The Wolff-Parkinson-White syndrome describes paroxysmal tachydysrhythmias in the presence of a specific accessory pathway which allows direct electrical connection between the atria and ventricles, which usually exclusively occurs via the atrioventricular (AV) node. The accessory pathway is usually referred to as the bundle of Kent, situated in the atrioventricular groove, and is thought to arise as a result of incomplete atrioventricular separation during antenatal life.
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Terminology
Three features must be present on the electrocardiogram (ECG) when a patient is in normal sinus rhythm to diagnose the Wolff-Parkinson-White syndrome.
shortening of the PR interval
a "delta" wave
slight widening of the QRS complex
Epidemiology
An estimated 1 in 2,000 people have an accessory pathway, most of whom will have otherwise structurally normal hearts.
Associations
Clinical presentation
The most common symptom reported is palpitations, which may be spontaneous or triggered by activity, last from seconds to days, and terminate abruptly. Most patients are hemodynamically stable on presentation. Other common symptoms include:
presyncope
dyspnea
weakness
Of note, patients who present in atrial fibrillation may be profoundly unstable, and may present with:
ECG
Features depend on whether the patient is in normal sinus rhythm, or presenting with a tachydysrhythmia; three types of tachydysrhythmia occur, all of which abolish the classic "pre-excitation" features found in sinus rhythm 6.
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short PR interval, delta wave, slight QRS widening, secondary ST-T changes
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shortening of the PR interval
the accessory pathway allows faster conduction than the AV node
normal PR interval lies between 0.12-0.20 seconds
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a "delta" wave
slurring of the initial portion of the QRS complex
myocyte-to-myocyte conduction, after accessory pathway conduction, is less organized than conduction through the specialized conduction system
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slight widening of the QRS
the initial disorganized conduction results in the total duration (normal duration <0.08 seconds) of the QRS being slightly (0.10-0.12 seconds) longer
These three ECG features define the "pre-excited" ECG, and must be present when a patient is in normal sinus rhythm to diagnose the Wolff-Parkinson-White syndrome.
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subdivided into two types based on the QRS complex in precordial lead V1
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type A WPW
dominant R wave in V1 (R wave > S wave)
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type B WPW
lead V1 has a predominantly negative QRS complex (S or Q wave > R wave)
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Features present during a paroxysm of a tachydysrhythmia depend on the pathway taken and the atrial activity present; the three classic presenting rhythms have the following ECG features:
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narrow complex, regular tachycardia
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orthodromic atrioventricular reciprocating tachycardia (AVRT)
most common presenting rhythm
an atrial ectopic beat initiates a re-entry circuit through the AV node, retrograde through the accessory pathway to the atria, completing the circuit through the AV node once more
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wide complex tachycardia
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atrial fibrillation with WPW
may result in hemodynamic instability
ventricular rate may reach up to 300 beats per minute
marked variation in R-R intervals, QRS width, and QRS morphology
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antidromic AVRT
conduction antegrade through the AP to the ventricles, retrograde through the AV node to the atria, then once more through the accessory pathway
regularity of the ventricular rate distinguishes this rhythm from atrial fibrillation with WPW
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If the impulse from the sinoatrial node conducts ("antegrade") through the bypass tract to the ventricles prior to (simultaneously occurring normal conduction) egress from the bundle of His (via the AV node), three features will be evident on the electrocardiogram
Pathology
In 10% of cases multiple accessory pathways coexist. There are three classically described types of pathways, classified based on the anatomical structures which they connect and the resultant features on the electrocardiogram. ECG features in sinus rhythm of the respective pathways include 4:
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bundle of James
connect the proximal atrioventricular node (AVN) to the distal AVN
short PR interval, no delta wave
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bundle of Kent
connect the atria to the ventricles
short PR interval and a delta wave
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Mahaim fibers
connect the right atrium to right bundle branch fascicles
normal (0.12-0.20 seconds) PR interval, delta wave
Accessory pathways may be right-sided, prematurely activating the right ventricle, left-sided or left-sided, pre-exciting the left ventricle. They may also be present on the inferior surface of the heart, located near the interventricular septum.
Radiographic features
Ultrasound
Fetal M mode echocardiography may be used to diagnose the presence of a fetal supraventricular tachycardia, a rare cause of which may be an atrioventricular reciprocating tachycardia (AVRT) due to an accessory pathway. The fetal heart rate in an SVT is usually above 200 beats per minute, with a normal fetal heart rate falling between 120-160 bpm.
Antegrade conduction down the accessory pathway results in a long R-P interval (time between the peak of the "R" of the QRS and the start of the P wave) on the electrocardiogram; the M-mode correlate of this finding is a short V-A interval 4.
The presence of re-entry through an accessory pathway (with fast retrograde conduction and slow antegrade conduction) is considered a likely etiology when the VA interval is shorter than the AV interval in the presence of a fetal SVT; this may affect choice of therapy and prognosis.
History and etymology
The tripartite eponym is derived from the three cardiologists who published the first study case study on eleven patients with this syndrome; Louis Wolff (1898 – 1972), Paul White (1886 – 1973), and John Parkinson (1885 – 1976) 1.