Dr. Raymond Dong, cardiologist
Atrial fibrillation is one of the most common cardiac dysrhythmias. It can be described as an irregularly irregular heartbeat. This means that the spacing or time between consecutive beats is constantly changing. Patients can have rapid heart rates or relatively slow heart rates, and symptoms are often dependent on the overall heart rate.
Patients may present with palpitations (or increased awareness of the heart beat), increased shortness of breath or fatigue with exertion. In some cases, the patient may feel lightheaded or experience chest discomfort. Many patients do not have any symptoms at all. The most reliable way to diagnose this rhythm is by 12-lead electrocardiogram. Patients will often undergo echocardiography (or cardiac ultrasound) to determine if there is any cardiac enlargement, myocardial dysfunction, or heart valve problem (too loose and leaking, or too narrow and tight). A history of chest pain associated with rapid atrial fibrillation may lead to diagnostic tests looking for blocked coronary arteries.
The medical conditions that are commonly associated with an increased chance of developing this rhythm are hypertension (high blood pressure), coronary artery disease, and valvular heart disease. Excessive alcohol consumption or an overactive thyroid gland can also lead to atrial fibrillation. The incidence of atrial fibrillation increases with age. In addition, there are some patients in whom no specific cause for this dysrhythmia can be found.
The major consequence of atrial fibrillation is that it may lead to an increase risk of stroke. When the left upper chamber of the heart is fibrillating, the blood in this chamber is more stagnant than usual, and a blood clot may develop within this part of the heart. If the clot becomes dislodged and travels to the lower chamber, it can then embolize to the brain. Patients are usually assessed for their risk of stroke by looking at specific risk factors, such as their age (especially if greater than 75 years of age), the presence or absence of high blood pressure, diabetes, a recent history of heart failure, or a past history of stroke or transient ischemic attack. The more of these features in any one individual patient, the greater the risk of stroke, which may range from 2-3% per year to as high as 15-16% per year. The strokes that occur as a result of atrial fibrillation tend to be more severe and debilitating, and are often more fatal.
The current recommendations for stroke prevention revolve around the use of anticoagulants (or blood thinners) in high-risk patients. Younger patients, with fewer risk factors for developing stroke may be managed with Aspirin alone. Decades of research have involved clinical trials comparing Aspirin and Warfarin (which has been the standard of care for over 50 years). It is clear that Warfarin is significantly better than Aspirin. Three new medications have been released over the past 5 years and have been compared to Warfarin. Results of studies comparing the new agents to Warfarin show that none of the newer therapies are inferior to Warfarin at preventing stroke, and two of the three may be slightly better. There are pluses and minuses with the use of these novel medications (such as cost, need for laboratory tests for monitoring therapy, and difficulty in reversing the medication), and patients should discuss the options with their own physicians.
Patients can be divided into those with intermittent (paroxysmal) episodes of atrial fibrillation, and those with permanent (chronic) atrial fibrillation. It is felt that patients with on-and-off atrial fibrillation have a similar stroke risk to the chronic patients, and therefore they should also be treated with anticoagulants.
With regards to the dysrhythmia itself, there are several treatment strategies available. First-time episodes may be treated medically or with electrical cardioversion, in order to restore normal heart rhythm. Patients that are quite symptomatic with their episodes may be given medications that help to prevent recurrent episodes. There are several antiarrhythmic drugs available, but none of them work with 100% reliability, and patients that do not respond to these medications may be referred for electrophysiological mapping studies (done with intracardiac catheters) and ablation may take place. This usually means using radiofrequency energy to heat very small portions of the heart muscle, setting up barriers within the heart that prevent the electrical fibrillation signals from spreading across the heart. On occasion, a permanent pacemaker may also be required. Once permanent atrial fibrillation occurs, the patient may be given medication that serve to control the rapid heart rate, as slowing the rate may decrease the severity of symptoms such as shortness of breath and fatigue. Examples of such medications include beta-blockers, certain calcium-channel blockers, and Digoxin. Patients who are treated with a rhythm-control strategy (i.e. preventing recurrent episodes) versus a rate-control-strategy (i.e. slowing down the overall heart rate) have similar outcomes.
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