All else being equal, I'd prefer to do nothing. Whether this is nihilism, laziness, or experience is a matter of debate. The American College of Chest Physicians (CHEST) Guidelines on therapy for venous thromboembolism (VTE) opened a door for withholding treatment for isolated subsegmental pulmonary embolism (ISSPE) in 2016 and kept it open in 2021. I was happy to walk through it and withhold therapy if it wasn't indicated.
ISSPE is truly a conundrum. With advances in technology, the distal vessels in the lung became visible on commercial CT a little more than 10 years ago. The subsegmental branches are located after the fourth bifurcation of the pulmonary arterial system, and the new technology offered resolution adequate to identify clot in these vessels. But the new technology told us nothing about how to manage clot isolated to the subsegmental vasculature.
Autopsy data say clot in these vessels is common, even in patients who were never diagnosed with VTE while they were alive. To some degree then, the pulmonary arterial system is thought to serve as a filter to prevent clot from crossing to the systemic circulation and causing strokeThis led some to speculate that the subsegmental pulmonary arteries are supposed to contain clot and that we simply couldn't see it before now. If this theory is correct, the practice of providing anticoagulation for ISSPE could increase bleeding without reducing the risk for VTE recurrence.
