What is the effect of propranolol (a beta blocker) on heart rate, specifically inducing bradycardia (abnormally slow heart rate)?

From the Guidelines

Propranolol can induce bradycardia as a potential adverse effect, and clinicians should evaluate patients for and educate caregivers about this risk, particularly in the context of treating infantile hemangiomas.

Key Considerations

• The effect of propranolol on heart rate is a known consequence of its beta-blocking properties, which can lead to a decrease in heart rate or blood pressure, as noted in the clinical practice guideline for the management of infantile hemangiomas 1.
• Although bradycardia and hypotension tend to be mild and asymptomatic in children treated for infantile hemangiomas without preexisting cardiac comorbidities, it is crucial to monitor for these adverse effects, as they can occur in some cases, with 1 of 906 patients exhibiting bradycardia in one report 1.
• The management of propranolol-induced bradycardia involves assessing the severity and patient symptoms, with potential interventions including dose reduction for asymptomatic mild bradycardia or temporary discontinuation of propranolol for symptomatic or severe bradycardia.

Clinical Implications

• Patients taking propranolol should be educated to monitor their pulse regularly and report rates consistently below 50 bpm or any symptoms like dizziness, fatigue, or syncope.
• In acute settings, atropine 0.5-1 mg IV may be administered to increase heart rate, and for patients requiring continued beta-blockade but experiencing bradycardia, consider switching to a more cardioselective beta-blocker like metoprolol or atenolol.
• The benefits of propranolol treatment, including its efficacy in managing infantile hemangiomas, outweigh the harms, which include the risk of bradycardia and other adverse effects, as determined by the benefit-harm assessment in the clinical practice guideline 1.

From the FDA Drug Label

ADVERSE REACTIONS The following adverse events were observed and have been reported in patients using propranolol. Cardiovascular: Bradycardia; When access to beta-receptor sites is blocked by propranolol, the chronotropic, inotropic, and vasodilator responses to beta-adrenergic stimulation are decreased proportionately. In angina pectoris, propranolol generally reduces the oxygen requirement of the heart at any given level of effort by blocking the catecholamine-induced increases in the heart rate, systolic blood pressure, and the velocity and extent of myocardial contraction

Propranolol can induce bradycardia (abnormally slow heart rate) as it decreases the chronotropic response to beta-adrenergic stimulation, which includes heart rate. This effect is a result of its beta-adrenergic receptor-blocking activity.

• Key points:
  • Propranolol blocks beta-adrenergic receptors, reducing heart rate and contractility.
  • Bradycardia is listed as a potential adverse reaction to propranolol.
  • The mechanism of action of propranolol involves decreasing the heart's response to catecholamines, which can lead to a reduction in heart rate 2, 2, 2.

From the Research

Effect of Propranolol on Heart Rate

• Propranolol, a beta blocker, can induce bradycardia (abnormally slow heart rate) in some individuals, as seen in a case study where an 18-month-old girl with tetralogy of Fallot experienced extreme intermittent bradycardia with pauses of up to 2.6 seconds after being treated with propranolol 3.
• The combination of beta-blockers, such as propranolol, and sodium channel blockers can lead to severe iatrogenic bradycardia, with heart rates ranging from 20 to 49 beats per minute, and can result in cardiogenic shock and heart failure in elderly patients 4.
• However, low-dose intravenous propranolol has been shown to not increase the number or severity of bradycardia and hypotensive events in patients with traumatic brain injury, and may even be associated with decreased ICU and hospital length of stay 5.
• Propranolol intoxication can also lead to Brugada-pattern electrocardiogram, a condition characterized by right bundle-branch block and ST-segment elevation in the precordial leads V1 to V3, which can increase the risk of sudden cardiac death 6.
• In heart failure patients, propranolol has been shown to be safe and well-tolerated, with beneficial effects on left ventricular function, although it can cause bradycardia-related symptoms in some patients 7.

Key Findings

• Propranolol can induce bradycardia in some individuals, particularly when combined with other medications or in cases of overdose.
• The risk of bradycardia and other cardiac complications should be carefully considered when prescribing propranolol, especially in elderly patients or those with pre-existing heart conditions.
• Low-dose propranolol may be safe and effective in certain patient populations, such as those with traumatic brain injury.