AV-reentry Tachycardia & Wolff-Parkinson White Syndrome

Background

  • AVRT is the most common ventricular pre-excitation syndrome and the second most common type of junctional tachycardia.
  • Incidence 0.1-0.3/1000
  • WPWS is associated with a small risk of sudden cardiac death

Pathophysiology and Pre-excitation

  • ‘Pre-excitation’ is a term used to describe early excitation of the ventricles due to impulses bypassing the AV node via an accessory pathway, or bypass tracts
    • These pathways are usually congenital and can occur in various locations.  The most common, as in WPWS, is known as the Bundle of Kent  which traverses the atrioventricular junction
    • The majority of these tracts can conduct both in an anterograde and retrograde direction
    • Pre-excitation is when a ‘normal’ impulse from the SA node is conducted through both the (fast) accessory pathway and the (slower) AV nodal pathway.
      • Results in a short PR interval and the delta wave
  • The accessory pathway can also act as a route for a re-entry tachycardia (NB the majority of patients with WPWS do not develop tachyarrhythmias but the result of an arrhythmia can often be serious)
    • If, for example, an atrial ectopic beat may be conducted initially through the AV node but not through the accessory pathway.  The impulse may then enter the ventricles and reenter the atria via the accessory pathway, which can pass the the AV node again.  This loop is the AVRT, and usually has a rate of between 150-250bpm
    • If atrial fibrillation or atrial flutter happen to occur in the presence of WPWS/accessory pathways, a severe tachycardia may be seen- as the 2:1 block does not occur.  Rates can be up to 300bpm (often these patients will have decompensated vital observations as a result)

Classification of WPWS

  • Type A: delta wave and QRS complex are predominantly upright in precordial leads (V1-V6).  There may also be a predominant R wave in V1 (looks like RBBB) i.e. communication is between the left ventricle and atrium
  • Type B: delta wave and QRS complex are predominantly negative in leads V1-2 (can look like LBBB) i.e. communication is between the right ventricle and atrium

Presentation

  • Commonly an incidental finding on an ECG performed for another reason.
  • Patient may present with palpitations, light-headedness, syncope etc if tachycardia is present
    • These patients can quickly deteriorate to VF if this is due to atrial fibrillation, and sudden collapse/sudden death can also occur

If the patient presents acutely, manage as adult tachycardia (ABCDE) approach (see here)

ECG

  • Pre-excitation and the delta wave:
    • DeltaWave09
    • Short PR Interval <120ms; wide QRS >120ms
  • IN AVRT that occurs in a retrograde direction (orthodromic conduction- most common)
    • Rate usually 200-300 bpm
    • P waves can be retrograde or buried in QRS complexes
    • QRS complex is usually narrow
    • Largely indistuinguishable from AVNRT

Management

  • If the patient presents acutely with an AVRT- the management is identical to AVNRT
    • Valsava manoeuvres/carotid sinus massage can be used- this may relieve the tachyarrhythmia
    • IV adenosine is the mainstay of treatment in a stable patient (Synchronised DC cardioversion is preferred in unstable patients)
      • NB A defibrillator should be at hand for cardioversion should adenosine send the tachycardia into VT/VF (secondary to Atrial flutter/fibrillation)
      • IV flecainide/sotalol/amiodarone can also help restore sinus rhythm, and may be used prophylactically after adenosine administration.
      • Calcium channel blockers e.g. verapamil or diltiazem may also be used.
  • Long-term management for WPWS is really radio-frequency ablation of the accessory pathway.
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