What are the causes of ST depression on a 12-lead electrocardiogram (ECG) in pregnancy?

Causes of ST Depression on 12-Lead ECG in Pregnancy

ST depression on a 12-lead ECG during pregnancy can be caused by both pregnancy-related physiological changes and pathological conditions, with acute coronary syndrome being the most concerning cause that requires immediate evaluation and management. 1

Physiological Causes in Pregnancy

• Normal physiological changes: Pregnancy causes hemodynamic alterations that may lead to ST depression, including:

  • Increased heart rate and cardiac output
  • Left axis deviation (15-20°) due to heart rotation 2
  • Attenuated Q wave in lead AVF
  • Inverted T waves in leads V1, V2, and occasionally V3 2

• Altered position of the heart: The enlarging uterus elevates the diaphragm, causing the heart to be rotated toward the left, which can mimic left ventricular hypertrophy on ECG 2

Pathological Causes

Acute Coronary Syndromes

• Non-ST elevation myocardial infarction (NSTEMI): ST depression is a hallmark finding in NSTEMI and indicates subendocardial ischemia 2

  • Approximately half of patients with ST-segment depression will develop MI within hours after presentation 2
  • ST depression has been shown to be a significant risk indicator for mortality and MI 2

• Posterior myocardial infarction: Depression of ST segments in leads V1 and V2 can be a manifestation of posterior or lateral ST-segment elevation infarction 2

• Left main coronary artery disease: Diffuse ST depression with ST elevation in aVR may suggest global ischemia due to left main coronary artery stenosis, though this pattern is not specific 3

• Coronary artery dissection: More common in pregnancy and peripartum period, can cause ST depression 2

Other Cardiac Causes

• Left ventricular hypertrophy (LVH): Common in pregnancy-induced hypertension and pre-eclampsia 4

• Cardiomyopathies: Including peripartum cardiomyopathy (PPCM), which typically presents with heart failure symptoms toward the end of pregnancy or in the months following delivery 2, 5

• Tachyarrhythmias: Can cause ST depression due to demand ischemia

• Bundle branch blocks: Particularly left bundle branch block, can cause secondary ST-T changes 4

Non-Cardiac Causes

• Pulmonary embolism: More common in pregnancy and can sometimes mimic acute coronary syndrome on ECG 6

• Electrolyte abnormalities: Particularly hypokalemia

• Medications: Some cardioactive drugs can cause ST depression 2

Evaluation Algorithm for ST Depression in Pregnancy

1. Immediate assessment:

   • Obtain detailed history focusing on chest pain characteristics, dyspnea, and risk factors
   • Perform physical examination looking for signs of heart failure, pre-eclampsia, or other complications
   • Check vital signs including oxygen saturation

2. Further diagnostic workup:

   • Serial ECGs at 15-30 minute intervals if symptoms persist 2
   • Cardiac biomarkers (high-sensitivity troponin) at presentation and 3-6 hours after symptom onset 2
   • Echocardiography to assess wall motion abnormalities and rule out peripartum cardiomyopathy
   • Consider coronary angiography in high-risk cases (with appropriate radiation protection)

3. Management based on diagnosis:

   • For ACS: Consider β-blockers and low-dose aspirin (relatively safe in pregnancy) 2
   • Avoid ACE inhibitors, ARBs, and renin inhibitors (contraindicated in pregnancy) 2
   • For NSTEMI with risk criteria: Consider invasive management 2
   • For stable conditions with exertional symptoms: Watchful waiting and medical therapy 2

Important Considerations in Pregnant Patients

• Pregnant women may present with atypical symptoms of ACS
• The threshold for cardiac biomarker testing should be lower in pregnant patients with suspicious symptoms
• Radiation exposure should be minimized but not avoided if necessary for diagnosis of life-threatening conditions
• Pregnancy increases risk of coronary dissection rather than atherosclerotic disease
• When performing coronary interventions during pregnancy, bare metal stents are preferred over drug-eluting stents 2

Remember that while ST depression on ECG during pregnancy often represents benign physiological changes, it can also indicate serious pathology requiring prompt evaluation and management.