Wolff-Parkinson-White Syndrome

Wolff-Parkinson-White syndrome is the commonest of the ventricular pre-excitation syndromes. Others include Lown-Ganong-Levine syndrome, and Mahaim-type pre-excitation. They are important because of the association with paroxysmal tachycardias that can result in serious cardiovascular complications and sudden death. In ECG terms they are important to recognise, because of the risk of misdiagnosis.

Wolff-Parkinson-White syndrome is a congenital abnormality which can result in SVT that uses an AV accessory tract. The accessory pathway may also allow conduction during other supraventricular arrhythmias, such as atrial fibrillation or flutter. The majority of patients with ECG findings of pre-excitation do not develop tachyarrhythmias. Wolff-Parkinson-White syndrome is classified into two types according to the ECG findings:

• Type A: the delta wave and QRS complex are predominantly upright in the precordial leads. The dominant R wave in lead V1 may be misinterpreted as right bundle branch block.
• Type B: the delta wave and QRS complex are predominantly negative in leads V1 and V2 and positive in the other precordial leads, resembling left bundle branch block.

• An accessory pathway is likely to be congenital, although it presents in later years and may appear to be acquired.
• May be associated with congenital cardiac defects, Ebstein anomaly, mitral valve prolapse, hypertrophic cardiomyopathy or other cardiomyopathies.

• Delta wave is seen in approximately 1.5/1000 population but most never experience paroxysmal tachycardias.
• Due to those with normal a ECG, or latent cases, the true prevalence may approach 4/1000.

Risk factors

• WPW syndrome is found in all ages.
• Prevalence decreases with age because of loss of pre-excitation.
• In patients with abnormal ECG findings indicative of WPW syndrome, the frequency of SVT paroxysms increases from 10% in people aged 20-39 years to 36% in people older than 60 years.
• Presentation In patients with WPW syndrome, the tachycardia that produces symptoms may be an SVT, atrial fibrillation, or atrial flutter.

• SVT in WPW syndrome may begin in childhood or not appear clinically until middle age.
• Asymptomatic: may be detected on incidental ECG.
• Symptomatic: palpitations, light-headedness or syncope.
• Paroxysmal SVT can be followed after termination by polyuria, which is due to atrial dilatation and release of atrial natriuretic factor.
• Sudden death: from deterioration of pre-excited atrial fibrillation into ventricular fibrillation.
• During SVT, the rhythm is constant and regular, with constant intensity of the first heart sound.
• The jugular venous pressure may be elevated, but the waveform remains constant.
• Clinical features of associated cardiac defects may be present, e.g. mitral valve prolapse, cardiomyopathy.

• Atrioventricular Nodal Reentry Tachycardia (AVNRT)
• Ebstein Anomaly
• Lown-Ganong-Levine Syndrome
• Other causes of syncope

ECG¹

• The electrical impulse may travel at the same speed as along the normal system (bundle of His), with no pre-excitation and the ECG is normal. The condition is described as latent, until the rate exceeds the refractory period of the AV node.
• Classic ECG findings of WPW syndrome include a short PR interval (less than 120 ms), a wide QRS complex of longer than 120 milliseconds with a slurred onset producing a delta wave in the early part of QRS, and secondary ST-T wave changes.
• Repolarisation abnormalities are common in patients with WPW syndrome.
• AV re-entry tachycardia, or circus movement tachycardia:
  • The accessory pathway only conducts in a retrograde manner, and the condition remains latent until triggered.
  • A premature atrial extrasystole, finding the accessory pathway refractory, travels via the AV node, with reactivation back from the ventricles along the accessory pathway (retrograde conduction), if time has allowed recovery of excitability.
  • Therefore a circuit is established, being seen as a tachycardia, with normal QRS but with inverted P-waves (because of retrograde atrial activation).
• Pre-excited atrial fibrillation:
  • Conduction is rapid, avoiding any rate-limiting effect of the AV node, the accessory pathway having a much shorter anterograde refractory period. Ventricular response is thus not limited.
  • Hypotension, by causing a sympathetic response, can further shorten the refractory period and ventricular fibrillation may result.
  • The appearance is irregular, variable QRS (normal to wide-complex), at rates often around 250 beats per minute.
• There is a much rarer form of AV tachycardia with anterograde conduction via the accessory pathway, and retrograde conduction via the AV node, seen as a regular, rapid, broad-complex tachycardia.

Other investigations

• Ambulatory ECG
• Routine blood tests may be needed to help rule out non-cardiac conditions triggering tachycardia, e.g. full blood count, urea, electrolytes and creatinine, liver function tests, thyroid function tests and blood levels of antiarrhythmic drugs
• Echocardiogram: may be needed to assess left ventricular function and wall motion and to help rule out valvular disease, Ebstein anomaly, hypertrophic cardiomyopathy (in which the incidence of accessory pathways is increased), or other congenital cardiac defects

Asymptomatic patients may just need periodic review. The main forms of treatment are drug therapy, radiofrequency ablation and surgical ablation. Ablation is the first-line treatment for symptomatic WPW syndrome. It has replaced surgical treatment and most drug treatment.

• Patients who present with tachyarrhythmic symptoms require drug therapy to prevent further episodes. Drugs used include amiodarone, and sotalol.
• A membrane-active antiarrhythmic drug (class IC or III) should be used with an AV nodal blocker, rather than just an AV nodal blocker, because of the potential for extremely rapid rates during pre-excited atrial fibrillation or flutter.
• Digoxin is contraindicated in patients with WPW syndrome. Most deaths from WPW syndrome have been associated with digoxin use.

Termination of an acute episode

• Narrow-complex AV re-entrant tachycardia is treated in the same way as AVNRT, by blocking AV node conduction with:
  • Vagal manoeuvres, e.g. valsalva, carotid sinus massage, splashing cold water or ice water on the face.
  • Intravenous adenosine (or intravenous verapamil or diltiazem if recurrent SVT, adenosine is ineffective or if the patient is taking theophylline). Do not use adenosine if atrial fibrillation is suspected, as blocking the AV node can paradoxically increase ventricular rate resulting in fall in cardiac output (ventricular refractory period after a normally conducted impulse through AV node may be critical in maintaining cardiac output) - cardioversion is more appropriate.
  • Atrial fibrillation can occur after drug administration, particularly adenosine, with a rapid ventricular response. An external cardioverter-defibrillator should be immediately available.
• Atrial flutter/fibrillation or wide-complex tachycardia
  • Atrial flutter/fibrillation causes abnormal QRS complexes and irregular R-R intervals.
  • Cardioversion may be best option, as conventional drugs such as digoxin, beta-blockers, or calcium channel blockers, may paradoxically increase the ventricular rate, with risk of ventricular fibrillation.
  • In stable patients, intravenous flecainide,² sotalol or amiodarone can restore sinus rhythm through slowing anterograde conduction through the accessory pathway.
  • Prophylactically, flecainide and sotalol are used to minimise the risk of recurrent atrial fibrillation.²
  • If ventricular tachycardia cannot be excluded, the drugs of choice is amiodarone. Lignocaine should be avoided and may increase the ventricular response if atrial fibrillation is present.

Long-term maintenance treatment

• Response to long-term antiarrhythmic therapy for the prevention of further episodes of tachycardia in patients with WPW syndrome is unpredictable. Some drugs may paradoxically make the reciprocating tachycardia more frequent.
• Two-drug therapy has been used.
• Class IC drugs (e.g. amiodarone, sotalol) are effective but should not be given if the patient has structural heart disease. Class IC drugs are usually used with an AV nodal blocking agent.

Radiofrequency ablation

• Radiofrequency ablation is increasingly being used in both common types of arrhythmia, and selected asymptomatic patients, with a 95% success rate.³
• This follows electrophysiological studies to determine the site of the accessory pathway. Rarely, there may be more than one accessory pathway.
• This is superseding open-heart surgical disconnection, and cardiac pacing.
• Patients who have accessory pathways with short refractory periods do not respond well to drug treatments and are best treated with ablation.
• Indications for RF ablation include:
  • Patients with symptomatic AV reentrant tachycardia.
  • Atrial fibrillation or other atrial tachyarrhythmias that have rapid ventricular rates via a bypass tract.
  • Asymptomatic patients with ventricular pre-excitation whose livelihood, profession, insurability, or mental well-being may be influenced by unpredictable tachyarrhythmias or in whom such tachyarrhythmias would endanger the safety of themselves or others.
  • Patients with atrial fibrillation and a controlled ventricular response via the bypass tract.
  • Patients with a family history of sudden cardiac death.

• Tachyarrhythmia:
  • Increased risk of dangerous ventricular arrhythmias due to fast conduction across the bypass tract if they develop atrial flutter or fibrillation.
  • Digoxin and perhaps other AV nodal blocking agents may accelerate conduction through the bypass tract, causing potentially lethal ventricular arrhythmias or haemodynamic instability during atrial fibrillation.
• Sudden cardiac death:
  • Occurs rarely, with an estimated frequency rate of 0.1%.
  • Other factors that appear to influence risk are the presence of multiple bypass tracts and a family history of premature sudden death.
  • Sudden cardiac death is unusual without preceding symptoms.

• In asymptomatic patients, the capacity for antegrade conduction across the accessory pathway often decreases with age. This is probably due to fibrotic changes at the site of insertion of the accessory bypass tract.
• Risk of sudden death is lowest in those who have not had any symptomatic tachycardias, or are intermittent, as this is associated with a long accessory pathway refractory period.
• Risk of sudden death can be assessed by measuring the shortest R-R interval, less than 250ms denoting high risk.
• Disappearance of the delta wave with class 1a or 1c drugs (e.g. flecainide) also suggests low risk of sudden death.