What is the first-line pharmacological management for a pregnant woman with Atrioventricular Reentrant Tachycardia (AVRT)?

First-Line Pharmacological Management for Pregnant Women with AVRT

For acute termination of AVRT in a pregnant woman, adenosine is the first-line pharmacological agent after vagal maneuvers fail, administered as a 6 mg rapid IV bolus, followed by up to two 12 mg doses if ineffective. 1

Acute Management Algorithm

Step 1: Vagal Maneuvers (First-Line Non-Pharmacological)

• Attempt vagal maneuvers immediately for stable AVRT, including Valsalva maneuver (bearing down against closed glottis for 10-30 seconds at ≥30-40 mmHg), carotid sinus massage (after confirming absence of bruit), or applying ice-cold wet towel to face 1
• These maneuvers are safe, effective, and should always be attempted first before pharmacological intervention 1, 2

Step 2: Adenosine (First-Line Pharmacological)

• If vagal maneuvers fail, administer IV adenosine 6 mg as rapid bolus 1
• If ineffective, give up to two subsequent 12 mg doses 1
• Adenosine is safe in pregnancy due to its extremely short half-life, preventing fetal exposure 1, 2
• Success rate approaches 90% for terminating AVRT 3
• Maternal side effects (chest discomfort, flushing) are transient and well-tolerated 1

Step 3: Beta-Blockers (Second-Line if Adenosine Fails)

• Administer IV metoprolol or propranolol as a slow infusion if adenosine is ineffective or contraindicated 1
• Beta-blockers have extensive safety data spanning decades in pregnancy 1, 2
• Slow infusion minimizes risk of maternal hypotension 1

Step 4: Calcium Channel Blockers (Third-Line Alternative)

• IV verapamil may be used if adenosine and beta-blockers fail or are contraindicated 2
• However, verapamil carries higher risk of maternal hypotension compared to adenosine 2
• Verapamil is also approximately 90% effective for acute AVRT termination 3

Emergency Intervention: Electrical Cardioversion

• Perform immediate synchronized electrical cardioversion if the patient becomes hemodynamically unstable at any point 1, 2
• Cardioversion is safe at all stages of pregnancy and should never be delayed due to pregnancy concerns 1, 2
• Use biphasic shock energy of 120-200 J with lateral defibrillator pad placed under breast tissue 2
• Maternal stability is essential for fetal survival 2

Long-Term Prophylactic Management

If recurrent AVRT requires chronic suppression:

First-Line Prophylactic Agents

• Metoprolol, propranolol, or digoxin are first-line agents for ongoing management 1
• These have the longest safety record in pregnancy 1
• Avoid first trimester use if possible, as risk of congenital malformations is greatest during this period 1

Second-Line Prophylactic Agents

• Flecainide, propafenone, or sotalol can be used if first-line agents fail 1
• These are reserved for patients without structural heart disease 1

Critical Pitfalls to Avoid

Absolute Contraindications

• Never use AV nodal blocking agents (adenosine, beta-blockers, verapamil, digoxin) in patients with manifest pre-excitation (Wolff-Parkinson-White pattern) on resting ECG 2, 4
• This can precipitate ventricular fibrillation by enhancing conduction down the accessory pathway 4

Specific Beta-Blocker to Avoid

• Never use atenolol in pregnancy 1, 2
• Atenolol is associated with intrauterine growth retardation, especially with early gestational use and longer duration 1

Amiodarone Restrictions

• Amiodarone should only be considered for life-threatening SVT when all other therapies have failed 1
• Fetal hypothyroidism occurs in approximately 17% of cases 1
• Use lowest effective dose for shortest duration possible 2

Monitoring Considerations

• Position patient in left lateral decubitus if symptomatic bradycardia or hypotension develops to relieve inferior vena cava compression 2
• Continuous fetal monitoring is essential during acute episodes to assess fetal heart rate and detect hypoperfusion 2
• Drug levels require more careful monitoring during pregnancy due to altered pharmacokinetics (increased plasma volume, renal clearance, and hepatic metabolism) 2, 5