Atrial Fibrillation
A Heart Rhythm Abnormality Requiring Control and Anticoagulation
Atrial fibrillation is a heart condition that is more common than people may realize. What should individuals with this condition know with regards to management?
Among the various abnormal heart rhythms, atrial fibrillation is one of the most common. About two million people in the United States are affected by this condition. Treatment for atrial fibrillation does exist, but one must understand the condition to manage it in the best way possible.
Normal Electrophysiology
The heart has four chambers: a left and right atrium above a left and right ventricle. During each cardiac cycle, the atria contract before the ventricles. Coordination of these contractions is made possible by an electrical system. The heart has conductive tissue through which electrical impulses travel and stimulation the cardiac muscle.
In the right atrium is the sinus node, the heart's natural pacemaker that constantly sends out electrical signals on its own. These signals travel through the atria, causing them to contract. The impulses also reach the atrioventricular node between the atria and ventricles. An electrical pathway called the bundle of His travels from the AV node and branch off into fibers that stimulate contraction of the ventricles.
The heart actually has additional pacemakers throughout the atria and the ventricles. Normally, they do not fire signals because the sinus node from above is already doing so. However, if the sinus node were to fail, the next pacemaker below can take over. While these electrical foci can act as backup, they are not a perfect substitute for the sinus node.
On an electrocardiogram (EKG), the cardiac cycle in a normal heart is represented as three upright waves: a P wave, a taller peak called the QRS complex, and a third wave called the T wave. By comparing an EKG to this normal pattern, clinicians can detect abnormalities in heart rate and rhythm, including atrial fibrillation.
Rate Control
Atrial fibrillation ("a-fib") is a heart rhythm abnormality in which the atria do not contract well. On an EKG, the cardiac cycle still has a QRS complex and T wave, but a distinct P wave is absent. Instead, the segment before the QRS is typically wavy in an irregular fashion..
There are several causes of atrial fibrillation. Myocardial infarction, high blood pressure, and diseases of the heart valves are some of the cardiovascular causes. Other causes include conditions of high stress (e.g., infection), hyperthyroidism, stimulant drugs, and binge drinking.
The potential problem with atrial fibrillation is an elevated heart rate. Electrical conduction in the atria is erratic and roundabout. If multiple impulses reach the AV node and travel to the ventricles, the result would be a dangerously rapid heart rate. Resulting symptoms include difficulty breathing and the sensation of the irregular heartbeats (palpitations). Initial treatment involves slowing the heart rate with medications that block the AV node, including calcium channel blockers (e.g., diltiazem, verapamil), beta-blockers (e.g., metoprolol), and digoxin.
Rhythm Control
Some cases of rapid atrial fibrillation are temporary and resolve on their own (paroxysmal atrial fibrillation). Others are either persistent until the rhythm is converted back to a normal sinus rhythm with the P-QRS-T pattern (cardioversion) or permanent with no chance for such a measure. Cardioversion can be done with either an electric shock through the chest or with medications that attempt to correct an abnormal rhythm (antiarrhythmics). The result is not 100% guaranteed, but the chance of success is still significant enough to give it a try.
Anticoagulation
For patients with chronic atrial fibrillation, there is another issue to address. A heart with atrial fibrillation does not pump blood into the ventricles as well as before. Blood travels more slowly, providing an opportunity for clotting factors in the blood to easily form clots. A clot in the left atrium can break off and get stuck in another part of the circulatory system. For example, a stroke can result from this clot when it travels to the brain circulation and obstructs blood flow. Patients with chronic atrial fibrillation should regularly take the blood-thinning medication warfarin, the details of which are beyond the scope here.
References
- American College of Cardiology - Guidelines For the Management of Patients With Atrial Fibrillation
- Dubin, Dale. Rapid Interpretation of EKGs. 6th ed. Tampa, FL: Cover Publishing Company, 2000.
- Merck Manual - Atrial Fibrillation
