Nothing Excludes Pulmonary Embolism?

It’s hard to find a diagnostic pathway with greater variation than that of pulmonary embolism. On one hand, you have the YEARS protocol, in which D-dimer is the definitive gatekeeper without carve-outs or exclusions. On the other hand, you have an article like this – saying even CT pulmonary angiograms are inadequate to rule-out PE.

These authors re-analyzed the data from a previous prospective study enrolling 7,940 patients across 12 Emergency Departments. In this analysis, these authors focused in on the 257 patients for whom a “High risk” Wells score was assigned. Of these, 201 underwent reliable CTPA, 71 of which were read as positive and 130 of which were read as negative. Within 45 days, using chart review and telephone follow-up, the authors determined 16 of these patients were ultimately diagnosed with PE. They conclude the CTPA missed these diagnoses at the index visit, and should not be considered adequate for rule-out in a high-risk patient. They go on to cite the inadequate sensitivity of CTPA as demonstrated in PIOPED-II as justification for their stance.

Unfortunately, there’s not nearly enough information presented here to fully evaluate their findings. The authors are attempting to refute the utility of CTPA as a reliable mechanism for rule-out, but, despite such a small sample, no individual scan follow-up was attempted to overread the initial CT. Then, patients with high Wells scores are obviously at high risk for VTE; it almost certainly reasonable some of these downstream PE are independent events, a possibility towards which the authors are fairly dismissive. The authors report many of these patients were positive for DVT, making a subsequent PE as an independent event even more likely. The PIOPED-II study, landmark or not, was conducted in a comparatively medieval era of CTPA, and those sensitivity findings should not impact current data interpretation. Finally, the CTPA is famous not so much for false negatives as it is false positives. The authors do not account for the possibility some of these downstream diagnoses are false positives, and no characterization of the subsequent diagnoses are given – an important consideration in this era of over-diagnosis of subsegmental PE of uncertain clinical significance.

I certainly do not believe these data should change practice or our opinion of the CTPA as a reliable rule-out for a clinically important PE. More robust, prospective study is necessary to confirm the veracity of their conclusion of these false negatives.

“Ruling out Pulmonary Embolism in Patients with High Pretest Probability”

https://escholarship.org/uc/item/74h4h8qb