The illustration shows a normal heart rhythm on the left with a blue background, and an abnormal heart rhythm on the right with a red background.

Undetected atrial fibrillation was the cause of many strokes. Nine out of ten had no symptoms

A Norwegian-led study found that atrial fibrillation was the hidden cause of stroke in many patients. Long-term heart rhythm monitoring of patients can prevent recurrent strokes in this group.

Many people who have a stroke are at risk of having a recurrence. Finding the cause of the first stroke is therefore important in order to prevent a second one.

However, using current practice, doctors cannot determine the cause in one in three people who have a stroke. These are called cryptogenic strokes.

Now a new, Norwegian-led study shows that atrial fibrillation was probably the cause in three out of ten of these patients.

The study was published in the European Stroke Journal this week.

Three of ten had atrial fibrillation

Doctors and researchers at Oslo University Hospital, UiO, and Østfold Hospital have now closely monitored such patients.

The Norwegian-led study included 260 patients who had strokes of unclear cause. The participants came from hospitals in all of Norway’s health regions, as well as hospitals in Denmark and Sweden.

The participants' heart rhythm was continuously monitored for 12 months.

In addition, they were followed up in hospital and their blood was analysed for biomarkers.

Heart rate monitoring revealed atrial fibrillation in three of ten of the participants, the probable underlying cause of the stroke.

One out of every four strokes affects individuals who have had a stroke previously.

“People with atrial fibrillation bear the greatest risk,” says Anne Hege Aamodt, senior consultant in the Department of Neurology at Oslo University Hospital (OUS), Rikshospitalet.

“In three out of ten stroke patients without a clear cause, we discovered atrial fibrillation to be the likely cause,” says Anne Hege Aamodt, senior consultant at OUS.

Nine out of ten had no symptoms

“More than nine out of ten of the participating study patients had no symptoms of atrial fibrillation,” says Aamodt.

Aamodt believes this finding indicates a need to record the heart rhythm over a longer period of time in this patient group.

She is the project manager in the Nordic atrial fibrillation and stroke study, NOR-FIB, which is a collaborative project with Nordic colleagues.

Discovered early

In 86 per cent of the cases, heart rhythm disturbances were detected soon after the start of monitoring.

On average, atrial fibrillation was detected after six to seven weeks.

Almost all the participants were given other drugs to prevent another stroke after the discovery. They received anticoagulant drugs instead of antiplatelet drugs, which provide better stroke prevention for patients with atrial fibrillation.

This is atrial fibrillation

  • Atrial fibrillation is not a life-threatening disease, but it increases the risk of stroke and heart failure.
  • Normally, our heartbeat is controlled by the heart's electrical system, which ensures a regular rhythm. In some people, this normal heart rhythm is "overridden" by other rhythms.
  • Atrial fibrillation is the most common type of abnormal heart rhythms. The condition causes rapid and irregular electrical activity in the atria of the heart, which causes them to contract rapidly and irregularly.
  • Atrial fibrillation affects middle-aged and elderly people in the vast majority of cases.
  • The exception is younger/middle-aged people who do highly intensive training. Acute alcohol poisoning ("binge drinking") can also cause fibrillation in very young people.
  • The condition occurs frequently. Among people over age 75, 10 percent have atrial fibrillation.
  • However, a good number of individuals who develop atrial fibrillation experience no symptoms, especially people who develop atrial fibrillation later in life.
  • Drug treatment is the most common way to manage atrial fibrillation.

Source: Norway’s Association for Heart and Lung Disease / LHL

Need to improve heart rhythm recording

Aamodt thinks better access to heart rhythm recording is needed for this group in clinical practice.

“More people would then discover the cause of their stroke and be able to receive the best preventive treatment,” she says.

One hospital in Norway is already doing it, and several more are planning to introduce the use of so-called insertable cardiac monitors (ICM) in stroke units, based on these results.

“It’s cheaper to prevent serious illness than to treat it. Stroke costs society close to a billion euros per year. So if we can do a better job at preventing it, we’ll be saving a lot,” Aamodt says.

Implantable monitor

ICM monitoring is done by having a heart monitor surgically implanted under the skin in the chest.

Neurologists and other doctors in the stroke units carried out the implantation and followed up on the patients.

“This study is important news for about 10 000 Norwegians who are affected by stroke every year,” says Aamodt.

Older and with more risk factors

A number of conditions were characteristic of patients diagnosed with atrial fibrillation.

Their average age of 72.6 years was higher than the entire group average of 62 years.

Patients with atrial fibrillation had more severe strokes and more frequent high blood pressure and unfavourable cholesterol levels than patients without atrial fibrillation.

The study was led by Anne Hege Aamodt and cardiologist Dan Atar. Neurologists Barbara Ratajczak-Tretel and Anna Tancin Lambert at Sykehuset Østfold Kalnes, as well as PhD candidates at the University of Oslo, were also key contributors to carrying out the study.


B. Ratajczak-Tretel, AH Aamodt Atrial fibrillation in cryptogenic stroke and TIA patients in the Nordic atrial fibrillation and stroke The Nordic Atrial Fibrillation and Stroke (NOR-FIB) Study: Main results. European Stroke Journal, 2022.


Read the Norwegian version of this article at


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