Lecture Notes: Atrioventricular Re-entry Tachycardia (AVRT)

Introduction to AVRT

• AVRT is a type of paroxysmal supraventricular tachycardia.
• Occurs in patients with accessory pathways, forming a re-entry circuit between the AV node and the accessory pathway.
• ECG features vary based on conduction direction: orthodromic or antidromic.

Types of AVRT

Orthodromic AVRT

• Anterograde conduction via the AV node.
• Produces regular narrow complex rhythm.
• ECG Features:
  • Rate: 200-300 bpm.
  • Retrograde P waves visible with long RP interval.
  • QRS < 120ms unless there's a pre-existing bundle branch block or rate-related aberrant conduction.
  • Associated with QRS alternans and rate-related ischaemia.
  • Narrow complex tachycardia, similar to AVNRT.
• Differentiation from AVNRT:
  • In AVNRT, retrograde P waves occur early, whereas in AVRT, they appear later with a long RP interval.
• Treatment:
  • Urgent DC cardioversion for unstable patients.
  • Vagal maneuvers, adenosine, or verapamil for stable patients.
  • Risk of inducing AF with AV nodal blocking drugs.

Antidromic AVRT

• Anterograde conduction via the accessory pathway.
• Produces regular wide complex rhythm.
• ECG Features:
  • Rate: 200-300 bpm.
  • Wide QRS complexes due to abnormal ventricular depolarization.
• Treatment:
  • Presume VT if in doubt.
  • Procainamide is the first-line antiarrhythmic, with ibutilide and amiodarone as alternatives.
  • Avoid AV nodal blocking agents due to risk of AF and potential cardiac arrest.

Clinical Examples

• Example 1: Orthodromic AVRT with narrow complex tachycardia; adenosine shows WPW pattern with left-sided AP.
• Example 2: Antidromic AVRT in a child with broad complex tachycardia; vagal maneuvers resolved rhythm.

Advanced Reading and Resources

• Various online courses and textbooks available for deeper understanding.
• Recommended readings on ECG interpretation and management of tachyarrhythmias.

Conclusion

• AVRT involves complex re-entry circuits requiring precise diagnosis.
• Understanding the differences between orthodromic and antidromic AVRT is crucial for effective treatment.
• Close monitoring is necessary when using specific treatments due to potential complications like AF.