Features April 2012 Issue

Understand the Stroke Risks Linked to “Silent” Atrial Fibrillation

Asymptomatic episodes of this common arrhythmia can significantly raise your odds of having a stroke.

Atrial fibrillation (AFib) is usually characterized by episodes that are noticeable to the patient, who feels a flutter or racing in his heart. But not all arrhythmias are obvious, and a recent study suggests that “silent” AFib episodes are associated with a 2.5-fold increase in the risk for ischemic stroke. That’s because the chaotic rhythm of a heart in AFib allows blood to pool in the atria (the heart’s upper chambers), which can lead to the formation of a blood clot that can break free of the heart, travel to the brain, and block blood flow in an artery, causing an ischemic stroke.

The study, published in the Jan. 12 issue of the New England Journal of Medicine, found that among patients with pacemakers but no history of AFib episodes, about one third of them experienced device-detected episodes of atrial tachyarrhythmias of at least six minutes in length. An atrial tachyarrhythmia are an umbrella term that covers AFib, atrial flutter and other fast rhythms that start in the atria.

In the study, 2,580 patients were monitored for three months to detect subclinical atrial tachyarrhythmias, defined as episodes with an atrial rate of greater than 90 beats per minute for more than six minutes. The patients were then followed for two and a half years. During those initial three months, 261 patients (10.1 percent) experienced subclinical tachyarrhythmias, and those episodes were strongly associated with higher risks of clinical AFib and of ischemic stroke.

Bruce Wilkoff, MD, Director of Cardiac Pacing & Tachyarrythmia Devices at Cleveland Clinic, says that because “silent” episodes often occur without symptoms they are more commonly documented in pacemaker patients, but they’re not necessarily more common in pacemaker patients.

“There’s nothing necessarily new in this study, but it emphasizes that silent AFib is common and just as risky as non-silent AFib,” Dr. Wilkoff says. Cleveland Clinic cardiologist Walid Saliba, MD agrees, adding that without a pacemaker, AFib-caused strokes can sometimes be misdiagnosed.

“This is a scientific confirmation that in patients who develop a stroke, sometimes it is not clear why the stroke developed, especially if the patient presents in normal rhythm,” he explains. “Since atrial fibrillation can be an episodic paroxismal (suddenly occurring) problem, and if the patient is asymptomatic, the diagnosis of AFib as a risk factor for this patient’s stroke is missed and therefore, appropriate therapy is not instituted. Pacemakers can track the occurrence of atrial fibrillation. This study confirms silent atrial fibrillation (as detected by an implanted pacemaker) can actually explain the occurrence of stroke in these patients.”

Know the Risks
Dr. Saliba adds that the main risk associated with this arrhythmia is an increased risk of stroke, especially in patients who have hypertension, heart failure, diabetes mellitus and/or have prior history of having had a stroke.

In addition to raising the risk of stroke, arrhythmias can lead to conditions including cardiomyopathy and heart failure.

Dr. Wilkoff explains that when the heart beats less efficiently, and if the heart beat is very rapid for a long time, the heart can weaken. The result can be a ventricular heart muscle disease called cardiomyopathy, which in turn can lead to heart failure, shortness of breath and more serious heart rhythms.

Devices and Treatment
A pacemaker works by sending electrical pulses to the heart to keep it in normal rhythm. It can speed up a slow heart rhythm and help control an abnormal or fast rhythm. An ICD primarily uses electrical pulses or shocks to treat life-threatening arrhythmias in the ventricles. People are given ICDs because they are in danger of a condition known as sudden cardiac arrest (SCA), which occurs when the heart stops beating.

While patients with an implanted device have an advantage in detecting and controlling arrhythmias, such technology requires ongoing care and maintenance.

“These patients need to regularly have their pacemaker or ICD checked so that their doctor can detect these atrial fibrillation episodes,” Dr. Wilkoff says. “Other parts of therapy can include anticoagulation medications, drugs to maintain normal rhythm, ablations, cardioversion, and even thyroid medication or CPAP (continuous positive airway pressure) for sleep apnea. The implanted devices help make the diagnosis, but the therapy is developed with respect to the individual patient.”

Lingering Questions
One of the main questions regarding AFib is how much is too much. How many episodes and of what duration should be considered “safe” or should warrant aggressive medical therapy?

If you have risk factors for AFib, but you don’t have an implantable device that could help confirm atrial tachyarrythmias, should you be checked for silent AFib? Most experts agree that if you are asymptomatic, you don’t need to rush out and be evaluated for silent AFib. However, you should have a conversation with your doctor about what you should be doing to manage your condition and what symptoms you should watch out for.