Can propranolol (beta-blocker) cause bradycardia (abnormally slow heart rate)?

Propranolol and Bradycardia

Yes, propranolol can cause bradycardia as a common and potentially serious side effect due to its beta-blocking properties.

Mechanism and Prevalence

Propranolol, a non-selective beta-adrenergic receptor blocking agent, directly affects the heart rate by:

• Blocking beta-1 receptors in the heart, reducing sympathetic stimulation
• Decreasing sinoatrial node automaticity
• Slowing atrioventricular conduction

According to the FDA drug label, bradycardia is listed as a common cardiovascular adverse reaction of propranolol 1. Clinical guidelines specifically mention "clinically symptomatic bradycardia" as a potential adverse effect requiring monitoring and patient education 2.

Risk Factors for Propranolol-Induced Bradycardia

Several factors increase the risk of developing bradycardia with propranolol:

• Dose-dependent relationship: Higher doses are more likely to cause bradycardia
• Pre-existing cardiac conditions: Patients with underlying conduction disorders
• Age: Elderly patients may be more susceptible
• Drug interactions: Concurrent use with other negative chronotropic agents
• Overdose: In overdose situations, bradycardia occurs in approximately 20% of cases 3

Clinical Significance

Bradycardia from propranolol can range from:

1. Asymptomatic: Detected only on routine monitoring
2. Mildly symptomatic: Fatigue, exercise intolerance
3. Severely symptomatic: Dizziness, syncope, or cardiovascular collapse

The American Heart Association guidelines note that beta-blockers like propranolol can cause bradycardia, heart block, and decreased cardiac contractility 2. In pediatric patients, clinicians are specifically advised to monitor for and educate caregivers about "clinically symptomatic bradycardia" as a potential adverse effect 2.

Management of Propranolol-Induced Bradycardia

For symptomatic bradycardia caused by propranolol:

1. Mild cases:

   • Dose reduction
   • Temporary discontinuation if clinically appropriate
   • Close monitoring

2. Severe cases:

   • Discontinue propranolol
   • Consider high-dose epinephrine infusion for severe bradycardia 2
   • Glucagon (5-10 mg IV followed by 1-5 mg/hour infusion) can be effective 2
   • In overdose situations, supportive care with inotropes may be required 3

Prevention and Monitoring

To minimize the risk of bradycardia:

• Start with lower doses and titrate gradually
• Regular monitoring of heart rate and blood pressure
• Educate patients about symptoms of bradycardia
• Use caution in patients with pre-existing bradycardia or heart block
• Be aware that propranolol can mask symptoms of hypoglycemia, which may compound cardiovascular effects 1

Special Considerations

• In patients with supraventricular tachycardia, the bradycardic effect may be therapeutic rather than adverse 2
• Patients with tetralogy of Fallot may experience extreme intermittent bradycardia with propranolol, requiring careful monitoring 4
• Concomitant use with calcium channel blockers can significantly increase the risk of bradycardia and heart block 1

Bradycardia is a well-documented side effect of propranolol that requires appropriate monitoring and management to prevent adverse outcomes related to decreased heart rate.