July 13, 2010

Q&A: Forms of Wolff-Parkinson-White Syndrome

In 1930, Louis Wolff, Sir John Parkinson, and Paul Dudley White published a seminal article describing 11 patients who suffered from attacks of tachycardia associated with a sinus rhythm electrocardiographic (ECG) pattern of bundle branch block with a short PR interval. This was subsequently termed Wolff-Parkinson-White (WPW) syndrome, although earlier isolated case reports describing similar patients had been published.

This article is for Medical Students & Professionals
This is a Question & Answer revision article designed for medical students and professionals preparing for the PLAB, MRCP or USMLE examinations. They are based on actual questions from these examinations. You may find the Electrocardiogram (ECG) article more useful, or one of our many articles on Diseases & Conditions, Medical Syndromes, Health & Wellness or Home Remedies.
In this article:
MCQ exam: clinical scenario
MCQ exam: answer
MCQ exam: explanation

MCQ exam: clinical scenario

A patient with symptomatic WPW syndrome undergoes an intracardiac electrophysiological study and is found to have a reciprocating tachycardia using the normal AV conduction system for the anterograde conduction and the accessory pathway for the retrograde conduction.

This is best described as:

a) Orthodromic tachycardia
b) atrial fibrillation
c) supraventricular tachycardia
d) atrial flutter
e) Ventricular tachyarrhythmias

MCQ questions & answers on medicalnotes.info

MCQ exam: answer

The correct answer is A.
Orthodromic tachycardia is best description.

MCQ exam: explanation

The exact nature of the preexcitation syndrome is assessed.

Most of the WPW syndrome are related to an atrioventricular accessory connection or Kent bundle: the degree of preexcitation increases during premature atrial stimulation until the refractory period of accessory pathway is reached, because the conduction time does not change in accessory pathway with the shortening of atrial cycle length while it increases in the AV node.

Rarely the WPW syndrome is related to a nodoventricular accessory pathway or Mahaim bundle and the degree of preexcitation remains unchanged during premature atrial stimulation.

- The accessory pathway refractory period depends on the driven cycle length. Refractory period of the accessory pathway decreases as the driven cycle length shortens.

- Beta adrenergic stimulation results in shortening of the anterograde refractory period of the accessory pathway and an increase in ventricular rates during atrial pacing and atrial fibrillation.

Isoproterenol test was also previously used to verify the efficacy of antiarrhythmic drug before the era of catheter ablation of accessory pathway. The loss of efficacy of some antiarrhythmic drugs was demonstrated after isoproterenol administration.

i). Atrial fibrillation is easily induced during intracardiac studies by salvos of rapid atrial stimulation and is not specific. The induction of an atrial fibrillation by intracardiac programmed stimulation is obtained in 45% in asymptomatic patients and in 75% of patients with only documented re-entrant tachycardia, atrial fibrillation is induced in 95% of those with documented atrial fibrillation. The important variations of the incidence of induced atrial fibrillation depends on the technique of programmed stimulation, on the interpretation of the duration of induced arrhythmia and on the use of isoproterenol infusion or other means to reproduce the effects of adrenergic stimulation.

The induction of an atrial fibrillation during trans-oesophageal pacing has a best clinical significance:

The incidence of induction of atrial fibrillation also depends on the presence of an associated heart disease and the age of the patient: the induction of atrial fibrillation is rarely noted in children younger than 10 years, is induced in 20% of teenagers and adults without heart disease and becomes relatively frequent in the elderly.

ii). Ventricular tachyarrhythmias also are easily induced in asymptomatic or symptomatic patients by programmed ventricular stimulation and are not specific in patients with WPW syndrome: the induction of a ventricular fibrillation is noted in 4 % of WPW syndrome and the induction of non-sustained multiform ventricular tachycardia in 37 % of them.

iii). Antidromic tachycardia which is a reciprocating tachycardia using the accessory pathway for the anterograde conduction and the normal AV conduction system for retrograde conduction, is a rare finding (5%), more frequently noted in young patients with a good retrograde normal VA conduction or in patients with several accessory pathways and seems more frequent in patients at risk of rapid arrhythmias.

iv). Orthodromic tachycardia which is a reciprocating tachycardia using the normal AV conduction system for the anterograde conduction and the accessory pathway for the retrograde conduction, is rarely induced in asymptomatic patients (< 10%) , but represents the most frequent tachycardia of symptomatic patients complaining of tachycardia and palpitations (90 %).

See also the separate Q&A articles, Treatment Options for Wolff-Parkinson-White Syndrome and Diagnosis of Wolff-Parkinson-White Syndrome.

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