🫀 Mirza's Cardiology Notes

Accessory Pathway Conduction

3 min read

  • Seen if there is antegrade conduction through the bypass (accessory) pathway

  • “WPW pattern” is asymptomatic pre-excitation, whereas “WPW syndrome” involves symptomatic arrhythmia.

  • Characterized by:

    • short PR interval
    • Normal P wave vector (to exclude junctional rhythm)
    • Prolonged QRS interval
      • QRS duration > 100 ms
    • Delta wave
      • dependent on accessory pathway location and AV nodal conduction time

  • The degree of pre-excitation depends on several factors:

    • AV nodal conduction time
      • the slower AV nodal conduction, the larger the delta wave
    • the conduction velocity of the bypass tract
      • rapid conduction velocity → more pre-excitation
    • the refractory period of the bypass tract
      • shorter RP → more pre-excitation
    • proximity of the bypass tract to the SA node
      • atrial impulses reach R-sided bypass tract earlier than a L-sided bypass tract; ∴ R-sided bypass tracts tend to have more pre-excitation

  • ⚠️ For someone with WPW, you won’t see the delta waves while they’re in SVT

  • ![[AV Reentrant Tachycardia AVRT-1745549180943.webp]]

  • Concern of WPW progressing - ![[AV Reentrant Tachycardia AVRT-1745549218573.webp]]

Diagnosis

  • Noninvasive testing is generally considered safe and should be considered in asymptomatic WPW patients. This includes standard 12-lead ECG, ambulatory monitoring, and exercise stress testing (EST).

Exercise testing

  • A significant proportion of patients with ventricular pre-excitation remain asymptomatic yet at the risk of life-threatening arrhythmias.
  • Intermittent ventricular pre-excitation during ambulatory monitoring or abrupt and complete termination of accessory pathway conduction during stress testing suggests a low-risk pathway.
  • Shortest pre-excited RR interval (SPERRI) during atrial fibrillation <250 ms, or accessory pathway effective refractory period <240 ms suggest a high-risk pathway.

1A: Typical WPW preexcitation pattern manifesting as a short PR interval, delta wave, and wide QRS complex. 1B: Loss of ventricular preexcitation (VPE) during noninvasive testing.1C: Noninvasive shortest preexcited R-R interval (SPERRI) measurement during rapid preexcited AF that can potentially precipitate ventricular fibrillation. (Source)

Wolf-Parkinson-White Syndrome

  • When you have arrhythmia ⚡ or Sx related to accessory pathway
    • In the absence of a documented tachyarrhythmia or related symptoms, the ECG findings alone are referred to as WPW pattern.
  • Wolff-Parkinson-White (WPW) syndrome affects 0.1-0.3% of the general population.
  • The characteristic ECG features in WPW Syndrome are:
    • shortened PR interval (<120 ms):
    • slurred QRS upstroke (delta wave)
    • prolonged QRS duration (>120 ms)
  • ☠️ The chief fear of both WPW syndrome and pattern is the risk for sudden cardiac death (SCD) – presumed to result from rapid VPE precipitating VFib.
  • 3 major arrhythmias:

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