Preexcitation syndromes are characterised by earlier-than-normal depolarisation of the ventricles due to an accessory conduction pathway which bypasses part of the conduction system. The most important one is Wolff-Parkinson-White syndrome (WPW), but others exist as well, like Lown-Ganong-Levine syndrome. Only WPW will be discussed here.
The WPW pattern is characterised by the presence of an accessory conduction pathway which bypasses the AV node, the bundle of Kent. The AV node delays the conduction to the ventricles, so this accessory pathway causes the depolarisation of the ventricles to occur earlier. This is apparent on the ECG as the “delta wave”, which is where the QRS complex gets a small “head start” at the expense of the PQ interval. The delta wave causes the QRS complex to be wider than normal. However, the delta wave pattern on the ECG may be intermittent. As such, the characteristic ECG findings are the follows:
- Shortened PQ/PR interval (< 120 ms)
- Presence of delta wave
- Widened QRS complex
WPW syndrome is characterised by the presence of WPW pattern and the occurrence of paroxysmal tachycardia. WPW syndrome occurs in as little as 2% of people with WPW pattern. The remaining 98% are asymptomatic.
The paroxysmal tachycardia is usually an AVRT or an Afib. Afib in the setting of WPW (preexcited Afib) allows the atrial impulses to be conducted to the ventricles in a 1:1 ratio, causing a ventricular rate of 300 bpm or more, which can degenerate into ventricular fibrillation. The patient present with palpitations and presyncope or syncope.
Asymptomatic people with WPW pattern rarely require treatment, although treatment should be considered if they develop an episode of paroxysmal tachycardia.
Haemodynamically unstable paroxysmal tachycardias should be treated with synchronised electrical cardioversion. In stable patients, vagal manoeuvres or IV adenosine can terminate the tachycardia.
Once terminated, the patient should receive therapy to prevent recurrence of the paroxysmal tachycardia. The first choice is catheter ablation of the accessory pathway. Oral flecainide or propafenone are second line options.
3. Blocks and conduction disorders, diagnosis and drug treatment
5. Non-pharmacological therapy of arrhythmias and conduction disorders (cardioversion, pacemakers, automatic implantable cardioverter defibrillator, catheter ablation)