Introduction
Wolff-Parkinson-White (WPW) syndrome 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 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 VT 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
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
- Often asymptomatic and may be discovered incidentally on ECG
- Acute episodes of SVT include features of SOB, palpitations, dizziness 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
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 occurs in up to 7% of patients with WPW
- 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
