Excerpted and adapted from "When the Beat is Off," Stroke Connection January/February 2004 (Science update May 2008)
An estimated 15 percent of strokes are a result of untreated atrial fibrillation (AF or AFib), but most people don’t know what AF is – much less know if they have it. AF 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 – approximately five times over the general population.
To the beat of a different drum
The heart has four chambers. The bottom two, called the ventricles, are thick, powerful pumps that force blood back into circulation.
- The upper two, the atria, serve as collecting chambers for the returning blood.
- The muscles of the atria are not thick because the atria only transport the blood to the ventricles next door.
- To contract and pump, the atria and ventricles must receive electrical stimulation.
- In a normal heart, a steady electrical impulse travels from a node in the atrium to the ventricle, signaling their successive contractions.
- Atrial fibrillation is a condition in which the atria quiver (or fibrillate) instead of fully contracting.
- Instead of a steady electrical impulse, a virtual blitzkrieg of electrical energy storms the atria.
- As a result of this quivering, only a portion of the atria’s blood is released into the ventricles.
Think of an atrium as a wet kitchen sponge. A few short squeezes would get only a little water out – even if you squeeze the sponge multiple times. But one hard squeeze (contraction) would empty the sponge more efficiently.
When blood has the opportunity to pool, it also has the opportunity to clot. 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 or some doctors call it a cardioembolic stroke. Watch an animation of atrial fibrillation.
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.
- The AV node serves as a “gatekeeper” for all of the electrical pulses going though the atrium.
- The electrical pulses are delayed at the AV node before they are allowed to move into the ventricles and signal them to contract.
- In AF, the AV node does its best to protect the ventricle from extra electrical impulses, but it can’t stop all of them.
- As a consequence, the ventricle beats more often than it should – giving rise to the noticeable symptoms of breathlessness and fatigue.
Risk Factors for Atrial Fibrillation
As with many health conditions, the prevalence of AF increases with age. According to the Mayo Clinic, fewer than one in every 100 people in their 50s has AF, but about 10 out of every 100 in their 80s experience it. 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." Other contributing factors include:
- Heart valve disease
- Coronary artery disease
- Cardiomyopathy with weakened heart muscle
- Chronic obstructive pulmonary disease (COPD)
- Chronic lung disease
- Excessive alcohol consumption
- Cigarette or stimulant use (such as caffeine)
- Periods of extreme stress or fatigue can trigger episodes of AF
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.
Doctors can use a variety of different medications to help control the heart rate during atrial fibrillation.
"These medications, such as beta blockers and calcium channel blockers, work on the AV node," says Dr. Andrea Russo of University of Pennsylvania Health System. "They 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 is also the most effective for patients with non-valvular AF.
- Warfarin patients reduce their stroke risk by 65 percent versus patients on no medication.
- Patients taking aspirin reduce their risk by 45 percent in comparison.
"Because Warfarin is such an exacting drug, it requires monthly blood tests and doctor visits to ensure proper dosage," says Dr. Russo. "More frequent monitoring may be required during the first few months. Excessive bleeding can occur in patients who suffer injuries, and care must be taken to avoid unnecessary trauma, such as contact sports."
- Other medications may be used to stop atrial fibrillation and return the heart to normal rhythm and maintain it.
- "These medications work directly on the tissue of the atrium," says Dr. Russo.
- "Although they may be reasonably effective in some patients, they need to be started in the hospital on a monitor due to the potential for causing other abnormal heart rhythms is other areas of the heart."
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.
This procedure involves:
- Making an electrical "road map" of the heart.
- Pinpointing the abnormal electrical signals.
- Abnormal heart tissue is then destroyed with heat from radiofrequency energy, disconnecting the tissue from the current.
- This ends the atria's electrical storm and consequent fluttering.
Radiofrequency energy is also used to destroy an overactive AV node in AV node ablation. "This procedure requires implantation of a permanent pacemaker and does not affect the fibrillating atria," says Dr. Russo. "It 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. Even after undergoing this procedure, patients must continue anticoagulant therapies since the atria continue to fibrillate and clots can still form."
A Third and Newer Type of Ablation is Called Pulmonary Vein Ablation
- The goal is to remove the arrhythmia "triggers," which are in the pulmonary veins in some patients, and thus maintain normal heart rhythm.
- This lengthy procedure is an option for patients who have very frequent symptoms despite medications.
- "The ideal candidates," says Dr. Russo, "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.
Read more about the important connection between high blood pressure, atrial fibrillation and stroke.
For more information about living with AFib, be sure to also visit our website: Heart.org/AFib