Abstract
Ventilation–perfusion scintigraphy may continue to be the first-line diagnostic method for pulmonary embolism in institutions that can ensure its uninterrupted availability and the expertise in its interpretation https://bit.ly/2y3Dlhx
From the author:
S.L. Hansen and colleagues present a number of arguments aiming to improve the “tarnished” (as the authors call it) reputation of ventilation–perfusion (VQ) scintigraphy, and to promote single photon emission computed tomography (VQ SPECT) in the diagnostic work-up of suspected pulmonary embolism. Among others, the authors provide a table showing the effective and absorbed doses in different imaging modalities used for the diagnosis or exclusion of pulmonary embolism. This information complements and extends the data provided in the 2019 European Society of Cardiology (ESC) guidelines for the diagnosis and management of acute pulmonary embolism, developed in collaboration with the European Respiratory Society (ERS) [1]. In agreement with these guidelines, S.L. Hansen and colleagues point to the significantly lower radiation dose absorbed by the breast tissue during VQ SPECT as opposed to computed tomography pulmonary angiography (CTPA). In view of these differences, the authors advocate the use of VQ SPECT as first-line diagnostic modality in young adult females with suspected pulmonary embolism.
The first update of the ESC guidelines for pulmonary embolism, including formal recommendations, was published in 2008 [2], replacing a more narrative earlier version [3]. The most important novelty of the update was the revised diagnostic algorithm for patients with suspected pulmonary embolism, in which CTPA replaced VQ scintigraphy (and invasive pulmonary angiography) as the new central imaging test and diagnostic “gold standard” [2]. The evidence for the shift to CTPA had been delivered a few years before by the results of major accuracy and management trials [4, 5]. The 2008 guidelines did acknowledge that the validity of the (planar) lung scan had been evaluated in several prospective clinical outcome studies, showing low event rates and suggesting that it is safe to withhold anticoagulant therapy in patients with a normal perfusion scan [2]. This fact had also been confirmed in a randomised trial comparing VQ scan with CTPA [6]. In parallel, it was mentioned [2] that the evolving SPECT technique promised to overcome the problem of frequent non-diagnostic intermediate probability planar scans [7, 8]. However, in the second update of the guidelines 6 years later [9], and although VQ scan continued to be explicitly mentioned as a valid diagnostic test for pulmonary embolism, no compelling new evidence was cited to question the central position of CTPA, which had meanwhile conquered the vast majority of hospitals in Europe and beyond. Specifically for VQ SPECT, with or without low-dose computed tomography, the conclusion of the guidelines was that large-scale prospective studies were needed to validate these new approaches [9]. Now, in the most recent 2019 update to which Hansen and co-workers refer, the wording and overall evaluation of VQ scintigraphy, including SPECT, remained largely unchanged [1].
Does this “stagnation” mean that the chapter of pulmonary embolism diagnosis should finally be considered closed? I agree with the authors that the answer is by no means so simple. Being experts in nuclear medicine, S.L. Hansen and colleagues eloquently defend the consistency of the diagnostic criteria for pulmonary embolism in VQ SPECT. One should also fairly admit that “large-scale” prospective trials required to provide high-level evidence in favour of VQ SPECT are hardly realistic in the era of CTPA dominance. In addition, if VQ SPECT is considered to be the technical evolution of planar VQ scan, its clinical evaluation may not need to be as extensive as would be required for a diagnostic method based on a totally new principle. The authors further emphasise the advantages of the technique, the strongest of which is the low dose of absorbed radiation compared to CTPA. In fact, their suggestion to consider VQ SPECT in the diagnostic work-up of young women is principally in line with the algorithm proposed by the 2019 ESC/ERS guidelines for suspected pulmonary embolism in pregnancy, in which (perfusion) scintigraphy assumes a clearly visible position as an alternative to CTPA [1]. S.L. Hansen and colleagues go further by proposing to extend these recommendations to VQ SPECT and broaden the target population to non-pregnant young women.
Overall, there is no fundamental disagreement between the arguments of Hansen and co-workers and the recommendations of the 2019 ESC/ERS guidelines. Except, perhaps for these few words in the concluding paragraph: “first-choice imaging modality”. To issue a broad recommendation in favour of VQ SPECT and against the current gold standard CTPA, the guidelines must, even if this is only for a specific clinical setting, ensure that two conditions are met, assuming that the two methods are otherwise equivalent: 1) the alternative is broadly available, as is the standard; and 2) the alternative is always and rapidly available, as is (in most cases) the standard, so that diagnosis or exclusion of pulmonary embolism will be equally fast. Unfortunately, however, we have to admit that, in the majority of European hospitals, these conditions are not met for VQ SPECT. Pulmonary embolism is an acute, potentially life-threatening situation, and nothing can be more dangerous for patients, including young women, than delaying its confirmation or exclusion by several hours or even days until the test can be performed. Transferring the patient to another facility that can perform VQ SPECT is also not an acceptable option. Consequently, it is unlikely that the CTPA-based “main” algorithm will change in the near future. On the other hand, and as the authors point out, VQ scintigraphy may certainly become (or continue to be) the first-line diagnostic method in institutions that can ensure its uninterrupted availability and the expertise in its interpretation.
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Footnotes
Conflict of interest: S.V. Konstantinides reports grants and personal fees from Bayer AG, Daiichi Sankyo, BTG – Boston Scientific Group and Actelion – Janssen, grants from Boehringer Ingelheim and Servier, personal fees from Pfizer – Bristol Myers Squibb and MSD, outside the submitted work.
Support statement: The work of Stavros Konstantinides was supported by the German Federal Ministry of Education and Research (BMBF 01EO1003 & 01EO1503). The author is responsible for the contents of this publication. Funding information for this article has been deposited with the Crossref Funder Registry.
- Received April 27, 2020.
- Accepted April 27, 2020.
- Copyright ©ERS 2020