Clinical Validity of a Normal Perfusion Lung Scan in Patients with Suspected Pulmonary Embolism

doi:10.1378/chest.97.1.23

Chest

Volume 97, Issue 1, January 1990, Pages 23-26

https://doi.org/10.1378/chest.97.1.23 Get rights and content

The objective of this study was to test the safety of withholding anticoagulant therapy in patients with clinically suspected pulmonary embolism who have normal perfusion lung scans, regardless of the clinical manifestations. Anticoagulant therapy was withheld or withdrawn in 515 consecutive patients except in patients in whom deep-vein thrombosis was detected. Only three of the 515 patients had symptomatic venous thromboembolism on follow-up. The frequency of symptomatic pulmonary embolism on follow-up was one of 515 patients. With knowledge of the normal findings by perfusion scanning, an alternative diagnosis was established in 367 of the 515 patients. Cause of symptoms remained uncertain in 148 patients. It is safe to withhold anticoagulant therapy in patients with suspected pulmonary embolism and normal perfusion scans, regardless of the clinical manifestations. The finding of a normal perfusion scan excludes the presence of clinically important pulmonary embolism and makes pulmonary angiography unnecessary.

(Chest 1990; 97:23-26)

Section snippets

Patients

Between 1981 and 1988, 1,420 consecutive patients with clinically suspected pulmonary embolism were referred to the Thromboembolism Service at Chedoke-McMaster Hospitals and were studied prospectively. The 515 (36 percent) of these patients who had normal perfusion lung scans are the subject of this report. The findings in the patients with abnormal perfusion scans have been described previously.9, 10, 11

Study Protocol

Each patient was examined on the day of referral by the consultant physician and the study

Patients

The 515 consecutive patients with clinically suspected pulmonary embolism and normal perfusion scans ranged in age from 14 to 93 years (mean, 45 years); 154 (30 percent) were men and 361 (70 percent) were women. Their clinical characteristics are shown in Table 1. Of the 515 patients, 361 patients (70 percent) were outpatients at the time of presentation and 154 (30 percent) were inpatients.

Findings by Impedance Plethysmography at Presentation

Impedance plethysmography was performed successfully in 493 of the 515 patients (it could not be

DISCUSSION

The results indicate that patients with suspected pulmonary embolism and a normal perfusion lung scan have an excellent prognosis without anticoagulant therapy. Symptomatic venous thromboembolism was rare on follow-up in our patients with normal perfusion scans (0.6 percent [three of 515 patients]). Further, two of the three patients with venous thromboembolism on follow-up had predisposing factors which placed them at continued risk for venous thromboembolism. The results on follow-up indicate

ACKNOWLEDGMENTS

We gratefully acknowledge the support of the members of the sections of Emergency Medicine, Family Practice, Medicine, Surgery, Obstetrics and Gynecology, Critical Care and Diagnostic Imaging at Chedoke-McMaster Hospitals; the members of the undergraduate and postgraduate training programs of McMaster University; D. Sackett, M.D.; J. Freiburger, M.A., T.W.; and N. Anderson, Ph.D.

In particular, the contributions of the members of the Regional Thromboembolism Program including J. Hirsh, M.D., and

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Interpretation schemes based on high probability patterns (PE present), normal or nearly normal patterns (PE absent), with the remaining patterns termed nondiagnostic, provide effective communication for clinicians.95 At least 2 studies have shown that it is safe to withhold anticoagulants when a technically satisfactory perfusion lung scan shows no perfusion defects.96,97 In one large well-designed study, anticoagulants were withheld or discontinued following evaluation of 515 consecutive patients who had a normal perfusion lung scan and clinically suspected acute PE.97
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This work was supported by grants from the Ontario Ministry of Health, the Heart and Stroke Foundation of Ontario, and the Canadian Heart Foundation

Manuscript received April 27; accepted May 2.

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Chest

Clinical InvestigationsClinical Validity of a Normal Perfusion Lung Scan in Patients with Suspected Pulmonary Embolism

Section snippets

Patients

Study Protocol

Patients

Findings by Impedance Plethysmography at Presentation

DISCUSSION

ACKNOWLEDGMENTS

Chest

Lancet

Chest

Lancet

Am Heart J

Am J Med

Am J Med

Diagnosis of massive pulmonary embolism in man by radioisotope scanning

N Engl J Med

Ventilation-perfusion lung imaging and selective pulmonary angiography in dogs with experimental pulmonary embolism

J Nucl Med

Assessment of pulmonary photoscanning and angiography in experimental pulmonary embolism

Circulation

On purple emperors, pulmonary embolism, and venous thrombosis

Ann Intern Med

Warfarin sodium versus low-dose heparin in the long-term treatment of venous thromboembolism

N Engl J Med

Clinical Investigations
Clinical Validity of a Normal Perfusion Lung Scan in Patients with Suspected Pulmonary Embolism