How should supraventricular tachycardia be treated in a pregnant woman?

Treatment of Supraventricular Tachycardia in Pregnancy

Begin with vagal maneuvers in all hemodynamically stable pregnant patients, followed immediately by IV adenosine if unsuccessful, and reserve synchronized cardioversion for unstable patients or drug-refractory cases. 1

Acute Management Algorithm

Step 1: Initial Intervention

• Perform vagal maneuvers first with the patient in the supine position, including Valsalva maneuver (bearing down against closed glottis for 10-30 seconds at 30-40 mmHg pressure), carotid sinus massage after confirming no bruit, or applying an ice-cold wet towel to the face 2, 1
• These techniques are safe throughout all trimesters and carry no fetal risk 1
• Success rates are modest (approximately 28% overall when switching between techniques), but the zero-risk profile makes them mandatory as first-line therapy 2

Step 2: Pharmacological Conversion

• Adenosine 6 mg rapid IV bolus is the first-line medication when vagal maneuvers fail 2, 3, 1
• If unsuccessful, give 12 mg IV (may repeat once); doses up to 24 mg have been used safely 1
• Adenosine's ultra-short half-life (seconds) limits fetal exposure, making it safe in any trimester 3, 1
• Maternal side effects (chest discomfort, flushing, transient dyspnea) are brief and self-limited 1

Step 3: Second-Line Pharmacological Options

• IV metoprolol or propranolol are reasonable alternatives if adenosine fails or is contraindicated 3, 1
• Administer as a slow infusion to minimize maternal hypotension 1
• Extensive safety data support beta-blocker use in pregnancy, particularly in the second and third trimesters 3

Step 4: Third-Line Options

• IV verapamil may be considered but carries higher risk of maternal hypotension compared to adenosine 1, 4
• IV procainamide is another option with documented safety for maternal and fetal arrhythmias, though long-term use risks lupus-like syndrome 1
• Both receive Class IIb recommendations due to limited comparative data 1

Step 5: Electrical Cardioversion

• Synchronized cardioversion is indicated immediately for hemodynamic instability (hypotension, shock, pulmonary edema) or drug-refractory SVT 1, 5
• Use 50-100 J with the same energy dosing as non-pregnant patients 5, 6
• Place electrode pads so current trajectory is directed away from the uterus 7, 1
• The procedure is safe at any gestational age 3, 1
• Perform fetal heart-rate monitoring during and immediately after cardioversion whenever time permits 3, 1

Chronic Suppression for Recurrent SVT

First-Line Oral Agents

• Metoprolol is the preferred beta-blocker for prophylactic therapy with Class I recommendation 3
• Digoxin has a long safety track record during pregnancy and is another first-line option 3
• Propranolol is a reasonable alternative to metoprolol, considered safe in the second trimester 3
• Flecainide, propafenone, sotalol, and verapamil are also Class IIa options for highly symptomatic recurrent SVT 1

Alternative Approaches

• Catheter ablation may be reasonable for drug-refractory, highly symptomatic SVT using zero-fluoroscopy or radiation-minimizing techniques, especially in the second or third trimester 1

Critical Medications to Avoid

• Never use atenolol at any stage of pregnancy due to well-documented association with intrauterine growth retardation 3, 7, 1
• Avoid amiodarone except as absolute last resort for potentially life-threatening SVT when all other therapies have failed, due to fetal thyroid toxicity and growth restriction risk 3, 1
• Do not use flecainide in patients with significant ventricular dysfunction due to increased cardiac arrest risk 2, 3

Key Clinical Pitfalls

• Do not delay cardioversion in unstable patients attempting pharmacologic conversion first 1
• Avoid all antiarrhythmic medications in the first trimester when possible, as the risk of congenital malformations is highest during organogenesis 2, 1
• Do not treat physiologic sinus tachycardia (gradual onset/offset, rates typically <150 bpm) with antiarrhythmics 1
• Use the lowest effective dose of any medication with regular monitoring of clinical response 2, 3
• Coordinate care through a multidisciplinary team including cardiology, obstetrics, anesthesia, and neonatology 1