Accessory Pathways

Accessory Pathways – SAQ & EMQ Series

Clinical Scenario:
A 20-year-old male presents to the Emergency Department after collapsing and striking his head during a football match. He experienced brief loss of consciousness and is now alert but confused. Witnesses report he had palpitations immediately before the fall. He denies chest pain. Neurological exam is normal. A non-contrast head CT reveals a mild cerebral contusion.An ECG is performed on arrival, see below

1. What is the typical age and presentation pattern of accessory pathway-mediated tachycardias? [+ Reveal Answer]

Typically occurs in adolescents or young adults. Commonly presents with palpitations, syncope during exertion, or sudden collapse without prodrome.

2. Name three red flags in the history that suggest high-risk pre-excitation. [+ Reveal Answer]

1. Syncope during exertion
2. Family history of sudden cardiac death
3. History of rapid palpitations or documented arrhythmia

3. What is the mechanism of orthodromic AVRT? [+ Reveal Answer]

Antegrade conduction through AV node and retrograde via accessory pathway, forming a reentrant loop.

4. What is the risk if AV nodal blockers are given to a patient with pre-excited AF? [+ Reveal Answer]

They can facilitate conduction through the accessory pathway, potentially causing ventricular fibrillation.

5. List three features of high-risk accessory pathways on electrophysiologic testing. [+ Reveal Answer]

1. Short anterograde ERP (<250ms)
2. Multiple accessory pathways
3. Inducible AF with rapid ventricular response

6. What is the first-line therapy for stable orthodromic AVRT? [+ Reveal Answer]

Vagal maneuvers followed by adenosine if ineffective.

7. What is the long-term management of symptomatic WPW syndrome? [+ Reveal Answer]

Catheter ablation is curative and first-line.

8. What is concealed accessory pathway? [+ Reveal Answer]

Pathway that conducts only retrogradely and is not visible on resting ECG.

9. What does intermittent pre-excitation imply? [+ Reveal Answer]

The accessory pathway does not conduct in every beat; it may suggest a longer ERP and potentially lower risk.

10. List 3 differential diagnoses for a young person with exertional syncope. [+ Reveal Answer]

1. Hypertrophic cardiomyopathy
2. Long QT syndrome
3. WPW or other accessory pathway disorders

11. What ECG features may be seen during sinus rhythm in WPW? See the ECG below. [+ Reveal Answer]

Short PR interval, delta wave, and widened QRS complex.

12. Name a pharmacologic option for stable pre-excited AF. [+ Reveal Answer]

IV procainamide or ibutilide under monitoring.

13. What investigation definitively confirms the presence and characteristics of an accessory pathway? [+ Reveal Answer]

Electrophysiology study (EPS).

14. In which WPW patients is observation rather than ablation reasonable? [+ Reveal Answer]

Asymptomatic patients with long accessory pathway ERP and no arrhythmias.

15. What is the risk of sudden cardiac death in asymptomatic WPW patients? [+ Reveal Answer]

Estimated at 0.1–0.45% per year but varies by pathway properties.

16. What occupations mandate ablation in asymptomatic WPW? [+ Reveal Answer]

Pilots, military personnel, professional athletes, or other safety-sensitive roles.

17. How does isoproterenol affect accessory pathways? [+ Reveal Answer]

May shorten refractory period and unmask conduction; used during EP testing.

18. Name two ECG patterns that can mimic delta wave. [+ Reveal Answer]

Early repolarization and bundle branch block.

19. What are typical symptoms of accessory pathway-mediated tachycardia? [+ Reveal Answer]

Palpitations, chest discomfort, dizziness, or syncope.

20. What is the recurrence rate after successful catheter ablation of WPW? [+ Reveal Answer]

Less than 5% in experienced centers.

21. Whilst in the ED, the patient appears to have another seizure. ECG shows a wide complex tachycardia. What are your differentials, and describe your management? [+ Reveal Answer]

Differentials:
1. Ventricular tachycardia (VT)
2. Antidromic AVRT via accessory pathway
3. SVT with aberrancy
Management:
- Assess stability: If unstable, perform synchronized cardioversion
- If stable and WPW suspected, avoid AV nodal blockers
- Consider procainamide IV if available
- Urgent electrophysiology referral if not already initiated
Sources: Braunwald’s, UpToDate, Clinical Electrophysiology

22. What is the definitive treatment for accessory pathway-mediated arrhythmias? [+ Reveal Answer]

Catheter ablation is the treatment of choice with curative intent. Indications include symptomatic patients, high-risk features on EP testing, and professions where syncope poses risk.
Sources: ESC Guidelines, Braunwald’s

23. Describe the prognostic value of accessory pathway effective refractory period (ERP). [+ Reveal Answer]

An anterograde ERP ≤250 ms is associated with risk of rapid ventricular response during AF and potential progression to VF. Longer ERP implies lower risk.
Sources: JACC EP, Braunwald’s

24. What should be included in the discharge and follow-up plan for this patient? [+ Reveal Answer]

1. Restrict from competitive sports pending EP study
2. Outpatient electrophysiology referral
3. Educate about arrhythmia symptoms and warning signs
4. Consider Holter monitoring if pathway is intermittent
Sources: Ferri’s, ESC Guidelines, UpToDate