What are the next steps in managing a pregnant woman with sudden tachycardia, faintness, and lower back pain, with a normal fetal heart rate?

Management of Pregnant Woman with Tachycardia, Faintness, and Lower Back Pain

For a pregnant woman with sudden tachycardia, faintness, and lower back pain but normal fetal heart rate (140 bpm), immediate evaluation for both cardiac arrhythmias and pregnancy-related complications is necessary, with a focus on ruling out life-threatening conditions.

Initial Assessment

• Position the patient in left lateral decubitus position to relieve potential compression of the inferior vena cava, which can cause paradoxical sinus slowing and hypotension during pregnancy 1
• Perform immediate vital sign assessment including continuous maternal heart rate monitoring, blood pressure, respiratory rate, and oxygen saturation 2, 1
• Continue fetal heart rate monitoring, as a normal fetal heart rate (120-160 bpm) is reassuring but does not rule out maternal pathology 3
• Obtain a 12-lead ECG to evaluate for arrhythmias and evidence of structural heart disease 1

Differential Diagnosis

• Supraventricular tachycardia (SVT), which occurs in 20-44% of pregnancies and requires prompt treatment 1
• Ventricular tachycardia, less common but potentially life-threatening 2
• Preterm labor, given the lower back pain and potential uterine contractions 1
• Placental abruption, which can present with back pain and maternal tachycardia 4
• Peripartum cardiomyopathy, which can present with new-onset arrhythmias 1
• Pulmonary embolism, which can cause tachycardia and faintness 2

Immediate Management

• For hemodynamically unstable tachycardia: immediate electrical cardioversion is recommended regardless of pregnancy status 2
• For stable SVT: vagal maneuvers followed by IV adenosine if vagal maneuvers fail 2, 1
• For ventricular tachycardia with stable hemodynamics: IV sotalol or procainamide may be considered 2
• Hydration with IV fluids to improve hemodynamic status and rule out dehydration as a cause 1

Further Evaluation

• Echocardiogram to rule out structural heart disease, particularly if arrhythmias are documented 1
• Holter monitor for 24-48 hours if symptoms are intermittent to detect any arrhythmias 1
• Assessment of uterine contractions to evaluate for preterm labor given the lower back pain 1
• Laboratory studies including complete blood count, electrolytes, thyroid function tests, and cardiac enzymes 2

Long-term Management

• For recurrent SVT requiring prophylaxis: cardioselective beta-blockers (particularly metoprolol) are first-line treatment during pregnancy 2, 1
• Avoid amiodarone for long-term use due to potential fetal thyroid effects (9% risk of neonatal hypothyroidism), unless other therapy has failed and the arrhythmia causes hemodynamic instability 2
• Class IC antiarrhythmic drugs may be considered in the absence of structural heart disease if beta-blockers are ineffective 2
• For life-threatening ventricular arrhythmias resistant to pharmacological therapy, ICD implantation should be considered even during pregnancy 2

When to Escalate Care

• Immediate escalation to emergency care for:
  • Persistent tachycardia despite initial interventions 1
  • Development of shortness of breath or syncope 1
  • Worsening or persistent abdominal/back pain 1
  • Any signs of hemodynamic instability 2
  • Changes in fetal heart rate pattern 4

Important Considerations

• Pharmacokinetics of antiarrhythmic drugs are altered during pregnancy, requiring careful monitoring of drug levels 2
• All commonly used antiarrhythmic drugs cross the placenta, necessitating careful selection 2
• Catheter ablation should be postponed until after delivery if possible, but if necessary during pregnancy, should be performed in the second trimester with appropriate lead shielding and echo guidance 2
• Stress and anxiety about pregnancy can exacerbate arrhythmias and should be addressed 1

Follow-up Plan

• Regular cardiac and obstetric follow-up to monitor maternal symptoms and fetal well-being 1
• Repeat ECG and echocardiogram as indicated by symptoms 1
• Continued fetal monitoring, particularly if maternal symptoms recur or worsen 5