Introduction

• Wolff Parkinson White syndrome is a combination of preexcitation caused by a congenital accessory pathway and paroxysms of tachyarrhythmia

• WPW is usually found in young otherwise healthy individuals that experience symptoms during paroxysms that can vary in severity from mild chest discomfort or palpitations with or without syncope to severe cardiopulmonary compromise and cardiac arrest

Causes

• Preexcitation occurs when impulses from atrium are conducted via an accessory pathway that directly connects the atria and ventricles and bypasses the AV node. This results in the earlier activation of the ventricles than if the impulse had travelled through the AV node
• Accessory pathways or bypass pathways are strands of myocardium that are created by incomplete embryological development of the AV annuli. They may be located anywhere along the AV ring or in the septum, but most commonly found along mitral or tricuspid annulus
• These pathways may conduct antegrade only, retrograde only, or antegrade and retrograde. Retrograde only pathways cannot be seen on the ECG 
• Various algorithms can help determine pathway location, but the same pathway may not always produce the identical ECG pattern. Furthermore 13% of patients with preexcitation have more than one accessory pathway

Classification

Wolff-Parkinson-White syndrome 

• pre-excitation caused by accessory pathway - usually the Kent bundle, which directly links the atria to the ventricles, bypassing the atrioventricular (AV) node in combination with recurrent tachyarrhythmia – most often atrioventricular reentrant tachycardia (AVRT)
• Specific pattern during sinus rhythm that is persistent or intermittent
• The prevalence of WPW pattern is estimated at 0.13 to 0.25 % in the general population

• WPW can be divided by position of accessory pathway to:
  - Type A - left sided accessory pathway resulting in tall R wave in leads V1-V3 (a positive or upward delta wave)
  - Type B - right sided accessory pathway in which there are QS complexes in leads V1-V3 (a negative or downward delta wave)

• The majority of patients with the WPW pattern on their ECG remain asymptomatic, although a small percentage of patients with the WPW pattern develop arrhythmias as a part of WPW syndrome

• The diagnosis of WPW syndrome is typically made with a 12-lead electrocardiogram (ECG) and sometimes with ambulatory monitoring (Holter monitoring)

Picture 1 Bundle of Kent 

http://ems12lead.com/2012/02/06/discussion-for-17-year-old-male-cc-chest-pain-and-palpitations-wpw-part-i/#gref

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‍ECG features

WPW has a typical pattern during sinus rhythm

1. the PR interval is short <120ms – rapid conduction through the accessory pathway that bypasses the AV node
2. delta wave - the initial part of ventricular activation is slowed, and the upstroke of the QRS complex is slurred, because of slow muscle-fiber-to-muscle-fiber conduction.
3. wide QRS complex >120ms - the QRS complex represents a fusion beat - the initial part results from slow ventricular activation via the accessory pathway, while the terminal portion of ventricular activation is via the normal conduction system. 

• ST segment and T wave abnormalities - reflecting abnormal ventricular repolarization.
• ST-T segment is usually directed oppositely to delta waves
• The more rapid the conduction along the accessory pathway, the greater the amount of myocardium depolarized via the accessory pathway, resulting in a more prominent or wider delta wave, and increasing prolongation of the QRS complex.

Delta waves can be misinterpreted as a different diagnosis due to similar patterns as:

• Myocardial infarction (MI) – A negative delta wave presented as a Q wave. On the other hand, a positive delta wave may mask the presence of a previous MI.
• Ventricular premature beats (VPBs) or idioventricular rhythm – Intermittent WPW may be mistaken for frequent VPBs. 
• Bundle branch block – The QRS duration is equal to or greater than 0.12 seconds because of preexcitation (the delta wave). Right-sided pre-excitation can be mistaken for LBBB; left sided pre-excitation can be mistaken for RBBB

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Tachyarrhythmias associated with WPW syndrome

1) Atrioventricular reentrant tachycardia (AVRT)

• AVRT is a supraventricular tachycardia that utilizes an accessory pathway between the atria and ventricles resulting in a circus movement.
• It is frequently, but not exclusively, associated with preexcitation syndrome (ie, the Wolff-Parkinson-White syndrome).
• The circuit involved in this reentrant arrhythmia includes the accessory bypass tract, AV node, and His Purkinje system, as well as the atria and ventricles.
• There is always 1:1 conduction of the impulse between the atria and ventricles since both structures, along with the AV node and accessory pathway, are a necessary part of the circuit. 
• AVRT is often triggered by premature atrial beats or premature ventricular beats – retrograde activation of atria.
• Orthodromic AVRT accounts for >90% of AVRT and 20-30% of all sustained SVT.

Based on direction of reentry circuit AVRT is divided into 2 groups:

Orthodromic AVRT 

• >90% of AVRT
• re-entrant impulse goes from the atrium to the ventricle through the AV node (normal ventricular activation) and then retrogradely activates atria through accessory pathway

ECG:

• narrow complex tachycardia
• ventricular rate 150-250 bpm
• inverted P wave following a QRS complex - retrograde activation of the atrium
• short RP interval that is usually less than half of RR interval (< ½ RR)

Antidromic AVRT

• the least common arrhythmia associated with WPW syndrome (3-8% of patients)
• Ventricles are activated through a very fast-conducting accessory pathway – anterograde conduction, atria are retrogradely activated over the AV node or another accessory pathway (30-60% of patients have multiple accessory pathways).

ECG:

• wide QRS complex tachycardia
• ventricular rate 150-250 bpm
• Inverted P waves are often hidden in ST-T segment and therefore the RP interval is usually difficult to assess

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‍2) FBI = Fast Broad Irregular tachycardia

• this arrhythmia comes from a pre-excited atrial fibrillation that degenerates into FBI
• Paroxysmal AF has been found in 50% of patients with WPW
• Typically young patients with no structural disease of the heart
• atrial fibrillation with fast ventricular response over an accessory pathway
• potentially life-threatening arrhythmia – due to 1:1 conduction the ventricular rate may be very rapid (even >300bpm) and it can degenerate into ventricular fibrillation!

ECG of atrial fibrillation in WPW:

• irregular wide complex tachycardia
• ventricular rate >200 bpm
• QRS complexes usually have variable morphology – APs bypassing the AV node can produce wide and bizarre looking complexes
• axis remains stable

Various algorithms have been developed to help determine pathway location from surface ECG. One of those is for example St. George’s algorithm.

Picture no. 2 St. George’s algorithm:

ECG 1  Wolff-Parkinson-White syndrome with orthodromic AVRT

• regular narrow complex tachycardia, ventricular rate 150 bpm
• inverted P waves following QRS complexes – short RP interval > AVRT

ECG 2 FBI - Fast Broad Irregular

• wide complex tachycardia
• irregular rhythm
• QRS morphology is variable in each lead
• Atrial fibrillation with 1:1 conduction over a fast-conducting accessory pathway

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Management

• risk stratification of asymptomatic patients with WPW pattern on a surface ECG using non-invasive tests (exercise ECG) or an electrophysiologic study.
• Recommended long-term treatment for symptomatic patients is catheter ablation of the accessory pathway. Precise localization of the anomalous pathway is critical for successful ablation.

Management of AVRT

Acute therapy

1. Hemodynamically unstable patient – urgent synchronized cardioversion
2. Hemodynamically stable patient

Vagal manoeuvres

• Carotid sinus massage - Pressure is applied to one carotid sinus for 5 to 10 seconds. Steady pressure is recommended because it may be more reproducible. If the expected response is not obtained, the procedure is repeated on the other side after a one- to two-minute delay.
• Valsalva manoeuvres – patient is instructed to exhale forcefully against a closed glottis (against closed mouth and compressed nose) for 10 – 15s and then release.
• Modified Valsalva manoeuvre – patient does classical Valsalva manoeuvre followed by 15 seconds of passive leg raise at 45 degree angle – this may be more successful in restoring sinus rhythm.

If vagal manoeuvres are ineffective:

For orthodromic AVRT:

Adenosine

• use with caution! – potential induction of atrial fibrillation with fast ventricular conduction or ventricular fibrillation
• electrical cardioversion should always be available when administering adenosine
• 6 mg i.v. as a rapid bolus with saline flush
• second dose – 12 mg i.v., safe within 1 min of the last dose
• maximum dose = 18 mg

If Adenosine is ineffective > pharmacological therapy directed at AV node:
- Beta blockers - i.v. esmolol, i. v. metoprolol
- Calcium channel blockers (verapamil/diltiazem i.v.)
- If this ineffective > Synchronized cardioversion

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For antidromic AVRT:

If vagal manoeuvres are ineffective:

Pharmacological therapy directed at fast-conducting AP (accessory pathway):

• i.v. ibutilide or procainamide
• i.v. propafenone or flecainide

Synchronized cardioversion

Chronic therapy

• The treatment of choice for patients with symptomatic and recurrent AVRT is catheter ablation of accessory pathway
• Propafenone or flecainide may be considered in patients with AVRT and without ischaemic or structural heart disease, if ablation is not desirable or feasible

Picture 3 Treatment of AVRT as per ESC guidelines

Management of atrial fibrillation in WPW / FBI 

Synchronized cardioversion in the first place !

• usually required due to the irregular rapid rhythm in hemodynamically unstable patients
• is recommended when pharmacological therapy fails to convert or control the tachycardia.

Pharmacological cardioversion

• drugs directed at AV node should be avoided! – they may contribute to a risk of ventricular fibrillation.
• CAVE – adenosine verapamil, diltiazem, beta blockers or digoxin
• ‍drugs directed at AP conduction - i.v. ibutilide or procainamide (IIa B), i.v. flecainide or propafenone (IIb B)

Picture 4 Treatment of FBI as per ESC guidelines

References

1. Camm, A. J., Lüscher, T. F., & Serruys, P. W. (2009). The ESC textbook of cardiovascular medicine. Oxford, Oxford University Press
2. Josep Brugada, Demosthenes G Katritsis, Elena Arbelo, Fernando Arribas, Jeroen J Bax, Carina Blomström-Lundqvist, Hugh Calkins, Domenico Corrado, Spyridon G Deftereos, Gerhard-Paul Diller, Juan J Gomez-Doblas, Bulent Gorenek, Andrew Grace, Siew Yen Ho, Juan-Carlos Kaski, Karl-Heinz Kuck, Pier David Lambiase, Frederic Sacher, Georgia Sarquella-Brugada, Piotr Suwalski, Antonio Zaza, ESC Scientific Document Group, 2019 ESC Guidelines for the management of patients with supraventricular tachycardia The Task Force for the management of patients with supraventricular tachycardia of the European Society of Cardiology (ESC): Developed in collaboration with the Association for European Paediatric and Congenital Cardiology (AEPC), European Heart Journal, Volume 41, Issue 5, 1 February 2020, Pages 655–720, https://doi.org/10.1093/eurheartj/ehz467
3. Jordan M Prutkin, MD, MHS, FHRS (2019). ECG tutorial: Preexcitation syndromes. In I. Gordon M Saperia, MD (Ed.), UpToDate. Retrieved February 3, 2021, from https://www-uptodate-com.ezproxy.is.cuni.cz/contents/ecg-tutorial-preexcitation-syndromes?search=preexcitation%20syndrome&source=search_result&selectedTitle=2~150&usage_type=default&display_rank=2
4. Bradley P Knight, MD, FACC (2019). Anatomy, pathophysiology, and localization of accessory pathways in the preexcitation syndrome. In I. Todd F Dardas, MD, MS (Ed.), UpToDate. Retrieved February 3, 2021 from https://www-uptodate-com.ezproxy.is.cuni.cz/contents/anatomy-pathophysiology-and-localization-of-accessory-pathways-in-the-preexcitation-syndrome?search=preexcitation%20syndrome&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1
5. Luigi Di Biase, MD, PhD, FHRS, Edward P Walsh, MD (2019). Wolff-Parkinson-White syndrome: Anatomy, epidemiology, clinical manifestations, and diagnosis. In I. Todd F Dardas, MD, MS (Ed.), UpToDate. Retrieved February 3, 2021 from https://www-uptodate-com.ezproxy.is.cuni.cz/contents/wolff-parkinson-white-syndrome-anatomy-epidemiology-clinical-manifestations-and-diagnosis?search=preexcitation%20syndrome&source=search_result&selectedTitle=3~150&usage_type=default&display_rank=3

Pictures

1. BAUMRIND, David. EMS 12-Lead [online]. [cit. 3.2.2021]. Accessible at WWW: http://ems12lead.com/2012/02/06/discussion-for-17-year-old-male-cc-chest-pain-and-palpitations-wpw-part-i/#gref
2. BRUGADA a kol. 2019 Guidelines on Supraventricular Tachycardia (for the management of patients with) [online]. [cit. 4.2.2021]. Accessible at WWW: https://academic.oup.com/eurheartj/article/41/5/655/5556821
3. Acute therapy of atrioventricular reentrant tachycardia. (2019). [Graph]. Accessible at: https://academic.oup.com/eurheartj/article/41/5/655/5556821
4. Acute therapy of pre-excited atrial fibrillation. (2019). [Graph]. Accessible at: https://academic.oup.com/eurheartj/article/41/5/655/5556821