Every year, about 800,000 Americans have a stroke.

Of those, about 200,000 are considered “cryptogenic,” meaning the cause of the stroke is undetermined. Stroke survivors are at an increased risk of recurrent stroke.

People who have been told that their stroke is cryptogenic are particularly vulnerable because they don’t know exactly what to do to try to prevent another one.

Consider the case of Bill Benedict. After careful investigation, doctors couldn’t find the cause of his “mini stroke.”

For Benedict, who was 79 with a personal history of heart disease and a family history of stroke, a “cryptogenic” diagnosis, which simply means doctors weren’t able to determine the cause of his mini stroke, was far from reassuring.

Sure enough, a month later, he had another one. Strike two.

After his second stroke, Benedict’s cardiologist suggested that an underlying cause may be atrial fibrillation, or AF, which is a rapid or irregular heartbeat. AF often has no symptoms and comes and goes. While it can be tricky to diagnose, it’s important because AF increases stroke risk up to five times.

Benedict’s cardiologist recommended using a small, insertable device that could continuously monitor heart rhythms for up to three years, to look for atrial fibrillation.

A few months after getting it, the device detected atrial fibrillation, and Benedict is now managing his AF through medication.

Undiagnosed AF is just one of the potential causes of cryptogenic stroke. Other causes for investigation include patent foramen ovale — a hole between the heart’s chambers — aortic arch atheroma and thrombophilia, a blood clotting disorder.

The American Heart Association/American Stroke Association, with support from Medtronic, launched an initiative to help people like Benedict by elevating the relatively unknown issue of cryptogenic stroke among health care professionals, patients and their loved ones.

For free educational resources about cryptogenic stroke, including a patient guide, visit

or call (888) 4-STROKE.