What is atrial fibrillation?

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Atrial fibrillation, A-Fib, or AF, is the most common type of arrhythmia. During an arrhythmia, the heart can beat too fast (300bpm), too slow, or with an irregular rhythm. In AF, “blood pools” in the atria and is not pumped completely into the heart's two lower chambers, called the ventricles. As a result, the heart's ventricles don't work together as they should. These “blood pools” form “blood clots”, which travel out of the heart and cause cardio embolic strokes. Both persistent and paroxysmal (intermittent) AF are predictors of first and recurrent stroke.

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How Does AF relate to stroke?

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AF represents 50% of cardioembolic strokes and 10% of all ischemic strokes. 75,000 US strokes per year are attributed to AF. Approximately 25% of patients with AF have “intermittent AF” (also known as “paroxysmal” or “occult” AF, see below) that is often asymptomatic and undetected by conventional methods of cardiac monitoring in cases of ischemic stroke (see Appendix B). Stroke patients with AF are at the greatest risk of recurrence. Patients who are initially diagnosed with cryptogenic stroke can be found subsequently to have intermittent AF through longer term cardiac monitoring in many clinical studies         . However, longer term cardiac monitoring is not standard of care in cryptogenic stroke patients, as it is considered “low yield”, not “cost effective” and poor compliance   . The ability of ISCDX to stratify the cryptogenic patients into cardioembolic cause would lead to a “higher yield” and “cost effective” approach to routing these patients into appropriate care to prevent recurrence.

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Paroxysmal and occult atrial fibrillation

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• Standard of care per AHA/ASA guidelines is to cardiac monitor patients for 24 hours while in hospital.

• When AF is persistent or the patient has a history of AF, AF is more readily detected in the evaluation of ischemic stroke. However, while history is a risk factor, it is not a "smoking gun" or same as biological change.

• Additionally, a significant portion of AF is intermittent (not regular) and termed paroxysmal atrial fibrillation (PAF) or occult atrial fibrillation (OAF).

• PAF and OAF are irregular in occurrence, difficult to detect in periodic cardiac monitoring.

• Cardiac monitoring beyond 24 hours is not standard of care.

• Considered to be 'low yield' and expensive to monitor cryptogenic patients.

• Poor patient compliance, once taken off (shower) unlikely to continue.

• PAF and OAF  events, due to their nature, may occur outside the 24 hour, 7 day and 30 day windows.

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Finding AF in cryptogenic changes care per stroke guidelines

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Per AHA Guidelines, the ability to identify cardioembolic patients within the cryptogenic patient populations, would lead to a change in outcomes:

1. Cryptogenic strokes are treated similar to atheroembolic with. The guidelines specifically state to treat cryptogenic stroke with anticoagulation.

2. Cardioembolic patients are typically treated with (if not structural or valve). There are also newer procedures to treat and detect atrial fibrillation, such as:

   1. Newer and safer anticoagulants recently approved by the AHA

   2. Short term/long term cardiac monitoring

   3. Ablation and electrophysiology studies.

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Atrial fibrillation (AF) and cryptogenic cause of stroke

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• AF is associated with a five-fold increase in the risk of ischemic stroke and accounts for 15-20% of all strokes.

• Cause of cryptogenic stroke is difficult to detect, including those that originate in the heart due to AF, PAF, OAF.

• Contributing factors include inconsistent rhythm monitoring results (Low Yield), controversy over ECG data and unclear AF definitions.

• Guideline driven anticoagulation therapy initiated after detection of AF provides an additional 40% risk reduction of stroke as compared to anti-platelet therapy alone.

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1. http://www.medpagetoday.com/resource-center/afib/Diagnosing-PAF-Patients-Cryptogenic-Stroke/a/34328#!

2. How to use implantable loop recorders. Jung W, et al, J Interv Card Electrophysiol. 2011 Dec;32(3):227-32. Epub 2011 Oct 13. PMID: 21993595

3. Atrial fibrillation detected in cryptogenic TIA or stroke. Tayal AH, et al Neurology. 2008 Nov 18;71(21):1696-701. Epub 2008 Sep 24. PMID: 18815386

4. Predictors of paroxysmal AF in cryptogenic strokes detected by long-term cardiac monitoring. Bhatt A, et al Stroke Res Treat. 2011 Feb 22;2011:172074.

5. Cronin EM, et al "Remote monitoring of cardiovascular devices - a time and activity analysis" Heart Rhythm 2012; DOI: 10.1016/j.hrthm.2012.08.002.

6. AHA: New Anticoagulants OK for Stroke Prevention, Todd Neale, Senior Staff Writer, MedPage TodayPublished: August 02, 2012

7. Update on Antithrombotic Therapy, New Anticoagulants, John W. Eikelboom, MBBS; Jeffrey I. Weitz, MD AHA Circulation. 2010; 121: 1523-1532

8. P. A. Wolf, R. D. Abbott, and W. B. Kannel, “Atrial fibrillation as an independent risk factor for stroke: the Framingham Study,” Stroke, vol. 22, no. 8, pp. 983–988, 1991.

9. Hart, et al, “Meta-analysis: antithrombotic therapy to prevent stroke in patients who have non valvular AF”, Annals of Internal Medicine, vol 146, no.12, pp. 857-867, 2007.