What is the recommended management for a pregnant woman with a secundum type atrial septal defect (ASD) and New York Heart Association (NYHA) class II symptoms at 40 5/7 weeks gestation in labor, considering beta blockers (e.g. metoprolol) or Lanoxin (digoxin)?

Management of Secundum ASD, NYHA II, at Term in Labor

For a pregnant woman with secundum ASD and NYHA class II symptoms at 40 5/7 weeks in active labor, beta-blockers (specifically metoprolol or propranolol) are the recommended first-line agents for rate control if arrhythmias develop, while digoxin should be considered as second-line therapy if beta-blockers are ineffective or not tolerated. 1

Hemodynamic Considerations During Labor

• Secundum ASD is generally well tolerated during pregnancy in the absence of severe pulmonary hypertension, though NYHA class II symptoms indicate some functional limitation that requires careful monitoring 1, 2
• The hemodynamic stress of labor can precipitate arrhythmias (occurring in 4-5% of ASD patients), particularly supraventricular tachyarrhythmias, which are the most common cardiac complication in this population 2, 3
• Pregnancy-related cardiovascular changes may paradoxically decrease left-to-right shunting (lower Qp/Qs ratio), though right ventricular strain increases 3

Medication Selection Algorithm

Beta-Blockers as First-Line Therapy

• Beta-1 selective blockers (metoprolol, propranolol, labetalol) are recommended for rate control during pregnancy and labor, with the critical exception of atenolol, which should be avoided 1, 4
• Atenolol is classified as Category D due to associations with intrauterine growth retardation and is contraindicated 4
• Metoprolol and propranolol are FDA Category C and considered safe for use during labor with appropriate fetal monitoring 1
• Beta-blockers effectively control heart rate in pregnant patients with structural heart disease and prevent arrhythmia-related hemodynamic deterioration 1

Digoxin (Lanoxin) as Second-Line Therapy

• Digoxin should be considered for rate control if beta-blockers are ineffective or not tolerated during labor 1
• Digoxin is FDA Category C and has extensive safety data in pregnancy 1
• It provides effective rate control without the negative inotropic effects that could worsen right ventricular function in the setting of volume overload 1

Specific Management During Active Labor

Immediate Interventions if Arrhythmia Develops

• If supraventricular tachycardia occurs, initiate vagal maneuvers first (Valsalva maneuver in supine position), followed by intravenous adenosine 6 mg rapid bolus if vagal maneuvers fail 1, 5
• For sustained arrhythmias requiring rate control, administer intravenous metoprolol or propranolol as first-line agents 1
• Synchronized cardioversion is recommended for hemodynamically unstable arrhythmias when pharmacological therapy fails 1

Monitoring Requirements

• Continuous cardiac monitoring and pulse oximetry throughout labor to detect arrhythmias or right-to-left shunting 2, 6
• Monitor for paradoxical emboli risk (occurs in 2-5% of ASD patients), particularly during Valsalva with pushing 2
• Fetal heart rate monitoring is essential, as beta-blockers can reduce fetal heart rate variability through beta-1 selective blockade, though this is generally well-tolerated 4

Critical Pitfalls to Avoid

• Never use atenolol - it has documented fetal risks including intrauterine growth retardation and is the only beta-blocker with Category D classification 4
• Avoid aggressive volume loading, as this can worsen right ventricular volume overload and increase left-to-right shunting 3
• Do not assume asymptomatic status based solely on oxygen saturation - "asymptomatic hypoxia" can occur with right-to-left shunting during labor 6
• Avoid prolonged Valsalva during second stage if possible, as this increases risk of paradoxical embolism and can precipitate right-to-left shunting 2

Mode of Delivery Considerations

• Vaginal delivery is preferred for most patients with secundum ASD and NYHA class II symptoms, as cesarean section increases bleeding risk without improving cardiac outcomes 1
• Assisted second stage (forceps or vacuum) may be considered to minimize prolonged Valsalva and maternal effort 1
• Epidural anesthesia is reasonable and preferred over general anesthesia, with precautions to avoid hypotension that could precipitate right-to-left shunting 1

Postpartum Vigilance

• The immediate postpartum period (first 24-48 hours) carries increased risk for arrhythmias and hemodynamic decompensation due to autotransfusion from uterine involution 1
• Continue cardiac monitoring for at least 24 hours postpartum 1
• If beta-blockers or digoxin were initiated during labor, continue them postpartum with cardiology follow-up for potential discontinuation after hemodynamic stabilization 1