Pre-excitation syndrome (WPW)

Overview

Wolff-Parkinson-White (WPW) syndrome or pre excitation syndrome is a very common cardiac disorder in which the heart beats excessively quickly for extended periods of time. An additional electrical connection in the heart is the source of the problem. This cardiac disease is present at birth (congenital), although symptoms may not appear until later in life. Auxiliary electrical channels that bypass the AV node are part of the disease.

 

Pre-excitation syndrome definition

Wolff-Parkinson-White (WPW) syndrome is a congenital cardiac preexcitation disease caused by aberrant cardiac electrical conduction via an auxiliary channel, which can result in symptomatic and sometimes life-threatening arrhythmias.

In the presence of sinus rhythm, the characteristic electrocardiographic (ECG) finding of WPW pattern or preexcitation is a short PR interval and prolonged QRS with an initial slurring upstroke ("delta" wave). The term WPW syndrome refers to an ECG pattern that is compatible with the above-mentioned results, as well as the presence of a tachyarrhythmia and clinical tachycardia symptoms such as palpitations, episodic lightheadedness, presyncope, syncope, or even cardiac arrest.

The atria and ventricles are two electrically insulated parts that make up the typical heart. A conduction system connects these units, allowing proper cardiac synchronization and function. The cardiac electrical potential begins in the right atrium's sinoatrial node and travels via the atria to the atrioventricular (AV) node.

The action potential is delayed in the AV node before being promptly transferred to the ventricular myocytes through the His-Purkinje pathway, allowing for fast ventricular depolarization and coordinated contraction. WPW syndrome patients have an auxiliary channel that breaches the electrical separation of the atria and ventricles, allowing electrical impulses to bypass the AV node.

This route can result in the transmission of aberrant electrical impulses, which can lead to malignant tachyarrhythmias in specific circumstances. The WPW pattern's ECG results are created by the merger of ventricular preexcitation via the auxiliary route with normal electrical conduction.

The majority of individuals with the WPW pattern will never develop arrhythmia and will remain asymptomatic. Some accessory pathways may not exhibit the above usual ECG symptoms, and as a result, some patients may develop tachyarrhythmias despite having no prior ECG indication that the route exists. These are known as covert bypass tracts.

This condition was later dubbed the Wolff-Parkinson-White (WPW) syndrome. In 1943, the electrocardiographic signs of preexcitation were first linked to anatomic evidence of abnormal conducting tissue or bypass pathways.

 

Epidemiology

The natural history of asymptomatic WPW patients has been predicted based on the existing data on symptomatic WPW patients and those who were identified to have a WPW ECG pattern by chance. The general frequency of WPW has been estimated to be between 1 and 3 per 1000 persons in large-scale population-based research encompassing pediatric and adult populations.

It is difficult to identify really asymptomatic patients with WPW pattern since these people, by definition, do not have clinical symptoms. Experts estimate that around 65 percent of teenagers and 40 percent of those over 30 with a WPW pattern on a resting ECG remain asymptomatic. The annual frequency of patients with the WPW pattern developing to arrhythmia is estimated to be about 1% to 2%, with WPW syndrome prevalence peaking between the ages of 20 and 24.

 

Etiology

The WPW pattern is caused by the combination of ventricular preexcitation via the accessory route and normal electrical conduction across the AV node. This auxiliary route is hypothesized to have developed from chamber myocardium during incorrect early atrial and ventricular folding during cardiac development. As a result, electrically conducting myocardial bundles breach the atrial and ventricle's typical electrical barrier, establishing the auxiliary channel.

In contrast to the features of the regular AV node, this route often possesses non-decremental or non-delayed conduction. The electrical conducting qualities of the auxiliary route might vary depending on aspects such as conduction speed, direction, and refractory time. These qualities, as well as the location and number of pathways, will define how a route may be implicated in the onset or transmission of an arrhythmia that leads to WPW syndrome.

 

Pathophysiology

The WPW ECG pattern results from aberrant electrical conduction via an auxiliary channel that bypasses the normal cardiac conduction system. This additional route permits cardiac electrical activity to circumvent the atrioventricular node conduction delay and reach the ventricle early, resulting in premature ventricular depolarization.

This preexcitation also skips the fast conducting His-Purkinje system, resulting in early but slowly propagated ventricular depolarization and the ECG pattern of a short PR interval with a "slurred" start to the QRS complex, referred to as a delta wave. As regular cardiac conduction catches up following AV node latency and rapid conduction through the His-Purkinje system, the rest of a normal QRS obliterates this delta wave.

An auxiliary route can cause WPW syndrome in one of two ways. The route can either trigger and sustain an arrhythmia or enable the conduction of an arrhythmia that was created elsewhere. The first kind happens when a circuit forms between the heart's regular conduction system and the accessory route (or two or more accessory pathways), allowing for atrioventricular reentrant tachycardia (AVRT).

An excess electrical impulse that is not properly timed might cause a recurrent cycle between the atria, AV node, ventricles, and accessory route. Orthodromic AVRT occurs when conduction proceeds from the atria to the ventricle via antegrade conduction through the AV node and retrograde conduction via the accessory route.

Unless there is abnormal conduction, this will normally result in a narrow complex QRS when the His-Purkinje system is employed. Antidromic AVRT is the inverse, with antegrade conduction from the atria to the ventricle through the accessory route and retrograde conduction back to the AV node, and is generally associated with a broad complex QRS.

An auxiliary route can also cause arrhythmia by enabling conduction of an arrhythmia created elsewhere to spread to a part of the heart that is ordinarily electrically isolated from this arrhythmia. The auxiliary route is usually made up of cardiac tissue and possesses non-decremental or non-delayed conduction, allowing for quick ventricular activation.

Patients with WPW syndrome are predisposed to abrupt cardiac mortality due to this non-decremental conduction characteristic. This happens as a result of fast ventricular rates in circumstances characterized by rapid atrial depolarization, such as atrial fibrillation (AF) or atrial flutter. These rapid ventricular rates have the potential to progress to ventricular fibrillation (VF) and cardiac arrest.

 

Wolff Parkinson White Syndrome Symptoms

Patients with a WPW pattern who have never had an arrhythmia will be asymptomatic, and their history and physical exam will be normal. Prior ECGs may have identified the pattern, and the patient may be aware of their condition, but some accessory route conduction may be temporary or hidden, resulting in prior normal or occasionally normal ECGs. WPW pattern patients may have a family history of the pattern or condition.

Patients with the WPW pattern who develop a tachyarrhythmia may have symptoms such as palpitations, chest discomfort, dyspnea, dizziness, lightheadedness, presyncope, syncope, collapse, and/or abrupt death. The history will be noted for these symptoms, which may be episodic and resolved at presentation, or continuous if the arrhythmia continues.

If the arrhythmia has resolved, the physical exam should focus on the patient's cardiovascular, pulmonary perfusion status, and neurological exam, and it may be perfectly normal. A persistent arrhythmia is frequently symptomatic, and vital signs will show tachycardia. Depending on the degree of the tachyarrhythmia, comorbidities, and the patient's capacity to adapt for the arrhythmia, blood pressure can range from normal to raised to hypotensive.

The rate of respiration will vary depending on the patient's level of discomfort and capacity to sustain perfusing blood pressure. Again, the physical exam will differ based on the severity of the arrhythmia. A regular or irregular tachycardia will be detected during the cardiac exam. Depending on the severity of the arrhythmia, the rest of the physical exam may be normal or exhibit indications of pain, distress, hypoperfusion, cardiogenic shock, and unresponsiveness.

 

Diagnosis

Because the WPW pattern is a collection of electrocardiographic observations, the initial examination is based on a surface electrocardiogram. The ECG will reveal a short PR interval (120 ms), a protracted QRS complex (>120 ms), and a slurred delta wave as the QRS morphology. This shape is caused by preexcitation of the ventricle via the auxiliary route, which creates a fusion complex with the typical QRS complex resulting from normal cardiac conduction.

Because certain routes can only carry impulses under particular conditions or in a retrograde direction, the lack of this pattern does not rule out the possibility of an auxiliary channel. A route like this could only carry current from the ventricle to the atrium and would not generate ventricular preexcitation during typical sinus beats.

This hidden supplementary channel will only be visible on ECG when a ventricle-generated electrical impulse, such as a premature ventricular contraction or ventricular pacing.

Recommendations for additional examination, risk stratification, electrophysiologic investigation, and accessory pathway ablation for asymptomatic WPW pattern individuals differ based on age, risk factors, history of symptoms, comorbidities, baseline ECG pattern, as well as personal and professional opinion. Young, healthy individuals without concomitant illnesses or severe risk factors who exhibit the WPW pattern on ECG but are asymptomatic and have no history of suspected tachyarrhythmia are likely safe for watchful waiting with primary care and/or cardiology follow up.

Patients who are at a higher risk for arrhythmia should be referred for close cardiology follow-up to consider risk stratification tests and/or electrophysiologic studies with accessory route mapping and potential ablation. It is also worth noting that, because the WPW pattern alters the baseline morphology of the ECG, the diagnosis of illnesses that rely on ECG criteria may be changed in WPW patients. In some circumstances, further testing, an adaption of ECG diagnostic criteria, or expert advice may be required.

Patients who come with a symptomatic tachyarrhythmia or an episode of recent arrhythmia will need an ECG to determine current heart rate, rhythm, and morphology, as well as additional examination.

This examination entails examining the clinical condition's appropriateness while collecting vital indicators such as heart rate, blood pressure, pulse oximetry, and placing the patient on a cardiac monitor to examine the cardiac rhythm. If possible, a history and preceding medical information should be acquired to check for a baseline ECG, previous occurrences of tachyarrhythmias, and family members with WPW syndrome or sudden cardiac death.

It is necessary to gather a history of present symptoms, especially ischemic chest pain and events preceding the arrhythmia. Mental status, cardiovascular, and pulmonary tests should be focused on assessing for acute altered mental state, indications of shock, or acute heart failure, all of which would be worrying for hemodynamic instability; if discovered, the patient should be given electrical cardioversion.

The hemodynamically stable patient should be assessed further using a 12-lead ECG to determine the heart rhythm. Imaging and laboratory assessment should be tailored to the clinical circumstances and should look for contemporaneous or precipitating clinical problems as well as signs of end-organ dysfunction caused by the tachyarrhythmia.

Based on the clinical situation, these examinations may include chest radiography, echocardiography, complete blood count, basic metabolic panel, cardiac enzymes, BNP, thyroid function, venous or arterial blood gas, and further testing to identify other metabolic or concomitant problems.

 

Management

Patients with the WPW pattern who are asymptomatic do not require immediate treatment. It may be advantageous for them to be evaluated by a cardiologist or electrophysiologist in order to establish the patient's risk of having a tachyarrhythmia.

Depending on their degree of risk, the kind and features of the route, their cardiac comorbidities, and other medical problems, patients thought to be at high risk may benefit from preventive antiarrhythmic medicines or prophylactic accessory pathway ablation. The risk of developing a severe arrhythmia must be balanced against the advantages and dangers of drugs and invasive procedures in these circumstances.

Patients with an asymptomatic WPW pattern are thought to be at minimal risk of cardiac arrest. Patients who have suffered a cardiac arrest nearly invariably have previous tachycardia-related symptoms. As a result, most asymptomatic individuals may be handled with reassurance and thorough clinical observation. Patients may be urged to contact their doctor immediately if they have fast palpitations or syncope.

An additional risk categorization approach may also be used. The risk categorization of an asymptomatic WPW pattern might be done invasively or non-invasively. Because of certain false positives and false negatives, neither risk-stratification approach is flawless. In most cases, non-invasive examination is the favored first method. Exercise treadmill testing, ambulatory ECG monitoring, and sodium channel blocker challenge are all options for patients.

On an ECG, the presence of an abrupt and evident decrease of preexcitation at higher sinus rates indicates a weak or low-risk route. As a result, these routes are unlikely to produce life-threatening ventricular rates during AF. They are frequently manageable with just careful monitoring, without the need for an intrusive EP examination.

If, on the other hand, preexcitation occurs at faster heart rates throughout exercise testing or during the full ambulatory monitoring time, it may indicate that an invasive assessment is required. However, this does not always imply that the approach is "high-risk."

The treatment of people with WPW syndrome may be divided into two types. Patients presenting with an acute tachyarrhythmia and those with a known WPW pattern and past symptomatic episodes but no arrhythmia or symptoms at the time. This second set of patients is identical to those with a documented WPW pattern, except that they do not require rapid treatment.

They are distinguished by the fact that they have demonstrated that their accessory route is capable of starting, sustaining, or conducting an arrhythmia. They are at a higher risk of recurrent arrhythmias as a result, and they should be assessed and treated. An auxiliary route catheter ablation is the therapy of choice for symptomatic individuals.

This is generally accomplished using radiofrequency current ablation, however cryoablation can also be used. Because of its high success rate and minimal risk profile, catheter ablation has become the first-line therapy for symptomatic individuals. According to the 2015 ACC/AHA/HRS recommendations, this is first-line treatment for symptomatic individuals. Other treatment options include surgical ablation, which has a higher success rate than catheter ablation and a lower overall mortality rate but is usually done only after catheter ablation fails owing to the greater invasiveness of the technique.

For individuals who are not candidates for catheter or surgical ablation or who do not choose to explore these procedures, medical therapy is available. The 2015 ACC/AHA/HRS recommendations consider flecainide and propafenone to be appropriate alternatives in individuals without structural or ischemic heart disease, whereas dofetilide or sotalol are reasonable options in patients with structural heart disease.

AV nodal blocking medications, such as beta-blockers, verapamil, diltiazem, or digoxin, may be appropriate only in the presence of orthodromic AVRT or WPW on the ECG. In individuals with AVRT or pre-excited AF, amiodarone may be recommended if other medicinal therapy are unsuccessful or contraindicated.

A patient who has a known WPW pattern on their baseline ECG or a past episode of WPW syndrome-related tachyarrhythmia and arrives with an acute tachyarrhythmia will require immediate medical attention. The "2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care" can be used to address a patient who has an acute tachyarrhythmia. 

The first stage in this procedure is to determine whether or not the patient has a pulse. If no pulse is found, CPR should be started and the patient should be handled according to the Advanced Cardiac Life Support (ACLS) Cardiac Arrest Algorithm. If a pulse is detected, the ACLS Tachycardia Algorithm can be used to treat the patient.

Patients with persistent tachyarrhythmia who are hemodynamically unstable as determined by hypotension, acutely altered mental status, signs of shock, ischemic chest discomfort, or acute heart failure should undergo synchronized cardioversion or defibrillation, according to the ACLS tachycardia algorithm. For a regular narrow complex tachycardia, an adenosine trial may be explored.

Pharmacological therapy of a hemodynamically stable acute tachyarrhythmia suspected of including an accessory route must be individualized based on the kind of arrhythmia and accessory pathway present, since certain pharmacological therapies can be harmful or even deadly. Pathways that do not participate in the onset and maintenance of an arrhythmia that leads to AVRT will conduct an arrhythmia generated elsewhere in the heart.

Fast atrial arrhythmias can be carried to the ventricle via an auxiliary channel capable of rapid antegrade conduction, causing rapid ventricular rates that can progress to ventricular fibrillation and cardiac collapse. If provided in the context of a bystander auxiliary route and fast atrial rhythm, such as in atrial fibrillation, atrial flutter, or other atrial tachycardias, AV nodal blockage might cause this situation.

Depending on the underlying arrhythmia, these arrhythmias will be broad complex tachycardias that can be regular or irregular. Antidromic AVRT will be difficult to identify definitively without electrophysiologic research and, as a result, should be handled similarly, with nodal blocking medications avoided. Procainamide is the preferred pharmacologic therapy for antidromic AVRT. AV nodal blockage is contraindicated in the presence of preexcitation and atrial fibrillation. Procainamide and ibutilide are the preferred medicines in atrial fibrillation with preexcitation on the ECG.

Amiodarone has been used to treat WPW pattern atrial fibrillation, however some research shows that it is less effective and has a higher risk of causing ventricular fibrillation. If there is any ambiguity regarding the diagnosis of a broad complex tachycardia, it is best to treat it as suspected ventricular tachycardia.

Patients with a WPW pattern on their ECG who have hemodynamic stability and orthodromic AVRT will have a regular narrow complex tachycardia. They can be treated in the same way as other typical narrow complicated supraventricular tachycardias are. First-line treatment consists of vagal manipulations followed by an adenosine trial.

According to the 2015 ACC/AHA/HRS recommendations, beta-blockers or calcium channel blockers should be used as second-line medicines, with electric cardioversion reserved for refractory arrhythmias. If there is any dispute regarding the diagnosis of orthodromic AVRT, or if there is aberrant conduction resulting in a broad complex appearance, nodal blocking drugs should be used with caution. It may be wise to treat as an undifferentiated broad complicated tachycardia.

 

Differential Diagnosis

The differential diagnosis for WPW pattern and syndrome is extensive and can be narrowed down by the patient's symptoms, ECG pattern, or kind of dysrhythmia. Because the WPW pattern is defined by its ECG findings of a short PR interval, enlarged QRS complex, and slurred delta wave, the differential diagnosis includes any illness that might induce comparable ECG abnormalities.

Myocardial infarction, bundle branch block, congenital or acquired structural heart abnormalities, hypertrophy, premature junctional or ventricular complexes, ventricular bigeminy, accelerated idioventricular rhythms, electrical alternans, pacemaker, or metabolic/electrolyte abnormalities are among the differential diagnoses. 

 

Prognosis

WPW pattern is an uncommon disorder, and the majority of people with preexcitation on ECG will never have symptoms, concomitant arrhythmias, or the most feared consequence, sudden cardiac death. According to two population studies, the risk of sudden cardiac mortality in individuals with the WPW pattern ranges from 0.0002 to 0.0015 per patient-year.

Male gender, age less than 35 years, history of atrial fibrillation or AVRT, numerous accessory pathways, septal placement of the accessory pathway, and ability for fast anterograde conduction of the accessory route are all risk factors for sudden cardiac death.

Regardless of the low prevalence of the WPW pattern or the low incidence of major consequences, it is nevertheless a risky medical condition. Over the last 80 years, antiarrhythmic drugs and ablation procedures have greatly improved the prognosis for individuals with WPW pattern. For individuals with WPW syndrome, high-risk characteristics, or a strong preference, radiofrequency catheter ablation can be curative, with high success rates and minimal complication rates.

 

Complications

Sudden cardiac death is the most feared consequence of WPW syndrome (SCD). According to population research, SCD is most commonly caused by ventricular fibrillation, which leads to cardiac arrest, or by atrial fibrillation or circus movement tachycardia. The mechanism for progression to ventricular fibrillation, which leads to SCD, is an auxiliary circuit capable of fast antegrade conduction, allowing rapid transfer of atrial impulses to the ventricle.

This can be aggravated or triggered by the use of AV nodal blocking medicines, and these medications should be avoided in the setting of a WPW pattern on resting ECG with fast atrial arrhythmias; atrial fibrillation and flutter are the most threatening due to their extremely rapid rates. Tachyarrhythmias that occur often or over an extended period of time might predispose to heart failure.

Comorbid medical disorders might be initiated or exacerbated by hemodynamic instability during a tachyarrhythmia. Patients who have syncope in conjunction with an abrupt arrhythmia are at risk of sustaining catastrophic injury.

 

Conclusion 

The existence of an auxiliary route in Wolff-Parkinson-White syndrome predisposes individuals to tachyarrhythmias and sudden death. Atrioventricular reentrant tachycardia (AVRT) is the most prevalent arrhythmia in individuals with WPW syndrome, accounting for 95 percent of re-entrant tachycardias.

It is believed that one-third of WPW syndrome patients have atrial fibrillation (AF). Afib is a potentially fatal arrhythmia. If an accessory route has a short anterograde refractory time, then fast repeated conduction to the ventricles during AF might result in a quick ventricular response, followed by ventricular fibrillation (VF). The auxiliary route might be anywhere along the atrioventricular valve. Because the majority of the patients are young and do not have structural heart disease, it is critical to risk stratify these individuals in order to prevent sudden death.

The treatment of asymptomatic WPW syndrome patients has long been contentious. Catheter ablation of auxiliary routes has become a well-established modality of treatment for both symptomatic and asymptomatic individuals working in high-risk occupations.

It is frequently difficult to design and conduct well-structured, rigorous research in uncommon medical disorders. The majority of the evidence for Wolff-Parkinson-White syndrome comes from case series and population research. The pathophysiologic foundation is well established, and surgical or catheter ablation has been demonstrated to be effective and low risk. Ablation is the most definite therapy in high-risk individuals, although additional future research would help define medical care and ablation thresholds in certain low-risk patients.