Fibrillation is the rapid, irregular, and unsynchronized

contraction Contraction may refer to: Linguistics * Contraction (grammar), a shortened word * Poetic contraction, omission of letters for poetic reasons * Elision, omission of sounds ** Syncope (phonology), omission of sounds in a word * Synalepha, merged ...

muscle fibers A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a muscl ...

. An important occurrence is with regard to the

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...

Cardiology

There are two major classes of cardiac fibrillation: atrial fibrillation and

ventricular fibrillation Ventricular fibrillation (V-fib or VF) is an abnormal heart rhythm in which the ventricles of the heart quiver. It is due to disorganized electrical activity. Ventricular fibrillation results in cardiac arrest with loss of consciousness and no p ...

. * Atrial fibrillation is an irregular and uncoordinated contraction of the

cardiac muscle Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle th ...

of atria. It can be a chronic condition, usually treated with anticoagulation and sometimes with

conversion Conversion or convert may refer to: Arts, entertainment, and media * "Conversion" (''Doctor Who'' audio), an episode of the audio drama ''Cyberman'' * "Conversion" (''Stargate Atlantis''), an episode of the television series * "The Conversion" ...

normal sinus rhythm A sinus rhythm is any cardiac rhythm in which depolarisation of the cardiac muscle begins at the sinus node. It is characterised by the presence of correctly oriented P waves on the electrocardiogram (ECG). Sinus rhythm is necessary, but not su ...

. In this condition the normal electrical pulses coming from the

sinoatrial node The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is an oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of cells known as pacemaker cells. The sinus node is approximat ...

are overwhelmed by disorganized electrical impulses usually originating in the roots of the

pulmonary veins The pulmonary veins are the veins that transfer oxygenated blood from the lungs to the heart. The largest pulmonary veins are the four ''main pulmonary veins'', two from each lung that drain into the left atrium of the heart. The pulmonary vein ...

, leading to irregular conduction of impulses to the ventricles which generate the heartbeat. *

Ventricular fibrillation Ventricular fibrillation (V-fib or VF) is an abnormal heart rhythm in which the ventricles of the heart quiver. It is due to disorganized electrical activity. Ventricular fibrillation results in cardiac arrest with loss of consciousness and no p ...

is an irregular and uncoordinated contraction of the cardiac muscle of ventricles. It is a common cause of

cardiac arrest Cardiac arrest is when the heart suddenly and unexpectedly stops beating. It is a medical emergency that, without immediate medical intervention, will result in sudden cardiac death within minutes. Cardiopulmonary resuscitation (CPR) and possib ...

and is usually fatal if not reversed by

defibrillation Defibrillation is a treatment for life-threatening cardiac arrhythmias, specifically ventricular fibrillation (V-Fib) and non-perfusing ventricular tachycardia (V-Tach). A defibrillator delivers a dose of electric current (often called a ''cou ...

. Fibrillation may sometimes be used after heart surgery to stop the heart from beating while any minor leaks are stitched up.

Musculoskeletal

Fibrillation also occurs with individual skeletal muscle fibers. This happens when muscle fibers lose contact with their innervating axon producing a spontaneous action potential, "fibrillation potential" that results in the muscle fiber's contraction. These contractions are not visible under the skin and are detectable through needle

electromyography Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyog ...

(EMG) and ultrasound. Fibrillations can occur in healthy individuals. If the fibrillations have irregular potentials then they don't have pathological significance. In other cases they are a major symptom in acute and severe peripheral nerve disorders, in myopathies in which muscle fibers are split or inflamed, and in

lower motor neuron lesion A lower motor neuron lesion is a lesion which affects nerve fibers traveling from the lower motor neuron(s) in the anterior horn/anterior grey column of the spinal cord, or in the motor nuclei of the cranial nerves, to the relevant muscle(s). On ...

s. They contrast with

fasciculations A fasciculation, or muscle twitch, is a spontaneous, involuntary muscle contraction and relaxation, involving fine muscle fibers. They are common, with as many as 70% of people experiencing them. They can be benign, or associated with more serio ...

that are ''visible'' spontaneous contractions involving ''small groups'' of muscle fibers. Fasciculations can be seen in lower motor neuron lesions as well, but they also do not necessarily denote pathology.

Terminology

The word ''fibrillation'' () is related to the word ''

fibril Fibrils (from the Latin ''fibra'') are structural biological materials found in nearly all living organisms. Not to be confused with fibers or filaments, fibrils tend to have diameters ranging from 10-100 nanometers (whereas fibers are micro ...

'' in the sense of muscle fibrils, the

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s that make up each

muscle fiber A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a muscl ...

(muscle cell).

References

{{Nervous and musculoskeletal system symptoms and signs Cardiac arrhythmia Symptoms and signs: Nervous system