Arrhythmias are caused by a disruption of the normal functioning of the electrical conduction system of the heart. Normally, the atria and ventricles contract in a coordinated manner.

In atrial fibrillation and flutter, the atria are stimulated to contract very quickly and differently from the normal activity originating from the sinoatrial node. This results in ineffective and uncoordinated contraction of the atria in atrial fibrillation, and in a peculiarly organized contraction pattern in atrial flutter.

The condition can be caused by impulses which are transmitted to the ventricles in an irregular fashion or by some impulses failing to be transmitted. This makes the ventricles beat irregularly, which leads to an irregular (and usually fast) pulse in atrial fibrillation.

In atrial flutter, however, the ventricles may beat rapidly, but regularly. If the atrial fibrillation/flutter is part of a condition called sick sinus syndrome, the ventricles may beat more slowly than normal. Thus, during atrial fibrillation the ventricles, by beating too fast or too slow, may fail to pump enough blood to meet the needs of the body.

Underlying causes of atrial fibrillation and flutter include dysfunction of the sinus node (the "natural pacemaker" of the heart) and a number of heart and lung disorders, including coronary artery disease, rheumatic heart disease, mitral valve disorders, pericarditis, and others.

Hyperthyroidism, hypertension, and other diseases can cause arrhythmias, as can recent heavy alcohol use (binge drinking). Some cases of atrial fibrillation or flutter occur in the setting of a heart attack (myocardial infarction) or soon after surgery on the heart.

Atrial fibrillation can affect both men and women. The prevalence of atrial fibrillation increases with age and varies from 1 case out of 200 persons for people younger than 60 years, to almost 9 cases out of 100 persons for people over 80 years.

• Sensation of feeling heart beat (palpitations)
• Pulse may feel rapid, racing, pounding, fluttering, or it can feel too slow
• Pulse may feel regular or irregular
• Dizziness, light-headedness
• Fainting
• Confusion
• Fatigue
• Shortness of breath
• Breathing difficulty, lying down
• Sensation of tightness in the chest

Note: Symptoms may begin and/or stop suddenly.

• An echocardiogram
• Nuclear imaging tests
• A coronary angiography
• An exercise treadmill ECG
• An electrophysiologic study (EP study) may be needed in some cases

In certain cases, atrial fibrillation may require emergency treatment to convert the arrhythmia to normal (sinus) rhythm, either with electrical cardioversion or with the administration of intravenous drugs, such as dofetilide or ibutilide.

Long-term treatment varies depending on the cause of the atrial fibrillation or flutter. Medication may include beta-blockers, calcium channel blockers, digitalis or other medications (such as antiarrhythmic agents) which slow the heartbeat or slow conduction of the impulse from the atria to the ventricles.

Medications may also include blood thinners, such as heparin or coumadin, to reduce the risk of a thromboembolic event such as a stroke.

Some selected patients with atrial fibrillation, rapid heart rates, and intolerance to medication may require a catheter procedure on the atria called radiofrequency ablation.

For most patients with atrial flutter, radiofrequency ablation is the current treatment of choice. Some patients with atrial fibrillation and rapid heart rates may need the radiofrequency ablation done not on the atria, but directly on the AV junction (i.e., the area that normally filters the impulses coming from the atria before they proceed to the ventricles).

Ablation of the AV junction leads to complete heart block. These patients then require a permanent pacemaker.

• A pulse that is too rapid or too slow may reduce the amount of blood the heart can pump and lead to syncope (fainting).
• Emboli to the brain (stroke) or elsewhere -- rare, but often treated with anticoagulation to reduce this risk.