A Study to Evaluate the Safety of Withholding Anticoagulation in Patients With Subsegmental PE Who Have a Negative Serial Bilateral Lower Extremity Ultrasound

Blood clots in lung arteries (pulmonary embolism) are usually detected using a radiological test called computed tomography (CT scan). As technology advances, the CT scans are able to detect smaller and smaller blood clots. Over time, the frequency of blood clots in the pulmonary arteries has increased significantly (CT scan are now detecting very small blood clots that the investigators could not see before). As a result, more and more people are on blood thinners to treat these small blood clots but their true clinical significance is unknown. The management of blood thinners is costly and also utilizes scarce healthcare resources. These blood thinners need to be monitored with frequent blood work. Furthermore, every year, approximately 3 percent of patients on blood thinners will have a major bleeding event requiring medical attention. The investigators don't think that treating these small blood clots in the pulmonary arteries detected on CT scan is worth the risk of bleeding from the blood thinners. The main goal of this study is to find out if it is safe to not treat very small blood clots in the pulmonary arteries. The investigators plan to follow 300 patients with small blood clots in their lungs for 90 days. These patients will not be treated with blood thinners but will be followed closely with other non-invasive tests to avoid progression or recurrence of blood clots.