What is the duration of atrial fibrillation (AFib) before the risk of thromboembolism increases?

From the Guidelines

The risk of thromboembolism in atrial fibrillation (AFib) increases after a duration of less than 48 hours, and it is common practice to cardiovert without pre-cardioversion anticoagulation if AFib is of short duration (< 48 h) [ 1 ].

Key Considerations

• The exact duration of AFib necessary for the development of thrombus is not clear [ 1 ]
• The presence of left atrial thrombus on transesophageal echocardiogram (TEE) has been observed in up to 14% of patients with AFib of short duration [ 1 ]
• A Finnish observational study of 5,116 successful cardioversions in 2,481 patients with acute (< 48 h) AFib showed a low incidence of stroke/thromboembolism (0.7%) during the 30 days following cardioversion, even without perioperative anticoagulation [ 1 ]
• The incidence of stroke/thromboembolism is lower with cardioversions performed during anticoagulation (0.1% vs 0.7%) [ 1 ]

Clinical Implications

• The decision regarding peri- and post-cardioversion anticoagulation should be based on the risk of stroke/thromboembolism, even if an individual is presenting for the first time with AFib [ 1 ]
• Patients with uncertainty about the precise time of AFib onset should be managed as if AFib is greater than 48 hours [ 1 ]

From the Research

Duration of Atrial Fibrillation and Thromboembolism Risk

The duration of atrial fibrillation (AFib) before the risk of thromboembolism increases is a complex topic. According to the studies, the risk of thromboembolism associated with AFib is low if the duration is less than 48 hours 2. However, this risk varies widely depending on patient characteristics.

Factors Influencing Thromboembolism Risk

Several factors influence the risk of thromboembolism in patients with AFib, including:

• The magnitude of atrial fibrillation burden, with 5 minutes of AFib in one day being the shortest time shown to independently predict thromboembolic events 3
• Patient characteristics, such as those assessed by the CHA2DS2-VASc score 2
• The presence of coexisting cardiac pathology, which may increase the risk of left atrial thrombus formation 4
• The role of the left atrial appendage, which is the main source of thromboembolism in patients with AFib 5

Burden of Atrial Fibrillation and Thromboembolism Risk

The burden of atrial fibrillation, defined as the percentage of analyzable wear time in AFib or flutter during a monitoring period, is associated with the risk of ischemic stroke or arterial thromboembolism in adults with paroxysmal atrial fibrillation 6. A higher burden of atrial fibrillation is associated with a higher risk of thromboembolism, independent of known stroke risk factors.

Key Findings

Key findings from the studies include:

• The risk of thromboembolism associated with acute cardioversion of patients with AFib of less than 48 hours duration is low, but varies widely depending on patient characteristics 2
• Atrial fibrillation burden of 5 minutes in one day is independently associated with a significantly increased risk of thromboembolic events 3
• The formation of an intracardiac thrombus, and respective embolic potential, is a dynamic process resulting from the interaction of anatomical and functional variables 3
• A greater burden of atrial fibrillation is associated with a higher risk of ischemic stroke independent of known stroke risk factors in adults with paroxysmal atrial fibrillation 6