Kryptós … it’s the Greek word for hidden, and when it was imported to English as “crypto,” it became a combining word, stuck onto the front of other words to mean hidden this or hidden that. Cryptogenic stroke is an example. The medical term refers to strokes with hidden sources, which makes treating them an imprecise and frustrating task, and unfortunately, a third of all strokes have no clearly identified source. That sleuthing task becomes even more difficult when a stroke is fleeting, lasting a minute or less and leaving minimal or no damage. These types of strokes are important to diagnose because they can often indicate conditions exist for the formation of a larger stroke in the future.

Many strokes originate with atrial fibrillation—an out-of-synch beating of the heart caused by irregular electrical signals. The abnormal rhythm leads to blood pooling in the heart and when blood pools, clots can form. Physicians always inspect a stroke patient’s heart rhythm looking for clues. But a-fib itself can be transient—appearing briefly, and then not again for days, weeks or months, explains Dr. Kersti Bruining, a neurologist who specializes in in-patient care. How can a doctor know if a-fib is the source of a cryptogenic stroke if the irregular beat is so ephemeral, so sporadic?

Physicians have a new tool that can uncover the hidden nature of a-fib-based strokes. Called Linq, the tiny implantable device (1 1/2 by 1/4 by 1/8 inches) is inserted under the skin just below the collarbone, and it continuously monitors the patient’s heart rhythm. Each night, the data from the day’s recording is automatically uploaded via a little device near the bed to a cloud-based storage system. A computer analyzes the rhythm, looking for irregularities. If the computer spots a problem, the medical team is notified, and the patient is treated for stroke prevention.

“The median time for detecting a-fib is 84 days,” Bruining says, meaning half the patients take even longer than that to have their a-fib reappear. External monitors, with sticky electrode attachments, are also available and have been for some time, but “a New England Journal of Medicine study showed that the new implanted monitor detected seven times more instances of a-fib than the standard monitors,” Bruining says. Since March 2017, when her team began the monitoring, several patients have uncovered a-fib as the source of their strokes, removing the “crypto” from their diagnosis, and allowing targeted and precise treatment to begin.

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