Abstract
Ventilation–perfusion SPECT should be preferred over CTPA in young adult females with suspected pulmonary embolism https://bit.ly/2XYWdJ7
To the Editor:
We read with interest the “2019 ESC Guidelines for the diagnosis and management of acute pulmonary embolism” developed by the European Society for Cardiology (ESC) in collaboration with the European Respiratory Society [1]. An important question addressed in the 2019 ESC Guidelines, which is also discussed in the recently updated guideline on ventilation–perfusion (VQ) scintigraphy from the European Association of Nuclear Medicine (EANM) [2], is whether computed tomography pulmonary angiography (CTPA) or VQ scintigraphy should be the diagnostic method of choice in suspected pulmonary embolism. This quandary is notably pertinent in young female adults who are at an increased risk of pulmonary embolism due to oral contraceptive use or pregnancy, and we would like to add to the discussion in relation to this patient group by raising specific points relating to the diagnostic performance and radiation exposure of VQ scintigraphy versus CTPA.
The 2019 ESC Guidelines provide specific recommendations regarding planar VQ scintigraphy, which is typically based on six consecutive static projections, and interpreted according to a widely criticised probabilistic diagnostic classification. The lower diagnostic accuracy compared to CTPA, as well as an unacceptably high rate of non-diagnostic scans, has undoubtedly contributed to the tarnished reputation of VQ scintigraphy. However, planar VQ scintigraphy has largely been abandoned throughout Europe and is no longer recommended by EANM [2]. It has been replaced by the single photon emission computed tomography (SPECT)-based technique mentioned in the 2019 ESC Guidelines, which provides three-dimensional images of the pulmonary VQ distribution. VQ SPECT is interpreted according to a trinary classification as 1) showing evidence of pulmonary embolism, 2) showing no evidence of pulmonary embolism, or 3) as non-diagnostic. We acknowledge several of the methodological limitations of the studies on the accuracy of VQ SPECT that are addressed in the 2019 ESC Guidelines, notably their retrospective design and the inclusion of VQ SPECT itself in the reference standard in some studies, as well as the paucity of outcome studies. Furthermore, as also mentioned, the optimal scanning technique, particularly the added clinical value of supplementing VQ SPECT with computed tomography (CT) remains to be defined in various categories of patients, but low-dose CT (without i.v. contrast), which increases the specificity of VQ SPECT while also providing information regarding the same range of differential diagnoses as CTPA, is currently the most widely used modality [2, 3]. We do, however, respectfully disagree with the notion in the 2019 ESC Guidelines that the criteria for diagnosing acute pulmonary embolism on VQ SPECT and their use in clinical practice are inconsistent. Since the previous EANM guideline on VQ SPECT from 2009, the consensus diagnostic criteria for acute pulmonary embolism has been the presence of at least one segmental or two subsegmental mismatched perfusion defects that conform with pulmonary vascular anatomy [4], and we are not aware of any European nuclear medicine facilities that currently use alternative definitions. With this approach, and while keeping the methodological limitations mentioned above in mind, the diagnostic performance of VQ SPECT is comparable to and may even exceed that of CTPA, while the non-diagnostic rates are similar (<5%) [2, 3, 5].
In terms of radiation exposure, the high rate of cell proliferation in the breast tissue of young females renders this tissue notably radiation sensitive. The risk of radiation-induced cancer is proportional to radiation dose [6], and according to a previous simulation-based study performed a decade ago, one case of radiation-induced breast cancer would develop for every 330 CTPA scans performed in 20-year old females [7]. Considerable progress in CT-technology has been made over the past years, aiming at both improving image quality and reducing radiation dose, but the difference in radiation exposure associated with VQ SPECT and CTPA nonetheless remains substantial. However, the difference in radiation dose to the breast tissue is largely underestimated when considering the effective (whole-body) doses alone. According to current data obtained from two state of the art CTPA protocols available at our institution, the effective doses of the CTPA protocols are only a few times higher than that of our VQ SPECT protocol, but the absorbed dose in breast tissue is nonetheless 18–40 times higher (table 1). Even if the VQ SPECT is supplemented with a low-dose CT, both the effective and absorbed dose remains less than that of CTPA (table 1).
On basis of the above, we posit that VQ SPECT should be considered the first-choice imaging modality in young adult females with suspected acute pulmonary embolism when a nuclear medicine facility is available. We furthermore suggest that specific recommendations regarding planar VQ scintigraphy are omitted from future clinical guidelines on the diagnosis and management of acute pulmonary embolism.
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Footnotes
Conflict of interest: S.L. Hansen has nothing to disclose.
Conflict of interest: R. de Nijs has nothing to disclose.
Conflict of interest: J. Mortensen has nothing to disclose.
Conflict of interest: R.M.G. Berg has nothing to disclose.
- Received February 26, 2020.
- Accepted April 15, 2020.
- Copyright ©ERS 2020