Wolff-Parkinson-White syndrome

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.

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.

Epidemiology

An estimated 1 in 2,000 people have an accessory pathway, most of whom will have otherwise structurally normal hearts.

Associations

• Fabry disease
• Danon disease
• hypertrophic cardiomyopathy (HCM)
• Ebstein anomaly

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:

• pulmonary edema
• hypotension
• angina

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 .

• normal sinus rhythm
  • short PR interval, delta wave, slight QRS widening, secondary ST-T changes
  • 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
  • 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
  • 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.

• subdivided into two types based on the QRS complex in precordial lead V1
  • type A WPW
    • dominant R wave in V1 (R wave > S wave)
  • type B WPW
    • lead V1 has a predominantly negative QRS complex (S or Q wave > R wave)

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:

• narrow complex, regular tachycardia
  • 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
• wide complex tachycardia
  • 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
  • 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

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 :

• bundle of James
  • connect the proximal atrioventricular node (AVN) to the distal AVN
  • short PR interval, no delta wave
• bundle of Kent
  • connect the atria to the ventricles
  • short PR interval and a delta wave
• 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

Antenatal 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 .

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) .