Atrial fibrillation is an extremely common arrhythmia that can affect as many as 20% of adults at one point in their lives. But how much atrial fibrillation is significant enough to cause problems? This question was raised by a recent report published at the Heart Rhythm Society convention in May 2018.

Although atrial fibrillation can cause a variety of symptoms such as palpitations, shortness of breath, lightheadedness, and exercise intolerance, it frequently occurs without any noticeable symptoms. It is often picked up incidentally on an ECG or a heart monitor. In many patients, atrial fibrillation is associated with an increased risk of stroke, especially in those over the age of 65 or in patients with other medical problems such as hypertension, diabetes, and vascular disease. In those patients with a potentially increased risk, physicians will often recommend anticoagulation (blood thinners) to help prevent a stroke. However, how much atrial fibrillation should be considered “significant” enough to start blood thinners (like warfarin or the “newer” oral anticoagulants), which are potent medications that could cause bleeding complications?

The notion of a “significant” amount of AF has varied over the years because no one definition is considered standard. Many different studies have looked at different durations to assess stroke risk. Some studies have suggested that as little as five minutes of atrial fibrillation is associated with an increase in stroke rates, whereas other studies suggest that it may require many hours of atrial fibrillation before the risk of stroke becomes a problem. Some studies, particularly those involving catheter ablation, consider anything more than 30 seconds to be a significant amount of AF. However, using 30 seconds as a cut off might lead to overdiagnosis and unnecessary treatment in some patients.

The study mentioned above analyzed 615 patients and assessed whether 30 seconds of atrial fibrillation predicts a significant AF “burden,” with the idea that the more time patients spend in atrial fibrillation, the more likely they are to have a stroke. It turns out that anything less than two minutes of atrial fibrillation seen on a monitor appears to be too sensitive since it is associated with a total AF burden of only 0.1%. They found that in their patients the episode had to be at least 3.8 hours before the total burden of atrial fibrillation reached 1% or more.

Although this was just one study, it underscores the importance of assessing the total burden of atrial fibrillation. Just a short burst of irregular palpitations associated with a minute or two of arrhythmia on a monitor is probably not enough to warrant starting blood thinners, even in patients who would otherwise be at increased risk of stroke. In those patients who have a suspected problem with significant atrial fibrillation, an implantable cardiac monitor is the only one that is nearly 100% accurate in diagnosing AF, and since they have a 2-3 year battery life they are used to monitor patients long-term.

You should speak with your physician at length before agreeing to start any blood thinner for atrial fibrillation. Discuss the reason, risks, and benefits of this serious medication and make sure that the indication for anticoagulation is appropriate. If you have any questions or other concerns, you should definitely discuss it with a cardiologist or a heart rhythm specialist (cardiac electrophysiologist).

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