Imaging for the exclusion of pulmonary embolism in pregnancy

Validating the safety of low-dose CTPA in pregnancy: results from the OPTICA (Optimised CT Pulmonary Angiography in Pregnancy) Study

BACKGROUND

Pulmonary embolism (PE) is a leading cause of pregnancy-related mortality. CT pulmonary angiogram (CTPA) is the first-line advanced imaging modality for suspected PE in pregnancy at institutes offering low-dose techniques; however, a protocol balancing safety with low dose remains undefined. The wide range of CTPA doses reported in pregnancy suggests a lack of confidence in implementing low-dose techniques in this group.

PURPOSE

To define and validate the safety, radiation dose and image quality of a low-dose CTPA protocol optimised for pregnancy.

MATERIALS AND METHODS

The OPTICA study is a prospective observational study. Pregnant study participants with suspected PE underwent the same CTPA protocol between May 2018 and February 2022. The primary outcome, CTPA safety, was judged by the reference standard; the 3-month incidence of venous thromboembolism (VTE) in study participants with a negative index CTPA. Secondary outcomes defined radiation dose and image quality. Absorbed breast, maternal effective and fetal doses were estimated by Monte-Carlo simulation on gestation-matched phantoms. Image quality was assessed by signal-to-noise and contrast-to-noise ratios and a Likert score for pulmonary arterial enhancement.

RESULTS

A total of 116 CTPAs were performed in 113 pregnant women of which 16 CTPAs were excluded. PE was diagnosed on 1 CTPA and out-ruled in 99. The incidence of recurrent symptomatic VTE was 0.0% (one-sided 95% CI, 2.66%) at follow-up. The mean absorbed breast dose was 2.9 ± 2.1mGy, uterine/fetal dose was 0.1 ± 0.2mGy and maternal effective dose was 1.4 ± 0.9mSv. Signal-to-noise ratio (SNR) was 11.9 ± 3.7. Contrast-to-noise ratio (CNR) was 10.4 ± 3.5.

CONCLUSION

The OPTICA CTPA protocol safely excluded PE in pregnant women across all trimesters, with low fetal and maternal radiation.

CLINICAL RELEVANCE

OPTICA (Optimised CT Pulmonary Angiography in Pregnancy) is the first prospective study to define the achievable radiation dose, image-quality and safety of a low-dose CT pulmonary angiogram protocol optimised for pregnancy (NCT04179487). It provides the current benchmark for safe and achievable CT pulmonary angiogram doses in the pregnant population.

KEY POINTS

• Despite the increased use of CT pulmonary angiogram in pregnancy, an optimised low-dose protocol has not been defined and reported doses in pregnancy continue to vary widely. • The OPTICA (Optimised CT Pulmonary Angiography in Pregnancy) study prospectively defines the achievable dose, image quality and safety of a low-dose CT pulmonary angiogram protocol using widely available technology. • OPTICA provides a benchmark for safe and achievable CT pulmonary angiogram doses in the pregnant population.

Use of YEARS Algorithm in Military Health Care Beneficiaries to Evaluate Use of Computed Tomography Pulmonary Angiography

INTRODUCTION

Pulmonary embolism (PE) can be difficult to rule out without computed tomography pulmonary angiograms (CTPAs), as presentations vary. Multiple clinical decision rules (CDRs) exist to risk-stratify patients to avoid unnecessary CTPAs. However, the currently used CDRs are complex, and research has shown low compliance with their usage. The YEARS algorithm is less complex and excludes patients from CTPA if PE is not the most likely diagnosis, they do not have a history of hemoptysis, and no clinical signs of deep vein thrombosis, is less complex. However, no studies have evaluated YEARS in the U.S. Military health care beneficiary population. Therefore, this study sought to determine if implementing the YEARS algorithm could decrease the number of CTPAs ordered to rule out PE in low-risk patients.

METHODS

This retrospective, single-center cohort study applied the YEARS algorithm to low-risk military beneficiaries presenting to the emergency department in the calendar year 2020 at a single U.S. Army MTF. The primary outcome was the number of CTPAs indicated by the YEARS algorithm versus the number ordered via standard practice. We used chi-square testing to compare the number of subjects in whom YEARS indicated CTPA (meets criteria/does not meet criteria) versus the actual number of subjects who underwent CTPA (meets criteria/does not meet criteria). The secondary outcomes included applying YEARS similarly to the number of subjects >50 years of age (as opposed to age-adjusted d-dimer), determining the number of pregnant patients who could have avoided CTPA via application of YEARS, and assessing possible cost savings via reduction of CTPA.

RESULTS

We included 353 subjects during the study period, 271 of whom underwent CTPA. YEARS would have only indicated 25 of them, P = .018. In patients >50 years of age, 164 underwent CTPA versus nine who met YEARS criteria, P = .014. Among pregnant patients, six underwent CTPA versus one who YEARS would have indicated, P = .130. Application of the YEARS algorithm would have led to a 90.8% reduction in CTPAs ordered with an overall known missed PE rate of 1.1%. Applying the YEARS algorithm in 2020 could have led to 246 fewer CTPAs at a minimum cost savings of $38,762.22 for the MTF based on the coded billing cost of $157.57 per CTPA when local staff radiologists performed image interpretation. This estimate does not consider the additional undisclosed cost of contracted radiologists interpreting after regular duty hours.

CONCLUSIONS

For our military beneficiaries, our study indicates that the YEARS algorithm would have reduced CTPA utilization in all age ranges and potentially among pregnant patients with a known missed PE rate of 1.1%.

Assessment of pulmonary embolism related to active SARS-CoV-2 infection in pregnant women

AIM

To analyze a sample of pregnant patients who underwent pulmonary perfusion scintigraphy to rule out suspicion of pulmonary embolism (PE) during the acute COVID-19 infection hospitalization period in our hospital.

MATERIAL AND METHODS

SPECT scintigraphy with a reduced dose (111MBq) of 99mTc-macroaggregated albumin was performed in all the patients (n=5). The images obtained were interpreted by comparing the findings with the radiological images according to the PISAPED criteria.

RESULTS

Only one of the 5 patients was diagnosed with PE. Two patients showed pathological scintigraphy findings attributable to radiological alterations due to COVID-19 pneumonia, and the other two had normal pulmonary perfusion.

CONCLUSION

Given the non-specific features of the clinical manifestations and d-dimer values ​​in COVID-19, as well as their similarity to those of PE, pulmonary perfusion scintigraphy plays a crucial role in the screening of PE in these patients due to its high sensitivity and lower irradiation compared to CT. Despite the limited number of patients, the results obtained have special relevance due to the absence of scientific publications in this group of patients within the exceptional context of the COVID-19 pandemic.

[Assessment of pulmonary embolism related to active SARS-CoV-2 infection in pregnant women.]

AIM

To analyze the sample of pregnant patients who underwent pulmonary perfusion scintigraphy to rule out the pulmonary embolism (PE) suspicion during the acute COVID-19 infection hospitalization period in our hospital.

MATERIAL AND METHODS

SPECT scintigraphy with a reduced dose (111 MBq) of 99mTc-macroaggregated albumin was performed in all of the patients (n=5). The obtained images were interpreted by comparing the findings with the radiological images according to the PISAPED criteria.

RESULTS

Only one of the 5 patients was diagnosed with PE. Two patients obtained pathological findings of the scintigraphy attributable to radiological alterations due to COVID-19 pneumonia, and the other two had normal pulmonary perfussion.

CONCLUSION

Given the non-specific features of the clinical manifestations and D-dimer values in COVID-19, as well as their similarity to those of PE, the pulmonary perfusion scintigraphy plays a crucial role in the screening of PE in these patients due to its high sensitivity and lower irradiation compared to CT. Despite the limited number of patients, the results obtained have special relevance related to the absence of scientific publications on this group of patients within the context of COVID-19 pandemic exceptional situation.

Pulmonary Embolism and Pregnancy-Challenges in Diagnostic and Therapeutic Decisions in High-Risk Patients

Diagnosis of acute PE in pregnant women with haemodynamic instability is following the general integrated risk-adapted diagnostic algorithm and starts with bedside echocardiography to assess RV function. If RV dysfunction is identified, a prompt and immediate reperfusion without further imaging should be initiated. Although pregnancy is listed as a relative contraindication of systemic thrombolysis, in pregnant women with acute PE and haemodynamic instability thrombolysis must be considered. In those cases, other treatment strategies as surgical embolectomy or catheter-directed low-dose thromboylysis or percutaneous thrombectomy should be taken into consideration as well. A multidisciplinary team with experience of PE management in pregnancy should be consulted to reach consensus on the best treatment approach.

Diagnostic imaging to investigate pulmonary embolism in pregnancy using CT-Pulmonary angiography versus perfusion scan

Background:

Pulmonary embolism (PE) is one of the major causes of maternal mortality; however, its diagnosis based on clinical presentation is a significant challenge; therefore, imaging is required. This study aims to determine the nondiagnostic rate of PE in pregnant women who initially undergone computed tomographic pulmonary angiography (CTPA) or perfusion scan.

Materials and Methods:

In this cross-sectional study, all pregnant or 6-week postpartum women with clinical suspicion of PE were evaluated and underwent CTPA or perfusion scan between March 2017 and June 2019. The nondiagnostic rate of each method was defined as the outcome of this study.

Results:

One hundred and eighty-two women with a clinical suspicion of PE were included, among which the initial imaging method was CTPA in 122 (67.03%) and perfusion scan in 60 (32.97%) women. The nondiagnostic imaging for CTPA was significantly lower than the perfusion scan (9 cases (7.4%) versus 25 cases (41.7%), respectively). Logistic regression assessment revealed a statistical outcome by controlling the confounders including gestational trimester at diagnosis, hypertension, ejection fraction, and tachycardia (odds ratio 15.911, 95% confidence interval: 5.177–48.897, P < 0.001).

Conclusion:

Based on the current study, CTPA is superior to perfusion scans to diagnose PE among pregnant or postpartum women with normal chest X-ray suspicion for PE.

Imaging modalities for confirming pulmonary embolism during pregnancy: results from a multicenter international study

OBJECTIVES

We explored the variations in use of imaging modalities for confirming pulmonary embolism (PE) according to the trimester of pregnancy.

METHODS

We included all pregnant patients with confirmed acute PE from RIETE, a prospective registry of patients with PE (03/2001-02/2020). Imaging modalities included computed tomography pulmonary angiography (CTPA), ventilation-perfusion (V/Q) scan, or presence of signs of acute PE along with imaging-confirmed proximal deep vein thrombosis (pDVT) without pulmonary vascular imaging. We compared the imaging modalities to postpartum patients with PE, and other non-pregnant women with PE.

RESULTS

There were 157 pregnant patients (age: 32.7 ± 0.5), 228 postpartum patients (age: 33.9 ± 0.5), and 23,937 non-pregnant non-postpartum women (age: 69.5 ± 0.1). CTPA was the most common modality for confirming PE, from 55.7% in first trimester to 58.3% in second trimester, and 70.0% in third trimester. From first trimester to third trimester, V/Q scanning was used in 21.3%, 16.7%, and 18.3% of cases, respectively. Confirmed pDVT along with the presence of signs/symptoms of PE was the confirmatory modality for PE in 21.3% of patients in first trimester, 19.4% in second trimester, and 6.7% in third trimester. The proportion of postpartum patients confirmed with CTPA (85.5%) was comparable to that of non-pregnant non-postpartum women (83.2%). From the first trimester of pregnancy to postpartum period, there was a linear increase in the proportion of patients with PE diagnosed with CTPA (p = 0.039).

CONCLUSION

CTPA was the primary modality for confirming PE in all trimesters of pregnancy, although its proportional use was higher in later stages of pregnancy.

KEY POINTS

• Computed tomography pulmonary angiography (CTPA) was the primary modality of diagnosis in all trimesters of pregnancy among patients with confirmed pulmonary embolism, even in the first trimester. • From the first trimester of pregnancy to postpartum period, there was a linear increase in the proportion of patients with pulmonary embolism who were diagnosed based on CTPA. • In the postpartum period, use of CTPA as the modality to confirm pulmonary embolism was comparable to non-pregnant patients.

Phenotyping placental oxygenation in Lgals1 deficient mice using 19F MRI

Placental hypoperfusion and hypoxia are key drivers in complications during fetal development such as fetal growth restriction and preeclampsia. In order to study the mechanisms of disease in mouse models, the development of quantitative biomarkers of placental hypoxia is a prerequisite. The goal of this exploratory study was to establish a technique to noninvasively characterize placental partial pressure of oxygen (PO2) in vivo in the Lgals1 (lectin, galactoside-binding, soluble, 1) deficient mouse model of preeclampsia using fluorine magnetic resonance imaging. We hypothesized a decrease in placental oxygenation in knockout mice. Wildtype and knockout animals received fluorescently labeled perfluoro-5-crown-15-ether nanoemulsion i.v. on day E14-15 during pregnancy. Placental PO2 was assessed via calibrated 19F MRI saturation recovery T1 mapping. A gas challenge with varying levels of oxygen in breathing air (30%, 60% and 100% O2) was used to validate that changes in oxygenation can be detected in freely breathing, anesthetized animals. At the end of the experiment, fluorophore-coupled lectin was injected i.v. to label the vasculature for histology. Differences in PO2 between breathing conditions and genotype were statistically analyzed with linear mixed-effects modeling. As expected, a significant increase in PO2 with increasing oxygen in breathing air was found. PO2 in Lgals1 knockout animals was decreased but this effect was only present at 30% oxygen in breathing air, not at 60% and 100%. Histological examinations showed crossing of the perfluorocarbon nanoemulsion to the fetal blood pool but the dominating contribution of 19F MR signal is estimated at > 70% from maternal plasma based on volume fraction measurements of previous studies. These results show for the first time that 19F MRI can characterize oxygenation in mouse models of placental malfunction.

Can pregnancy-adapted algorithms avoid diagnostic imaging for pulmonary embolism?

The low prevalence of pulmonary embolism (PE) among pregnant patients presenting with suspected PE implies that most of these patients will be found not have the disease. Given this low prevalence, excluding PE in this population has necessitated the use of sensitive and specific diagnostic imaging, such as computed tomography pulmonary angiography or ventilation-perfusion scanning. Recent studies suggest that a clinical prediction rule with D-dimer testing can also be used to exclude a subset of pregnant patients with suspected PE without the need for diagnostic imaging. The YEARS criteria, which consist of clinical signs and symptoms of deep venous thrombosis, hemoptysis, and PE as the most likely diagnosis (a subjective variable), combined with selective D-dimer levels, seem to safely exclude up to one-third of these patients without imaging. The revised Geneva rule using objective variables, combined with nonpregnancy cutoffs for D-dimer levels, offers some promise, although fewer patients avoided imaging (14%). These recent studies provide evidence in support of radiation avoidance for some patients; however, for most, imaging remains the only option. Future studies should focus on improving the safety and techniques of imaging modalities, in addition to improving the specificity of D-dimer testing and objective prediction rules. Studies assessing patients' and physicians' values, preferences, and risk perceptions are also required to assist clinicians in shared decision making when counseling pregnant patients with suspected PE.

Current Challenges in Diagnosis of Venous Thromboembolism

In patients with suspected venous thromboembolism, the goal is to accurately and rapidly identify those with and without thrombosis. Failure to diagnose venous thromboembolism (VTE) can lead to fatal pulmonary embolism (PE), and unnecessary anticoagulation can cause avoidable bleeding. The adoption of a structured approach to VTE diagnosis, that includes clinical prediction rules, D-dimer testing and non-invasive imaging modalities, has enabled rapid, cost-effective and accurate VTE diagnosis, but problems still persist. First, with increased reliance on imaging and widespread use of sensitive multidetector computed tomography (CT) scanners, there is a potential for overdiagnosis of VTE. Second, the optimal strategy for diagnosing recurrent leg deep venous thrombosis remains unclear as is that for venous thrombosis at unusual sites. Third, the conventional diagnostic approach is inefficient in that it is unable to exclude VTE in high-risk patients. In this review, we outline pragmatic approaches for the clinician faced with difficult VTE diagnostic cases. In addition to discussing the principles of the current diagnostic framework, we explore the diagnostic approach to recurrent VTE, isolated distal deep-vein thrombosis (DVT), pregnancy associated VTE, subsegmental PE, and VTE diagnosis in complex medical patients (including those with impaired renal function).

Pulmonary embolism: update on management and controversies

Pulmonary embolism is a common and potentially fatal cardiovascular disorder that must be promptly diagnosed and treated. The diagnosis, risk assessment, and management of pulmonary embolism have evolved with a better understanding of efficient use of diagnostic and therapeutic options. The use of either clinical probability adjusted or age adjusted D-dimer interpretation has led to a reduction in diagnostic imaging to exclude pulmonary embolism. Direct oral anticoagulation therapies are safe, effective, and convenient treatments for most patients with acute venous thromboembolism, with a lower risk of bleeding than vitamin K antagonists. These oral therapeutic options have opened up opportunities for safe outpatient management of pulmonary embolism in selected patients. Recent clinical trials exploring the use of systemic thrombolysis in intermediate to high risk pulmonary embolism suggest that this therapy should be reserved for patients with evidence of hemodynamic compromise. The role of low dose systemic or catheter directed thrombolysis in other patient subgroups is uncertain. After a diagnosis of pulmonary embolism, all patients should be assessed for risk of recurrent venous thromboembolism to guide duration of anticoagulation. Patients with a venous thromboembolism associated with a strong, transient, provoking risk factor can safely discontinue anticoagulation after three months of treatment. Patients with an ongoing strong risk factor, such as cancer, or unprovoked events are at increased risk of recurrent events and should be considered for extended treatment. The use of a risk prediction score can help to identify patients with unprovoked venous thromboembolism who can benefit from extended duration therapy. Despite major advances in the management of pulmonary embolism, up to half of patients report chronic functional limitations. Such patients should be screened for chronic thromboembolic pulmonary hypertension, but only a small proportion will have this as the explanation of their symptoms. In the remaining patients, future studies are needed to understand the pathophysiology and explore interventions to improve quality of life.

Advances in the Diagnosis of Venous Thromboembolism: A Literature Review

The incidence of venous thromboembolism (VTE), including lower extremity deep vein thrombosis (DVT) and pulmonary embolism (PE) is increasing. The increase in suspicion for VTE has lowered the threshold for performing imaging studies to confirm diagnosis of VTE. However, only 20% of suspected cases have a confirmed diagnosis of VTE. Development of pulmonary embolism rule-out criteria (PERC) and update in pre-test probability have changed the paradigm of ruling-out patient with low index of suspicion. The D-dimer test in conjunction to the pre-test probability has been utilized in VTE diagnosis. The age appropriate D-dimer cutoff and inclusion of YEARS algorithm (signs of the DVT, hemoptysis and whether PE is the likely diagnosis) for the D-dimer cutoff have been recent updates in the evaluation of suspected PE. Multi-detector computed tomography pulmonary angiography (CTPA) and compression ultrasound (CUS) are the preferred imaging modality to diagnose PE and DVT respectively. The VTE diagnostic algorithm do differ in pregnant individuals. The prerequisite of avoiding excessive radiation has recruited planar ventilation-perfusion (V/Q) scan as preferred in pregnant patients to evaluate for PE. The modification of CUS protocol with addition of the Valsalva maneuver should be performed while evaluating DVT in pregnant individual.

Imaging evaluation of nonobstetric conditions during pregnancy: what every radiologist should know

In recent decades, there has been a significant increase in the number of imaging examinations performed on pregnant patients. That increase has occurred across the various modalities, including ultrasound, computed tomography, and magnetic resonance imaging. However, little is known about the risks that these examinations generate for the mother and fetus, related to the use of ionizing radiation or the use of contrast media. When pregnant patients are submitted to imaging studies, the principles of protection established by the International Commission on Radiological Protection should always be respected, to avoid injury to the pregnant woman and the fetus. The potential deleterious effects on the fetus must be weighed against the damage caused by not performing an examination that is clearly indicated, given that a delayed or missed diagnosis can be even more harmful to the health of the mother and of the fetus itself. The purpose of this review article is to address concerns regarding the safety of imaging methods used during pregnancy, as well as to identify typical clinical situations that require decisions to be made about the indication and optimal planning of imaging examinations.

Conduct and reporting of citation searching in Cochrane systematic reviews: A cross-sectional study

BACKGROUND

The search for studies for a systematic review should be conducted systematically and reported transparently to facilitate reproduction. This study aimed to report on the conduct and reporting of backward citation searching (ie, checking reference lists) and forward citation searching in a cross section of Cochrane reviews. Citation searching uses the citation network surrounding a source study to identify additional studies.

METHODS

Cochrane reviews were identified by searching the Cochrane Database of Systematic Reviews using the wildcard symbol and date limiting to the 3-month period November 2016 to January 2017. Cochrane reviews thus identified were screened for mention of citation searching. Descriptive detail on the conduct and reporting of citation searching was captured in data extraction forms and described and evaluated.

RESULTS

Two hundred fifteen Cochrane reviews were identified. One hundred seventy-two reviews reported backward citation searching, and 18 reviews reported forward citation searching. Web of Science was the most frequently reported citation index. The studies used for backward citation searching consisted mainly of studies meeting the inclusion criteria. One-third of reviews that reported forward citation searching used selected studies of importance. Reporting of citation searching was compliant with the Methodological Expectations of Cochrane Intervention Reviews (MECIR) standards, but full transparency requires additional detail that only a minority of reviews reported.

CONCLUSION

The conduct of backward citation searching was more uniform than forward citation searching. This might be due to lack of MECIR guidance for forward citation searching. Reporting was generally compliant with MECIR, but this is not always sufficient to ensure full transparency.

Contemporary best practice in the management of pulmonary embolism during pregnancy

Approximately 1-2 per 1000 pregnancies are complicated by venous thromboembolism (VTE). VTE includes deep vein thrombosis (DVT) and pulmonary embolism (PE) and the diagnostic management of pregnancy-related VTE is challenging. Current guidelines vary greatly in their approach to diagnosing PE in pregnancy as they base their recommendations on scarce and weak evidence. The pregnancy-adapted YEARS diagnostic algorithm is well tolerated and is the most efficient diagnostic algorithm for pregnant women with suspected PE, with 39% of women not requiring computed tomographic pulmonary angiography. Low-molecular-weight heparin is the first-choice anticoagulant treatment in pregnancy and should be continued until 6 weeks postpartum and for a minimum of 3 months. Direct oral anticoagulants should be avoided in women who want to breastfeed. Management of delivery needs a multidisciplinary approach in order to decide on an optimal delivery plan. Neuraxial analgesia can be given in most patients, provided time windows since last low-molecular-weight heparin dose are respected. Women with a history of VTE are at risk of recurrence during pregnancy and in the postpartum period. Therefore, in most women with a history of VTE, thromboprophylaxis in subsequent pregnancies is indicated. The reviews of this paper are available via the supplemental material section.

EANM guideline for ventilation/perfusion single-photon emission computed tomography (SPECT) for diagnosis of pulmonary embolism and beyond

These guidelines update the previous EANM 2009 guidelines on the diagnosis of pulmonary embolism (PE). Relevant new aspects are related to (a) quantification of PE and other ventilation/perfusion defects; (b) follow-up of patients with PE; (c) chronic PE; and (d) description of additional pulmonary physiological changes leading to diagnoses of left ventricular heart failure (HF), chronic obstructive pulmonary disease (COPD) and pneumonia. The diagnosis of PE should be reported when a mismatch of one segment or two subsegments is found. For ventilation, Technegas or krypton gas is preferred over diethylene triamine pentaacetic acid (DTPA) in patients with COPD. Tomographic imaging with V/PSPECT has higher sensitivity and specificity for PE compared with planar imaging. Absence of contraindications makes V/PSPECT an essential method for the diagnosis of PE. When V/PSPECT is combined with a low-dose CT, the specificity of the test can be further improved, especially in patients with other lung diseases. Pitfalls in V/PSPECT interpretation are discussed. In conclusion, V/PSPECT is strongly recommended as it accurately establishes the diagnosis of PE even in the presence of diseases like COPD, HF and pneumonia and has no contraindications.

American Society of Hematology 2018 guidelines for management of venous thromboembolism: venous thromboembolism in the context of pregnancy

BACKGROUND

Venous thromboembolism (VTE) complicates ∼1.2 of every 1000 deliveries. Despite these low absolute risks, pregnancy-associated VTE is a leading cause of maternal morbidity and mortality.

OBJECTIVE

These evidence-based guidelines of the American Society of Hematology (ASH) are intended to support patients, clinicians and others in decisions about the prevention and management of pregnancy-associated VTE.

METHODS

ASH formed a multidisciplinary guideline panel balanced to minimize potential bias from conflicts of interest. The McMaster University GRADE Centre supported the guideline development process, including updating or performing systematic evidence reviews. The panel prioritized clinical questions and outcomes according to their importance for clinicians and patients. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach was used to assess evidence and make recommendations.

RESULTS

The panel agreed on 31 recommendations related to the treatment of VTE and superficial vein thrombosis, diagnosis of VTE, and thrombosis prophylaxis.

CONCLUSIONS

There was a strong recommendation for low-molecular-weight heparin (LWMH) over unfractionated heparin for acute VTE. Most recommendations were conditional, including those for either twice-per-day or once-per-day LMWH dosing for the treatment of acute VTE and initial outpatient therapy over hospital admission with low-risk acute VTE, as well as against routine anti-factor Xa (FXa) monitoring to guide dosing with LMWH for VTE treatment. There was a strong recommendation (low certainty in evidence) for antepartum anticoagulant prophylaxis with a history of unprovoked or hormonally associated VTE and a conditional recommendation against antepartum anticoagulant prophylaxis with prior VTE associated with a resolved nonhormonal provoking risk factor.

Trends in Medical Imaging During Pregnancy in the United States and Ontario, Canada, 1996 to 2016

IMPORTANCE

The use of medical imaging has sharply increased over the last 2 decades. Imaging rates during pregnancy have not been quantified in a large, multisite study setting.

OBJECTIVE

To evaluate patterns of medical imaging during pregnancy.

DESIGN, SETTING, AND PARTICIPANTS

A retrospective cohort study was performed at 6 US integrated health care systems and in Ontario, Canada. Participants included pregnant women who gave birth to a live neonate of at least 24 weeks' gestation between January 1, 1996, and December 31, 2016, and who were enrolled in the health care system for the entire pregnancy.

EXPOSURES

Computed tomography (CT), magnetic resonance imaging, conventional radiography, angiography and fluoroscopy, and nuclear medicine.

MAIN OUTCOMES AND MEASURES

Imaging rates per pregnancy stratified by country and year of child's birth.

RESULTS

A total of 3 497 603 pregnancies in 2 211 789 women were included. Overall, 26% of pregnancies were from US sites. Most (92%) were in women aged 20 to 39 years, and 85% resulted in full-term births. Computed tomography imaging rates in the United States increased from 2.0 examinations/1000 pregnancies in 1996 to 11.4/1000 pregnancies in 2007, remained stable through 2010, and decreased to 9.3/1000 pregnancies by 2016, for an overall increase of 3.7-fold. Computed tomography rates in Ontario, Canada, increased more gradually by 2.0-fold, from 2.0/1000 pregnancies in 1996 to 6.2/1000 pregnancies in 2016, which was 33% lower than in the United States. Overall, 5.3% of pregnant women in US sites and 3.6% in Ontario underwent imaging with ionizing radiation, and 0.8% of women at US sites and 0.4% in Ontario underwent CT. Magnetic resonance imaging rates increased steadily from 1.0/1000 pregnancies in 1996 to 11.9/1000 pregnancies in 2016 in the United States and from 0.5/1000 pregnancies in 1996 to 9.8/1000 pregnancies in 2016 in Ontario, surpassing CT rates in 2013 in the United States and in 2007 in Ontario. In the United States, radiography rates doubled from 34.5/1000 pregnancies in 1996 to 72.6/1000 pregnancies in 1999 and then decreased to 47.6/1000 pregnancies in 2016; rates in Ontario slowly increased from 36.2/1000 pregnancies in 1996 to 44.7/1000 pregnancies in 2016. Angiography and fluoroscopy and nuclear medicine use rates were low (5.2/1000 pregnancies), but in most years, higher in Ontario than the United States. Imaging rates were highest for women who were younger than 20 years or aged 40 years or older, gave birth preterm, or were black, Native American, or Hispanic (US data only). Considering advanced imaging only, chest imaging of pregnant women was more likely to use CT in the United States and nuclear medicine imaging in Ontario.

CONCLUSIONS AND RELEVANCE

The use of CT during pregnancy substantially increased in the United States and Ontario over the past 2 decades. Imaging rates during pregnancy should be monitored to avoid unnecessary exposure of women and fetuses to ionizing radiation.

Computed tomography pulmonary angiography versus ventilation-perfusion lung scanning for diagnosing pulmonary embolism during pregnancy: a systematic review and meta-analysis

Differences between computed tomography pulmonary angiography and ventilation-perfusion lung scanning in pregnant patients with suspected acute pulmonary embolism are not well-known, leading to ongoing debate on which test to choose. We searched in PubMed, EMBASE, Web of Science and the Cochrane Library databases and identified all relevant articles and abstracts published up to October 1, 2017. We assessed diagnostic efficiency, frequency of non-diagnostic results and maternal and fetal exposure to radiation exposure. We included 13 studies for the diagnostic efficiency analysis, 30 for the analysis of non-diagnostic results and 22 for the radiation exposure analysis. The pooled rate of false negative test results was 0% for both imaging strategies with overlapping confidence intervals. The pooled rates of non-diagnostic results with computed tomography pulmonary angiography and ventilation-perfusion lung scans were 12% (95% confidence interval: 8-17) and 14% (95% confidence interval: 10-18), respectively. Reported maternal and fetal radiation exposure doses were well below the safety threshold, but could not be compared between the two diagnostic methods given the lack of high quality data. Both imaging tests seem equally safe to rule out pulmonary embolism in pregnancy. We found no significant differences in efficiency and radiation exposures between computed tomography pulmonary angiography and ventilation-perfusion lung scanning although direct comparisons were not possible.

Magnetic resonance angiography for the primary diagnosis of pulmonary embolism: A review from the international workshop for pulmonary functional imaging

Pulmonary contrast enhanced magnetic resonance angiography (CE-MRA) is useful for the primary diagnosis of pulmonary embolism (PE). Many sites have chosen not to use CE-MRA as a first line of diagnostic tool for PE because of the speed and higher efficacy of computerized tomographic angiography (CTA). In this review, we discuss the strengths and weaknesses of CE-MRA and the appropriate imaging scenarios for the primary diagnosis of PE derived from our unique multi-institutional experience in this area. The optimal patient for this test has a low to intermediate suspicion for PE based on clinical decision rules. Patients in extremis are not candidates for this test. Younger women (< 35 years of age) and patients with iodinated contrast allergies are best served by using this modality We discuss the history of the use of this test, recent technical innovations, artifacts, direct and indirect findings for PE, ancillary findings, and the effectiveness (patient outcomes) of CE-MRA for the exclusion of PE. Current outcomes data shows that CE-MRA and NM V/Q scans are effective alternative tests to CTA for the primary diagnosis of PE.

Imaging for the exclusion of pulmonary embolism in pregnancy

BACKGROUND

Pulmonary embolism is a leading cause of pregnancy-related death. An accurate diagnosis in pregnant patients is crucial to prevent untreated pulmonary embolism as well as unnecessary anticoagulant treatment and future preventive measures. Applied imaging techniques might perform differently in these younger patients with less comorbidity and altered physiology, who largely have been excluded from diagnostic studies.

OBJECTIVES

To determine the diagnostic accuracy of computed tomography pulmonary angiography (CTPA), lung scintigraphy and magnetic resonance angiography (MRA) for the diagnosis of pulmonary embolism during pregnancy.

SEARCH METHODS

We searched MEDLINE and Embase until July 2015. We used included studies as seeds in citations searches and in 'find similar' functions and searched reference lists. We approached experts in the field to help us identify non-indexed studies.

SELECTION CRITERIA

We included consecutive series of pregnant patients suspected of pulmonary embolism who had undergone one of the index tests (computed tomography (CT) pulmonary angiography, lung scintigraphy or MRA) and clinical follow-up or pulmonary angiography as a reference test.

DATA COLLECTION AND ANALYSIS

Two review authors performed data extraction and quality assessment. We contacted investigators of potentially eligible studies to obtain missing information. In the primary analysis, we regarded inconclusive index test results as a negative reference test, and treatment for pulmonary embolism after an inconclusive index test as a positive reference test.

MAIN RESULTS

We included 11 studies (four CTPA, five lung scintigraphy, two both) with a total of 695 CTPA and 665 lung scintigraphy results. Lung scintigraphy was applied by different techniques. No MRA studies matched our inclusion criteria.Overall, risk of bias and concerns regarding applicability were high in all studies as judged in light of the review research question, as was heterogeneity in study methods. We did not undertake meta-analysis. All studies used clinical follow-up as a reference standard, none in a manner that enabled reliable identification of false positives. Sensitivity and negative predictive value were therefore the only valid test accuracy measures.The median negative predictive value for CTPA was 100% (range 96% to 100%). Median sensitivity was 83% (range 0% to 100%).The median negative predictive value for lung scintigraphy was 100% (range 99% to 100%). Median sensitivity was 100% (range 0% to 100%).The median frequency of inconclusive results was 5.9% (range 0.9% to 36%) for CTPA and 4.0% (range 0% to 23%) for lung scintigraphy. The overall median prevalence of pulmonary embolism was 3.3% (range 0.0% to 8.7%).

AUTHORS' CONCLUSIONS

Both CTPA and lung scintigraphy seem appropriate for exclusion of pulmonary embolism during pregnancy. However, the quality of the evidence mandates cautious adoption of this conclusion. Important limitations included poor reference standards, necessary assumptions in the analysis regarding inconclusive test results and the inherent inability of included studies to identify false positives. It is unclear which test has the highest accuracy. There is a need for direct comparisons between diagnostic methods, including MR, in prospective randomized diagnostic studies.