Symptomatic subsegmental pulmonary embolism: what is the next step?

The introduction of computed tomography pulmonary angiography (CTPA) has led to an increase in the incidence of pulmonary embolism (PE) diagnosis. However, the case fatality rate is lower and the mortality rates of PE have remained unchanged, suggesting a lower severity of illness. Specifically, the multiple-detector CTPA increased the rate of subsegmental filling defect reported in patients with suspected PE. Whether these filling defects reported on CTPA would correlate with true subsegmental PE (SSPE) on pulmonary angiography or are actually artifacts is unknown. The inter-observer agreement for SSPE diagnosis among radiologists with varied levels of experience is low (κ of 0.38; 95% CI, 0.0-0.89). Furthermore, the clinical importance of a symptomatic SSPE diagnosed by CTPA is unclear. SSPE are frequent on pulmonary angiography in patients with a low probability ventilation-perfusion (V/Q) scan for suspected PE. Several prospective management cohort studies have demonstrated that patients with low or intermediate V/Q scan results can be safely managed without anticoagulation by combining the scan results with the pretest probability (PTP) of PE and compression ultrasonography. Although clinical equipoise exists, the majority of patients diagnosed with SSPE on CTPA are currently treated with anticoagulant therapy. Only a small number of patients with SSPE diagnosed by CTPA and without DVT who did not receive anticoagulation treatment have been reported in the literature. None of these patients suffered recurrent symptomatic VTE (PE or DVT) during the 3-month follow-up period (0%; 95% CI, 0-7.4%), suggesting that SSPE might be clinically unimportant. These conclusions are only hypothesis generating and need to be confirmed in prospective clinical management studies before changing clinical practice.