Subsegmental Pulmonary Embolisms (SSPE) are Important

Subsegmental Pulmonary Embolisms (SSPE) are Important


0125Multi-detector computed tomographic pulmonary angiography (CTPA) allows for better visualization of peripheral pulmonary arteries allowing for diagnosis of small peripheral emboli limited to the subsegmental pulmonary arteries. Interestingly as these SSPE’s get diagnosed more and more, two questions come to mind:

  1. What is the prognostic utility of diagnosing SSPEs?
  2. What is the morbidity and mortality of SSPEs compared to more proximal PEs?

A recent study in 2013 Blood looked at these questions. 1

Cohorts for this study?

  • 116/748 (15.5%) of patients had diagnosis of isolated SSPE
  • 632/748 (84.5%) of patients had diagnosis of segmental or more proximal PE
  • 2,980 patients had PE ruled out by clinical probability and a normal (D-Dimer or CTPA)

Cumulative risk for recurrent venous thromboembolism (VTE) at 3 months?

  • SSPE = 3.6%
  • Segmental and More Proximal PE = 2.5%
  • PE Ruled-Out at Baseline = 1.1%
  • Of note: There was a 99.9% follow-up rate of patients
  • SSPE vs Segmental and More Proximal PE did not meet statistical significance

Percentage of patients with bleeding complications associated with treatment of PE?

  • SSPE = 1.7%
  • Segmental and More Proximal PE = 1.6%
  • SSPE vs Segmental and More Proximal PE did not meet statistical significance

Cumulative mortality risk associated with each cohort?

  • SSPE = 10.7% 
  • Segmental and More Proximal PE = 6.5%
  • PE excluded = 5.4%
  • SSPE vs Segmental and More Proximal PE did not meet statistical significance

What were the limitations of the study?

  • Independent radiologists were not used to confirm the diagnosis of SSPE in majority of cases
  • The definition of SSPE included both single and multiple SSPEs
  • The absolute incidences of recurrent VTE, bleeding complications, and mortality were small
  • An underpowered study to detect small changes in outcomes (i.e. SSPE vs Segmental and Proximal PE did not meet statistical significance)

Take Home Points

  • SSPE has a similar rate of recurrent VTE at 3 months, bleeding complications from treatment, and mortality when compared to segmental and proximal PEs (no statistical significance among the 3 outcome measures).
  • Should we question the conflicting data by Weiner et al stating: “ We have increased the incidence of PE diagnosis with CTPA ,but not changed the mortality risk”? 2
den E, van E, Klok F, et al. Risk profile and clinical outcome of symptomatic subsegmental acute pulmonary embolism. Blood. 2013;122(7):1144-9; quiz 1329. [PubMed]
Wiener R, Schwartz L, Woloshin S. Time trends in pulmonary embolism in the United States: evidence of overdiagnosis. Arch Intern Med. 2011;171(9):831-837. [PubMed]

Salim Rezaie, MD

Salim Rezaie, MD

ALiEM Associate Editor
Clinical Assistant Professor of EM and IM
University of Texas Health Science Center at San Antonio
Founder, Editor, Author of R.E.B.E.L. EM and REBEL Reviews
  • Bjorn

    I don’t agree:
    “Multivariate analysis identified malignancy (HR: 5.6; 95% CI: 4.2-7.6), male gender, age, COPD and heart failure as independent predictors for mortality.”
    “After adjustment for these covariates, the HR for mortality was 1.4 (95% CI: 0.8-2.6)
    for patients with SSPE compared with those in whom PE was ruled out.” = non significant.

    Isn’t this study implying that patients with PE die because of their risk factor profile (malignancy, …), not of their DVT/PE. And therefore it doesn’t matter if they have a proximal or subsegmental PE.

    • Salim R. Rezaie

      Hello Bjorn,
      I agree that independent factors such as malignancy, COPD and heart failure do increase mortality in patients with PE, but if you look at the P values associated with SSPE vs proximal PE, none were statistically significant, which I specifically stated in the post, but they were significant in SSPE vs no PE as you stated.
      And you are exactly right regardless of proximal or distal PE….it was the independent factors that increased risk of death not the fact that the PE was proximal or distal. There are some that say, distal PEs don’t matter period, but this study says they have the same chance of death with the independent factors or without them. Although not statistically significant, maybe clinically important?


  • Nick Manville

    I guess the alternate interpretation of Weiner is that the treatment is ineffective (or at least the risks and benefits cancel each other out) in preventing mortality in the modern era. What’s the latest data on efficacy of anti-coagulation?

    • Michelle

      Excellent points. So many confounders to muddy the final outcome measure of mortality from PE’s. Good point about better treatment and prophylaxis measures today. I’m sold on the fact that SSPE’s DO matter. They are NOT clinically insignificant clots. Like Bjorn stated above, it seems that the underlying risk factors that are deadly.

      Thanks for commenting.

      Here’s figure 2 from the Weiner paper.