What labs and scans should I order for a pregnant patient with shortness of breath and a history of Deep Vein Thrombosis (DVT) and Supraventricular Tachycardia (SVT)?

From the Guidelines

For a pregnant patient with shortness of breath and history of DVT and SVT, I recommend ordering both laboratory tests and imaging studies to evaluate for pulmonary embolism (PE) and cardiac causes, starting with D-dimer, complete blood count, comprehensive metabolic panel, troponin, BNP, and arterial blood gases, and proceeding with a chest X-ray (with abdominal shielding) and electrocardiogram. Given the patient's symptoms and history, it is crucial to prioritize tests that can quickly and accurately diagnose or rule out life-threatening conditions such as PE. The initial laboratory tests are aimed at assessing the patient's overall condition, detecting any signs of thrombosis or cardiac strain, and guiding further diagnostic steps.

Initial Laboratory Tests

• D-dimer: To assess for thrombosis, although it may be elevated in pregnancy, its negative predictive value is useful in ruling out PE in low-risk patients 1.
• Complete blood count: To evaluate for signs of infection, anemia, or thrombocytopenia.
• Comprehensive metabolic panel: To assess renal and liver function, which can be affected by pregnancy and certain medications.
• Troponin and BNP: To evaluate cardiac function and detect any signs of cardiac strain or myocardial infarction.
• Arterial blood gases: To assess oxygenation and ventilation status.

Initial Imaging Studies

• Chest X-ray (with abdominal shielding): To quickly assess the lungs and cardiac silhouette, and to rule out other causes of shortness of breath such as pneumonia or pneumothorax 1.
• Electrocardiogram: To evaluate the heart rhythm and detect any signs of ischemia or arrhythmias, including SVT.

Further Diagnostic Steps

If PE is suspected and D-dimer is elevated, or if the clinical probability of PE remains high after initial tests, consider proceeding with compression ultrasonography of the lower extremities to evaluate for DVT, as the presence of DVT increases the likelihood of PE 1.

For patients where PE needs to be further evaluated, a V/Q scan may be considered over CT pulmonary angiography to minimize radiation exposure to the fetus, although the choice between these tests should be guided by clinical judgment, patient factors, and institutional capabilities 1.

Cardiac Evaluation

Echocardiography should be performed to assess cardiac function, rule out structural abnormalities that might explain the SVT, and evaluate for signs of right ventricular dysfunction, which can be associated with PE 1. Continuous cardiac monitoring is important if the patient is symptomatic with arrhythmias to promptly detect and manage any life-threatening rhythms.

These recommendations prioritize the patient's safety, the need for accurate diagnosis, and the minimization of risks associated with diagnostic tests during pregnancy, particularly radiation exposure. The approach is guided by the principles of minimizing morbidity, mortality, and improving quality of life for both the mother and the fetus.

From the Research

Labs and Scans for Pregnant Patient with Shortness of Breath and History of DVT and SVT

• The patient's symptoms of shortness of breath and history of Deep Vein Thrombosis (DVT) and Supraventricular Tachycardia (SVT) suggest the need for diagnostic tests to rule out pulmonary embolism (PE) 2.
• Laboratory tests such as D-dimer and arterial blood gas may be ordered, but their diagnostic value is limited in pregnant patients 2.
• Imaging tests such as ventilation/perfusion scans and computed tomography pulmonary angiograms (CTPA) are commonly used to diagnose PE in pregnant patients 2, 3, 4.
• CTPA is often preferred over ventilation/perfusion scans due to its higher sensitivity and specificity, but it may not always detect chronic thromboembolic pulmonary disease (CTEPD) 5.
• The quality of CTPA scans may be affected by physiological changes during pregnancy, and techniques such as bolus triggering and high flow rates may be used to optimize image quality 3, 6.
• Ventilation/perfusion scans may be used as an alternative to CTPA, especially if there is a high clinical suspicion for PE or CTEPD despite a negative CTPA result 5.

Recommended Labs and Scans

• D-dimer test to rule out PE, although its diagnostic value is limited in pregnant patients 2.
• Arterial blood gas to assess oxygenation and ventilation 2.
• CTPA to diagnose PE, using optimized protocols to minimize radiation exposure and maximize image quality 3, 6.
• Ventilation/perfusion scan as an alternative to CTPA or if CTPA is negative but clinical suspicion for PE or CTEPD remains high 2, 5.
• Electrocardiogram (ECG) to monitor for SVT and other cardiac arrhythmias.
• Complete blood count (CBC) and blood chemistry tests to assess overall health and detect any potential complications.