Wolff-Parkinson-White syndrome (WPW) is a congenital malformation involving the presence of an abnormal conductive tissue between the atria and ventricles which is frequently associated with the appearance of supraventricular tachycardia. It requires activation of the ventricles before the normal contraction (pre-excitation) through an extra ventricular path, called accessory, bypasses the AV node.
the presence of a short PR interval (<120 ms)
a wide QRS complex of more than 120 ms steep upward wave – delta wave
changes in the ST segment and T-wave
Patients with Wolff-Parkinson-White syndrome are at risk for dangerous ventricular arrhythmias due to very fast conductance through the accessory path in case of supraventricular arrhythmia, like flutter of fibrillation. Only a small number of patients are at risk of sudden death. In these patients, the cardiac electrophysiological studies and radiofrequency catheter ablation may be curative. Other presentations include symptomatic supraventricular tachyarrhythmia, which can be treated by catheter ablation. Asymptomatic patients, who represent the majority of patients, require periodic observation.
Children with this syndrome who develop arrhythmias or dyspnea may be lethargic, with eating difficulties or rapid pulse in the precordial zone. Heart failure may occur. Adolescents or people in their 20’s who experience arrhythmia with this syndrome show palpitations episodes that begin suddenly, often during physical exercise. These episodes can take a few seconds or can persist for several hours. For most people fast heart rate creates discomfort and emotional stress. They can also experience syncopes. Older people who have Wolff-Parkinson-White syndrome tend to produce a richer clinical picture, with more symptoms such as syncope, dyspnea and chest pain.
Episodes of paroxysmal supraventricular tachycardia can be stopped by manoeuvres that stimulate the valgus and which slow the heart rate. They are most effective if applied immediately after the onset of the arrhythmia. If they are ineffective, antiarrhythmic agents are administered intravenously, such as verapamil or adenosine. For children under 10 years digoxin is administered to suppress episodes of tachycardia. Adults should not be administered, as it facilitates conductance through the accessory pathway and increases the risk of atrial fibrillation which can degenerate into a more dangerous ventricular fibrillation. For this reason digoxin is stopped when the patient reaches puberty.
Destruction of the accessory pathway using ablation with radiofrequency through a catheter inserted in the heart is a successful method for over 95% of the patients. The risk of death during surgery is less than 1 per 1,000 cases. Radiofrequency ablation is used mainly on young people who would have to follow antiarrhythmic therapy for life.
The patients with cardiac pre-excitation are at risk of developing supraventricular tachycardia through a resumed mechanism that is facilitated by the accessory connections. The genesis of tachycardia involves the presence of dual pathways between the atria and ventricles.
These pathways are:
Natural pathway Hiss-Purkinje
Accessory pathway (atrioventricular bypass tracts, Kent fibres, Mahaim fibres).
These two pathways show different leading properties and different refractory periods favouring re-entry. The effective refractory period of the accessory pathway is longer than the Hiss-Purjinje tract of the atrioventricular node.
There have been described several types of supraventricular tachycardia, including orthodromic tachycardia, orthodromic tachycardia with hidden accessory pathway and antidromic tachycardia.
When initiating premature ectopic atrial impulse it starts to cross the lower ventricles and can block the accessory pathway but the conductance in the traditional normal way towards the ventricles will not be affected. Then, the impulse re-enters in an anterograde way in the accessory pathway in a circular motion. These are described as re-entrant orthodromic tachycardia . Premature ventricular contractions may also initiate orthodromic tachycardia.
In orthodromic tachycardia, the normal path is used for ventricular depolarization and the accessory pathway is used for re-entry. Delta wave on the electrocardiogram is absent, the QRS complex is normal and the P waves in the inferior and lateral leads are reversed.
Orthodromic tachycardia with an accessory pathway
Some pathways cannot lead in an anterograde manner. These are called hidden pathways. Although there is no evidence of this kind of pathway during sinus rhythm, orthodromic tachycardia may occur.
The difference between this type of nodal re-entrant tachycardia, supraventricular tachycardia and ordinary tachycardia can be difficult to observe. If the heart rate is over 200 beats per minute and a retrograde P wave is observed after a QRS complex, hidden accessory pathway is suspected.
More rarely, a short refractory period in the accessory pathway can cause the blockage of an atrial ectopic impulse in the normal leading path, with anterograde conduction down the accessory pathway and retrograde re-entry of the pathway. This is called antidromic tachycardia. The electrocardiogram QRS complex is wide, with exaggeration of the delta wave during sinus rhythm. These tachycardias are difficult to distinguish from ventricular tachycardias
The mechanism that underlies most tachycardias in patients with Wolff-Parkinson-White syndrome is determined by the anterograde conduction through the Hiss and atrioventricular pathway and retrograde conduction through an accessory pathway-orthodromic. Rare in patients with Wolff-Parkinson-White syndrome is the antidromic way, when the accessory pathway leads only retrograde manner and can still participate in the re-entrant circuit, causing orthodromic atrioventricular tachycardia of exchange.
Causes and risk factors
In patients with Wolff-Parkinson-White syndrome the structural cardiac malformation consists of a tissue of accessory conduction that bypasses the normal pathway of the Hiss-Purkinje system. These paths are considered to be of congenital origin.
Causes of Wolff-Parkinson-White syndrome can be classified as:
Congenital or hereditary
An accessory pathway may be congenital although its manifestations may occur over years. Relatives of patients with cardiac pre-excitation, especially those with multiple paths, show an increased prevalence of pre-excitation suggesting a hereditary link.
Associated with congenital heart defects
Patients with Ebstein anomaly may develop Wolff-Parkinson-White syndrome. They often have multiple pathways, mostly on the right side of the heart, on the back of the septum and posterolateral wall. Cardiac pre-excitation occupies the ventricles, generally. Orthodromic tachycardia of exchange in these patients is manifested by right bundle branch block.
Other heart diseases associated include:
Hypertrophic subaortic stenosis
Signs and symptoms
Wolff-Parkinson-White syndrome can cause supraventricular tachycardia using an accessory pathway. The accessory pathway may be in standby and may allow conduction during other supraventricular arrhythmias such as atrial fibrillation or flutter. The possibility of a hidden accessory pathway as an underlying mechanism of certain types of supraventricular tachyarrhythmias should be considered, as treatment options vary.
Supraventricular tachycardia in Wolff-Parkinson-White syndrome may begin in childhood or may not occur until the patient reaches 50 years. In some patients who experience the first manifestation during childhood, it is characterized by episodes of tachyarrhythmia. The probability tachyarrhythmias persist is only 75% in patients over 5 years.
In asymptomatic patients, the probability of losing the ability to conduct in anterograde manner along the accessory pathway increases with age due to fibrotic changes at the site of the insertion of the accessory pathway.
In patients with Wolff-Parkinson-White syndrome tachycardia that produces symptoms can be a supraventricular tachycardia, an atrial fibrillation or atrial flutter.
Mild headache and syncope occurs more frequently in people with Wolff-Parkinson-White syndrome and with paroxysmal supraventricular tachycardia or atrial fibrillation than those with atrioventricular nodal re-entrant. Tachycardia may be followed by polyuria due to atrial dilatation and release of atrial natriuretic factor.
Physical examination is characterized by:
increased jugular venous pressure
clinical features include cardiomyopathy and cardiac defects associated with Ebstein anomaly
during supraventricular tachycardia the rhythm is regular
heart beats are of constant intensity
patients may experience diaphoresis, cold extremities
palpitations, hypotension, dizziness, syncope
During an episode of paroxysmal supraventricular tachycardia, the patient is tachypneic and irritable, and pallor is common. The pulse is rapid and diminished. The heart rate is 200-250 beats per minute and blood pressure is low. If the episode is untreated for several hours, the patient will present hypoperfusion, liver enlargement and heart failure. The patient is anxious but hemodynamically stable. Tachypnea frequently accompanies tachycardia. After the arrhythmia has ceased, the physical examination is normal.
CBC is needed to exclude non-cardiac pathological conditions which may trigger tachycardia
Biochemical tests include blood urea nitrogen and creatinine for renal function and bilirubin and transaminases levels for liver function
Tests to evaluate thyroid function
The blood levels of antiarrhythmic drugs during therapy.
Electrocardiography has the following elements:
Shortened PR interval
Presence of delta wave (a bump on the upward slope of the QRS
Widened QRS complex over 0.12 seconds
Secondary repolarization changes reflected in changes in the ST segment and T-wave
Depending on the location of the accessory pathway in relation to the sinus and the relative characteristics of the transmission path accessories and atrioventricular node, electrocardiogram morphology varies greatly compared to a normal classical presentation.
Wolff-Parkinson-White syndrome was described as type A or B, depending on the morphology of the delta wave and QRS in the precordial leads. Type A is described as having a positive delta wave in all precordial leads with a resultant R higher than S in amplitude in V1 derivation. Type B has a predominantly negative delta wave and the QRS complex becomes positive in leads V1 and V2 comparing to the lateral derivations, suggesting a left bundle-branch block.
Arrhythmias in the Wolff-Parkinson-White syndrome
Although many arrhythmias may occur in WPW syndrome, tachycardia and atrial fibrillation with circular motion are the most common. Tachycardia with circular motion is called orthodromic conduction and includes paroxysmal supraventricular tachycardia. Differentiation of the two in a patient with acute symptomatic regular rhythm is difficult. Cardiac dysrhythmia with frequencies higher than 220 beats per minute in adults suggests dysrhythmia with bypassing the atrioventricular node and is suggestive of the existence of an accessory pathway or ventricular tachycardia.
Atrial fibrillation in patients with Wolff-Parkinson-White syndrome is common with an incidence of 11-38%. It is the most dangerous arrhythmia for these patients because of the potential deterioration in ventricular fibrillation. In healthy people the heart is protected from rapid ventricular rates due to the long refractory period of the atrioventricular node. In patients with Wolff-Parkinson-White syndrome the accessory pathway has a shorter refractory period, allowing faster transmission of the impulse and corresponding frequencies increased.
Atrial fibrillation through an accessory path occurs as a bizarre tachycardia, irregular, with wide QRS complex, whose frequencies reach 250 beats per minute or more.
Esophageal electrophysiology tests may be useful to investigate the onset of supraventricular tachycardia and response during therapy.
The indications for electrophysiological studies include:
Indications Class I:
Ventricular pre-excitation patients who survived sudden death or unexplained syncope
Symptomatic patients for whom is needed to determine the mechanism of arrhythmia.
Indications Class II:
Asymptomatic patients with a family history of sudden cardiac death or ventricular pre-excitation
Patients with pre-excitation upcoming heart surgery for other pathologies
Indications for class III include patients with asymptomatic ventricular pre-excitation, except those in class II.
Stress test may be useful to reproduce a transient paroxysmal arrhythmia, to document the relationship between exercise and the onset of tachyarrhythmias, to evaluate the therapeutic efficiency and to investigate the answers. An ergometric bicycle or a triple scale will be used
Paroxysmal supraventricular tachycardia
Atrioventricular node re-entrant tachycardia
Glycogen storage disease types I and II.
Treatment of arrhythmia depends on the triggering cause and and factors. The main cause includes primary arrhythmias due to Epstein abnormalities in the heart because of the structural heart disease, independent of metabolic or hemodynamic disorders. Such arrhythmias include coronary heart disease, ischemia, cardiomyopathy, pericarditis and WPW syndrome. Factors that perpetuate the arrhythmia include secondary arrhythmias such as electrolyte imbalance, metabolic defects and metabolic disorders and hypoxemia.
Patients with ECG evidence of pre-excitation only, without documented episodes of tachycardia, do not require aggressive therapy.
There are three major therapies for this syndrome:
Antiarrhythmic drugs acting on the atrioventricular node, myocardial tissue and / or the accessory pathways. These decrease the sensitivity to flutter and atrial fibrillation.
Agents that act on the atrioventricular node:
Adenosine, verapamil, metoprolol, digital – extend the conduction and the refractory period in the atrioventricular node
Verapamil and metoprolol do not affect conduction in the accessory pathway
The digital shows variable effects and may even decrease the refractory period
None should be administered in the acute phase of pre-excitation with atrial fibrillation
Digoxin is contraindicated in Wolff-Parkinson-White syndrome.
Agents acting on the accessory pathway:
Procainamide and flecainide, propafenone block the conduction in the accessory pathway
Amiodarone and sotalol influence the atrioventricular node and the accessory pathway
IA and IC antiarrhythmic agents that prolong the refractory period and the accessory pathway are indicated.
For patients who finish the episode of tachycardia in atrial fibrillation and / or atrial flutter Valsalva maneuver will be applied, intravenous adenosine, verapamil or diltiazem intravenous, procainamide and propranolol. Hemodynamically unstable patients are indicated for synchronous electrical cardioversion.
It is used successfully used the ablation of the accessory pathway through electicity or radiofrequency, criotherapy, laser, microwave.
Radiofrequency ablation is the predominant treatment for most adults and children with symptomatic Wolff-Parkinson-White syndrome. The success rate is 90%. First, an electrophysiological study is performed to locate the ablation site. The accessory pathways can be located in the cardiac wall or septum. Multiple accessory pathways are found in more than 5% of patients.
Indications for radiofrequency ablation include:
symptomatic atrioventricular reentrant tachycardia
atrial fibrillation or other tachyarrhythmias with a rapid ventricular response
asymptomatic patients with ventricular pre-excitation whose job stress and mental state is influenced
atrial fibrillation with controlled ventricular response through the accessory pathway
patients with a family history of sudden cardiac death.
Surgical ablation is indicated in:
repeated failure of radioablation
patients requiring simultaneous surgical intervention on the heart
patients with other tachycardias with multiple ectopies.
For patients presenting only elements of electrocardiographic pre-excitation and are asymptomatic there is a very good prognosis. Most of these patients do not develop symptoms during life. Patients with a family history of sudden cardiac death or significant symptoms of tachyarrhythmias are subject to a poor prognosis without treatment.