Contents
Introduction
Wolff-Parkinson-White Syndrome (WPW) is a genetic disorder that allows abnormal conduction to occur in the heart, via an accessory pathway. It is sometimes called a pre-excitation syndrome, and Wolff-Parkinson-White is by far the most common of these. Others include Lown-Ganong-Levine syndrome, and Mahaim-type pre-excitation.
It is important because it can lead to arrhythmias, which potentially can cause VF and lead to death.
WPW can lead to atrial fibrillation, atrial flutter, and a type of SVT, known as Atrioventricular re-entry tachycardia (AVRT) – not to be confused with AV node re-entry tachycardia (AVNRT). They are both types of SVT – supraventricular tachycardia.
- In AVNRT the tachycardia exists due to aberrant conduction through the AV node itself, and occurs in structurally normal hearts
- In AVRT (including WPW) the abnormal conduction occurs through an accessory pathway which is an anatomical abnormality
AVRT can pre-dispose to VF and cardiac arrest.
All pre-excitation syndromes result in faster conduction of impulses through an accessory pathway. This causes a short PR interval on ECG. Once this impulse reaches the ventricles, conduction does not occur via the normal conducting system route, which causes an altered QRS complex – in the cases of WPW this leads to a sloping R wave – known as the delta wave. There are also often multiple and non-specific T-wave changes.
Hence, the defining ECG features of WPW are:
- Short PR interval
- Delta wave
- Non-specific T-wave changes
Epidemiology and Aetiology
- Incidence 0.3 per 1000
- Prevalence 0.1-0.3%
- More common in men
- Congenital structural heart abnormality, although most often does not present until teenage years or early adulthood. Can present later
- 10% of those with WPW with have SVT episodes when age 20-40
- Can be associated with other structural heart abnormalities, including valve defects (particularly mitral valve prolapsed) and cardiomyopathies
Presentation
- Wolff-Parkinson-White Syndrome is often asymptomatic and may be discovered incidentally on ECG
- Acute episodes of SVT include features of SOB, palpitations, dizziness, chest pain and syncope
- May also present with atrial fibrillation or atrial flutter
- Acute episodes may be followed by polyuria – SVT causes dilation of the atria, which releases atrial naturetic factor
- In severe cases, VF and cardiac arrest can occur
Pathology
In most individuals, the accessory pathway allows conduction in both directions. In 15% of cases, it allows only retrograde conduction
Atrioventricular Re-entry Tachycardia
Orthodermic conduction
- The accessory pathway allows the electrical signal to return to the atria from the ventricles. (usually the only route by which this can occur is the AV node, and in a healthy individual, the AV node only allows conduction in one direction, and thus this cannot occur)
- In WPW the accessory pathway is sometimes referred to as the Bundle of Kent
Atrial Flutter and Atrial Fibrillation
- Atrial flutter occurs in up to 7% of patients with Wolff-Parkinson-White Syndrome
- Atrial fibrillation occurs in around 20%
- Can lead to VF or VT as the rapid atrial rate can be transferred directly to the ventricles via the accessory pathway without passing through the moderating effect of the AV node
ECG changes
Pre-excitation – i.e. not during an acute episode
Most patients with features of pre-excitation do not go on to develop arrhythmias.
- Delta wave – the classical WPW sign, which may be seen outside of the acute episode in an otherwise normal asymptomatic patient. Refers to a ‘slurred upstroke’ of the QRS complex, often in associated with a short PR interval
- Presence of delta wave may make base of QRS complex broad
- May also be ST changes – usually discordant (changes occur in opposite direction to QRS complex)
- WPW is sometimes divided into two types:
- Type A – positive delta wave and QRS throughout. Can look like right bundle branch block
- Type B – negative delta wave in V1 and V2, positive in other precordial leads. Can look like left bundle branch block.
Orthodermic Conduction – i.e. retrograde conduction through the accessory pathway
- Rate 200-300
- Absent p waves (not visible behind fast QRS complexes)
- Narrow QRS (<120ms) unless other abnormalities (e.g. Bundle branch block) are present
- T wave inversion
- ST segment depression
Antidromic Conduction
- Rate 200-300
- Wide QRS due to abnormal ventricular depolarisation through accessory pathway
Atrial fibrillation
- Rate >200
- Irregular
- Wide QRS as abnormal ventricular conduction and depolarisation as signal bypasses AV node
Diagnosis
- May involve the use of 24-hour Holter monitors to try to capture episodes of arrhythmia
- Stress testing can help elicit arrhythmias
- Routine bloods will likely be normal, but can rule out other causes of arrhythmias
- Echo may be performed to rule out other visible structural heart abnormalities
- Electrophysiology studies can show where the accessory pathway is to mark a site for ablation
Management
AVRT episodes / Haemodynamically unstable patients
- DC cardio version is treatment of choice
- Manage as per Resus Council SVT acute management guidelines
- If haemodynamically unstable then synchronised DC cardioversion
- If haemodynamically stable:
- Attempt vagal manoeuvres (e.g. ask patient to blow on 50ml syringe, carotid sinus massage)
- If unsuccessful, give adenosine (6mg initially, followed by 12mg if required. Further 12mg dose can also be given)
- Consider synchronised DC cardioversion if above unsuccessful
- Avoid adenosine in AF as can paradoxically increase ventricular rate
- AVRT episodes with antidromic conduction may be difficult to recognise, as the wide QRS means they can be mistaken for VT. If haemodynamically unstable, synchronised DC cardioverison. If any doubt as to the diagnosis, treat as VT
Asymptomatic Patients
- May just have regular follow up
- Can have radio-frequency (RF) ablation therapy to destroy the accessory pathway
- 95% successful
- Usually done after electrophysiology studies have confirmed the site of the accessory pathway
- Has now largely replaced surgical ablation. Surgical may still be used in those in which RF ablation has failed, or who have other structural heart abnormalities
- Drug treatment may be used in those unsuitable or unwilling to undergo ablation therapy
Symptomatic Patients
After resolution of acute episode:
- May require drug therapy to prevent further episodes. Often amiodarone, flecainide or sotalol are used
- An anti-arrythmic (usually calss IC or III) plus an AV node blocker should be used. AV node blocker alone is not enough to control the rapid rates seen in WPW involving the accessory pathway
- Digoxin is contraindicated in Wolff-Parkinson-White Syndrome – and is associated with increased risk of death
- Consider for RF ablation as above
- May have implications for driving and operating heavy machinery
Prognosis
- Prognosis generally very good. Radio frequency ablation is often curative
- Sudden death can occur but is rare – around 0.1%
- Risk correlates with short R-R interval. <250ms indicates highest risk
- Family History of sudden cardiac death also indicates higher risk
- In asymptomatic patients, risk of arrhythmia declines with age
Risk of VF or VT due to conduction across the accessory pathway