Volume 183 - Issue 4
Venous thromboembolism: diagnosis and management of pulmonary embolism
Authors: John W Eikelboom, Graeme J Hankey, Wai Khoon Ho and Cindy H Lee
Med J Aust 2005; 183 (4): 220-221. || doi: 10.5694/j.1326-5377.2005.tb07010.x
Published online: 15 August 2005
Published online: 15 August 2005
John W Eikelboom,* Graeme J Hankey,† Wai Khoon Ho,‡ Cindy H Lee§
* Haematologist, Thrombosis Service, McMaster University, HHS General Divison, 237 Barton Street East, Hamilton, ON L8L2X2, Canada; † Neurologist, ‡ Fellow in Haematology, § Senior Registrar in Haematology, Royal Perth Hospital, Perth, WA. eikelbj@mcmaster.ca
In reply: Pulmonary embolism (PE) remains a complex diagnosis despite the availability of validated prediction models and D-dimer testing to direct the need for diagnostic imaging.
We agree with Bailey that the ability to exclude the diagnosis of PE on clinical grounds in patients with a low pretest probability is highly desirable. Unfortunately, clinical features lack sensitivity and specificity for the diagnosis of PE, and clinical prediction models, laboratory investigations, and diagnostic imaging are likely to remain an integral part of the clinical work-up.
As suggested by Bragg, it may be possible to simplify the diagnostic approach by using a highly sensitive D-dimer assay, and simplified pretest probability models have been proposed. However, this may come at a cost of reduced specificity,1 which leads to unnecessary diagnostic imaging studies and thus limits the clinical utility of these approaches. Further improvements in the diagnostic approach to PE are clearly needed.
There are emerging data demonstrating the accuracy of computed tomography pulmonary angiography (CTPA) for the diagnosis of PE. However, CTPA has limitations (a large contrast load, high radiation dose, and lack of sensitivity of first generation scanners for small thrombi2), some of which are evident in the recently published validation study referred to by Bailey:3 25% of screened patients with suspected PE were not eligible for this study because of renal impairment, a contraindication to CT, or other reasons.
The diagnostic algorithm that we provided in our review suggests that either ventilation perfusion (V/Q) scanning or CTPA can be used for patients with suspected PE who require diagnostic imaging,2 with the choice determined by patient factors and availability.
The diagnosis of PE during pregnancy is challenging because of concerns about radiation exposure and uncertainty about whether CTPA or V/Q delivers more radiation to the fetus.4 Furthermore, clinical decision rules have not been validated in pregnancy. However, recommendations from experts and professional bodies suggest that V/Q scanning can be used in combination with compression ultrasound to establish or exclude the diagnosis of PE during pregnancy in most cases with minimal fetal radiation exposure.5,6
The comments by Bailey and Bragg concerning the interpretation of high probability V/Q scan results highlight the pitfalls of performing diagnostic imaging without considering the patient’s pretest probability of PE. Although a high probability V/Q scan is diagnostic in patients with a moderate or high pretest probability of PE (prevalence of disease ≥ 90%), the prevalence of disease is only about 50% in those with a low pretest probability.7,8 Therefore, V/Q scanning should not be performed in patients with a low pretest probability unless the D-dimer test is positive. In this situation the algorithm for moderate or high pretest probability should be followed,2 and a high probability scan reliably establishes the diagnosis.
References
- Carrier M, Wells PS, Rodgers MA. Excluding pulmonary embolism at the bedside with a low pretest probability and D-dimer: safety and the clinical utility of full methods to assign pretest probability. Thromb Res 2005. In press.
- Lee C, Hankey GJ, Ho W, Eikelboom JW. Venous thromboembolism: diagnosis and management of pulmonary embolism. Med J Aust 2005; 182: 569-574. 0_i1091562
- Perrier A, Roy PM, Sanchez O, et al. Multi-detector-row computed tomography in suspected pulmonary embolism. N Engl J Med 2005; 352: 1760-1768. 0_i1091564
- Winer-Muram HT, Boone JM, Brown HL, et al. Pulmonary embolism in pregnant patients: fetal radiation dose with helical CT. Radiology 2002; 224: 487-492. 0_i1091566
- Bates SM, Ginsberg JS. How we manage venous thromboembolism during pregnancy. Blood 2002; 100: 3470-3478. 0_i1091568
- ACOG Committee on Obstetric Practice. ACOG Committee Opinion. Number 299, September 2004 (replaces No. 158, September 1995). Guidelines for diagnostic imaging during pregnancy. Obstet Gynecol 2004; 104: 647-651. 0_i1091570
- PIOPED Investigators. Value of the ventilation/perfusion scan in acute pulmonary embolism: results of the prospective investigation of pulmonary embolism diagnosis (PIOPED). JAMA 1990; 263: 2753-2759. 0_i1091572
- Hull RD, Hirsh J, Carter CJ, et al. Diagnostic value of ventilation-perfusion lung scanning in patients with suspected pulmonary embolism. Chest 1985; 88: 819-828. 0_i1091574