Excerpted and adapted from "When the Beat is Off," Stroke Connection January/February 2004 (Last science update April 2014)
Atrial fibrillation (AF or AFib) occurs in an estimated 2.7 million Americans and is the most common type of irregular heartbeat (arrhythmia). AF dramatically increases the risk of stroke, so let’s take some time to understand it.
The heart has four chambers. The bottom two, called the ventricles, are powerful pumps that force blood back into circulation. The upper two, the atria, serve as collecting chambers for the returning blood from the lungs. To contract and pump, the atria and ventricles must receive electrical stimulus. Atrial fibrillation is a condition in which the atria quiver (or fibrillate) instead of fully contracting. As a result of this quivering, only a portion of the atria’s blood is released into the ventricles.
If a blood clot forms in the atria, it can be pumped out of the heart, to the brain, blocking off the blood supply to an artery in the brain, causing a stroke. This type of stroke is called an embolic stroke. Watch an animation of atrial fibrillation(link opens in new window).
Healthy atria contract 60-80 times per minute, but fibrillating atria quiver at 300-400 times per minute.
Essentially, the heart of an AF patient works as if it’s enduring a marathon, even if the patient is relaxing in a chair. Because of the overactive heart, symptoms of AF most commonly include fatigue, lightheadedness, shortness of breath and even fainting. Some atrial fibrillation patients feel a “flopping” or pounding sensation in their chest. Some patients don’t feel a thing.
Risk Factors for Atrial Fibrillation
As with many health conditions, the prevalence of AF increases with age. The most common cause of atrial fibrillation is longstanding, uncontrolled high blood pressure and heart disease. Additionally, atrial fibrillation is the most common complication after heart surgery.
An entire spectrum of seemingly unrelated conditions can send the atria into "overdrive," including:
- Heart valve disease
- Coronary artery disease
- Cardiomyopathy with weakened heart muscle
- Chronic obstructive pulmonary disease (COPD/emphysema or asthma)
- Excessive alcohol consumption
- Cigarette smoking or stimulant use (such as caffeine)
- Periods of extreme stress or fatigue can trigger episodes of AF
- Sleep Apnea
- Heart Failure
Treating Atrial Fibrillation
Avoiding atrial fibrillation and subsequently lowering your stroke risk can be as simple as foregoing your morning cup of coffee. In other words, some AF cases are only as strong as their underlying cause. If hyperthyroidism is the cause of AF, treating the thyroid condition may be enough to make AF go away.
Some medications, such as beta blockers and calcium channel blockers, work to slow the heart rate and may help improve symptoms. However, they do not 'cure' the rhythm abnormality, and patients still require medication to prevent strokes while remaining in atrial fibrillation.
In Terms of Stroke Prevention
Most AF patients have to seek other treatments, primarily anticoagulant therapy (Warfarin) and/or radiofrequency catheter ablation.
Warfarin is a rather high-maintenance drug. It requires monthly blood tests and doctor visits to ensure proper dosage, but Warfarin patients reduce their stroke risk by 65 percent versus patients on no medication. In comparison, patients taking aspirin reduce their risk by 45 percent.
Patients whose heart rates cannot be controlled with drugs (or patients who simply don't want to take drugs) have to take other measures, such as targeted radiofrequency catheter ablation, a non-surgical procedure with a menacing name. For this procedure, an electrical "road map" of the heart is created to pinpoint the abnormal electrical signals. Abnormal heart tissue is then destroyed with heat from radiofrequency energy, disconnecting the tissue from the current.
Radiofrequency energy is also used to destroy an overactive AV node in AV node ablation requiring the implantation of a permanent pacemaker. This procedure only affects the electricity going into the ventricles. Because the ventricles no longer receive rapid signals from the atria, they don't have to work as hard and the symptoms of breathlessness and fatigue go away. Another procedure involves Ablation of the Pulmonary Vein where arrhythmia “triggers” are removed in the pulmonary veins. The ideal candidates for this surgery are younger patients who do not have a lot of other underlying heart disease.
The good news is that with these advances in technology, plus the use of Warfarin, AF patients can reduce their risk of stroke, and lead active, satisfying lives.
For more information about living with AFib, be sure to also visit our website: Heart.org/AFib