Treatment Guidelines for Symptomatic Bradycardia
For symptomatic bradycardia, atropine 0.5 mg IV every 3-5 minutes (maximum 3 mg) is the first-line treatment, followed by transcutaneous pacing (TCP) for non-responders, and then consideration of β-adrenergic agonists like dopamine, epinephrine, or isoproterenol as temporizing measures while preparing for transvenous pacing. 1
Initial Assessment and Diagnosis
Confirm bradycardia (heart rate <60 bpm) with 12-lead ECG
Assess for signs and symptoms of instability:
- Altered mental status
- Ischemic chest discomfort
- Acute heart failure
- Hypotension
- Other signs of shock
Identify the type of bradycardia:
- Sinus bradycardia
- Atrioventricular (AV) blocks (first, second, or third-degree)
- Sinus node dysfunction
- Junctional bradycardia
Evaluate for reversible causes:
- Medications (beta-blockers, calcium channel blockers, digoxin)
- Electrolyte abnormalities
- Hypothyroidism
- Increased vagal tone
- Acute myocardial infarction
Treatment Algorithm for Symptomatic Bradycardia
First-Line Treatment
- Atropine 0.5-1 mg IV (Class IIa, LOE B)
- May repeat every 3-5 minutes to a maximum total dose of 3 mg
- Avoid doses <0.5 mg (may paradoxically worsen bradycardia)
- Monitor for response 1
Second-Line Treatments (if atropine ineffective)
Transcutaneous pacing (TCP) (Class IIa, LOE B)
- Initiate in unstable patients who don't respond to atropine
- Consider immediate TCP in high-degree AV block when IV access unavailable (Class IIb, LOE C)
- Note: TCP is painful in conscious patients and is a temporizing measure 1
β-adrenergic agonists (if atropine ineffective or inappropriate)
- Dopamine: 5-20 mcg/kg/min IV infusion (Class IIb, LOE B)
- Epinephrine: 2-10 mcg/min IV or 0.1-0.5 mcg/kg/min IV
- Isoproterenol: 2-10 mcg/min IV (use with caution in patients with coronary artery disease) 1
Transvenous pacing (Class IIa, LOE C)
- Indicated if patient does not respond to drugs or TCP 1
Special Considerations
Type II Second-Degree or Third-Degree AV Block
- Atropine may be ineffective in:
- Type II second-degree AV block
- Third-degree AV block with new wide-QRS complex
- Blocks in non-nodal tissue (bundle of His or distal conduction system)
- For these cases, proceed directly to TCP or β-adrenergic support while preparing for transvenous pacing 1
Heart Transplant Patients
- Do not use atropine in patients with heart transplant without evidence of autonomic reinnervation (Class III: Harm, LOE C-LD)
- Transplanted hearts lack vagal innervation, making atropine ineffective 1
Calcium Channel Blocker or Beta-Blocker Overdose
- Consider calcium administration:
- 10% calcium chloride: 1-2 g IV every 10-20 min or infusion of 0.2-0.4 mL/kg/h
- 10% calcium gluconate: 3-6 g IV every 10-20 min or infusion at 0.6-1.2 mL/kg/h
- Consider glucagon: 3-10 mg IV with infusion of 3-5 mg/h 1, 2
Acute Inferior MI with AV Block
Monitoring and Follow-up
- Continuous cardiac monitoring during treatment
- For patients with infrequent symptoms (>30 days between symptoms), consider long-term ambulatory monitoring with an implantable cardiac monitor if initial evaluation is nondiagnostic (Class IIa, LOE C-LD) 1
- Electrophysiology study may be considered in selected patients for diagnosis if noninvasive evaluation is nondiagnostic (Class IIb, LOE C-LD) 1
Pitfalls and Caveats
- Paradoxical bradycardia: Atropine can paradoxically worsen bradycardia in patients with infranodal AV blocks (at His-Purkinje level) 5
- Atropine in coronary ischemia: Use atropine cautiously in patients with acute coronary ischemia or MI as increased heart rate may worsen ischemia or increase infarction size 1
- Inadequate atropine dosing: Doses <0.5 mg may paradoxically result in further slowing of heart rate 1
- Delayed definitive treatment: Atropine and other pharmacological interventions are temporizing measures; do not delay preparation for pacing when indicated 1
- TCP limitations: TCP is painful in conscious patients and may achieve inconsistent capture; prepare for transvenous pacing when TCP is initiated 1