Fibrillation

Fibrillation is the rapid, irregular and unsynchronized contraction of muscle fibers, most significant clinically when it affects the heart. Atrial fibrillation is an irregular and uncoordinated contraction of the heart's upper chambers, caused when disorganized electrical impulses, usually arising near the pulmonary veins, overwhelm the normal signal from the sinoatrial node and produce chaotic conduction to the ventricles; it can become a chronic condition managed with anticoagulation therapy and sometimes cardioversion to restore a normal rhythm. Ventricular fibrillation is the equivalent uncoordinated contraction of the heart's lower chambers, is a common and usually fatal cause of cardiac arrest unless reversed promptly by defibrillation, and represents a medical emergency. Fibrillation can also occur outside the heart, in skeletal muscle fibers that have lost contact with their nerve supply, where it is detected through electromyography or ultrasound rather than by outward symptoms.