Subsegmental Pulmonary Embolisms (SSPE) are Important

Multi-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

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