A 79-Year-Old Woman With a Pacemaker and High Atrial Rates

Jeff S. Healey, MD, MSc, FRCPC; Jonathan P. Piccini, MD, MHS, FACC; Christian T. Ruff, MD, MPH


March 22, 2019

Editorial Collaboration

Medscape &


Atrial fibrillation, detected by surface-ECG methods, is associated with a 4- to 5-fold increase in the risk for stroke,[1] and treatment with oral anticoagulation reduces this risk by more than 60%.[2,3] However, most patients with atrial fibrillation have a high burden of the arrhythmia, and many are in atrial fibrillation all or most of the time.

In the 1990s, implanted pacemakers were developed that could detect and document atrial arrhythmias, even if they were asymptomatic and lasted only a few seconds or minutes. Such episodes were termed "atrial high-rate episodes."[4] In many cases, these detections were not actual atrial arrhythmias at all but were the result of noise or other "false-positive" detections (Figure 2).

Figure 2.


Physicians questioned their significance, and it was uncommon that they led to any form of treatment. Two large cohort studies then evaluated the prevalence of atrial high-rate events and their relationship with stroke.[5,6] These studies both found that atrial high-rate episodes occurred in 30%-40% of patients with pacemakers who did not have prior clinical atrial fibrillation. The studies also concluded that the presence of atrial high-rate episodes was associated with a 2- to 2.5-fold increase in the risk for stroke. One of the studies conducted a manual review and adjudication of all episodes to determine that they were in fact atrial arrhythmias, which it described with the term subclinical atrial fibrillation.[6]


Although subclinical atrial fibrillation was associated with an increased risk for stroke in two studies,[5,6] the relative risk for stroke was only half of that seen in studies of ECG-detected atrial fibrillation,[1] with an absolute risk that was also substantially lower. This raised questions about the benefits of treating such patients with an oral anticoagulant.[7,8] As a result, many patients with subclinical atrial fibrillation continue to be managed without oral anticoagulation.[9] The use of oral anticoagulation must balance the potential for stroke reduction against the risk of bleeding due to anticoagulation. Most patients with pacemakers are in their mid-70s or older, and the risk of bleeding with all antithrombotic therapies increases in those older than 75 years; it is also higher among individuals with more cardiovascular risk factors (ie, a higher CHA2DS2-VASc score).[10,11] Many different mechanisms are responsible for strokes in older individuals, not all of which can be prevented with oral anticoagulation.[12] Even among anticoagulated patients with subclinical atrial fibrillation, the background rate of stroke is around 1% per year.[3]


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