fine fibers (e.g., approximately 1 nm in diameter)
Cytoplasmic fibrils are observed on the protoplasmic cylinders found in most spirochetal species, although no function of the cytoplasmic fibrils has been ascribed.
It is not uncommon to identify atrial fibrillation on a routine physical examination or electrocardiogram, as it may be asymptomatic in some cases.
In atrial fibrillation, the regular impulses produced by the sinus node to provide rhythmic contraction of the heart are overwhelmed by the rapid randomly generated discharges produced by larger areas of atrial tissue.
Because the diagnosis of atrial fibrillation requires measurement of the electrical activity of the heart, atrial fibrillation was not truly described until 1874, when Edmé Félix Alfred Vulpian observed the irregular atrial electrical behavior that he termed "fremissement fibrillaire" in dog hearts.
Underlying causes of atrial fibrillation and flutter include dysfunction of the sinus node (the "natural pacemaker" of the heart) and a number of heart and lung disorders, including coronary artery disease, rheumatic heart disease, mitral valve disorders, pericarditis, and others.
In certain cases, atrial fibrillation may require emergency treatment to convert the arrhythmia to normal (sinus) rhythm, either with electrical cardioversion or with the administration of intravenous drugs, such as dofetilide or ibutilide.
Some patients with atrial fibrillation and rapid heart rates may need the radiofrequency ablation done not on the atria, but directly on the AV junction (i.e., the area that normally filters the impulses coming from the atria before they proceed to the ventricles).
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