Pre-excitation syndrome is a heart condition in which part of the cardiac ventricles are activated too early. Pre-excitation is caused by an abnormal electrical connection or accessory pathway between or within the cardiac chambers. Pre-excitation may not cause any symptoms but may lead to palpitations caused by abnormal heart rhythms. It is usually diagnosed using an electrocardiogram, but may only be found during an electrophysiological study. The condition may not require any treatment at all, but symptoms can be controlled using medication or catheter ablation. Types
Several types of pre-excitation syndrome have been described. Pathophysiology
Normally, the atria and the ventricles are electrically isolated, and electrical contact between them exists only at the "atrioventricular node". In all pre-excitation syndromes, at least one more conductive pathway is present. Physiologically, the normal electrical depolarization wave is delayed at the atrioventricular node to allow the atria to contract before the ventricles. However, there is no such delay in the abnormal pathway, so the electrical stimulus passes to the ventricle by this tract faster than via normal atrioventricular/bundle of His system, and the ventricles are depolarized (excited) before (pre-) normal conduction system. References


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Treatment
Treatment is mainly for the symptoms that toxic encephalopathy causes, and vary depending on how severe the case is. Diet changes and nutritional supplements may help some patients. To reduce or halt seizures, anticonvulsants may be prescribed. Dialysis or organ replacement surgery may be needed in some severe cases.Lifelong abstinence from alcohol, a well-established neurotoxin and cause of the condition, is encouraged to prevent further loss of neurocognitive function.Management of affected individuals consists of immediate removal from exposure to the toxic substance(s), treatment of the common clinical manifestation of depression if present, and counselling for the provision of life strategies to help cope with the potentially debilitating condition. Prognosis
Toxic encephalopathy is often irreversible. If the source of the problem is treated by removing the toxic chemical from the system, further damage can be prevented, but prolonged exposure to toxic chemicals can quickly destroy the brain. Long-term studies have demonstrated residual cognitive impairment (primarily attention and information-processing impairment resulting in dysfunction in working memory) up to 10 years following cessation of exposure. Severe cases of toxic encephalopathy can be life-threatening. Research
Research is being done by organizations such as NINDS (National Institute of Neurological Disorders and Stroke) on what substances can cause encephalopathy, why they do this, and eventually how to protect, treat, and cure the brain from this condition. See also
Brain damage
Chronic solvent-induced encephalopathy
Encephalopathy
Neurology

Notes
References
Lerner, David P.; Tadevosyan, Aleksey; Burns, Joseph D. (November 2020). "Toxin-Induced Subacute Encephalopathy". Neurologic Clinics. 38 (4): 799–824. doi:10.1016/j.ncl.2020.07.006. PMID 33040862. S2CID 222301922. Bradley, Walter (2004). Neurology in Clinical Practice (4 ed.).