What is the appropriate treatment for a 20‑week pregnant woman with supraventricular tachycardia?

Treatment of SVT at 20 Weeks Gestation

Start with vagal maneuvers (Valsalva, carotid massage after confirming no bruit, or facial ice pack), then immediately give adenosine 6 mg IV rapid bolus if vagal maneuvers fail—this is the safest and most effective acute treatment for SVT in pregnancy at any gestational age. 1

Acute Management Algorithm

First-Line: Vagal Maneuvers

• Attempt vagal maneuvers first in all hemodynamically stable patients—these are completely safe at 20 weeks and should be your initial intervention. 1
• Specific techniques include Valsalva maneuver, carotid sinus massage (only after confirming no bruit), or applying ice to the face 1

Second-Line: Adenosine

• If vagal maneuvers fail, adenosine is the drug of choice: give 6 mg rapid IV bolus, followed by 12 mg if needed (may repeat 12 mg once), and doses up to 24 mg have been safely used. 2, 1
• Adenosine's ultra-short half-life (seconds) minimizes fetal exposure, making it safe throughout all trimesters 1
• Maternal side effects (chest discomfort, flushing, transient dyspnea) last only seconds 1
• This is preferred over verapamil because adenosine carries lower risk of maternal hypotension 1, 3

Third-Line: Beta-Blockers

• When adenosine is ineffective or contraindicated, use IV metoprolol or propranolol as slow infusions to minimize maternal hypotension. 2, 1
• Beta-blockers have extensive safety data in pregnancy across decades of use 2, 1
• Critical pitfall: Never use atenolol at any stage of pregnancy—it causes well-documented intrauterine growth retardation. 1

Fourth-Line: Calcium Channel Blockers

• IV verapamil may be considered only after adenosine and beta-blockers have failed, but carries higher risk of maternal hypotension compared to adenosine. 2, 1
• This receives only a Class IIb recommendation due to hypotension risk 2, 1

Fifth-Line: Procainamide

• IV procainamide is another option for acute conversion when other agents fail—it has been used safely for maternal and fetal arrhythmias. 2, 1
• Avoid for long-term therapy due to lupus-like syndrome risk 2, 1

Immediate Cardioversion Indications

Proceed directly to synchronized cardioversion if the patient is hemodynamically unstable (hypotension, shock, pulmonary edema) or if pharmacologic therapy fails—do not delay cardioversion attempting further drug trials. 2, 1

Cardioversion Technique at 20 Weeks

• Use the same energy dosing as non-pregnant patients 2, 1
• Place electrode pads so the current trajectory is directed away from the uterus 2, 1
• Perform fetal heart rate monitoring during and immediately after cardioversion 2, 1
• Cardioversion is safe at all gestational ages including 20 weeks 2, 1, 4

Critical Pitfalls to Avoid

• Do not delay cardioversion in unstable patients attempting pharmacologic conversion—maternal mortality takes priority. 1
• Do not treat physiologic sinus tachycardia (gradual onset/offset, rate typically <150 bpm) with antiarrhythmics—this is a normal pregnancy adaptation. 1
• Never use atenolol due to intrauterine growth retardation risk. 1
• Avoid verapamil as first-line due to higher hypotension risk compared to adenosine. 1, 3

If Recurrent Episodes Occur

For highly symptomatic recurrent SVT requiring chronic suppression, oral metoprolol (preferred beta-blocker), propranolol, or digoxin are first-line options. 1

• Sotalol, flecainide, propafenone, and verapamil are also reasonable alternatives 1
• Reserve amiodarone exclusively for life-threatening SVT refractory to all other options—it causes fetal thyroid toxicity and growth restriction. 1, 5