What is the initial treatment for supraventricular tachycardia (SVT) in a pregnant woman?

Initial Treatment for Supraventricular Tachycardia (SVT) in Pregnant Women

Vagal maneuvers are the recommended first-line intervention for initial treatment of SVT in pregnant women, followed by adenosine if vagal maneuvers fail. 1

Treatment Algorithm for SVT in Pregnancy

First-line Treatment

• Vagal maneuvers should be performed with the patient in the supine position 1
  • Valsalva maneuver: Patient bears down against closed glottis for 10-30 seconds (equivalent to 30-40 mmHg) 1
  • Carotid sinus massage: Apply steady pressure over right or left carotid sinus for 5-10 seconds after confirming absence of bruits 1
  • Cold stimulus: Applying an ice-cold wet towel to the face 1
  • Valsalva has been shown to be more successful than carotid sinus massage in terminating SVT 1

Second-line Treatment

• Intravenous adenosine when vagal maneuvers fail 1, 2
  • Initial dose: 6 mg rapid IV bolus
  • If ineffective: Up to 2 subsequent doses of 12 mg may be administered
  • Safe for fetus due to adenosine's short half-life (unlikely to reach fetal circulation) 1
  • Maternal side effects (chest discomfort, flushing) are usually transient 1
  • Higher doses up to 24 mg have been safely administered in some cases 1

Third-line Treatment

• Intravenous beta-blockers (metoprolol or propranolol) when adenosine is ineffective or contraindicated 1
  • Considered safe in pregnancy with extensive reports of use for various maternal conditions 1
  • Administer as slow infusion to minimize risk of hypotension 1

Fourth-line Treatment

• Intravenous verapamil may be reasonable when adenosine and beta-blockers are ineffective or contraindicated 1
  • Higher risk of maternal hypotension compared to adenosine 1
  • Similar effects expected with diltiazem, though evidence is more limited 1

For Hemodynamically Unstable Patients

• Synchronized cardioversion (50-100 J) is recommended when pharmacological therapy is ineffective or contraindicated 1, 3
  • Safe at all stages of pregnancy 1
  • Apply electrode pads to direct energy trajectory away from uterus 1
  • Fetal monitoring during and after cardioversion is recommended if time allows 1
  • Energy dosing should be the same as in non-pregnant patients 1

Special Considerations

• Medications should be avoided if possible during the first trimester when risk of congenital malformations is greatest 1
• Start with the lowest recommended dose and monitor clinical response regularly 1
• For pregnant women with recurrent SVT, early epidural during labor may help prevent arrhythmia recurrence by minimizing catecholamine release 4
• Potential triggers like smoking, caffeine, and alcohol should be eliminated 2

Pitfalls and Caveats

• Avoid applying pressure to the eyeball as a vagal maneuver as this is potentially dangerous 1
• Vagal maneuvers will typically not be effective if the arrhythmia does not involve the AV node as part of a reentrant circuit 1
• When performing cardioversion, ensure proper positioning of electrode pads to minimize fetal exposure 1
• Be aware that verapamil carries a higher risk of maternal hypotension than adenosine 1
• If catheter ablation becomes necessary during pregnancy, only fluoroscopy-free mapping systems should be used 5