Localized spontaneous, rapid contractions of individual muscle fibres. Unlike fasciculation (muscular quivering), fibrillation cannot be seen through the skin. In skeletal muscles, fibrillation is detected by an EMG. In heart muscle, it is detected by an ECG.Fibrillation usually occurs once a nerve supplying a muscle is destroyed, which causes the affected muscle to become weak and waste away.
Fibrillation of the heart muscle is caused by disruption to the spread of nerve impulses through the muscle wall of a heart chamber (see atrial fibrillation; ventricular fibrillation).
A term applied to rapid contraction or TREMOR of muscles, and especially to a form of abnormal action of the heart muscle in which individual bundles of ?bres take up independent action. It is believed to be due to a state of excessive excitability in the muscle associated with the stretching which occurs in dilatation of the heart. The main causes are ATHEROSCLEROSIS, chronic rheumatic heart disease and hypertensive heart disease (see HEART, DISEASES OF). Fibrillation is distinguished as atrial or ventricular, depending on whether the muscle of the atria or of the ventricles is affected. In atrial ?brillation, the heartbeats and the pulse become extremely irregular, both as regards time and force; when the atrium is ?brillating there is no signi?cant contraction of the atrial muscle but the cardiac output is maintained by ventricular contraction. In ventricular ?brillation there is no signi?cant contractile force, so that there is no cardiac output. The commonest cause is myocardial infarction. Administration of DIGOXIN, timolol or verapamil may restore normal rhythm, and in some patients, CARDIOVERSION – a controlled direct-current electric shock given via a modi?ed de?brillator placed on the chest wall – is e?ective.
n. chaotic electrical and mechanical activity of a heart chamber, which results in loss of synchronous contraction. The affected part of the heart then ceases to pump blood.
Fibrillation may affect the atria or ventricles independently. In atrial fibrillation (a common type of *arrhythmia), the chaotic electrical activity of the atria is conducted to the ventricles in a random manner resulting in a rapid and irregular pulse rate. The main causes are atherosclerosis, chronic rheumatic heart disease, and hypertensive heart disease. It may also complicate various other conditions, including chest infections and thyroid overactivity. The heart rate is controlled by the administration of *digoxin; in some cases the heart rhythm can be restored to normal by *cardioversion. Anticoagulant therapy reduces the risk of blood-clot formation, which could cause a stroke.
When ventricular fibrillation occurs the ventricles stop beating (see cardiac arrest). It is most commonly the result of *myocardial infarction.
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