Wolff-Parkinson-White syndrome overview

# Overview
Wolff-Parkinson-White (WPW) syndrome 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 WPW syndrome may present with abrupt palpitation, presyncope, syncope, or sudden cardiac death (SCD). In some patients, SCD is the first presentation of WPW syndrome, especially in the setting of atrial fibrillation with a rapid ventricular response. Wolff-Parkinson-White syndrome is named after the cardiologists Louis Wolff, John Parkinson, and Paul Dudley White who gave a definitive description of the conduction disorder of the heart in 1930.  The term Wolff-Parkinson-White syndrome 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. Wolff-Parkinson-White (WPW) syndrome is the occurrence of arrhythmia in the presence of an accessory pathway. WPW 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, WPW 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 Wolf-Parkinson-White syndrome (WPW) 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 WPW 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 WPW syndrome 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 WPW  pattern. The incidence of sudden cardiac death in patients with Wolff-Parkinson-White syndrome was estimated to be 70-450 per 100000 patient-years. WPW syndrome is more commonly observed among young patients. In one study WPW syndrome was observed in 7% of individuals over 60-year-old. Men are more commonly affected with WPW syndrome than women. The men to women ratio is approximately 2 to 1. There is no racial predilection for WPW syndrome. High-risk criteria for sudden cardiac death in Wolff-Parkinson-White syndrome during electrophysiology study include the presence of multiple accessory pathways, R-R interval 240/min to the ventricles via the accessory bypass tract leading ventricular fibrillation. Prognosis is generally excellent in asymptomatic WPW 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 WPW  remains high despite ablation. Increased risk of atrial fibrillation in ablated WPW patients may be related to atrial fibrillation genesis. The diagnose of WPW 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  WPW syndrome and episodes of atrial fibrillation may present rapid irregular wide-complex tachycardia on EKG.  The combination of atrial fibrillation and WPW 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 WPW 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. Wolff-Parkinson-White syndrome is sometimes associated with Leber's hereditary optic neuropathy (LHON), a form of mitochondrial disease. Symptoms of WPW syndrome may include Palpitation, chest pain or chest tightness, diziness, light-headedness, Brief loss of consciousness, shortness of breath, exercise intolerance, anxiety. WPW syndrome, uncommonly presents as cardiac arrest or sudden cardiac death.The accessory pathway of WPW syndrome 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  WPW syndrome in infants may include lethargy, breathlessness, loss of appetite. Atrial fibrillation in a patient with WPW 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 WPW syndrome 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. Wolff-Parkinson-White syndrome 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 WPW syndrome 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 WPW syndrome depends on the presence or absence of symptoms and their severity.  Patients who have poorly tolerated symptomatic WPW syndrome 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.

# Historical Perspective
Wolff-Parkinson-White syndrome is named after the cardiologists Louis Wolff, John Parkinson, and Paul Dudley White who gave a definitive description of the conduction disorder of the heart in 1930.  The term Wolff-Parkinson-White syndrome 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.

# Classification
Wolff-Parkinson-White (WPW) syndrome is the occurrence of arrhythmia in the presence of an accessory pathway.  WPW 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, WPW 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.

# Pathophysiology
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 Wolf-parkinson-White (WPW) 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 WPW 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.

# Differentiating WPW syndrome from Other Diseases
WPW syndrome should be differentiated from other causes of  narrow QRS tachycardia such as AVNRT, PJRT,,SNRT.

# Epidemiology and Demographics
The prevalence of WPW syndrome 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 WPW  pattern. The incidence of sudden cardiac death in patients with Wolff-Parkinson-White syndrome was estimated to be 70-450 per 100000 patient-years. WPW syndrome is more commonly observed among young patients. In one study WPW syndrome was observed in 7% of individuals over 60-year-old. Men are more commonly affected with WPW syndrome than women. The men to women ratio is approximately 2 to 1. There is no racial predilection for WPW syndrome.

# Risk Factors
High-risk criteria for sudden cardiac death in Wolff-Parkinson-White syndrome 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, precence of Structural heart disease such as ebstein anomaly or hypertrophic cardiomyopathy.

# Natural History, Complications, and Prognosis
Patients with WPW pattern can remain asymptomatic through all their lives, nearly 65% of adolescents and 40% of adults present ECG changes but remain asymptomatic. Complications Wolff-Parkinson-White syndrome is a consequence of symptomatic tachycardias and can occur at any age. Common complications of tachyarrhythmia associated WPW disease include reduced blood pressure and syncope, tachycaria induced cardiomyopathy, cardiac arrest, ventricular fibrillation, usdden cardiac death, complications of ablation, side effects of medications. SCD may occur in WPW syndrome 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 WPW 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 WPW  remains high despite ablation. Increased risk of atrial fibrillation in ablated WPW patients may be related atrial fibrillation genesis.

# Diagnosis

## Diagnostic Study of Choice
The diagnose of WPW 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, therefore 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 WPW syndrome with episodes of atrial fibrillation will present ECG  with rapid irregular wide-complex tachycardia.  The combination of atrial fibrillation and WPW may increase the risk of very rapid antidromic AVRT and occurrence of ventricular fibrillation. AV node blocking agents are contraindicated in these patients because it will enhance the conduction through the accessory pathway. Patients with WPW may exhibit more than one accessory pathway which is common in patients with Ebstein's anomaly. The most common combination of accessory pathways in Ebstein anomaly was the right posteroseptal and right free wall pathway. Wolff-Parkinson-White syndrome is sometimes associated with Leber's hereditary optic neuropathy (LHON), a form of mitochondrial disease.

## History and Symptoms
Symptoms of WPW syndrome may include Palpitation, Chest pain or chest tightness, Dizziness, Light-headedness, Brief loss of consciousness, Shortness of breath, Exercise intolerance, Anxiety. The most common arrhythmias associated with Wolff-Parkinson-White syndrome is AV reentry tachycardia. WPW syndrome, uncommonly presents as cardiac arrest or sudden cardiac death.The accessory pathway of WPW syndrome is present since birth.  The age of presentation of tachyarrhythmia varies from patient to patient. Infants may develop heart failure if not treated immediately. Symptoms of tachycardia related  WPW syndrome in infants may include Lethargy, Breathlessness, Loss of appetite.

## Physical Examination

## Laboratory Findings
There is no laboratory finding related to WPW syndrome.

## Electrocardiogram
Wolff-Parkinson-White (WPW) pattern is characterized by  ECG findings such as a short PR interval and a delta wave and wide QRS complex.WPW syndrome is the occurrence of tachycardia with or without associated symptoms in a subject with existing WPW pattern. WPW syndrome can present as an orthodromic or antidromic AVRT during which the delta wave no longer appears.  Atrial fibrillation in a patient with WPW 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.

## Other Diagnostic Studies
.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

## Risk stratification
Treatment is based on the risk stratification of the individual.  Risk stratification is performed to determine which individuals with WPW syndrome 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.

## Cardioversion
Wolff-Parkinson-White syndrome 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.

## Medical Therapy
The medical therapy of hemodynamically stable patients with WPW syndrome depends on the type of the tachycardia.  When the ECG findings suggest orthodromic AVRT, the patient should be managed similarly to patients with supreventricular tachycardia followed by the sequential administration of adenosine, verapamil and procainamide in case of failure to improve.  Among patients with antidromic AVRT, AV nodal blocking agents should be avoided and patients should be treated with either procainamide, ibutilide or flecainide. The long term treatment of patients with WPW syndrome depends on the presence or absence of symptoms and their severity.  Patients who have poorly tolerated symptomatic WPW syndrome should undergo catheter ablation.

## Drug prophylaxia
Oral beta-blocker, diltiazem, and verapamil for prevention of AVRT in patients without preexcitation in resting ECG. Oral flecainide and propaphenone in patients with preexcitation in resting ECG that are not candidates for catheter ablation and do not have structural or ischemic heart disease.