What is the initial management of a term pregnant woman who presents with a heart rate below 60 beats per minute?

Management of Bradycardia in Term Pregnancy

For a term pregnant woman presenting with a heart rate below 60 bpm, immediately place her in the left lateral decubitus position to relieve inferior vena cava compression, which often resolves symptomatic bradycardia caused by supine hypotensive syndrome. 1, 2

Initial Positional Management

• Sinus bradycardia during pregnancy is frequently benign and related to reflex cardiac slowing (Valsalva maneuver during delivery) or supine hypotensive syndrome caused by uterine compression of the inferior vena cava with paradoxical sinus slowing. 1, 2

• Left lateral decubitus positioning is the first-line intervention for symptomatic bradycardia in pregnancy and should be attempted before any pharmacologic or invasive therapy. 1, 2

• If bradycardic symptoms persist after positional changes, proceed with further evaluation and intervention. 1, 2

Assessment of Symptoms and Hemodynamic Stability

• Evaluate whether the bradycardia is causing symptoms by assessing for signs of poor perfusion: altered mental status, ischemic chest discomfort, acute heart failure, hypotension, or shock. 2, 3

• Bradyarrhythmias may become symptomatic during pregnancy due to increased demands for higher heart rate and cardiac output, particularly in patients with structural heart disease. 1

• However, bradyarrhythmias usually have a favorable outcome in the absence of underlying heart disease. 1

Diagnostic Evaluation

• Obtain a 12-lead ECG immediately to document rhythm, rate, conduction abnormalities, and screen for structural heart disease. 2, 3

• Distinguish sinus node dysfunction from atrioventricular (AV) block, as therapeutic strategies differ for each mechanism. 2

• First-degree AV block can be observed during pregnancy in the absence of underlying heart disease; the site of AV delay is usually located above the bundle of His and does not progress to complete heart block. 1

• Second-degree AV block occurs rarely and is usually associated with structural heart disease or drug therapy; the majority of cases are second-degree type I Wenckebach block, unassociated with symptomatic bradycardias. 1

• Isolated congenital complete heart block has a favorable outcome during pregnancy, especially when the escape rhythm has a narrow QRS complex; supportive pacing during pregnancy is usually not necessary. 1, 2

Management Algorithm for Persistent Symptomatic Bradycardia

For Hemodynamically Unstable Patients

• Atropine 0.5-1 mg IV bolus is first-line pharmacologic therapy for acute symptomatic bradycardia, repeated every 3-5 minutes to a maximum total dose of 3 mg. 3

• Atropine crosses the placenta but is not associated with increased risk of congenital malformations based on surveillance studies of 381 newborns exposed during the first trimester. 4

• If atropine is ineffective, consider IV infusion of β-adrenergic agonists such as dopamine (2-10 μg/kg/min) or epinephrine (2-10 μg/min). 3

• Initiate transcutaneous pacing in unstable patients who don't respond to atropine as a bridge to transvenous pacing or until bradycardia resolves. 3

For Persistent Symptoms Despite Conservative Measures

• Temporary pacing during delivery is recommended in selected women with complete heart block and symptoms due to the risk of bradycardia and syncope. 1, 2

• For persistent symptomatic bradycardia that does not improve with conservative measures, implant a permanent single-chamber pacemaker. 1, 2

• Permanent pacemaker implantation carries low maternal risk and can be performed safely at any stage of pregnancy, especially if the fetus is beyond 8 weeks gestation. 1, 2

• Use echocardiographic guidance for device implantation to minimize fetal radiation exposure. 1, 2

Special Considerations for Delivery

• Vaginal delivery carries no extra risks in a mother with congenital complete heart block, unless contraindicated for obstetric reasons. 1, 2

• Approximately 30% of congenital AV blocks remain undiscovered until adulthood and may present during pregnancy. 1, 2

Critical Pitfalls to Avoid

• Do not postpone essential interventions because of pregnancy concerns; maternal hemodynamic stability is paramount for fetal survival. 2

• Avoid assuming all bradycardia in pregnancy is benign; increased cardiac demand can convert an asymptomatic rhythm disturbance into a symptomatic one. 2

• Do not overlook coexisting structural heart disease, especially in patients with repaired congenital lesions such as tetralogy of Fallot or ventricular septal defect repair. 1, 2

• Continuous fetal monitoring should be employed whenever maternal bradycardia is present to detect potential fetal hypoperfusion. 2