What is the appropriate workup for bradycardia (abnormally slow heart rate) in a cardiology clinic?

From the Guidelines

A bradycardia workup in a cardiology clinic should begin with a thorough history and physical examination, focusing on symptoms like dizziness, syncope, fatigue, or exercise intolerance, as recommended by the 2019 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1. The initial evaluation should include a 12-lead ECG to document the bradycardia and identify any conduction abnormalities, along with basic laboratory tests including electrolytes, thyroid function, and complete blood count.

• Key points to consider in the workup include:
  • The presence of left bundle branch block on electrocardiogram, which markedly increases the likelihood of underlying structural heart disease and of diagnosing left ventricular systolic dysfunction, as noted in the 2019 guideline 1.
  • The importance of establishing temporal correlation between symptoms and bradycardia in determining the need for permanent pacing, as emphasized in the guideline 1.
  • The consideration of sleep apnea as a potential cause of nocturnal bradycardias, and the potential benefits of treating sleep apnea in reducing the frequency of these arrhythmias and improving cardiovascular outcomes, as discussed in the guideline 1. For intermittent symptoms, ambulatory monitoring is essential - options include 24-48 hour Holter monitoring for frequent symptoms, event recorders for occasional symptoms, or implantable loop recorders for very infrequent episodes.
• An echocardiogram should be performed to assess cardiac structure and function, as recommended in the guideline 1. Exercise stress testing may be valuable to evaluate chronotropic incompetence.
• If structural heart disease or conduction system disease is suspected, additional testing might include cardiac MRI or electrophysiology studies, as noted in the guideline 1. Management depends on the cause - addressing reversible factors like medication side effects or thyroid dysfunction, or considering pacemaker implantation for symptomatic bradycardia due to sinus node dysfunction or atrioventricular block, as recommended in the guideline 1.
• Temporary discontinuation of rate-limiting medications (beta-blockers, calcium channel blockers, digoxin) may be necessary during evaluation to determine if bradycardia is medication-induced or intrinsic, as discussed in the guideline 1.

From the FDA Drug Label

Atropine abolishes various types of reflex vagal cardiac slowing or asystole The drug also prevents or abolishes bradycardia or asystole produced by injection of choline esters, anticholinesterase agents or other parasympathomimetic drugs, and cardiac arrest produced by stimulation of the vagus.

The appropriate workup for bradycardia in a cardiology clinic is not directly addressed in the provided drug label. However, atropine can be used to treat bradycardia by abolishing vagal cardiac slowing or asystole.

• Key points to consider when using atropine for bradycardia:
  • Administration: Atropine can be administered intravenously.
  • Effect: Atropine can increase heart rate by counteracting vagal stimulation.
  • Precautions: Atropine may have variable effects on heart rate and blood pressure, and its use should be carefully considered in different patient populations, such as children and the elderly 2.

From the Research

Diagnosis of Bradycardia

• Bradycardia can be diagnosed using noninvasive diagnostic studies such as 12-lead electrocardiogram, Holter electrocardiogram, exercise testing, event recorder, and implantable loop recorder 3
• Persistent bradycardia can be diagnosed by standard ECG, while intermittent bradycardia may require long-term ECG monitoring and/or additional testing 4

Treatment of Bradycardia

• The treatment of choice for chronic, symptomatic bradycardia is the placement of a cardiac pacemaker 5
• Symptomatic bradycardias are the standard indication for cardiac pacing after exclusion of reversible causes 4
• For patients who refuse or cannot tolerate pacemaker insertion, pharmacologic therapy such as theophylline may be considered 5
• Atropine is recommended as a first-line therapy for unstable bradycardic patients, but may not be effective in patients with atrioventricular blocks at the level of the His-Purkinje fibres (infranodal) 6
• Traditional Chinese medicine (TCM) may be an effective alternative therapy for sinus bradycardia and cardiac sinus arrests 7

Indications for Pacemaker Implantation

• Pacemaker implantation is indicated in symptomatic bradycardias after exclusion of reversible causes 4
• Pacemaker implantation is indicated in third degree AV block and second degree AV block Mobitz Type II, even if asymptomatic 4
• Cardiac pacing for recurrent unpredictable neurocardiogenic syncope due to a cardioinhibitory reflex should be considered in certain circumstances 4