Two new multicenter studies assessing hundreds of stroke patients clearly show that cryptogenic stroke stroke of seemingly unknown cause is more often provoked by mobile clots (emboli) from the heart to the brain secondary to atrial fibrillation (A-fib) than had been previously thought.
A-fib is an arrhythmia (irregular heartbeat) common in America; indeed, six million of us have it, although many more may suffer from undetected occurrences, as it is often asymptomatic. But the absence of palpitations the most common warning sign does not mean there is no danger. The ineffective contractions of the heart s upper chambers (the atria), the hallmark of A-fib, allows blood to pool or stagnate in those smaller chambers, and clots form. Those clots, when pumped out into the systemic circulation via the arteries, become emboli. When an embolus of the right size travels to a major brain artery and blocks it, the resultant oxygen deprivation causes death of part of the brain: a stroke.
About 500,000 (or more) Americans have an ischemic stroke (caused by arterial blockage rather than hemorrhage/bleeding), and one-fourth of these have no apparent cause: the focus of the new studies. They appear in the current New England Journal of Medicine, and the sum and substance of them indicates that up to one-third of such strokes may be caused by occult A-fib.
The EMBRACE trial, led by Dr. David Gladstone of the University of Toronto, studied 572 stroke patients. One group wore an EKG monitor for 24 hours, the others had extended monitoring for one month. While only 3 percent of the one-day monitors detected A-fib, those who were tracked for 30 days had a 16 percent rate of A-fib.
The other study, CRYSTAL-AF, was led by Dr. Tommaso Sanna of the Catholic University of the Sacred Heart in Rome, Italy. This group assessed heart rhythm in 441 cryptogenic stroke patients at 55 medical centers worldwide. The subjects were divided into two groups, one of which had a monitor implanted under the skin for continuous monitoring over a 30-day period, the others had regular care, which included a 24-hour (Holter) monitor. By the time one year had passed, A-fib had been diagnosed in 12.4 percent of the implanted-monitor group, vs. 2.0 percent of the 24-hour monitored group.
In an editorial in the same NEJM, Dr. Hooman Kamel of the Dept. of Neurology of the Weill-Cornell Medical College in New York had this overview: ...[H]ow should the results of the CRYSTAL AF and EMBRACE trials change practice? The weight of current evidence suggests that subclinical atrial fibrillation is a modifiable risk factor for stroke recurrence, and its presence should be thoroughly ruled out in this high-risk population. Therefore, most patients with cryptogenic stroke or transient ischemic attack should undergo at least several weeks of rhythm monitoring.
ACSH Dr. Gil Ross had this comment: When I was in practice, these patients would often be treated with only aspirin to prevent small clots. Nowadays, we know a lot more about this situation: aspirin alone is inadequate to protect A-fib patients from embolic stroke; even the old standard blood thinner, coumadin, is fraught with peril due to its unpredictable activity and thus its risk of bleeding. There are several newer anticoagulants which are safer, at least as effective, and don t require frequent blood test monitoring. All stroke patients who have no obvious causative factors should get long-term screening for A-fib and be treated with potent anticoagulants to prevent further devastating strokes.