LINQ™ing Cardiology and Neurology to Diagnose and Treat Cryptogenic Stroke

Stroke is the fifth leading cause of death in the U.S.¹ and also accounts for significant long-term disability in many of its survivors.² It is estimated that approximately 800,000 strokes occur each year in the U.S.³ with about 20% as recurrent strokes in previous victims.⁴

Most strokes result from ischemic events, depriving the brain of adequate oxygen and resulting in brain tissue damage. Causes range from vascular disease in the major blood vessels or intracranial branches to embolic events as a result of thrombus formation. It is important to find the cause of a stroke to help reduce the risk of recurrence. In as many of 25% to 40% of cases, the cause remains unclear on completion of the initial evaluation.⁵ This type of stroke is termed “cryptogenic stroke.”    

Currently, there are serious gaps in clinical knowledge regarding the treatment of cryptogenic stroke that leave the patient at risk for another stroke. At OhioHealth Riverside Methodist Hospital, we have developed a stroke care team approach that pairs members of the electrophysiology and neurology teams together to diagnose and treat cryptogenic stroke. 

Traditionally, stroke evaluation included carotid Doppler studies, CT angiography, or magnetic resonance angiography (MRA) to assess for vascular disease. Culprit vessels were addressed with carotid endarterectomy or, more recently, with carotid stenting. Those patients with cardiac risk factors might have a cardiac echo or even a transesophageal echocardiogram (TEE) performed to look for structural heart abnormalities that predisposed them to embolic risk or the presence of an actual thrombus. Cardiac telemetry combined with a 24-hour Holter monitor or a month-long event monitor may have been used to look for arrhythmias, specifically to look for atrial fibrillation (AF) as a potential cause for stroke.

However, recent studies indicate even cardiac event monitors placed for 30 days yield only 6% of patients identified as having atrial fibrillation.⁶

One of the most common cardiac conditions, atrial fibrillation, significantly contributes to the risk of thrombus formation. Patients with atrial fibrillation have a five-fold increase in embolic stroke when compared to the general population.⁷ Yet due to the paroxysmal nature of this arrhythmia, it often goes undetected, despite its presence in an estimated three million Americans.⁸

To help address the issue of underdetection of atrial fibrillation, OhioHealth Heart and Vascular Physicians began partnering with our neurology colleagues. We were fortunate to be able to jointly participate in Medtronic’s CRYSTAL AF trial as one of 45 sites from the U.S. and Europe. The study evaluated an insertable cardiac monitor (ICM) for long-term arrhythmia monitoring in patients with cryptogenic stroke and compared it to standard monitoring. The ICMs used in the study were small, implantable devices capable of continuously monitoring a patient’s heart rhythm for up to three years and transmitting that information remotely to practitioners. The initial device, the Reveal® ICM, the size of a small flash drive, was placed in a left prepectoral location via a minor surgical procedure. The newest version, Reveal LINQ™ ICM, smaller than the size of an AAA battery, can be inserted under the skin with only a small puncture and no actual surgery.  The miniaturization of the device eased the implant process and new remote monitoring technology has more rapidly alerted us to abnormal rhythms.

The CRYSTAL AF study brought our cardiology and neurology services to work together in order to better determine the cause of cryptogenic stroke in our patient population. CRYSTAL AF showed us that the root cause of stroke in our patients could be attributed to atrial fibrillation far more often than was previously known. The results of the CRYSTAL AF study indicated that the incidence of atrial fibrillation was 8.9% at six months, 12.4% at one year, and 30% at 3 years. The success of atrial fibrillation detection found in the CRYSTAL AF study invigorated our efforts to work collaboratively in detecting and treating atrial fibrillation as a cause of cryptogenic stroke. 

Regular meetings were scheduled to coordinate the interdisciplinary efforts and organize the workflow process. The team members included administrators, stroke neurologists, EP physicians, nurse practitioners from the neurology and electrophysiology service, and members of the EP lab team and Device Clinic staff. We developed protocols and workflow processes (Figure 1) for both inpatients and outpatients, which continually evolved as our experience and patient volumes grew. We even involved a process excellence team to assist in optimizing our efforts. Our goal was to identify appropriate candidates as well as streamline the process for implant, follow-up, and education of the patient and family. 

Working collaboratively was crucial to the success and growth of the program. Proper screening of candidates required input from neurology and cardiology. We relied heavily on our physicians and nurse practitioners for this, as well as for the consent and educational portions of the process. Our EP lab staff and nursing personnel supply additional education specific to the Reveal LINQ ICM and its remote transmitter. The high volume of recordings received requires experienced and dedicated staff in our Device Clinics for arrhythmia screening. Accurate and timely interpretation comes from our EP physicians, who then relay that information to our stroke team and on to the primary care physicians. Neurology input is critical in determining the safety and timing of anticoagulation following a recent stroke. Primary care physicians are always involved in the anticoagulation decision as well as in determining if additional arrhythmia treatment may be needed from electrophysiologists.

Our experience, now with over 600 patients being followed at OhioHealth, improves upon that of CRYSTAL AF results with an even higher yield. We have found atrial fibrillation in 12.2% of patients with the Reveal LINQ ICM at 6 months (CRYSTAL AF = 8.9%) and our median time to diagnosis of atrial fibrillation is 58 days, compared to 41 days in the CRYSTAL AF study.

By working together, we have been able to streamline a process that crosses departmental lines and involves the many members of this interdisciplinary team to achieve a better patient experience. The end result is early and accurate diagnosis of cryptogenic stroke and targeted treatment to help decrease the incidence of recurrent stroke.

References

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2. Mozaffarian D, Benjamin EJ, Go AS, et al. Heart disease and stroke statistics—2015 update: a report from the American Heart Association. Circulation. 2015;131:e29-322.
3. Heart Disease and Stroke Statistics, 2014 Update. American Heart Association. Available online at https://www.heart.org/HEARTORG/General/Heart-and-Stroke-Association Statistics_UCM_319064_SubHomePage.jsp. Accessed November 25, 2014.
4. Lloyd-Jones D, Adams R, Carnethon M, et al. Heart disease and stroke statistics—2009 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation. 2009;119:e21-e181.
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6. Sanna T, Diener H, Passman RS, et al. Cryptogenic stroke and underlying atrial fibrillation. N Engl J Med. 2014;370:2478-2486.
7. Wolf PA, Abbott RD, Kannel WB. Atrial fibrillation as an independent risk factor for stroke: the Framingham Study. Stroke. 1991;22;983-988.
8. Naccarelli GV, Varker H, Lin J, Schulman KL. Increasing prevalence of atrial fibrillation and flutter in the United States. Am J Cardiol. 2009;104:1534-1539.