Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED)
Condition: Lung Diseases; Pulmonary Embolism
MeSH terms: Lung Diseases; Pulmonary Embolism; Embolism
Study type: Interventional
Phase: Phase 3

Summary: 
      To evaluate the sensitivity and specificity of two major, widely used technologies,
      radionuclear imaging (ventilation-perfusion scanning) and pulmonary angiography, for the
      diagnosis of pulmonary embolism.
    

Detailed description: 
      BACKGROUND:

      In 1983, reliable data on the incidence of pulmonary embolism in the adult population and in
      groups identified at risk were not available because the sensitivity and specificity of the
      diagnostic procedures had not been determined. Estimates suggested there were about half a
      million episodes of pulmonary embolism in hospitalized patients each year in the United
      States. Deaths attributable to pulmonary embolism would be expected in about one third of
      these patients if left untreated.

      The clinical diagnosis of pulmonary embolism was subject to a high frequency of false
      positives and false negatives. The most definitive diagnostic procedure was pulmonary
      angiography, an invasive, expensive procedure which was not without risk. It required
      specialized equipment and highly trained personnel both for performance and for
      interpretation. Therefore, it was used to diagnose pulmonary embolism only in the major
      medical centers. Another technique utilized as a method to diagnose pulmonary embolism
      involved a combination of perfusion and ventilation scanning; this method was only minimally
      invasive. A normal perfusion scan was thought to be of considerable value because it
      essentially excluded the diagnosis of pulmonary embolism. In selected patient populations,
      abnormal perfusion scans combined with normal ventilation scans were of substantial help in
      diagnosis.

      Although there had been no acceptable validation of the use of perfusion scans in the
      diagnosis of pulmonary embolism, thousands of patients had been evaluated for pulmonary
      embolism based on perfusion scanning often using methods of imaging now considered to be
      inadequate. In the early 1980s, clinical practice interpreted a negative perfusion scan as
      overwhelming evidence against the presence of pulmonary emboli. This interpretation had not
      been adequately tested either in a prospective study or by long-term follow-up of patients to
      determine clinical outcome. With regards to positive perfusion scans, there were data to
      suggest that as many as two-thirds of positive perfusion scans could not subsequently be
      confirmed by pulmonary angiography. Prospective studies in which timely angiograms using
      selective injections and improved imaging techniques were needed to evaluate the usefulness
      of positive perfusion scans.

      Phase I was initiated in September 1983. Protocols developed during Phase I underwent
      independent assessment review in April 1984 and were reviewed and approved by the May 1984
      National Heart, Lung, and Blood Advisory Council. Recruitment and intervention started in
      January 1985 and ended in September 1986. Follow-up was completed on September 30, 1987.

      DESIGN NARRATIVE:

      Patients suspected of pulmonary embolism underwent a ventilation-perfusion scan. Patients
      with an abnormal perfusion scan underwent angiography. All patients were followed for one
      year.
    

Intervention name(s): ventilation-perfusion ratio; angiography
Intervention type(s): Procedure; Procedure
Primary purpose: Diagnostic