How to manage moderate variability with bradycardia?

From the Guidelines

Moderate variability with bradycardia requires careful monitoring and management, with a focus on identifying and addressing the underlying cause, and first-line treatment with atropine 0.5-1 mg IV repeated every 3-5 minutes as needed up to 1.5-3 mg total, as recommended by the 2019 ACC/AHA/HRS guideline 1.

Key Considerations

• Assess maternal vital signs and fetal heart rate patterns to determine if this is a reassuring or non-reassuring pattern.
• Bradycardia with moderate variability is often less concerning than bradycardia with minimal or absent variability, as the presence of variability suggests intact fetal autonomic function.
• If the bradycardia is mild (100-110 bpm) with good variability and no decelerations, consider conservative measures such as:
  • Maternal position change (usually to the left lateral position)
  • Oxygen administration at 8-10 L/min via face mask
  • Discontinuation of oxytocin if being administered
  • Ensuring adequate maternal hydration with IV fluids (typically lactated Ringer's solution at 125-150 mL/hour)

Management

• If bradycardia persists beyond 10 minutes or worsens, prepare for possible delivery.
• The underlying physiology relates to fetal compensatory mechanisms - variability indicates intact central nervous system control of the heart, suggesting the fetus is compensating despite the slow heart rate.
• This pattern may result from maternal hypotension, cord compression, placental insufficiency, or maternal medication effects, so identifying and addressing the underlying cause is essential for effective management.
• According to the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1, atropine is the first-line treatment for symptomatic bradycardia, and epinephrine or dopamine may be considered if atropine is not effective.
• The 2010 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations 1 also emphasizes the importance of evaluating and managing bradycardia based on the underlying cause and clinical condition.

From the FDA Drug Label

Atropine-induced parasympathetic inhibition may be preceded by a transient phase of stimulation, especially on the heart where small doses first slow the rate before characteristic tachycardia develops due to paralysis of vagal control Adequate doses of atropine abolish 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.

Managing Moderate Variability with Bradycardia:

• Atropine can be used to manage bradycardia by abolishing vagal cardiac slowing or asystole.
• The initial dose for antivagal effects, including bradycardia, is 0.5 to 1 mg given intravenously.
• The dose may be repeated as needed, with caution, to manage the bradycardia while monitoring for signs of excessive antimuscarinic effects.
• It is essential to titrate the dose according to heart rate, PR interval, blood pressure, and symptoms to avoid adverse reactions such as tachycardia 2.
• In patients with coronary artery disease, the total dose should be limited to 0.03 mg/kg to 0.04 mg/kg 2.

From the Research

Managing Moderate Variability with Bradycardia

• Moderate variability in heart rate can be a normal phenomenon, but when combined with bradycardia (a heart rate of less than 50-60 bpm), it may require medical attention 3.
• The management of bradycardia depends on the underlying cause and the presence of symptoms such as decreased end-organ perfusion 4.
• For unstable bradycardic patients, treatment options may include the use of atropine, beta agonists, and transcutaneous or transvenous pacing 4, 5.
• Transcutaneous cardiac pacing (TCP) has been shown to be a clinically effective treatment modality in patients with atropine-resistant unstable bradycardia, with significant improvements in heart rate and blood pressure 5.
• The 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients with Bradycardia and Cardiac Conduction Delay emphasizes the importance of evaluating and managing the underlying disease state, rather than just treating the bradycardia itself 3.
• Various management strategies for symptomatic bradycardia, including observation, non-invasive management, and permanent pacemaker implantation, have been compared in clinical studies, with outcomes such as length of stay and adverse events related to bradycardia 6.
• Cardiac pacing, including temporary and permanent pacemakers, can be used to treat bradyarrhythmias and ensure a steady heart rate, with patients requiring information, support, monitoring, and follow-up 7.