<unk><unk><unk>  <unk>  is the most common cause of ventricular pre-excitation and the second common cause of supraventricular tachycardia. There is a muscle fiber that bridges the atrioventricular groove providing electrical continuity between the atrium and ventricle in parallel to the atrioventricular node-His-Purkinje axis. The atrial impulse activates the entire or part of the ventricle or the ventricular impulse activates the entire atrium or part of it, earlier than normally be expected. Patients with<unk>  may present with abrupt palpitation, presyncope, syncope, or sudden cardiac death (SCD). In some patients, SCD is the first presentation of<unk> , especially in the setting of atrial fibrillation with a rapid ventricular response.<unk>  is named after the cardiologists Louis<unk> , John<unk> , and Paul Dudley<unk>  who gave a definitive description of the conduction disorder of the heart in 1930.  The term<unk>  was coined in 1940. Bundle of Kent was first discovered by Albert Frank Stanley Kent, a British physiologist following finding the lateral branch in the atrioventricular groove of the monkey heart.<unk><unk><unk>  <unk>  is the occurrence of arrhythmia in the presence of an accessory pathway.<unk>  can be classified according to the site of origin, location in the mitral or tricuspid annulus, type of conduction (antegrade vs retrograde), and characteristics of the conduction (decremental vs nondecremental).  In addition,<unk>  can be classified based on the type of atrioventricular reciprocating tachycardia (AVRT) it causes, which can be either orthodromic (~95% of the cases) or antidromic.In normal individuals, electrical activity in the heart is initiated in the sinoatrial (SA) node (located in the right atrium), propagates to the atrioventricular (AV) node, and then through the bundle of His to the ventricles of the heart.  Individuals with<unk>  <unk>  have an accessory pathway, known as the bundle of Kent, that communicates between the atria and the ventricles.  The conduction through the accessory pathway can be bidirectional (most commonly), only retrogarde (less common), or only antegrade (least common).  The most common type of tachycardia associated with<unk>  is atrioventricular reciprocating tachycardia (AVRT). The accessory pathway does not share the rate-slowing properties of the AV node; therefore, the combination of an accessory pathway and cardiac arrhythmia can trigger ventricular fibrillation, a leading cause of sudden cardiac death. The prevalence of<unk>  is approximately 100-300 per 100000 individuals worldwide. The incidence of tachyarrhythmia was estimated to be 1000 cases per 100000 individuals in the year in patients with<unk>   pattern. The incidence of sudden cardiac death in patients with<unk>  was estimated to be 70-450 per 100000 patient-years.<unk>  is more commonly observed among young patients. In one study<unk>  was observed in 7% of individuals over 60-year-old. Men are more commonly affected with<unk>  than women. The men to women ratio is approximately 2 to 1. There is no racial predilection for<unk> . High-risk criteria for sudden cardiac death in<unk>  during electrophysiology study include the presence of multiple accessory pathways, R-R interval <250 milliseconds in antegrade conduction of accessory pathway during inducing atrial fibrillation, sustained atrial fibrillation induced by AV re-entry tachycardia, presence of Structural heart disease such as ebstein anomaly or hypertrophic cardiomyopathy. Patients with<unk>  pattern can remain asymptomatic throughout all their lives, nearly 65% of adolescents and 40% of adults present ECG changes but remain asymptomatic. Common complications of tachyarrhythmia associated<unk>  disease include reduced blood pressure and syncope, tachycaria induced cardiomyopathy, cardiac arrest, ventricular fibrillation, sudden cardiac death, complications of ablation, side effects of medications. SCD may occur in<unk>  due to rapid conduction of atrial fibrillation with heart rate >240/min to the ventricles via the accessory bypass tract leading ventricular fibrillation. Prognosis is generally excellent in asymptomatic<unk>  pattern. Catheter ablation (radiofrequency ablation) has a success rate between 95 - 98%, which varies depending on the location and number of accessory pathways. Successful ablation prevents future supraventricular tachyarrhythmia. The risk of lethal arrhythmia in asymptomatic children is higher than in adults. Long-term rates of atrial fibrillation in adult patients that present with<unk>   remains high despite ablation. Increased risk of atrial fibrillation in ablated<unk>  patients may be related to atrial fibrillation genesis. The diagnose of<unk>  pattern is commonly made by an incidental ECG finding in an asymptomatic individuals. The characteristic EKG finding is a delta wave, which represents the pre-excitation of the ventricles through the accessory pathway. This phenomenon presents because the AV node has the property of slowing the impulses, therefore the conduction through the accessory pathway is faster and the ventricles are excited through two different pathways. The delta wave is an upstroke in the R wave of the QRS complex that is associated with a short PR interval. Delta waves are only present when the patient is in sinus rhythm, whentachycardia starts the delta wave is no longer present. Patients with<unk>  and episodes of atrial fibrillation may present rapid irregular wide-complex tachycardia on EKG.  The combination of atrial fibrillation and<unk>  may increase the risk of very rapid antidromic AVRT and occurrence of ventricular fibrillation. AV node blocking agents are contraindicated in these patients because of enhancement of the conduction through the accessory pathway. Patients with Ebstein anomaly and<unk>  may exhibit more than one accessory pathway. The most common combination of accessory pathways in Ebstein anomaly are the right posteroseptal and right free wall pathway.<unk>  is sometimes associated with Leber's hereditary optic neuropathy (LHON), a form of mitochondrial disease. Symptoms of<unk>  may include Palpitation, chest pain or chest tightness, diziness, light-headedness, Brief loss of consciousness, shortness of breath, exercise intolerance, anxiety.<unk> , uncommonly presents as cardiac arrest or sudden cardiac death.The accessory pathway of<unk>  is present since birth.  The age of presentation of tachyarrhythmia varies from patient to patient. Infants may develop heart failure if the tachyarrhythmia keeps without treatment. Symptoms of tachycardia related<unk>  in infants may include lethargy, breathlessness, loss of appetite. Atrial fibrillation in a patient with<unk>  should be suspected when there is ECG findings of an irregularly irregular rhythm and absent P waves suggestive of atrial fibrillation in the context of a heart rate higher than 240 beats per minute. The electrophysiologic study is used for determining the location and number of accessory pathways, determining the mechanism of tachycardia, establishing the diagnosis in those patients with questionable resting EKG. Treatment is based on the risk stratification of the individual.  Risk stratification is performed to determine which individuals with<unk>  are at risk for sudden cardiac death (SCD). Sudden cardiac death in these individuals is due to the propagation of an atrial arrhythmia to the ventricles at a very high rate. Noninvasive tests have a 70% positive predictive value and 30% negative predictive value for identifying pathways with life-threatening properties.Electrophysiologic studies are useful for evaluation of patients' symptoms.<unk>  patients who are hemodynamically unstable, as reflected by the presence of hypotension, cold extremities, mottling or peripheral cyanosis, or those who present with ischemic chest pain or decompensated heart failure must undergo cardioversion urgently. The medical therapy of hemodynamically stable patients with<unk>  depends on the type of the tachycardia. When the ECG findings suggest orthodromic AVRT, the patient should be managed similar to AVNRT, and administration of adenosine, beta-blocker verapamil, and procainamide is recommended. Among patients with antidromic AVRT, AV nodal blocking agents should be avoided and patients should be treated with either procainamide, ibutilide. The long term treatment of patients with<unk>  depends on the presence or absence of symptoms and their severity.  Patients who have poorly tolerated symptomatic<unk>  should undergo [[catheter ablation. Effective medication for prevention of tachyarrhythmia AVRT  in patients without preexcitation in resting ECG include oral beta-blocker, diltiazem, and verapamil. Oral flecainide and propaphenone for prevention of tachyarrhythmia is recommended in patients with preexcitation in resting ECG that are not candidates for catheter ablation and do not have structural or ischemic heart disease.
Wolff-Parkinson-White syndrome
West syndrome
Wright dick syndrome
Pallister–Killian syndrome
Wernicke-Korsakoff syndrome
Shy-Drager syndrome
Cohen syndrome
Ohtahara syndrome