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 perfusion defects compared with 227 of 376 (60%) treated patients (p<0.001). Pulmonary arteries showed thromboemboli in segmental or smaller arteries in 16 of 19 (84%) untreated patients compared with 132 of 362 (36%) treated patients (p<0.001). Untreated and treated patients, when grouped according to the size of the ventilation/perfusion lung scan defect or size of vessels involved on the pulmonary angiogram, showed no statistically significant difference in the frequency of fatal PE or nonfatal recurrent PE.
Conclusion: Mild untreated PE carries a lower immediate mortality and lower mortality from recurrent PE than overt PE described in prior decades.