How to manage a patient with bradycardia?

Management of Sustained Bradycardia (HR 36 BPM)

For a patient with sustained heart rate of 36 BPM, immediately assess for hemodynamic instability and symptoms of poor perfusion—if present, administer atropine 0.5-1 mg IV as first-line therapy, repeatable every 3-5 minutes up to 3 mg total, while preparing for transcutaneous or transvenous pacing if medical therapy fails. 1, 2

Immediate Assessment

Determine if the bradycardia is causing hemodynamic compromise:

• Signs of poor perfusion requiring immediate treatment include: altered mental status, ischemic chest pain, acute heart failure, hypotension (SBP <90 mmHg), or other signs of shock 3, 2
• Obtain 12-lead ECG immediately to identify the rhythm mechanism (sinus bradycardia, AV block, sinus arrest, etc.) 3, 2
• Establish IV access, continuous cardiac monitoring, and pulse oximetry 3
• Critical distinction: A heart rate of 36 BPM is well below the 50 BPM threshold where bradycardia typically becomes symptomatic and requires intervention 3

Identify and Address Reversible Causes

Before escalating therapy, rapidly evaluate for treatable etiologies:

• Medications: Beta-blockers, calcium channel blockers, digoxin, antiarrhythmics 3, 2
• Metabolic: Hypothyroidism, severe acidosis, hypokalemia, hypothermia 3
• Cardiac: Acute myocardial infarction (especially inferior MI), increased intracranial pressure 3, 2
• Infections: Lyme disease in endemic areas 2
• Special populations: Recent heart transplant (atropine ineffective due to denervation), spinal cord injury (may be refractory to atropine) 3, 1

Pharmacologic Management Algorithm

First-Line: Atropine

Atropine 0.5-1 mg IV push, repeat every 3-5 minutes to maximum total dose of 3 mg 1, 2

• Atropine has Class IIa recommendation (reasonable to use) for symptomatic bradycardia with hemodynamic compromise 1
• Works by competitive antagonism of muscarinic acetylcholine receptors, abolishing vagal cardiac slowing 4
• Response rates: Approximately 50% of patients achieve partial or complete response; 50% have no response 5
• Contraindications: Heart transplant patients without autonomic reinnervation (Class III: Harm) 1; may worsen infranodal AV block 3

Second-Line: Catecholamines (if atropine fails)

If atropine is ineffective and patient remains unstable, initiate chronotropic infusions:

• Dopamine 5-20 mcg/kg/min IV: Start at 5 mcg/kg/min, increase by 5 mcg/kg/min every 2 minutes (Class IIb) 1
• Epinephrine 2-10 mcg/min IV: Titrate to effect (Class IIb) 1, 2
• Isoproterenol 1-20 mcg/min IV: Based on heart rate response (Class IIb), but avoid in suspected coronary ischemia as it increases myocardial oxygen demand 1

Alternative Agents for Special Situations

Heart transplant or spinal cord injury patients (atropine-refractory):

• Aminophylline 6 mg/kg in 100-200 mL IV over 20-30 minutes 3, 1
• Theophylline (oral dosing for subacute management) 3
• These methylxanthines provide adenosine receptor blockade, targeting unopposed parasympathetic stimulation 3

Temporary Pacing Indications

If bradycardia remains hemodynamically unstable despite medical therapy, proceed to temporary pacing:

Transcutaneous Pacing (Class IIb)

• Immediate bridge therapy for critically ill patients 3, 1
• Place pads on all high-risk patients as preparation strategy 3
• Requires: Adequate sedation/analgesia in conscious patients; verify capture by pulse or arterial waveform 3
• Limitation: Less reliable capture verification than transvenous pacing 3

Transvenous Pacing (Class IIa)

• Preferred for persistent hemodynamic instability refractory to medical therapy 3
• More reliable than transcutaneous, but carries 14-40% complication rate 3
• Avoid in mildly symptomatic patients with intermittent episodes—risks outweigh benefits 3

Clinical Decision Algorithm

Follow this structured approach:

1. HR 36 BPM + hemodynamic instability (altered mental status, chest pain, hypotension, heart failure) → Atropine 0.5-1 mg IV immediately 1, 2

2. No response to atropine after 3 mg total → Start dopamine or epinephrine infusion + prepare for pacing 1, 2

3. Persistent instability despite medications → Initiate transcutaneous pacing as bridge, then transvenous pacing if prolonged support needed 3

4. Stable patient with reversible cause identified → Treat underlying cause, observe, avoid unnecessary pacing 3, 2

5. Persistent symptomatic bradycardia without reversible cause → Permanent pacemaker indicated 3

Critical Pitfalls to Avoid

• Do not use atropine in heart transplant patients—it is ineffective and potentially harmful due to cardiac denervation 1
• Avoid isoproterenol in acute coronary syndrome—it worsens ischemia by increasing oxygen demand while decreasing coronary perfusion 1
• Do not rush to permanent pacing within 72 hours of acute MI—conduction may recover, especially with inferior MI 3
• Recognize infranodal block patterns (Mobitz II, third-degree with wide QRS)—atropine may paradoxically worsen block 3
• Temporary transvenous pacing increases infection risk for subsequent permanent pacemaker—use judiciously 3

Specific Rhythm Considerations

The underlying mechanism matters:

• High-grade AV block (48% of cases): More likely to require temporary pacing (20% of all bradycardia presentations), less responsive to atropine 6, 5
• Sinus bradycardia/sinus arrest (32% combined): Better response to atropine, often achieves normal sinus rhythm with single dose 6, 5
• Acute MI with bradycardia: Inferior MI typically has better prognosis than anterior MI with conduction disease 3

Disposition

• 50% of patients with compromising bradycardia ultimately require permanent pacemaker 6
• 30-day mortality is approximately 5% in patients presenting with hemodynamically compromising bradycardia 6
• Patients achieving normal sinus rhythm typically do so during initial prehospital/ED interval—if not responsive early, escalate therapy promptly 5