The quivering-heart syndrome known as atrial fibrillation can cause deadly strokes, but it can be difficult to even confirm someone has it.

On Friday, Medtronic announced the results of a clinical study of a blockbuster device called Reveal that detected previously undiagnosed atrial fibrillation (AF) in a large proportion of high-risk patients. Proponents say the results show the Reveal implantable device can prevent deadly ischemic strokes.

Detecting atrial fibrillation using "insertable cardiac monitors in a high-risk population combined with appropriate AF treatment could prevent many initial strokes," said a statement from New York cardiologist Dr. James Reiffel, who was Medtronic's principal investigator for the REVEAL AF study. Results of the study were presented Friday morning at the annual conference of the Heart Rhythm Society in Chicago.

The Medtronic study followed the experiences of 385 patients between the ages of 60 and 80 who were at high risk for atrial fibrillation but had never been diagnosed with it. Each person got a Reveal XT or Reveal Linq device. After 18 months, the devices positively detected atrial fibrillation in 29 percent of the group. The detection rate climbed to 40 percent after two years, according to data presented at the conference.

About half the patients in the REVEAL AF study who were diagnosed with atrial fibrillation using a Reveal device ended up being prescribed anticoagulation drugs to cut their risk of blood-clot formation.

The Reveal is a minimally invasive insertable cardiac monitor (ICM) about one-third of the size of a AAA battery. The device monitors a person's heartbeat and then sends the data wirelessly to a bedside monitor that communicates with Medtronic's CareLink network.

Atrial fibrillation occurs when the upper chambers of the heart flutter chaotically instead of beating properly, allowing blood to pool in the heart and potentially form clots. Such clots can travel through the bloodstream and end up in the brain, where they may block blood flow and cause paralysis or death.

About 1 in 6 strokes can be attributed to atrial fibrillation. But as many as 1 in 4 of the estimated 12 million ischemic strokes have no identified cause and are labeled "cryptogenic" strokes, according to an independent study published in the New England Journal of Medicine (NEJM).

Doctors say it's important to positively diagnose atrial fibrillation because it affects treatment decisions.

People at risk for atrial fibrillation are typically prescribed antiplatelet drugs, which reduce the risk of stroke by 22 percent compared to a placebo. But once fibrillation is identified, doctors will often move patients onto anticoagulation drugs, which reduce the risk of stroke by up to 64 percent compared to antiplatelet drugs, according to the 2014 report in NEJM.

"The prevention of stroke related to atrial fibrillation is a global public health priority," the NEJM report said. "Strokes due to atrial fibrillation are common and frequently devastating (70 to 80 percent of patients die or become disabled), yet they are largely preventable with anticoagulant therapy."

The Reveal device generates about $500 million in annual revenue for Medtronic. The company told investors in 2015 that the sales figure could double within five years as the device becomes more widely used in atrial fibrillation and cryptogenic stroke cases.

The Reveal Linq device is FDA-cleared for patients at increased risk for cardiac arrhythmias, and those who have symptoms — such as dizziness, fainting and chest pain — that may suggest a heart problem. The latest iteration of the device is called the Reveal Linq ICM with TruRhythm Detection.

Joe Carlson • 612-673-4779