What is the workup for syncope (fainting) in a patient at 20 weeks gestation?

Workup of Syncope at 20 Weeks Gestation

Begin with a focused history and 12-lead ECG, recognizing that while syncope in pregnancy is often benign, you must not allow pregnancy to dissuade evaluation for life-threatening cardiac, hemorrhagic, or obstetric causes that directly impact maternal and fetal mortality.

Initial Assessment Priority

The cornerstone of syncope evaluation remains history and physical examination, which identifies the cause in up to 85% of cases where a diagnosis is established 1. However, at 20 weeks gestation, you must simultaneously consider pregnancy-specific etiologies while not missing cardiac causes that carry high mortality risk.

Critical History Elements to Obtain

Circumstances of the event:

• Position when syncope occurred (supine, standing, sitting) and activity (rest, positional change, post-void, post-defecation) 1
• Prodromal symptoms: nausea, diaphoresis, visual changes, palpitations 1
• Witness description of the event: duration of unconsciousness, presence of tonic-clonic movements, tongue biting (lateral biting is highly specific for seizure) 1
• Recovery pattern: immediate vs. prolonged confusion 1

Pregnancy-specific red flags:

• Vaginal bleeding or abdominal pain suggesting ectopic pregnancy (even at 20 weeks, consider heterotopic pregnancy or other hemorrhagic causes) 2
• Severe nausea/vomiting with tachycardia suggesting gestational thyrotoxicosis 3
• Right upper quadrant pain, headache, visual changes, or hyperreflexia suggesting preeclampsia (though uncommon before 20 weeks) 1, 4

Cardiac risk stratification:

• History of structural heart disease or congestive heart failure 1
• History of ventricular arrhythmias 1
• Family history of sudden cardiac death 1
• Syncope during exertion (high-risk feature suggesting cardiac etiology) 1

Mandatory Initial Testing

12-Lead ECG (Perform Immediately)

A 12-lead ECG is warranted in all pregnant patients with syncope, as it is noninvasive, inexpensive, and can immediately identify life-threatening conditions despite a low overall yield of 5%. 1

Look specifically for:

• Evidence of myocardial infarction or ischemia 1
• Arrhythmias or conduction abnormalities 1
• Prolonged QT interval (>460 ms in women) 1
• Ventricular hypertrophy 1
• Pre-excitation patterns 1

An abnormal ECG (any rhythm/conduction abnormality, ventricular hypertrophy, or prior MI evidence) is a multivariate predictor for arrhythmia or death within 1 year 1.

Orthostatic Vital Signs

Measure blood pressure and heart rate supine and after 2 minutes of standing 1. At 20 weeks gestation, aortocaval compression begins to affect maternal hemodynamics, so position the patient in left lateral tilt if supine measurements are needed 1. Note that orthostatic hypotension is common in syncope patients regardless of etiology and is present in up to 40% of asymptomatic elderly patients, limiting its diagnostic specificity 1.

Pregnancy-Specific Evaluation

Confirm Pregnancy Status and Viability

While the patient is known to be 20 weeks pregnant, document fetal heart tones and perform obstetric assessment 1. At 20 weeks, the fundal height should be approximately at the umbilicus 1.

Point-of-Care Ultrasound

Perform focused assessment for:

• Free fluid in Morrison's pouch or pelvis (hemorrhage from any source) 2
• Intrauterine pregnancy confirmation 2
• Basic cardiac function if trained 2

Laboratory Testing (Selective, Not Routine)

Blood tests rarely yield diagnostic information in syncope and routine use is not recommended 1. However, obtain:

• Hemoglobin/hematocrit if hemorrhage suspected (though may be normal early in acute blood loss) 1
• Thyroid function tests if tachycardia, tremor, or hyperemesis present (gestational thyrotoxicosis) 3
• Basic metabolic panel only if volume depletion or metabolic cause suspected 1

Do NOT order routine comprehensive metabolic panels, cardiac enzymes, or other labs without specific clinical indication 1.

Risk Stratification for Disposition

High-Risk Features Requiring Admission 1

Admit if ANY of the following are present:

• Age >45 years 1
• History of congestive heart failure 1
• History of ventricular arrhythmias 1
• Abnormal ECG (as defined above) 1
• Physical exam findings of heart failure 1
• Cardiac murmur suggesting outflow obstruction 1

Patients with 3-4 risk factors have 57.6-80.4% risk of 1-year mortality or significant arrhythmia 1. Patients with zero risk factors have 0% 72-hour cardiac mortality and 0.7% risk of arrhythmia 1.

Low-Risk Features Allowing Discharge

Patients without structural heart disease, normal ECG, and clinical features suggesting vasovagal or orthostatic syncope can be safely discharged with outpatient follow-up 1, 5. The presence of pregnancy should not dissuade evaluation for other risk factors, but syncope related to pregnancy is generally innocuous 1.

Pregnancy-Specific Considerations

Physiologic Changes Predisposing to Syncope

• Cardiac output increases 30-50% by 20 weeks 1, 6
• Systemic vascular resistance decreases, lowering mean arterial pressure 1, 6
• Aortocaval compression begins at approximately 12-20 weeks, reducing venous return when supine 1
• Functional residual capacity decreases 10-25%, predisposing to rapid hypoxemia 1

Common Benign Causes in Pregnancy

• Vasovagal syncope (most common) 7, 5
• Orthostatic hypotension from volume shifts 1
• Supine hypotensive syndrome from aortocaval compression 1

Life-Threatening Causes Not to Miss

• Pulmonary embolism (pregnancy is hypercoagulable state) 1
• Ruptured ectopic pregnancy (even at 20 weeks, consider heterotopic) 2
• Cardiac arrhythmias (same risk as non-pregnant patients) 1
• Amniotic fluid embolism (rare but catastrophic) 1
• Aortic dissection (rare but increased risk in pregnancy) 1

Monitoring and Follow-Up

If admitted, continuous cardiac monitoring is appropriate for the first 24 hours if arrhythmia suspected 1. Monitoring beyond 24-72 hours rarely increases diagnostic yield unless the patient has age >65, male sex, known heart disease, or non-sinus rhythm on initial ECG 1.

For discharged patients, arrange outpatient cardiology follow-up if any concerning features present, and routine obstetric follow-up to monitor pregnancy 1.

Critical Pitfalls to Avoid

• Do not assume syncope is benign simply because the patient is pregnant 1
• Do not position pregnant patients >20 weeks flat supine for prolonged periods (use left lateral tilt) 1
• Do not order extensive laboratory testing without clinical indication (low yield and not cost-effective) 1
• Do not discharge patients with abnormal ECG or cardiac risk factors without cardiology consultation 1
• Do not forget to assess for pregnancy-specific emergencies (hemorrhage, preeclampsia, pulmonary embolism) 1, 2