From the Journals

Perfusion-only scan rules out PE in pregnancy

 

Key clinical point: In the evaluation of pregnant women with suspected pulmonary embolism, low-dose perfusion scintigraphy may offer diagnostic performance that’s comparable to CTPA.

Major finding: The negative predictive value of a pulmonary embolism was 100% for the low dose perfusion scan, compared with 97.5% for CTPA.

Study details: A retrospective, single-center cohort study including 322 pregnant women who underwent imaging studies for suspected pulmonary embolism.

Disclosures: One study coauthor is on an advisory panel for Jubilant DraxImage, and another has a spouse who is a board member of Kyron Pharma Consulting. The remaining authors, including Dr. Sheen,reported no conflicts of interest.

Source: Sheen JJ et al. Chest. 2018 Feb. doi: 10.1016/j.chest.2017.08.005.

Nirmal Sharma, MD, comments: During pregnancy, all radiation is bad radiation, but when it was really needed, we did use this low-radiation perfusion scan quite a bit at my past institution. This article definitely shines light on the utility/validity of this technique because most centers still use a computed tomographic pulmonary angiography study in pregnant females (with shielding methods) if suspicion of pulmonary embolism is high. The downside to low-dose perfusion scintigraphy is that it cannot be used in patients with grossly abnormal chest x-rays.

Dr. Nirmal S. Sharma

Dr. Nirmal S. Sharma

If you are doing a low-dose perfusion scan alone, without ventilation studies, in subjects who have ventilation issues caused by severe parenchymal disease or an obstructive lung disease, such as asthma, interpretation becomes an issue. Such patients may have segmental and subsegmental perfusion defects caused by loss of ventilation.


 

FROM CHEST®

For pregnant women with suspected pulmonary embolism (PE), evaluation with low-dose perfusion scintigraphy may be preferable to computed tomographic pulmonary angiography (CTPA), according to authors of a recent retrospective study.

Pulmonary embolism causes 9% of maternal deaths in the United States, according to the authors of the study, which was published online in the journal CHEST®. While it’s clear that perfusion scans yield lower radiation exposure than CTPA, to date, there has only been limited study of its diagnostic performance in women with suspected PE.

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The new study is believed to be the largest to date of perfusion-only imaging in this setting, according to first author Jean-Ju Sheen, MD, of the department of obstetrics and gynecology at Columbia University Medical Center, New York, and her coauthors.

The low-dose perfusion scan offered comparable diagnostic efficacy while potentially limiting radiation exposure, according to the single-center cohort study.

The retrospective study included pregnant women (mean age, 27.3 years) who underwent imaging for pulmonary embolism at Montefiore Medical Center, New York, between 2008 and 2013. A total of 225 women underwent perfusion-only scans, while 97 underwent CTPA.

Chest pain and dyspnea were the most common symptoms for patients in both groups: 136 of the patients (60.4%) in the low-dose perfusion group reported chest pain versus 40 patients (41.2%) in the CTPA group. About half of the patients in both groups had dyspnea.

Tachycardia was found in 43 of patients (44.3%) who underwent CTPA, compared with 77 of patients (34.2% ) who underwent the diagnostic test involving less radiation exposure.

Imaging was negative for PE in 198 of the patients (88.0%) who were scanned with low-dose perfusion, while 84 of patients (86.6%) who had CTPAs were negative for PE. For both groups of patients, the percentage who had indeterminate imaging was 9.3%. Only one study participant had a deep vein thrombosis at the time she presented with PE symptoms.

The primary end point of the study, negative predictive value, was 100% for the perfusion-only group and 97.5% for CTPA, according to the report. It was determined by a diagnosis of venous thromboembolism within 90 days of evaluation.

Those “indistinguishable” negative predictive values suggest that low-dose perfusion scintigraphy performs comparably to CTPA, making it an appropriate first diagnostic modality for pregnant women who are suspected of having pulmonary embolism, Dr. Sheen and her colleagues wrote.

The negative predictive value was a particularly important endpoint to evaluate because pulmonary embolism is rare among pregnant women and most perfusion-only imaging is negative, the authors stated.

Of the women in the study, 252 (89%) of those who tested negative for PE – either by a low-dose perfusion scan or a CTPA – returned to the medical center for follow-up 90 days later. Thromboembolic events occurred in two of the women who previously had a negative CTPA, but none occurred in patients who had been tested for PE with low-dose perfusion scan. The two thromboembolic events were detected in women who were no longer pregnant.

Ten patients in the study (3.1%) were treated for pulmonary embolism, the authors reported. The PE diagnoses were based on four positive low-dose perfusion scans and six positive CTPAs “in conjunction with clinical suspicion.” These patients’ most common symptoms were chest pain and dyspnea, and one of these patients had recently been diagnosed with a deep vein thrombosis.

When perfusion defects are found, they should be interpreted cautiously, particularly in asthmatic patients, according to authors: “Segmental perfusion defects secondary to abnormal ventilation cannot be distinguished from PE without a ventilation scan,”they noted.

Three of the patients diagnosed with a PE had asthma. In a subanalysis of the 77 patients with asthma who participated in this study, the negative predictive values were 100% for both those who received a low-dose perfusion scan and those who received a CTPA. For patients in this subgroup, the negative rates of PE from low-dose perfusion scan and CTPA were 74.1% and 87.1%, respectively.

“Maternal-fetal radiation exposure should be of utmost importance when considering the choice of diagnostic test,” the authors wrote. “When available, [a low-dose perfusion scan] is a reasonable first choice modality for suspected pulmonary embolism in pregnant women with a negative chest radiograph.”

One study coauthor is on an advisory panel for Jubilant DraxImage, and another has a spouse who is a board member of Kyron Pharma Consulting. The remaining authors, including Dr. Sheen,reported no conflicts of interest.

SOURCE: Sheen JJ et al. Chest. 2018 Feb. doi: 10.1016/j.chest.2017.08.005.

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