The concept of "R on T ectopics" was further brought out by Katz in 1928. This was called the "vulnerable period" by Wiggers and Wegria in 1940, who brought to attention the concept of the danger of premature ventricular beats occurring on a T wave.Another definition of VF was produced by Wiggers in 1940. He described ventricular fibrillation as "an incoordinate type of contraction which, despite a high metabolic rate of the myocardium, produces no useful beats. As a result, the arterial pressure falls abruptly to very low levels, and death results within six to eight minutes from anemia [ischemia] of the brain and spinal cord".Spontaneous conversion of ventricular fibrillation to a more benign rhythm is rare in all but small animals. Defibrillation is the process that converts ventricular fibrillation to a more benign rhythm. This is usually by application of an electric shock to the myocardium and is discussed in detail in the relevant article. See also
References
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Interactive models and information on ventricular fibrillation and other arrhythmias
Acephalgic migraine (also called migraine aura without headache, amigrainous migraine, isolated visual migraine, and optical migraine) is a neurological syndrome. It is a relatively uncommon variant of migraine in which the patient may experience some migraine symptoms such as  aura, nausea, photophobia, and hemiparesis, but does not experience headache. It is generally classified as an event fulfilling the conditions of migraine with aura with no (or minimal) headache. It is sometimes distinguished from visual-only migraine aura without headache, also called ocular migraine. Symptoms and misdiagnosis
Acephalgic migraines can occur in individuals of any age. Some individuals, more commonly male, only experience acephalgic migraine, but frequently patients also experience migraine with headache. Generally, the condition is more than twice as likely to occur in females than males. Pediatric acephalgic migraines are listed along with other childhood periodic syndromes by W.A. Al-Twaijri and M.I. Shevell as "migraine equivalents" (although not listed as such in the International Classification of Headache Disorders), which can be good predictors of the future development of typical migraines. Individuals who experience acephalgic migraines in childhood are highly likely to develop typical migraines as they grow older. Among women, incidents of acephalgic migraine increase during perimenopause.Scintillating scotoma is the most common symptom which usually happens concurrently with Expanding Fortification Spectra. Also frequently reported is monocular blindness. Acephalgic migraines typically do not persist more than a few hours and may last for as little as 15 seconds.