44 AJTCCM VOL. 29 NO. 2 2023
EDITORIAL
Pulmonary embolism (PE) is a prevalent condition worldwide, with an
annual incidence of 1 in 1 000 people. Mortality rates vary from 2% to
17% at 3 months, depending on underlying causes and comorbidities.
Long-term physiological and psychological sequelae aect up to 50%
of patients, with chronic thromboembolic pulmonary hypertension
being the most severe. Undiagnosed PE or PE with delayed diagnosis
is associated with signicant morbidity and mortality.[1] However,
deciding who to investigate can be challenging, especially in the public
sector, where the required imaging techniques are not always readily
available. Additionally, treatment is prolonged with the potential
forharm.[2]
e ventilation: perfusion (V/Q) scan is a commonly performed
study in nuclear medicine, and has been used in the evaluation of PE
since 1964. It involves two parts: the ventilation component using a
radiolabelled aerosol or radioactive gas, and a perfusion component
using radiolabelled macroaggregated albumin. Pulmonary emboli
are characterised by defects on the perfusion study that correspond
to vascular anatomy and exhibit relatively preserved ventilation
(mismatch). Several systems for the interpretation of V/Q scans exist,
most of which predate the widespread availability of single-photon
emission computed tomography (SPECT) techniques. Depending
on the number and size of mismatched V/Q defects and the chest
radiograph appearance, some of these interpretative systems classify
scan results into dierent likelihood categories of PE, ranging from
‘very low probability’ to ‘high probability’, with corresponding
numerical values of certainty. Proponents of such systems point out
that they are standardised and validated, while critics argue that they
are confusing, that assigning probabilities of a diagnosis purely on a
test result ignores fundamental Bayesian principles by not accounting
for pre-test probability, and that they make insucient allowance
for the application of gestalt. e European Association of Nuclear
Medicine, for example, has recommended for some time that V/Q
scans performed for suspected acute PE be reported as either positive
or negative for PE, or (in a small minority of cases) non-diagnostic.[3,4]
V/Q SPECT’s high sensitivity and specicity make it well suited to
ruling out and ruling in a diagnosis of acute PE, and the study also has
an important role in quantifying embolic burden, which is prognostic
of outcome and may aect management decisions. Regardless of the
reporting system employed, it is crucial for clinicians ordering and
acting on the test results to understand how they are generated and
what they mean.[5]
Computed tomography pulmonary angiography (CTPA) is
considered by many as the current reference standard for diagnosing
acute PE. It oers numerous advantages in the diagnosis of PE, being
more readily available than the V/Q scan and faster to perform. CTPA
also has higher utility than V/Q in identifying alternative diagnoses
when PE is not the cause of a patient’s symptoms, although V/Q
SPECT-CT shows promise in this regard. CTPA’s benets come at the
cost of increased ionising radiation dose (especially to female breast
tissue in pregnant or lactating women) and the need for contrast
material. e primary advantages of the V/Q scan are that it can
be performed in situations where it is preferable to limit radiation
dose, and where allergy or renal dysfunction contraindicate the use of
intravenous contrast.[5,6]
Invasive pulmonary angiography, magnetic resonance angiography
and echocardiography are additional imaging modalities that may
have niche applications in the evaluation of acute PE.[6]
In this edition of the AJTCCM, Ismail etal.[7] present the ndings of
their research on the communication gap between nuclear medicine
physicians and clinicians in interpreting V/Q scan reports and its
eects on patient management. e authors note that historically
there has been a wide variation in the interpretation of V/Q scan
reports by both clinicians and nuclear medicine physicians. e
group conducted a cross-sectional study using a questionnaire and
included 162 participants across three departments most likely to
request a V/Q scan. Respondents were able to correctly interpret
phrases conveying high and low probabilities of PE. However, most
clinicians in the study indicated that they would request alternative
investigations for PE in the event of a normal V/Q scan (which has a
high negative predictive value) when the pre-test probability is high.
e authors speculate whether this discrepancy indicates mistrust
in the test or lack of understanding of the negative predictive
value of thetest. The multiple-choice nature of the instrument
usedinthisstudy may not have fully interrogated respondents’
knowledge.
The study presented some interesting findings regarding the
preferences of respondents for the terms recommended in guidelines
such as the Modified Prospective Investigation of Pulmonary
Embolism Diagnosis (PIOPED II) system that make use of
probabilistic reporting.[8] However, it is important to note that the
study was conducted in a single academic complex, which limits the
generalisability of the results. Furthermore, the ndings are contrary to
those of other studies, which raises questions about their implications
outside of the study setting.
Worryingly, the study revealed that few clinicians ever contacted the
nuclear medicine department when the ndings of a report were not
clearly understood. is highlights a clear gap in communication and
opportunities for improvement, which could prevent errors in patient
care and enhance clinician education.
To address this issue, it may be desirable for nuclear medicine
physicians to contact requesting clinicians to discuss inconclusive
results. Furthermore, reports could include additional instruction
from guidelines as an educational opportunity. This would help
promote better communication between nuclear medicine physicians
and clinicians, which would ultimately benet patient care.
Muhammad Saadiq Moolla, MB ChB, MMed (Int Med), FCP (SA),
Dip HIV Man (SA)
Pulmonology Fellow, Division of Pulmonology, Department of Medicine,
Faculty of Medicine and Health Sciences, Stellenbosch University and Tygerberg
Hospital, Cape Town, South Africa
saadiq.moolla@gmail.com
Bridging the gap: Communicating the results of ventilation:
perfusion scans to clinicians
AJTCCM VOL. 29 NO. 2 2023 45
EDITORIAL
Alex Doruyter, MB ChB, Dip PEC (SA), FCNP (SA), MMed (Nuc
Med), PhD
Consultant Nuclear Physician, NuMeRI Node for Infection Imaging, Central
Analytical Facilities, Stellenbosch University, Cape Town, South Africa; Division
of Nuclear Medicine, Department of Medical Imaging and Clinical Oncology,
Faculty of Medicine and Health Sciences, Stellenbosch University and Tygerberg
Hospital, Cape Town, South Africa
Brian W Allwood, MB BCh, FCP (SA), MPH, Cert Pulm (SA), PhD
Consultant Pulmonologist, Division of Pulmonology, Department of Medicine,
Faculty of Medicine and Health Sciences, Stellenbosch University and Tygerberg
Hospital, Cape Town, South Africa
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2023;29(2):e271. https://doi.org/10.7196/AJTCCM.2023.v29i2.271
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