Untreated Patients With Pulmonary Embolism*

Purpose: The purpose of this investigation was to evaluate the clinical characteristics of acute pulmonary embolism (PE) among patients with PE who did not receive treatment to assess how the natural course of untreated PE relates to its severity. Methods: Data are from the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED). Among patients with PE diagnosed either by pulmonary angiography or at autopsy, 376 received treatment and 24 escaped treatment in the hospital and were not prescribed anticoagulant therapy at the time of hospital discharge. Among these untreated patients, however, four received anticoagulant therapy during the first 3 months of follow-up. We report the 3-month course of PE in the remaining 20 untreated patients. Results: Among untreated patients, 1 of 20 (5.0%) died from the effects of the original PE and possibly some contribution from recurrent PE. Nonfatal recurrent PE occurred in 1 of 20 (5.0%). All untreated patients, 20 of 20 (100%), had less than three mismatched segmental