Atrial fibrillation is a common and serious cardiac arrhythmia, affecting more than two million people in the United States alone. Clinically, atrial fibrillation involves an abnormality of electrical impulse formation and conduction that originates in the atria, that is, the upper chambers of the heart. Atrial fibrillation is characterized by multiple swirling wavelets of electrical current spreading across the atria in a disorganized manner. The irregularity of electrical conduction throughout the atria creates irregular impulse propagation through the atrioventricular node into the ventricle.
For example, impulse conduction can be extremely rapid, leading to reduced diastolic filling of the heart chambers and a corresponding reduction of the cardiac pumping action. Increased heart rate and loss of A-V synchrony may also exacerbate any underlying heart problems, such as heart failure, coronary blood flow, or other pulmonary disorders.
Alternatively, impulse conduction from the atria to the ventricles may be very limited so that atrial fibrillation can be sustained indefinitely, since the ventricles continue to drive circulation, albeit inefficiently. The risks of sustained atrial fibrillation are nevertheless serious including stroke and myocardial infarctions caused by the formation of blood clots within stagnant volumes in the atria.
Therefore, the relatively quick reversion to sinus rhythm of an episode of atrial fibrillation can reduce the risk of emboli formation or other complications. However, current devices do not sufficiently distinguish between sustained episodes of atrial fibrillation and atrial fibrillation episodes which are haemodynamically benign and likely to self terminate or those that are amenable to reversion with appropriately timed trains of pacing pulses.