Does Atrial Fibrillation Cause Pulmonary Embolism?
No, atrial fibrillation does not cause pulmonary embolism. AF causes left atrial thrombus formation that leads to systemic arterial emboli (particularly stroke), not right-sided thrombi that would cause PE 1.
The Directional Mismatch
The fundamental reason AF doesn't cause PE relates to cardiac anatomy and blood flow direction:
- AF creates left atrial stasis and thrombus formation in the left atrial appendage, which when embolized, travels through the left ventricle into the systemic arterial circulation, causing stroke and other arterial emboli 2, 1
- PE requires right-sided thrombi that embolize through the right ventricle into the pulmonary arterial circulation 1
- The pathophysiology of AF involves left atrial/left atrial appendage dysfunction with reduced flow velocities, spontaneous echo contrast, and thrombus formation—all on the left side of the heart 2
The Evidence Base
Large-scale population data confirms no causal relationship:
- A Swedish registry study of 1.4 million residents found that after adjustment for age and comorbidities, AF without anticoagulation was not associated with increased PE risk (HR 1.03, CI 0.94-1.13) 3
- The higher crude rates of PE observed in AF patients (2.91 vs 1.09 per 1000 person-years) were fully explained by the 25-year age difference and greater comorbidity burden, not by AF itself 3
The Reverse Relationship: PE Can Cause AF
Importantly, the causal arrow points in the opposite direction:
- Pulmonary embolism is listed as an acute precipitant of AF, along with surgery, myocardial infarction, and other acute medical conditions 2, 4
- PE causes right heart strain and atrial stretch, which can trigger AF as a secondary phenomenon 2
Clinical Implications for Anticoagulation Decisions
Use separate risk stratification for each condition:
- For stroke prevention in AF: Use CHA₂DS₂-VASc scoring and guideline-directed anticoagulation based on AF-specific stroke risk 1
- For PE prevention: Base decisions on traditional VTE risk factors (immobility, malignancy, surgery, thrombophilia), not on AF diagnosis 1
- The presence of AF should not influence your assessment of PE risk or prophylaxis decisions 1, 3
Common Pitfall to Avoid
Do not assume that because AF patients are at high risk for arterial thromboembolism (stroke), they are also at high risk for venous thromboembolism (PE). These are distinct pathophysiologic processes requiring separate risk assessment 1, 3.