Main ECG criteria
Diagnostics of ventricular pre-excitation syndrome (Wolff-Parkinson-White or WPW syndrome) is based exclusively on electrocardiogram data.
Key ECG changes include:
- Shortened P-Q (P-R) interval: its duration is less than 0.12 sec. This happens because the impulse is not delayed in the atrioventricular (AV) node, but rapidly passes through the accessory pathway (Kent bundle).
- Altered QRS complex: it becomes widened. A characteristic sign is the appearance of a delta wave ($\Delta$) at the beginning of the complex. It occurs because a portion of the ventricular myocardium is depolarized prematurely via the Kent bundle, while the rest follows the normal pathway through the AV junction.
- Secondary repolarization abnormalities: discordant displacement of the ST segment (directed opposite to the main QRS wave) and a change in T wave polarity are observed.
Topographic diagnostics (typing)
The location of the accessory conduction pathway can be inferred from the ECG morphology in lead $V_1$, based on the polarity of the delta wave.
There are two main types:
- Type A: characterized by a positive $\Delta$ wave in lead $V_1$.
- Type B: distinguished by a negative $\Delta$ wave in lead $V_1$.
Clinical significance and association with arrhythmias
WPW syndrome can be registered as an incidental ECG finding in completely healthy individuals. However, its main clinical manifestation is a predisposition to paroxysmal rhythm disorders.
Most commonly, this syndrome is associated with attacks of supraventricular paroxysmal tachycardia. The mechanism of its occurrence is related to a re-entrant circuit (re-entry) involving the accessory conduction pathway. The onset of such arrhythmias often occurs in childhood or adolescence. Much less frequently, pre-excitation syndrome is accompanied by episodes of atrial flutter or fibrillation.
Class and exam questions
Why is the P-Q interval shortened in WPW syndrome?
The interval is shortened (less than 0.12 s) because the electrical impulse bypasses the AV node via the accessory Kent bundle, where there is no physiological conduction delay.
What is a delta wave and how is it formed?
The delta wave is a slurred initial upstroke of the QRS complex. It reflects the premature depolarization of the part of the ventricles reached by the impulse via the accessory pathway.
Which rhythm disturbance is most typical for this syndrome?
The development of paroxysms of supraventricular tachycardia via a re-entry mechanism involving the Kent bundle is most characteristic.
What else to study on this topic
- Classification of excitability disorders
- ECG signs of supraventricular extrasystole
- Variants of atrioventricular extrasystoles
- Criteria for functional extrasystole
- Ventricular paroxysmal tachycardias
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