What is the significance of persistent sinus bradycardia in a 45-year-old male with a history of syncope and migraines, taking Propranolol (propranolol)?

From the Guidelines

I strongly recommend discontinuing propranolol and switching to a migraine prophylactic medication that doesn't cause bradycardia, such as topiramate or amitriptyline, to alleviate the patient's symptoms of bradycardia and dizziness. The patient's symptoms are likely side effects of propranolol, a beta-blocker known to lower heart rate, as evidenced by the consistent finding of sinus bradycardia on both current and 2017 ECGs, along with the history of syncope 1. According to the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay, symptomatic bradycardia is defined as a documented bradyarrhythmia that is directly responsible for the development of clinical manifestations such as syncope or presyncope, transient dizziness or lightheadedness, heart failure symptoms, or confusional states resulting from cerebral hypoperfusion attributable to slow heart rate 1. The patient's history of syncope and current symptoms of bradycardia and dizziness suggest that propranolol may be exacerbating an underlying tendency to bradycardia, and discontinuation of the medication is necessary to prevent further symptoms. Topiramate starting at 25mg daily and gradually increasing to 50-100mg daily over 2-4 weeks, or amitriptyline starting at 10mg nightly and gradually increasing to 25-50mg nightly, are suitable alternatives for migraine prophylaxis that do not cause bradycardia. Close monitoring during medication transition is essential, with follow-up in 2-4 weeks to assess symptom improvement and medication tolerability. If symptoms persist after discontinuation of propranolol, further cardiac evaluation including Holter monitoring may be warranted to rule out underlying conduction abnormalities, as suggested by the 2012 ACCF/AHA/HRS focused update incorporated into the ACCF/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities 1.

From the FDA Drug Label

Propranolol is a nonselective, beta-adrenergic receptor-blocking agent possessing no other autonomic nervous system activity. It specifically competes with beta-adrenergic receptor-stimulating agents for available receptor sites When access to beta-receptor sites is blocked by propranolol, the chronotropic, inotropic, and vasodilator responses to beta-adrenergic stimulation are decreased proportionately.

The patient's symptoms of bradycardia and dizziness could be related to the effects of propranolol, as it decreases the chronotropic response to beta-adrenergic stimulation, which can lead to a decrease in heart rate.

• The patient's history of syncope and current symptoms of bradycardia and dizziness may indicate that the patient is experiencing adverse effects from propranolol.
• The EKG results showing sinus bradycardia support this possibility. The FDA drug label does not provide direct information on how to manage these specific symptoms in this patient, but it does describe the mechanism of action of propranolol and its effects on the heart 2 2.

From the Research

Patient Presentation

• The patient is a 45-year-old male with a history of syncope, presenting with bradycardia and dizziness.
• He has been taking Propranolol since 02/2023 for migraines.
• EKG results from 2017 and the current month show sinus bradycardia with otherwise normal ECG.

Diagnostic Approach

• According to 3, a thorough history and physical examination, including orthostatic assessment, are crucial for making a diagnosis of syncope.
• The patient's history of syncope and current presentation of bradycardia and dizziness suggest the need for further evaluation to determine the underlying cause of syncope.
• 4 suggests that the first step in syncope diagnostic assessment is to identify patients with cardiac syncope, and if cardiac syncope is unlikely, reflex (neurally mediated) syncope and orthostatic hypotension are the most frequent causes of transient loss of consciousness.

Management of Bradycardia

• 5 states that management of bradycardia is based on the severity of symptoms, the underlying causes, presence of potentially reversible causes, presence of adverse signs, and risk of progression to asystole.
• Pharmacologic therapy and/or pacing are used to manage unstable or symptomatic bradyarrhythmias.
• In this case, the patient is already taking Propranolol, which may be contributing to his bradycardia.

Treatment of Syncope

• 4 suggests that the identified mechanism of syncope should be carefully assessed and assigned either to hypotensive or bradycardic phenotype, which will determine the choice of therapy.
• 6 found that Propranolol, nadolol, and placebo are equally effective treatments in reducing the recurrence of syncope and presyncope, as well as improving patients' well-being.
• However, it is essential to consider the patient's individual response to treatment and potential side effects, as noted in 6.