Wolff-Parkinson-White syndrome

Ventricular preexcitation syndrome

Under physiological conditions, the atrial myocardium is electrically connected to the ventricular myocardium only through the His bundle, which passes through the fibrous skeleton into the interventricular septum. The excitation from the SA node spreads as follows: SA node → internodal atrial connections → AV node → His bundle → Tawara branches → Purkinje fibers → ventricular myocardium.

In the case of preexcitation syndromes, in addition to His's bundle, there is another connection between the atria and ventricles. These so-called accessory pathways (accessory conductive bundles) do not connect to the AV node, therefore there is no slowing down of the transfer from the atria to the ventricles, which results in premature activation (excitation) of the ventricular myocardium (→ ventricular preexcitation syndrome).

Accessory bundles directly connect the atrias with the ventricles. In most patients with ventricular preexcitation syndrome (these bundles) are found in the left heart.

The best known 3 ventricular preexcitation syndromes are:

1. WPW syndrome (Wolff-Parkinson-White syndrome)

2. LGL syndrome (Lown-Ganong-Levine syndrome)

3. Mahaim type preexcitation

Wolff-Parkinson-White syndrome (WPW) is the most common ventricular preexcitation syndrome. It is a cardiac arrhythmia in which the excitation (depolarization waves) spreads from the atria to the ventricles outside the AV node. The accessory pathway here is formed by the so-called Kent bundle (= pathological connection between the atria and ventricles).

Etiology

 * It is most often a congenital disease, which is associated with Ebstein's anomaly, tuberous sclerosis, etc.
 * For acquired reasons, WPW syndrome can be caused, for example, by endocarditi or myocarditis.

In a small group of patients, the cause of WPW syndrome is a mutation in the PRKAG2 gene. This gene encodes a protein that is part of an enzyme called AMP-activated protein kinase (AMPK).

There is also a familial form of WPW syndrome (AD inheritance), but it is extremely rare.

Symptoms
WPW syndrome can manifest with the following symptoms:


 * dizziness, sincope
 * palpitations (heartbeat feelings)
 * "short breath” feeling, need to breathe

Diagnostics
The diagnostics is based on an ECG image. In WPW syndrome on the ECG we observe the following changes:


 * shortening of PQ (PR) interval → PQ ≤ 0.12 s (there is no delay of depolarization wave in AV node)
 * delta wave (beginning of QRS complex is deformed by delta wave, ventricular myocardium is preexcited)
 * the other half of the QRS complex is normal (the wave of depolarization that reached the ventricles through the Kent bundle encounters the wave of depolarization that reached the chambers normally through the His bundle)
 * QRS complex widening beyond 0.10 s (due to the delta wave, the QRS complex may expand).

In symptomatic patients (WPW + tachyarrhythmia) electrophysiological examination is also necessary.

Complications
Abnormal ventricular atrial connection (Kent bundle) may be associated with other arrhythmias. It is most often paroxysmal supraventricular tachycardia, less often permanent supraventricular tachycardia, rarely ventricular tachycardia. Very rarely, WPW syndrome can result in ventricular fibrillation and sudden cardiac death.

The danger lies in the formation of the so-called reentry circuit and the so-called AV reentry tachycardia (AVRT, atrioventricular reentry tachycardia).


 * In the case of orthodromic AVRT, the depolarization wave propagates from the atria to the ventricles normally through the His bundle and through the Kent bundle back from the ventricles to the atrium (95%).
 * In the case of antidromic AVRT, the depolarization wave propagates from the atria to the ventricles through the Kent bundle and from the ventricles to the atria through the His bundle (5%).

→ In both cases, atrial reactivation occurs and a pathological circuit develops, resulting in tachycardia.

Treatment
Asymptomatic patients - treatment is not necessary (catheter ablation is indicated in patients with high-risk occupations: pilots, drivers,…)

Symptomatic patients:

1. Abolition of acute paroxysm of tachyarrhythmia: antiarrhythmics I. or III. class.

2. Pharmacological treatment: single administration of an antiarrhythmic at the onset of tachycardia paroxysm or long-term regular antiarrhythmic therapy.

3. Catheter ablation (as part of electrophysiological examination): radiofrequency disruption of the Kent beam.