What is the appropriate management of tachyarrhythmia in a third‑trimester pregnant woman?

Management of Tachyarrhythmia in Late Pregnancy

For hemodynamically unstable tachyarrhythmias in the third trimester, perform immediate electrical cardioversion; for stable supraventricular tachycardia, attempt vagal maneuvers first, then give IV adenosine, followed by IV metoprolol if adenosine fails 1.

Acute Management Algorithm

Step 1: Assess Hemodynamic Stability

• Unstable (hypotension, altered mental status, chest pain, pulmonary edema): Proceed directly to electrical cardioversion 1
  • This is safe for both mother and fetus
  • Sustained tachycardia, particularly atrial flutter, causes fetal hypoperfusion in structural heart disease 1

Step 2: For Hemodynamically Stable Supraventricular Tachycardia

The treatment sequence is clearly defined:

1. Vagal maneuvers (modified Valsalva maneuver - 43% effective) 1
2. IV adenosine if vagal maneuvers fail (91% effective, first-line drug) 1
3. IV metoprolol if adenosine fails to terminate the tachycardia 1

Critical caveat: Do NOT use AV nodal blocking agents (adenosine, beta-blockers, calcium channel blockers) in patients with manifest pre-excitation on resting ECG (Wolff-Parkinson-White syndrome) 1.

Step 3: For Atrial Fibrillation/Flutter in Late Pregnancy

Hemodynamically unstable: Immediate electrical cardioversion 1

Hemodynamically stable with structurally normal heart:

• Consider pharmacological cardioversion with IV ibutilide or flecainide (though pregnancy experience is limited) 1
• Avoid amiodarone unless all other options fail due to fetotoxic effects 1

Anticoagulation requirements:

• If AF/flutter duration ≥48 hours or unknown: Anticoagulate with LMWH for at least 3 weeks before cardioversion, continue 4 weeks after 1
• If AF/flutter <48 hours: Consider IV heparin or therapeutic LMWH pericardioversion 1
• Any pregnant woman with structural heart disease and documented AF/flutter requires anticoagulation 2, 1

Ongoing/Prophylactic Management

When to Use Prophylactic Antiarrhythmic Therapy

Only initiate if:

• Symptoms are intolerable, OR
• Tachycardia causes hemodynamic compromise 1

First-Line Prophylactic Agents

1. Digoxin or selective β-blocker (metoprolol) 1
2. Second-line: Sotalol, flecainide, or propafenone 1

Special Considerations for Structural Heart Disease

• β-blockers, class I antiarrhythmics, and sotalol should be used with caution if LV or RV function is impaired 1
• Digoxin controls ventricular rate but has no prophylactic antiarrhythmic effect 1
• Amiodarone is reserved only for treatment failure and should be used at the lowest effective dose due to fetotoxicity 1

Critical Pitfalls to Avoid

1. Do not delay cardioversion in hemodynamically unstable patients - fetal outcomes worsen with maternal compromise
2. Do not use adenosine/beta-blockers in pre-excitation syndromes (risk of accelerating ventricular response)
3. Do not forget anticoagulation for AF/flutter in structural heart disease - therapeutic anticoagulation is mandatory 2, 1
4. Do not use amiodarone as first-line - significant fetal thyroid and developmental toxicity 1
5. Do not overlook underlying causes - hyperthyroidism and structural heart disease are common precipitants of AF/flutter in pregnancy 1

When to Consider Catheter Ablation

Reserve for special cases during pregnancy:

• Drug-resistant arrhythmias
• Poorly tolerated cases despite optimal medical therapy
• Can be performed with minimal fluoroscopy 1

The most recent Canadian guidelines 2 emphasize consultation with an electrophysiologist within a cardiac obstetrics program for complex cases, though the ESC guidelines 1 provide the most detailed algorithmic approach to acute management that remains the standard of care.