Suspected Pulmonary Embolism in Pregnancy

Abstract & Commentary

Synopsis: Ventilation/perfusion scanning appears to be safe and effective, at least in ruling out significant clinical pulmonary embolism in pregnant patients. However, prospective studies over longer time periods should be undertaken to validate these conclusions.

Source: Chan WS, et al. Suspected pulmonary embolism in pregnancy: Clinical presentation, results of lung scanning, and subsequent maternal and pediatric outcomes. Arch Intern Med. 2002;162:1170-1175.

Pulmonary embolism (PE) is a preventable cause of maternal mortality during pregnancy and the postpartum period. Once PE is suspected, many clinicians begin their evaluation with a ventilation/perfusion scan. Although scanning is assumed to be safe during pregnancy based on low fetal radiation exposure,1 no clinical data exist to support the notion that there are no adverse outcomes in pregnancy. In addition, little is known about ventilation/perfusion scan interpretation in pregnant women and the safety of withholding anticoagulation in those with normal or nondiagnostic scans.

The purpose of this multicenter, retrospective, observational study was to examine the distribution and safety of ventilation/perfusion scanning in pregnant patients. The safety of withholding anticoagulation therapy in pregnant women with normal or nondiagnostic scans was also examined.

A total of 120 consecutive pregnant patients who presented with suspected PE and had ventilation/perfusion scans were identified through the nuclear medicine departments. Patient demographics, stage of pregnancy, symptomatology, and treatment strategy at the time of original evaluation were recorded. Two independent experts re-interpreted the original ventilation/perfusion scans and categorized them as normal, nondiagnostic, or high probability. Patients were later contacted by telephone to determine postpartum venous thromoembolic events, and pregnancy outcomes.

Scan readings were as follows 87 (72.5%) normal, 29 (24.2%) nondiagnostic, and 4 (3.3%) high probability. Seven were receiving anticoagulation prior to presentation for previously diagnosed PE or deep venous thrombosis; eight women received anticoagulation subsequent to their evaluation. Of the 104 untreated women (1 died secondary to primary pulmonary hypertension), 80 had normal scans and 20 scans were nondiagnostic. In this group, no thromboembolic event was reported after a mean follow-up of 20 months.

Of 110 obstetrical and pediatric outcomes examined over 20 months, 3 spontaneous abortions, 4 congenital, and 4 developmental abnormalities were reported. No childhood cancers or leukemias were reported.

Comment by Alan Fein, MD, & Jonathan Edelson, MD

In this retrospectively examined group of pregnant patients, the prevalence of high probability scans is low (1.8%), compared to the other patients with suspected PE (10%). There were no thromboembolic events reported in those with normal or intermediate probability lung scans, suggesting that ventilation/perfusion scanning in pregant patients has a good negative pedictive value. Importantly, fetal risk was minimal in this population. The percentage of adverse fetal outcomes after ventilation/perfusion scanning was similar to that in the general population, 2.6% compared to 3.6%. These numbers are supported by previous studies that suggested no increase in fetal malformation risk for exposures less than 1 rad; radiation exposure in ventilation/perfusion scans is significantly lower.2

In summary ventilation/perfusion scanning appears to be safe and effective, at least in ruling out significant clinical PE in pregnant patients. However, prospective studies over longer time periods should be undertaken to validate these conclusions.

References

1. Ginsberg JS, et al. Risks to the fetus of radiologic procedures used in the diagnosis of maternal thromboembolic disease. Thromb Haemost. 1989;61:189-196.

2. McCabe J, et al. Ventilation perfusion scintigraphy. Emerg Med Clin North Am. 1991;9(4):805-825.

Dr. Fein is Director and Dr. Edelson is Fellow, Division of Pulmonary and Critical Care Medicine, North Shore University Hospital, Manhasset, New York.