Atrial fibrillation is a disturbance in the normal process for awakening a heartbeat.
The heart is separated into two upper chambers (atria) that receive blood and two lower chambers (ventricles) that forcefully eject blood into arteries. The movement of upper and lower must be coordinated to achieve an effective heartbeat. Thus, each beat is complex and highly organized, beginning with an intrinsic biological bandleader known as the sinus node.
Without external influence, the heart repeats the motions of a beat unceasingly unless it is deprived of energy. The sinus node is at the topmost point of the heart, where it functions like a clock to undergo a periodic electrical change. That change spreads outward from cell to cell and awakens atrial muscle, causing it to contract and gently coax blood into the ventricles. The awakening does not spread directly to the lower chambers because heart muscle cells of the atria are separated from the heart muscle cells of the ventricles in all but one location.
When the electrical awakening reaches the center of the heart, between the two upper and two lower chambers, it arrives at another focus of special heart cells called the “junction” or Atrio-Ventricular (AV) node. The junction spreads out into the ventricles as a specialized network of cable-like cells that pass along the awakening and coordinate the muscular action of these pumping chambers.
The natural basis for the timing with which the sinus node drives the heart is based largely upon the mechanical coupling between the heart and arteries. Eons of evolution have tuned the heart’s rhythm to match perfectly with dance of the bouncy, springy arteries that it fills. However, the tempo of the node also changes to match the mood of the body, synthesized from needs, hormonal urgings (such as adrenalin) and the brain’s commands.
In atrial fibrillation, a single point in the atrium is no longer responsible for awakening. There may be many points awakening independently of each other, no longer clockwork in their behavior. Alternatively, the electrical message that spreads through the atria may get caught in a circle, like a dog chasing its tail or the message may become fractured as it spreads. In any case, the atria are undergoing a constant electrical change that is roiling and chaotic like bubbles of boiling water. Facing such noise from above, the junction is overwhelmed. Its design is to pass along a message, but only a fraction of the chaotic messages of atrial fibrillation are allowed to pass through.
A heart driven by atrial fibrillation is robbed of order and efficiency to beat with erratic haste. It no longer responds to the body’s wants and needs. The effect is to sap stamina from the healthy and make the ill worse.