ATRIAL FIBRILLATION



ATRIAL FIBRILLATION

INTRODUCTION

Atrial fibrillation is a supraventricular arrhythmia. It is defined as rapid, uncoordinated atrial activity with a rapid, irregular ventricular response.

Atrial fibrillation also features deterioration of atrial function.

Atrial fibrillation is the most common arrhythmia. It is a significant cause of morbidity such as stroke, thromboembolisms, and heart failure. There are medical conditions that are clearly the cause of some cases of atrial fibrillation, but often times the reason why atrial fibrillation happens is not known. Risk factors have been identified that increase the chances of developing atrial fibrillation. However, atrial fibrillation can also occur in healthy individuals when these risk factors are absent.

Atrial fibrillation is treated by with medications that control the heart rate and rhythm and reduce the risk of complications. It can also be treated surgically and with procedures that restore the heart to a normal sinus rhythm.

OBJECTIVES

When the student has finished this module, he/she will be able to:

1. Identify the correct definition of atrial fibrillation.

2. Identify the two basic pathophysiological causes of atrial fibrillation.

3. Identify the four types of atrial fibrillation.

4. Identify three signs and symptoms of atrial fibrillation.

5. Identify the characteristics of the ECG in a patient with atrial fibrillation.

6. Identify the four basic causes of atrial fibrillation

7. Identify two drugs that are known to cause atrial fibrillation.

8. Identify three medical conditions that are causes/risk factors for atrial fibrillation.

9. Identify two types of surgical procedures that are risk factors for atrial fibrillation.

10. Identify three cardiac disease that are risk factors for atrial fibrillation.

11. Identify the most important cardiac risk factor for atrial fibrillation.

12. Identify three important complications of atrial fibrillation.

13. Identify the two drugs commonly used to prevent stroke in patients with atrial fibrillation.

14. Identify three drugs that are used for rate control of atrial fibrillation.

15. Identify the drug most commonly used for rhythm control of atrial fibrillation.

16. Identify the two methods that are used for cardioversion in patients with atrial fibrillation.

17. Identify the scoring system used to asses the risk of stroke in patients with atrial fibrillation.

18. Identify the most common non-pharmacological treatment for correcting atrial fibrillation.

19. Identify a surgical technique that can be used to correct atrial fibrillation.

20. Identify the indications for immediate, emergency cardioversion of atrial fibrillation.

THE NORMAL CARDIAC CYCLE

In a normal heart beat, the cardiac contraction is initiated by an electrical impulse from the sinoatrial (SA) node. This electrical impulse exits the SA node and travels through the atria (producing the P wave) and stimulates atrial contraction. At the same time, the electrical impulse moves though intranodal tracts in the atria to the atrioventricular (AV) junction. The impulse is paused briefly at the AV, and is then conducted through the AV junction, through the bundle of His, through the left and right bundle branches and into the Purkinje fibers in the ventricles. At that point the impulse stimulates depolarization and contraction of the ventricles.

Approximately 70% of the ventricular volume that is ejected with each heart beat (stroke volume) comes from passive drainage from the vena cavae and the pulmonary veins, and approximately 20% to 30% is contributed from atrial contraction. The heart beat is normally initiated at the SA, but almost every part of the myocardium is capable of spontaneous depolarization that can initiate a contraction.

EPIDEMIOLOGY

As mentioned previously, atrial fibrillation is the most common arrhythmia. It affects approximately 2.2 million Americans and approximately 5.5% of the population over the age of 69.1 It accounts for approximately one-third of all hospitalizations related to cardiac arrhythmias. The incidence of atrial fibrillation increases with age. Approximately 13.7% of individuals over the age of 80 have atrial fibrillation, and most people with atrial fibrillation are between the ages of 65 and 85.2,3 Atrial fibrillation is slightly more common in men than in women. It is less common in African Americans and Latinos.4

Precisely identifying those at risk for developing atrial fibrillation has always been challenging. A system for assessing the 10-year risk was recently developed. The system included information about age, body mass index , blood pressure, age of diagnosis of heart failure and/or heart murmur, presence of heart failure, the PR interval, and the use of antihypertensive medications.5 The authors felt that their assessment tool could be clinically useful, but it is not known if it is being widely used.

The incidence of atrial fibrillation is expected to rise by 2 to 2.5 fold by 2050.6 This increase will most likely be caused by better and more aggressive diagnostic techniques, the aging of the population, and people living longer with diseases such as hypertension, congestive heart failure and coronary artery disease that are considered to be significant risk factors for developing atrial fibrillation.

PATHOPHYSIOLOGY

The exact cause of atrial fibrillation is not known.7 However, it is generally thought that atrial fibrillation is basically caused by a triggering event in an abnormal atrial myocardium.8,9 In the past, these processes were considered independent, but they are probably both necessary for atrial fibrillation to begin and to continue.

• The triggering event may be an automatic focal point – or multiple focal points – that discharges rapidly and irregularly, or it may be something that has been termed the multiple wavelet hypothesis. The focal points are often located in the pulmonary veins, but may be found in other areas, as well. The multiple wavelet hypothesis considers atrial fibrillation to be the result of many reentry circuits (the wavelets) in the atrium.

• The atrial myocardium in patients with atrial fibrillation is often dilated and fibrotic and these patients have also have decreased atrial muscle mass. The fibrosis may be due to inflammation or by disorders in the renin-angiotensin system. The atrial dilation is likely caused by cardiovascular diseases such as hypertension, valvular heart disease, congestive heart failure, or coronary atherosclerosis. It can also be a direct result of the arrhythmia itself. All of these changes may give rise to ectopic foci, and the fibrotic changes, dilation, and loss of muscle mass lead to erratic conduction.10

Regardless of the mechanism of any particular case of atrial fibrillation, the result is atrial impulses formed at the rate of between 350 and 600 beats per minute. These impulses are obviously formed at a more rapid rate than the rate of impulse formation from the SA node, so the heart responds to the ectopic foci rather than the SA node. Because of the refractory period of the cardiac conduction system, only a certain number of these beats are transmitted to the ventricles: the ventricular rate in atrial fibrillation is often very fast, up to 160 to 180 beats per minute.

Learning Break: Reentry is common cause of arrhythmias. Reentry occurs when an ectopic foci fires a premature impulse. This premature impulse is blocked due to an abnormality in the myocardium, but it finds an alternative pathway. The impulse moves through this pathway in a circular fashion, creating a loop – the reentry loop – of depolarization that is stimulated over and over by the same impulse.

Learning Break: The exact number of atrial beats that is transmitted through the cardiac conduction system varies and is very irregular. Consequently, the heart rate is irregularly irregular.

CLASSIFICATION OF ATRIAL FIBRILLATION

Atrial fibrillation is divided into four primary categories that are based on the length of the symptoms, the onset, and the cause.11 Atrial fibrillation can also be secondary to a specific medical condition.

• Lone atrial fibrillation: Lone atrial fibrillation occurs in people under the age of 60 who have no clinical or electrocardiographic evidence of cardiopulmonary disease. People with lone atrial fibrillation are less likely to develop complications, and their mortality rate is similar to people who never had atrial fibrillation.12

• Paroxysmal atrial fibrillation: This form of the arrhythmia is defined as atrial fibrillation that terminates in seven days or less and often within 24 hours. In approximately 25% of all patients with paroxysmal atrial fibrillation, the arrhythmia will become permanent within five years.

• Persistent atrial fibrillation: Persistent atrial fibrillation lasts more than seven days and requires treatment.

• Permanent atrial fibrillation: If the arrhythmia persists beyond on year and is refractory to treatment, it is designated as permanent atrial fibrillation.

• Secondary: Secondary atrial fibrillation is caused by reversible influences such as a myocardial infarction, pericarditis, cardiothoracic surgery, hyperthyroidism, drugs, or other exogenous influences. In these cases, once the underlying problem has resolved, the arrhythmia disappears.

SIGNS AND SYMPTOMS OF ATRIAL FIBRILLATION

The typical signs and symptoms of atrial fibrillation are irregular palpitations, chest pain, fatigue, shortness of breath, irregular heart rate, and dyspnea on exertion.13 The heart rate is often quite rapid with rates up to 150-160 or higher. However, patients may have periods during which they are asymptomatic.14 Occasionally, the first sign of atrial fibrillation is a complication such as a stroke.

Learning Break: Although the heart rate in atrial fibrillation is usually > 100 beats per minute, the ventricular response can at times be < 100 beats per minute.

Learning Break: The signs and symptoms of atrial fibrillation are due to the asynchronous atrial activity, loss of atrial contribution to cardiac output (up to 20% to 30%), rapid, irregular ventricular response, and decreased coronary artery blood flow.

THE ELECTROCARDIOGRAM AND ATRIAL FIBRILLATION

The electrocardiogram (ECG) is atrial fibrillation is characterized by:15

• Absence of regular, distinct P waves.

• Replacement of the P waves with rapid oscillatory waves that vary in amplitude, shape, and timing.

• A rapid and irregularly irregular ventricular response.

• A narrow QRS complex.

CAUSES OF ATRIAL FIBRILLATION

There are many causes of atrial fibrillation. These can be conveniently divided into four basic categories: cardiac, medical/surgical, pharmacological, and genetic.

Genetic

There are rare forms of atrial fibrillation that are due to genetic single mutations.16 There is also increasing evidence that the risk of developing atrial fibrillation increases as much as 30% to 41% – even when risk factors have been accounted for – if one’s first or second degree relatives have atrial fibrillation. This appears to be especially so for patients with lone atrial fibrillation.17,18

Pharmacological

There are several drugs that can cause atrial fibrillation. Ethanol – drinking alcohol – has long been known to be a cause of atrial fibrillation. Atrial fibrillation can occur as a result of chronic ethanol abuse and can occur acutely after binge drinking – the latter syndrome being called “holiday heart.”19 It is not clear why ethanol causes atrial fibrillation. In acute cases, it may be that metabolic breakdown products of ethanol, e.g., acetylaldeyde, stimulate the release of catecholamines from the myocardium. When it is chronically abused, ethanol may cause structural damage and metabolic derangements to the heart. In people who drink heavily, the risk for developing atrial fibrillation is approximately 1.6 times greater than among people who abstain or drink less.20,21 Stimulants such as cocaine, methamphetamine, and caffeine (in excess) may cause atrial fibrillation. It does not appear that moderate consumption of caffeine increases the risks of developing atrial fibrillation.22 Cigarette smoking may increase the risk of developing trial fibrillation.23

Medical/Surgical

There are many medical conditions that can cause atrial fibrillation. Atrial fibrillation occurs in approximately 15% of all patients with hyperthyroidism, and sub-clinical hyperthyroidism is associated with a three-fold increase in the incidence of atrial fibrillation.24 Diabetes has long been considered to be a risk factor for the development of atrial fibrillation. There is evidence for and against this association, but a recent study that controlled for other risk factors associated with atrial fibrillation indicated that for some people, diabetes can definitely increase the risk of developing atrial fibrillation.25 Atrial fibrillation is commonly seen (up to 76% incidence) after subarachnoid hemorrhage.26 Obstructive sleep apnea has also been strongly implicated as a risk factor for atrial fibrillation.27 Obesity increases the risk of atrial fibrillation by approximately 49%, and the level of risk increases as body mass index increases.28

Atrial fibrillation is common as a postoperative event after cardiac surgery, and to a lesser extent, pulmonary surgery. Approximately 40% of all patients who have coronary artery bypass graft surgery or valvular surgery develop atrial fibrillation after the operation; if the two surgeries are combined this rate is approximately 60%.29 Advanced age, obesity, the metabolic syndrome, and cardiopulmonary disease are thought to increase the risk of post-operative atrial fibrillation.30. It has been associated with an increase in morbidity and mortality and prolonged hospital stay.31 The arrhythmia is usually transient, and preoperative treatment with amiodarone, beta-blockers, corticosteroids, sotalol, magnesium, ACE inhibitors, and some calcium channel blockers has been shown to reduce the incidence of post-operative atrial fibrillation.32,33 Post-operative atrial fibrillation is also a relatively common occurrence after pulmonary surgery.34,35

Atrial fibrillation also commonly occurs during renal dialysis. However, it generally resolves spontaneously within several hours after the dialysis session has ended.36

Cardiac

There are strong associations between cardiac disease and atrial fibrillation. Hypertension, congestive heart failure, valvular heart disease, and coronary artery disease are all important risk factors for the development of atrial fibrillation.37 Hypertension, especially, is considered to be the most reliable predictor of risk for atrial fibrillation.38 There is ongoing research that is attempting to discover the exact incidence and the relationship between these diseases an atrial fibrillation: one of the biggest questions seems to be whether or not some of the conditions are the cause of atrial fibrillation or an effect of the arrhythmia.39,40,41

COMPLICATIONS OF ATRIAL FIBRILLATION

Atrial fibrillation is associated with a 1.5 to 1.9 fold increase in risk of death when compared to people with sinus rhythm.42,43 It is also strongly associated with a substantial increase in the risk for stroke due to embolism. The fibrillation in the atria leads to stasis, and atrial fibrillation itself causes a hypercoaguable state. Approximately 15% to 25% of all strokes in the United States are directly related to atrial fibrillation, and the presence of atial fibrillation increases the risk of stroke 4 to 5 fold.44,45 Patients with atrial fibrillation who have had a prior stroke or a transient ischemic attack, who have hypertension, diabetes, or valvular disease, or are over the age of 75 are especially at risk for a stroke.46 Most of the embolic strokes caused by atrial fibrillation are caused by a thrombus in the atria, but this is not always the case.47 A stroke that is caused by atrial fibrillation is usually serious: the one-year mortality rate has been estimated to be 50%.48

Atrial fibrillation is also considered to be a cause for congestive heart failure (or at the least a strong contributor to its development and progression) and tachycardia-induced cardiomyopathy.49 Patients with atrial fibrillation have approximately three times the risk of developing congestive heart failure when compared to the general population.

EMERGENCY TREATMENT OF UNSTABLE ATRIAL FIBRILLATION

Patients with atrial fibrillation who are hemodynamically unstable, or who have chest pain or dyspnea related to the arrhythmia are candidates for emergent cardioversion. Cardioversion applies electrical current to the heart that is synchronized to the QRS complexes, and it converts the heart to a sinus rhythm. It is performed while the patient is sedated.

TREATMENT OF ATRIAL FIBRILLATION

Atrial fibrillation is treated in order to increase the quality of life, decrease the frequency and intensity of symptoms, and decrease the risk of complications and death. Unfortunately, there is no conclusive evidence that the therapies available reduce the mortality rate associated with atrial fibrillation.50 However, treatment is appropriate for patients who are hemodynamically unstable, patients who have a high risk for embolic complications, and patients whose quality of life is severely impacted. The basic goals of the treatment atrial fibrillation are to 1) Correct the arrhythmia, 2) control the rate and/or rhythm, and 3) prevent the embolic complications.

Learning Break: It is also important to treat atrial fibrillation because there is strong evidence that atrial fibrillation causes changes in the myocardium that sustain and worsen the arrhythmia. “Atrial fibrillation begets atrial fibrillation,” is the common wisdom.

Prevention of Embolic Complications

Preventing the thromboembolic complications of atrial fibrillation – especially stroke – is one of the most important goals in treating this arrhythmia.51

Patients with atrial fibrillation have a higher risk of suffering a stroke than the general population, but this risk varies significantly. The medications that can be used to prevent a stroke can have serious side effects, so it is important that the right patients are treated prophylactically with the right drugs. Physicians often use an assessment system called CHADS2. CHADS stands for cardiac failure, history of hypertension, age of 75 years or older, diabetes mellitus, and history of stroke or transient ischemic attack (TIA). In the CHADS2 scoring system, cardiac failure, hypertension, age, age of 75 year or older, and diabetes are each assigned one point; a stroke or a TIA are assigned two points. The relative risk and the treatment decisions are based on the total number of points. Fr example, a CHADS2 score of 3 reflects a 5.9% risk of stroke; a CHADS2 score of 5 reflects a risk for stroke of 12.5%.52

Treating patients with oral anticoagulants – most often with warfarin – has been the primary method for preventing the embolic complications of atrial fibrillation.53 Unfortunately, warfarin therapy has significant drawbacks. There is a narrow therapeutic index, very unpredictable dose-response relationship, the need for constant monitoring, drug and diet interactions, and risk for bleeding and hemorrhagic stroke.54 Because of these issues, many patients with atrial fibrillation who need anti-thrombotic therapy do not receive it or are treated sub-optimally, and this has a significant affect on these patient’s health.55

The common therapies used to prevent stroke in patients with atrial fibrillation are:

• Antiplatelet therapy with aspirin: Aspirin prevents platelet activation, which is one of the important steps in thrombus formation. In several large studies, it has been shown that aspirin reduces the risk of stroke in patients with atrial fibrillation by 21% to 22%.56,57

• Warfarin therapy: Warfarin is effective at preventing stroke in patients who have atrial fibrillation. It has been estimated that anti-coagulation with warfarin reduces the risk of stroke by approximately three fold, from 4.5% in a control group to 1.4% in a group treated with warfarin.58 Warfarin appeared to more effective than aspirin.59

• Warfarin and aspirin combination therapy: There is no evidence that using a combination of warfarin and aspirin is more effective than using warfarin alone, and using both definitely increases the risk of bleeding.60

• Combination antiplatelet therapy: There have been several studies that have examined the use of combining antiplatelet drugs for preventing the embolic complications of atrial fibrillation. These studies used aspirin and clopidogrel (Plavix®), a drug that prevents platelet aggregation. This combination was more effective than aspirin alone, but not as effective as warfarin, and compared to aspirin alone, there was greater risk of bleeding.61,62

Learning Break: The goal for a patient receiving warfarin is to maintain an international normalized ratio (INR) of between 2.0 to 3.0. This decreases the risk of stroke. If the INR is below 2.0, the risk of stroke increases dramatically.

These are the only currently FDA-approved drugs for the use of stroke prevention in patients with atrial fibrillation. Patients with atrial fibrillation who have a moderate to high risk of stroke, e.g., several risk factors such as a history of embolic events, etc., might need both warfarin and aspirin, but this approach should be used very cautiously. If the risk of stroke is less, warfarin or aspirin can be used.63

Short-Term Management of Atrial Fibrillation

For the patient who is hemodynamically unstable and symptomatic, immediate direct current caridoversion should be performed.64 If the patient is hemodynamically stable but symptomatic, oral or intravenous medications that block transmission through the AV node can be used; the goal of therapy is rate control. These would include calcium channel blockers, β-blockers, and possibly digoxin.65

Patients who are symptomatic and do not respond to rate controlling drugs should be cardioverted to establish a sinus rhythm. This can be accomplished using direct electrical current cardioversion or drugs. Ideally, the patient who is a candidate for electrical cardioversion will have been in atrial fibrialltion for 48 hours or less; if so, the patient does not need anticoagulation. If the arrhythmia has peristed longer than 48, the patient should be anticoagulated with warfarin for four weeks before the procedure. The presence of a thrombus in the atria can also be ruled out using transesophageal electorcardiography. There is a risk of stroke after cardioversion – a mural thrombus can be dislodged from the atria – but this can be greatly reduced by anticoagulation before and after cardioversion. Electrical current cardioversion will correct the arrhythmia in approximately 90% of all cases. However, atrial fibrillation commonly recurs.66

Class I or Class II antiarrhythmic drugs can be used for cardioversion, as well. If this therapy is started within 24 hours, the rate of conversion has been reported to be 47% to 84%. If the therapy is initiated after atrial fibrillation has been present for longer than 48 hours, the conversion rate has been reported to be 15% to 30%.67 Pharmacologic conversion is considered less effective than electrical cardioversion.68

Long-Term Management of Atrial Fibrillation: Rate Control and Rhythm Control with Medications

There has long been a question as to whether or rate control or rhythm control was a better strategy for treating atrial fibrillation. An analysis of several large clinical trials did not show that either approach was preferable or more effective; the outcomes were essentially the same.69

However, because atrial fibrillation frequently recurs, rate control should be attempted first. It is safe and very often effective. Β-blockers, calcium channel blockers and digoxin can be used.

If rate control is unsuccessful, rhythm control should be tried. Either medications or non-pharmacological treatments can be used. Amiodarone, sotalol, flecainide, propafenone, and dofetilide can all be used. The choice of drug will depend on the presence of other cardiac diseases such as hypertension, coronary artery disease and valvular heart disease; for example, flecainide should be avoided if the patient has structural heart disease.70 Amiodarone is probably the most effective and most popular drug used for maintaining rhythm, but it is also associated with many serious side effects.71 The long-term success rate of pharmacological cardioversion has not been not high. In several large studies, the recurrence rate was 67% to 94% within a year 72,73

Dronedarone is a relatively recently introduced drug that has shown an effectiveness equivalent to amiodarone in maintaining a normal rhythm, and it appears to have fewer and less serious side effects.74

Long-Term Management of Atrial Fibrillation: Rate Control and Rhythm Control with Non-Pharmacologic Measures

The long-term effectiveness of medications in restoring and maintaining a normal rate and/or rhythm is poor, and the drugs available have serious side effects. In addition, there is evidence that suggests that there is electrical and structural remodeling of the myocardium that occurs during atrial fibrillation, and this would limit the effectiveness of medications for correcting the arrhythmia.75 Non-pharmacological approaches to rate and rhythm control have gained popularity. They appear to be more effective and safer than treatment with drugs.75,76

The most popular of these procedures is catheter-based radiofrequency ablation. This procedure is used if the patient with atrial fibrillation continues to have symptoms and antiarrhythmic drugs were tried and discontinued because of ineffectiveness or intolerable side effects.

Pulmonary vein ablation is the most commonly performed technique of radiofrequency ablation. The patient is heparinized and a catheter is placed in the pulmonary vein, the ectopic foci are identified and radiofrequency energy, cold thermal energy, microwave energy, laser, or ultrasound are used to eliminate them. Pulmonary vein ablation is most effective for treating paroxysmal atrial fibrillation in patients with a normal atrial myocardium. The success rate for this procedure is usually reported to be from 60% to 70%77, but it can vary from 31% to 88%.78 Major complications of this procedure include pulmonary vein stenosis, thrombomembolic events, and left atrial-esophageal fistula.

Many patients with atrial fibrillation do not have a normal atrial myocardium, and pulmonary vein foci are not the cause of the arrhythmia. In these situations, there are ablation techniques that can be used. Another approach is surgical ablation. Surgery for atrial fibrillation is designed to a) reduce the amount of atrial tissue that is capable of forming reentry circuits by resection, and b) creating large, full-thickness lesions that will prevent conduction of ectopic impulses.79 There are three surgical techniques that are commonly used.

• Cox-Maze III: This procedure has been reported to be highly effective, and has been use to treat persistent and permanent atrial fibrillation. The success in maintaining sinus rhythm has been reported to be between 85% and 95%80,81 and it has also been shown to be very effective in reducing the incidence of stroke. Full thickness lesions are created in the left atrium and pulmonary veins by cutting and sewing, and the left atrial appendage is removed. These lesions, as mentioned previously, block aberrant electrical impulses. Because the operation is difficult to perform and there are complications that can be difficult to treat, this operation is not first-line therapy and the Cox-Maze III is not often done.

Learning Break: The left atrial appendage is a muscular sac that is part of the left atrium. It acts as a reservoir for blood, and it can often be a source of ectopic foci that cause atrial fibrillation.

• Pulmonary vein isolation: Pulmonary vein isolation surgery can be very effective (a 9% recurrence rate) for patients who have paroxysmal atrial fibrillation, but it is ineffective for patients who do not have this form of the arrhythmia.82,83

• Other techniques: There are other surgical approaches used for treating atrial fibrillation. These techniques use an energy source (radiofrequency, laser, microwave, ultrasound, cryothermy) to form atrial lesions – left atrial or bi-atrial – that will block conduction. The pulmonary vein and the left atrial appendage are isolated, as well.84,85,86

SUMMARY

• Atrial fibrillation is the most common arrhythmia.

• Atrial fibrillation is defined as rapid, uncoordinated atrial activity with a rapid, irregular ventricular response.

• The basic causes of atrial fibrillation are a triggering event in an abnormal atrial myocardium.

• In atrial fibrillation, the atria beat very rapidly and irregularly, and a varying and irregular number of those atrial impulses are transmitted through the AV node.

• People with atrial fibrillation typically experience a rapid, irregular heart beat, palpitations, shortness of breath, dyspnea on exertion, and chest pain.

• The signs and symptoms of atrial fibrillation are basically caused by a decrease in cardiac output; this is caused by the absence of regular, forceful atrial contractions. Decreased coronary blood flow also is part of the cause of the signs and symptoms.

• The ECG is atrial fibrillation features a lack of P waves, rapid oscillatory waves of varying size and shape, narrow QRS complexes, and an irregularly irregular ventricular response.

• Atrial fibrillation can be paroxysmal, persistent, permanent, or lone.

• Atrial fibrillation has genetic, pharmacological, medical-surgical, and cardiac causes.

• Hypertension is one of the biggest risk factors for developing atrial fibrillation.

• Complications of atrial fibrillation include embolic stroke, congestive heart failure, and cardiomyopathy.

• The CHADS2 is used to assess the risk of stroke in patients with atrial fibrillation.

• Either warfarin or aspirin are given to patients who have atrial fibrillation in order to prevent embolic stroke.

• Treatment of atrial fibrillation focuses on rate control or rhythm control.

• Rate control is accomplished using cardioversion or medications such as β-blockers, calcium channel blockers, and digoixin.

• Rhythm control is accomplished using medications such as amiodarone.

• Rhythm control can also be accomplished using radiofrequency ablation or surgical techniques.

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