This commentary explores the clinical conundrums arising when caring for patients with acute pulmonary embolism isolated to the subsegmental pulmonary arteries. We discuss ways to confirm the radiologic diagnosis, how to distinguish patients for whom anticoagulation is indicated from those who are eligible for structured surveillance without anticoagulation, what surveillance entails, and why ensuring continuity of care matters. We report a case from our own experience that illustrates these decision-making crossroads and highlights the importance of cross-disciplinary collaboration. Because the evidence in the literature is currently weak and indirect, we draw on expert opinion in US and European guidelines, a recent statement from a multidisciplinary consensus panel, and several ongoing well-designed clinical trials. This discussion will help clinicians better manage the spectrum of patients who present with isolated subsegmental embolism.

Importance

Approximately 8% of acute pulmonary emboli are confined to the subsegmental arteries. The 2016 and 2021 American College of Chest Physicians (CHEST) guidelines and expert panel reports suggest the use of structured surveillance without anticoagulation for select ambulatory patients with subsegmental pulmonary embolism who do not have active cancer, deep vein thrombosis, impaired cardiopulmonary reserve, marked symptoms, or increased risk of recurrent venous thromboembolism; however, guideline uptake in community practice is unknown, as is the proportion of outpatients eligible for surveillance.

Objective

To describe the prevalence of surveillance among outpatients with acute subsegmental pulmonary embolism and to estimate the proportion of patients eligible for structured surveillance using modified CHEST criteria.

Design, setting, and participants

This retrospective cohort study was conducted across 21 US community hospitals in the Kaiser Permanente Northern California integrated health system from January 1, 2017, to December 31, 2021. Adult outpatients with acute subsegmental pulmonary embolism were included. Patients with the following higher-risk characteristics were excluded: codiagnoses requiring hospitalization, non-low-risk vital signs (ie, systolic blood pressure <90 mm Hg, pulse ≥110 bpm, or peripheral cutaneous pulse oximetry ≤92%), prediagnosis anticoagulant use, or hospice care. Data analysis was performed from November 2022 to February 2023.

Main outcomes and measures

The main outcomes were the (1) prevalence of surveillance and (2) eligibility for surveillance using 2 sets of criteria: the CHEST criteria modified by excluding patients with higher-risk characteristics or right ventricular dysfunction and a stricter set of criteria requiring age younger than 65 years and no more than 1 embolus. The prevalence of structured surveillance was calculated and the proportion of patients eligible for surveillance was estimated.

Results

Of the 666 outpatients with acute subsegmental pulmonary embolism included in this study, 229 with lower-risk characteristics were examined. Their median age was 58 (IQR, 42-68) years; more than half were men (120 [52.4%]) and self-identified as non-Hispanic White (128 [55.9%]). Six patients (2.6%) were initially not treated with anticoagulants. Among the lower-risk cohort, only 1 patient (0.4% [95% CI, 0.01%-2.4%]) underwent structured surveillance, without 90-day sequelae. Thirty-five patients (15.3% of the lower-risk group and 5.3% of the full cohort) were surveillance eligible using modified CHEST criteria. Fifteen patients (6.6% of the lower-risk group and 2.3% of the full cohort) were surveillance eligible using stricter criteria.

Conclusions and relevance

In this cohort study of lower-risk outpatients with subsegmental pulmonary embolism, few were eligible for structured surveillance, and only a small proportion of eligible patients underwent surveillance despite the CHEST guideline. If forthcoming trials find surveillance safe and effective, substantial uptake into clinical practice may require more than passive diffusion.