevated parasympathetic tone 2, 4. There is no minimum heart rate threshold for treatment—correlation between symptoms and documented bradycardia is the key determinant 2, 4.

Identify and Treat Reversible Causes

Before initiating definitive therapy, evaluate for:

• Medications: Beta blockers, calcium channel blockers, digoxin, antiarrhythmic drugs 1, 3
• Electrolyte abnormalities: Hyperkalemia, hypokalemia 1, 3
• Metabolic causes: Hypothyroidism, hypothermia 1, 3
• Cardiac causes: Acute myocardial infarction (especially inferior MI), increased intracranial pressure 1, 3
• Infections: Lyme disease, other infectious etiologies 1

In patients with symptomatic AV block attributable to a known reversible cause that does not resolve despite treatment, permanent pacing is recommended 1. Conversely, permanent pacing should not be performed if the AV block completely resolves with treatment of the underlying cause 1.

Acute Pharmacologic Management

First-Line: Atropine

Atropine 0.5-1 mg IV bolus, repeated every 3-5 minutes to a maximum total dose of 3 mg 1, 2, 5. Atropine blocks muscarinic acetylcholine receptors, facilitating sinoatrial conduction and increasing sinus node automaticity 5. It is most effective for sinus bradycardia and AV nodal-level blocks 4.

Critical pitfall: Doses less than 0.5 mg may paradoxically slow heart rate 4. Atropine should NOT be used in heart transplant patients without evidence of autonomic reinnervation, as it can cause paradoxical effects 1, 3.

Second-Line: Beta-Adrenergic Agonists

When atropine is ineffective or contraindicated, consider 1:

• Dopamine: 5-20 mcg/kg/min IV, starting at 5 mcg/kg/min and increasing by 5 mcg/kg/min every 2 minutes. Dosages >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, 2
• Isoproterenol: 20-60 mcg IV bolus followed by 10-20 mcg doses, or infusion of 1-20 mcg/min based on heart rate response 1

These agents are reasonable for second-degree or third-degree AV block with symptoms or hemodynamic compromise in patients with low likelihood of coronary ischemia 1.

Special Situations

• Acute inferior MI with AV block: Aminophylline 250 mg IV bolus may be considered 1
• Calcium channel blocker overdose: 10% calcium chloride 1-2 g IV every 10-20 minutes or 10% calcium gluconate 3-6 g IV every 10-20 minutes 1
• Beta-blocker or calcium channel blocker overdose: Glucagon 3-10 mg IV with infusion of 3-5 mg/h 1, 3
• Digoxin overdose: Digoxin antibody fragments (dosage dependent on amount ingested) 1

Temporary Pacing

For patients with second-degree or third-degree AV block with symptoms or hemodynamic compromise refractory to medical therapy, temporary transvenous pacing is reasonable 1. Transcutaneous pacing may be considered as a bridge until transvenous or permanent pacing is placed 1, 2.

Important caveat: Temporary pacing should NOT be performed in patients with minimal and/or infrequent symptoms without hemodynamic compromise 1. The risks outweigh benefits when episodes are intermittent without hemodynamic instability 2.

Permanent Pacing Indications

Sinus Node Dysfunction

Permanent pacing is indicated (Class I) for patients with symptoms directly attributable to sinus node dysfunction 1. This includes 1:

• Symptomatic sinus bradycardia
• Symptomatic chronotropic incompetence (rate-responsive programming recommended)
• Tachy-brady syndrome with symptoms attributable to bradycardia

For symptomatic patients with sinus node dysfunction and intact AV conduction, atrial-based pacing is recommended over single chamber ventricular pacing 1. In patients with dual chamber pacemakers and intact AV conduction, programming to minimize ventricular pacing is reasonable 1.

Atrioventricular Block

Permanent pacing indications vary by block type and symptoms:

• First-degree AV block: Generally benign, requires no treatment 4
• Second-degree Mobitz type II or third-degree AV block with symptoms: Permanent pacing indicated 4
• Asymptomatic vagally mediated AV block: Permanent pacing should NOT be performed 1

Monitoring and Follow-up

For patients with symptoms of unclear etiology who have first-degree AV block or second-degree Mobitz type I AV block on ECG, ambulatory electrocardiographic monitoring is reasonable to establish correlation between symptoms and rhythm abnormalities 1. Choose monitoring duration based on symptom frequency: 24-72 hour Holter for daily symptoms, 30-day event monitor for weekly symptoms, or implantable loop recorder for infrequent symptoms 4.

Common Pitfalls to Avoid

• Do not pace asymptomatic bradycardia, regardless of heart rate 2, 4
• Do not use atropine in heart transplant patients without documented autonomic reinnervation 1, 3
• Avoid atropine doses <0.5 mg due to paradoxical bradycardia 4
• Do not implant permanent pacemakers for reversible causes that have completely resolved 1
• Recognize that beta-adrenergic agonists should be used cautiously in patients with potential coronary ischemia due to increased myocardial oxygen demand 1