Friday, February 24, 2012

Pulmonary Embolism and Atrial Fibrillation

Motivation: Last November, I admitted a patient with dyspnea.  He had new onset atrial fibrillation, and discussion in the morning predictably revolved around causes of atrial fibrillation.  One of the causes mentioned was pulmonary embolism (the "green book" lists it under pulmonary triggers).  I find PE to be a strange trigger though.  I associate atrial fibrillation with processes that chronically stretch the atria resulting in a dilated atrium, but PE is an acute process.  Searching the literature at that time did not reveal any evidence for or against assoication of atrial fibrillation with PE.  Recently, when revisiting the question, I found an article by a European group published in December of 2011 addressing this issue.

Paper: Gex, G., Righini, M., Gal, G.L., et. al. "Is atrial fibrillation associated with pulmonary embolism?" J. of Thrombosis and Haemostasis (2011) [e-pub ahead of print]

Methods: To analyze association, the authors pooled together data from two large trials (CT-EP3 and CT-EP4) investigating PE diagnostic strategies.  In both studies, patients were included if they presented with clinical suspicion of PE defined largely as acute dyspnea or chest pain without obvious cause.  All patients had EKG at baseline with confirmation of PE diagnosis by CT.

Results:
Cohort: Total of 2,449 patients were analyzed.  The mean age was 59.9 years and 43.7% were males.  Of this group with clinical suspicion of PE, 22.6% had PE confirmed by CT.

Association with AF: Atrial fibrillation was detected at baseline in 133 patients.  Prevalence of PE was 22.8% (n=519) in patients without atrial fibrillation but 18.8% (n=25) in patients with atrial fibrillation (p = 0.28).  To adjust for differences in comorbidities between patients with AF and those without AF, the authors next created an adjusted model accounting for age, sex, CHF, COPD, stroke, renal clearance, and neoplasm.  After adjustment, there was no increased association with AF and PE (OR of 0.68, 0.42-1.11, p = 0.122).   AF failed to be associated with PE even in patient less than age 65 (OR 0.86, 0.35-2.12) or with no heart failure (OR 0.63, 0.37-1.06).  Authors attempted to separate association of AF with presenting symptoms (dyspnea or chest pain), but the numbers were too small to make meaningful conclusions.

Discussion: This paper establishes that in patients presenting with acute dyspnea or chest pain, finding atrial fibrillation on EKG does not meaningfully change the likelihood of PE.  If anything, finding atrial fibrillation had a trend towards reducing the likelihood of PE (adjusted OR of 0.68, 0.42-1.11).  This effect is likely from similar presenting symptoms of atrial fibrillations and PE.  While this paper in part answers my initial question of the utility of using atrial fibrillation to suspect PE, there are some important limitations.  First, the paper only examined patients presenting with acute dyspnea or chest pain.  The paper did not examine patients with new onset AF and ask how many had PE.  Therefore, the results cannot be extended to patients with atrial fibrillation without obvious symptoms though presumably the incidence of PE would be even lower.  Also, given the structure of the paper in which PE had to be a likely diagnosis, patients with AF with RVR and dyspnea were likely excluded.  Incidence of PE in this population is also unclear.  Depsite these limitations, I think that this paper provides important insights into the limited utility of considering AF in the diagnosis of PE.

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