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Related Subjects: | Wolff-Parkinson White syndrome (WPW) AVRT | Lown Ganong Levine Syndrome AVRT | Supraventricular Tachycardia (SVT) | Atrioventricular Nodal Reentrant Tachycardia AVNRT | Atrial Flutter | Atrial Fibrillation | Sinus Tachycardia | Sinus Arrhythmia | Multifocal Atrial Tachycardia | Resuscitation - Adult Tachycardia Algorithm

IN WPW an accessory pathway that only conducts retrogradely (i.e. no resting ECG delta wave) is called a CONCEALED pathway and those with antegrade conduction where the delta wave is obvious is called a MANIFEST pathway.

About

• WPW - there is an abnormal electrical connection between atrium and ventricle (e.g. bundle of Kent) - this is called an accessory pathway.
• This allows quick conduction from the atria to the ventricles bypassing the AV node.
• Ventricles are depolarized earlier than they would be and this is called pre-excitation.

Causes

• Normal conduction passes anterogradely through the AV node with no retrograde conduction.
• The bypass tract can conduct both directions depending on its characteristics.
• This can lead to an Atrioventricular reentrant tachycardia which may pass anterogradely or retrogradely through the AV node and accessory pathway.
• In AF the bypass tract can conduct unhindered to the ventricles with a risk of VF

Associations

• Septum secundum ASD
• Ebstein anomaly of tricuspid valve
• Hypertrophic cardiomyopathy
• Mitral valve prolapse

Clinical

• Often asymptomatic all lifelong despite ECG changes.
• Palpitations, Syncope, Presyncope.
• Very rarely sudden cardiac death possibly due to AF down accessory pathway

ECG Findings

• Resting ECG
  • A concealed pathway: ECG is normal between arrhythmias no delta wave
  • A manifest pathway: ECG: Short PR and slurred delta wave. May be an RSR pattern in V1 with Type A however there are several different types depending on location of accessory pathway.
• Arrhythmias
  • Atrioventricular reentrant tachycardia (AVRT): Narrow complex with ressntrant pathway involving accessory pathway
  • AF conducted to Ventricle across accessory pathway: irregularly irregular + delta wave. Can degenerate to VF

ECG showing Pre excitation

ECG showing AVNRT

Investigations

• FBC, U&E, TFT, CRP, ECG, CXR
• Echocardiogram or Cardiac MRI
• Electrophysiological studies

AF in a patient with ventricular pre-excitation

If suspect AF and Aberrant conduction down the accessory pathways then you must avoid Adenosine, Digoxin, Beta Blockers or Calcium Channel blockers

Acute Management: There are two scenarios that have specific management

• Regular Narrow Complex Tachycardia AVRT SVT: Can be treated with Vagal Manoeuvres or if that fails then Adenosine or if unstable DC cardioversion which should terminate the SVT. See SVT topic for more options. The arrhytmia can be antidromic (going down the AVNode and then back via accessory pathway) or antidromic going the opposite direction.
• Pre-excited AF: May have known WPW. Wide complex irregular (? AF). AF + delta down accessory pathway vent rate 200+. If compromised DC shock. Suggest IV Procainamide, Ibutilide, Propafenone, Flecainide. (NEVER GIVE Dig/BB/CCB/Adenosine) Needs Cardio consult and Catheter ablation. Amiodarone not recommended
• Patients presenting with pre-excited AF once managed should be referred for definitive treatment which is radiofrequency catheter ablation of the accessory pathway, not only to eliminate symptoms of palpitations but also to eliminate the risk of sudden death. The accessory pathway responsible for pre-excited AF or supraventricular tachycardia can be eliminated in about 95% of patients with a low risk of complications (1%).
• Some Patients may well require a pacemaker after Radiofrequency ablation as 1% end up with CHB as the pathway ablated lies very close to the AV node

References

• Statpeearls on WPW