Abstract 17847: Venous Thromboembolism in an Industrial North American City: Temporal Distribution and Associate with Air Pollution
Background: Emerging evidence, mainly from Europe, indicates that venous thromboembolism (VTE) occurs most often in winter. Two factors implicated in such seasonality are exacerbation of coagulation by low temperatures and increased particulate matter (PM) pollution provoking VTE after inhalation. In contrast to most European cities, air pollution in many North American cities peaks in summer rather than winter. We hypothesized that analysis of the temporal distribution of VTE in a cold-weather industrial city (Detroit) with a summer pollution peak could resolve the role of these factors and offer insight into possible prothrombotic environmental effects.
Methods: Using ICD-9-CM codes, we identified 3,310 suspected VTEs in ambulatory patients at local emergency departments between 2004 and 2008; we excluded cases of in-hospital VTE. VTE was confirmed by CT scan or sonography in 1,907 cases: the remainder served as comparators. We recorded demographic data, divided the cases by location (Detroit vs. suburban) and plotted the monthly VTE distributions. Using data from the Environmental Protection Agency, we determined the temporal distribution of different size categories of PM pollution in Detroit. Suburban pollution data was not monitored (presumed negligible). We compared distributions using circular statistics.
Results: Monthly Detroit VTE cases (1,490) exhibited a unimodal peak (mean June 23rd) and differed from both a uniform distribution (P<0.01) and that of the 1,123 non-VTE cases (P<0.02). Levels of 10 μ m diameter PM and 2.5-10 μ m PM exhibited summer peaks versus a winter peak for 2.5 μ m PM. Temporal distribution of Detroit VTE cases differed from that of 2.5 μ m and 2.5-10 μ m PM (P<0.001), but not from 10 μ m PM (P>0.50). In contrast, suburban VTE cases (417) showed no monthly variation (P>0.20).
Conclusions: Our finding of a summer VTE peak in Detroit is in marked contrast to European findings and indicates that low temperature is not a factor in VTE pathogenesis. The close concordance between the 10 µm diameter PM and Detroit VTE distributions, combined with no monthly suburban VTE variation, is consistent with a role for air pollution. Moreover, the divergence of the Detroit VTE and 2.5 µm PM distributions suggests that particle size is important.
- © 2012 by American Heart Association, Inc.