McMaster University

McMaster University

Faculty of
Health Sciences

Silent heart flutters confirmed as stroke risk

By Suzanne Morrison
Published: November 15, 2010
Jeff Healey
Dr. Jeff Healey, associate professor in the Department of Medicine in the Michael G. DeGroote School of Medicine

McMaster University researchers have confirmed for the first time that even brief, clinical silent atrial arrhythmias put patients at an increased risk of a stroke.

"Although other studies have suggested a connection, the ASSERT trial is the first to clearly establish this link and show that even a few minutes of atrial arrhythmia is associated with a measurable increase in the risk of stroke”, said cardiologist Dr. Jeff Healey, associate professor in the Department of Medicine in the Michael G. DeGroote School of Medicine and principal investigator for the arrhythmias program at the Population Health Research Institute (PHRI).

Atrial fibrillation, the most common cardiac arrhythmia of an abnormal or irregular heart beat, affects an estimated 250,000 Canadians and six million people worldwide. It results in approximately 32,206 hospitalizations each year in Canada at a cost of $203.6 million to the healthcare system.

Atrial fibrillation is felt to be responsible for 15% of all strokes; however, if atrial fibrillation is detected, treatment with blood thinners such as warfarin or Dabigatran is very effective at reducing the risk of stroke. The problem is that the majority of atrial arrhythmias (including atrial fibrillation) are clinically silent. However; modern, dual-chamber pacemakers have the ability to detect and catalogue even brief episodes of atrial arrhythmias with a high degree of sensitivity.

Healey presented results of the ASSERT study during the clinical sciences special reports session at the American Heart Association’s annual meeting in Chicago on Monday, Nov. 15.

The ASSERT (ASymptomatic AF and Stroke Evaluation in Pacemaker Patients and the AF Reduction Atrial Pacing Trial) study was designed to determine if brief runs of atrial fibrillation detected by pacemakers predicted an increased risk of stroke.

The study enrolled and followed 2,580 pacemaker patients in 136 centres in 23 countries for up to five years, the largest and longest study of its kind. The patients were all 65 years or older and receiving treatment for hypertension. None had previously been diagnosed with atrial fibrillation or were taking Vitamin K antagonists such as warfarin.

Pacemakers detected brief, silent episodes of atrial fibrillation in about one-third (34 per cent) of patients who had no history of irregular heartbeat. Over 85% of these episodes "would have been missed without the pacemaker”, Healey said. The presence of even one of these episodes lasting at least six minutes had the impact of more than doubling the risk of stroke or embolism.

The ASSERT trial suggest that particularly among patients with pacemakers, the proportion of strokes that are associated with atrial fibrillation may be much higher than previously thought.

The study also found that among patients with additional risk factors for stroke such as diabetes, the presence of atrial arrhythmias increased a patient’s annual risk of a stroke or embolism to approximately 2.2 % per year, high enough for doctors to consider therapy with warfarin or other blood thinners.

The study was funded by St. Jude Medical.

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