investigations

Last reviewed 01/2018

• ECG:
• often normal except for sinus tachycardia
• atrial fibrillation is not uncommon
• the classic S1,Q3,T3 with right axis deviation and right bundle branch block is uncommon
• evidence of myocardial ischaemia
• chest radiography occasionally show reduced vascular markings
• blood gases show impaired gas exchange with arterial hypoxaemia and hypocapnia
• pulmonary infarction causes an increased ESR
• D-dimer - this is a highly sensitive but nonspecific test for diagnosing pulmonary embolism. A d-dimer below a certain cut point rules out PE with a high predictive value, at least in patients with a low or moderate clinical probability
• ventilation-perfusion scan:
  • demonstrate areas of ventilation-perfusion mismatch
  • emboli are frequently multiple
  • the lower lobes are more frequently involved than the upper part of the lungs
• CT pulmonary angiogram (CTPA) - generally performed for anybody with a clinically high risk for PE, or patients with low or moderate clinical risk and a positive D-dimer result. If a ventilation-perfusion scan is performed and the result is equivocal then CTPA should subsequently be performed
• CT venography - a US review notes the combination of CTPA and CT venography increases the sensitivity of detection of pulmonary embolism (3)

Notes:

• there is study evidence that clevated troponin levels identify patients with acute pulmonary embolism at high risk of short-term death and adverse outcome events (4)
• study evidence revealed that CTPA was not inferior to V/Q scanning in ruling out pulmonary embolism (5)
  • however, significantly more patients were diagnosed with pulmonary embolism using the CTPA approach
• a review examined the diagnostic process for pulmonary embolism (3):
  • state of the art of diagnostic evaluation of hemodynamically stable patients with suspected acute pulmonary embolism was reviewed
    • diagnostic evaluation should begin with clinical assessment using a validated prediction rule in combination with measurement of D-dimer when appropriate
      • sensitivity for detection of pulmonary embolism was increased by combining CT angiography (4-slice or 16-slice) with CT venography
        • methods to reduce the radiation exposure of CT venography include imaging only the proximal leg veins (excluding the pelvis) and obtaining discontinuous images. Compression ultrasound can be used instead
        • in young women, radiation of the breasts produces the greatest risk of radiation-induced cancer. It may be that scintigraphy (V/Q scan) is the imaging test of choice in such patients
        • patient-specific approach to the diagnosis of pulmonary embolism can be taken safely in hemodynamically stable patients to increase efficiency and decrease cost and exposure to radiation

Reference:

• (1) Ann Emerg Med 2002 Aug;40(2):133-44
• (2) Evidence Based Medicine 2002; 8 (2), 29.
• (3) Stein PD et al. Challenges in the diagnosis of acute pulmonary embolism. Am J Med. 2008 Jul;121(7):565-71.
• (4) Becattini C et al. Prognostic value of troponins in acute pulmonary embolism: a meta-analysis.Circulation. 2007 Jul 24;116(4):427-33
• (5) Anderson DR et al. Computed tomographic pulmonary angiography vs ventilation-perfusion lung scanning in patients with suspected pulmonary embolism: a randomized controlled trial. JAMA. 2007 Dec 19;298(23):2743-53