"Our understanding of the risk factors and complications of atrial fibrillation (AF) is based mostly on studies that have evaluated AF in a binary fashion (present or absent) and have not investigated AF burden….a review of recent evidence suggests that higher AF burden is associated with higher risk of stroke. It is unclear whether the risk increases continuously or whether a threshold exists; if a threshold exists, it has not been defined."1

— 2018 AHA Scientific Statement, "Atrial Fibrillation Burden: Moving Beyond Atrial Fibrillation as a Binary Entity"

Matthew Solomon, MD, PhD, senior author on KP-RHYTHM describes below the study results and its real-world clinical implications.

Accurately Assessing Stroke Risk with 14-day Continuous Monitoring

The KP-RHYTHM* study found that an atrial fibrillation (AF) burden of 11.4 percent or higher was associated with a more than 3-fold increased risk of stroke or thromboembolic (TE) events in patients off anticoagulants, independent of known stroke risk factors.

The 5-year retrospective study using the continuous Zio patch monitor worn for up to 14 days determined an association between AF burden — the percentage of analyzable monitoring time spent in AF — and the risk of ischemic stroke or arterial thromboembolism in adults with paroxysmal atrial fibrillation (PAF).

Significantly, the 3-fold increase in stroke and TE events was found:

  • At a threshold of AF burden of 11.36 percent or higher (Tertile 3)
  • Independent of the duration of the longest AF episode
  • Independent of the standard CHA2DS2-VASc and ATRIA stroke risk scores
  • Independent of other subgroup characteristics including, age, sex, chronic kidney disease (CKD), hypertension and stroke history, which demonstrated no significant interactions

"Characterizing the burden of atrial fibrillation in patients with paroxysmal atrial fibrillation could assist patients and physicians in having a more informed, shared decision-making discussion about stroke prevention strategies."2

— KP-RHYTHM

Rethinking AF Burden

Recently, the American Heart Association (AHA) released a scientific statement, "Atrial Fibrillation Burden: Moving Beyond Atrial Fibrillation as a Binary Entity," further supporting the case to emphasize AF burden as an important stroke risk indicator.

The results of the KP-RHYTHM study, as well as AHA's scientific statement, point to AF burden as a potentially more precise method of assessing stroke risk than AF duration alone in patients with PAF.

“A review of recent evidence suggests that higher AF burden is associated with higher risk of stroke. It is unclear whether the risk increases continuously or whether a threshold exists; if a threshold exists, it has not been defined."1

— 2018 AHA Scientific Statement

KP-RHYTHM suggests that a threshold of AF burden for stroke risk likely exists. Further definition may be beneficial for guiding discussion on prevention strategies.

Zio by iRhythm enabled the KP-RHYTHM investigators to assess patients using uninterrupted, continuous monitoring for up to 14 days. Zio delivered a comprehensive view of True AF Burden™, using Intelligent Bridging™, the ability to bridge AF episodes that may be separated by noise or artifact. While more research is warranted to further explore these implications, the future of AF detection and stroke risk management will be driven by 14-day continuous monitors such as Zio by iRhythm.

Study Methodology

From October 2011 to October 2016, 1,965 adults not taking anticoagulants were eligible for the study and were monitored for PAF or atrial flutter for up to 14 days using the Zio patch.

Patients were divided into three groups (tertiles) and percentage of AF burden was noted.

Tertile 1

Patients with the lowest burden
(.01 to 2.03 percent)

Tertile 2

Patients with an AF burden between
2.05 and 11.28 percent

Tertile 3

Patients with the highest AF burden
(11.36 percent or higher)

A nearly 3-fold increase in risk for stroke or TE event was observed for patients in tertile 3 compared to tertile one and two combined.

See the full KP-RHYTHM study here.

For the entire AHA scientific statement, please visit ahajournals.org

*Kaiser Permanente Real-world Heart Monitoring StrategY Evaluation, Treatment Patterns and Health Metrics in Atrial Fibrillation

References
1. Chen L., et al. Atrial Fibrillation Burden: Moving Beyond Atrial Fibrillation as a Binary Entity: A Scientific Statement From the American Heart Association. Circulation, 2018.
2. Go A., et al. Association of Burden of Atrial Fibrillation With Risk of Ischemic Stroke in Adults With Paroxysmal Atrial Fibrillation. JAMA Cardiology 2018.

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