What are the ECG (electrocardiogram) characteristics of Avnet and how are they managed?

ECG Characteristics of AVNRT and Management

AVNRT (Atrioventricular Nodal Reentrant Tachycardia) has distinctive ECG characteristics including a narrow QRS complex with retrograde P waves that are often hidden within or appear immediately after the QRS complex, creating a "pseudo S wave" in inferior leads and a "pseudo R'" in lead V1. 1

Key ECG Features of AVNRT

Typical (Slow-Fast) AVNRT

• Regular narrow QRS tachycardia (unless aberrant conduction is present)
• Heart rate typically 150-250 beats per minute
• P waves often hidden within the QRS complex or appearing at the terminal portion of the QRS
• Characteristic findings:
  • "Pseudo S wave" in inferior leads (II, III, aVF)
  • "Pseudo R'" pattern in lead V1
  • Short RP interval (P wave closer to preceding QRS than to following QRS)
  • 1:1 AV relationship 1, 2

Atypical (Fast-Slow) AVNRT

• Long RP interval (P wave closer to following QRS than preceding QRS)
• Retrograde P waves with negative polarity in inferior leads
• Can be difficult to distinguish from other long RP tachycardias like PJRT or low septal atrial tachycardia 1

Diagnostic Approach

1. Obtain 12-lead ECG during tachycardia

   • Essential for accurate diagnosis
   • Single-lead monitoring may miss critical P wave morphology 2

2. Key diagnostic findings:

   • Regular RR intervals
   • Absence of distinct repeating P waves separate from QRS complexes
   • When visible, P waves appear immediately after QRS 1, 2

3. Differential diagnosis considerations:

   • AVRT (orthodromic) - P wave usually visible in ST segment, separated from QRS by ~70ms
   • Atrial tachycardia - P waves precede QRS with different morphology from sinus P waves
   • Junctional tachycardia - typically slower rate (70-120 bpm) 2

Common Diagnostic Pitfalls

• Misdiagnosing wide-complex tachycardia as SVT when it could be ventricular tachycardia
• Failing to recognize AV dissociation, which helps distinguish junctional rhythm from AVNRT
• Overlooking P waves that may be hidden within QRS complexes 2
• Misinterpreting artifact as P waves or QRS complexes 1

Management Algorithm

Acute Management

1. Hemodynamically unstable patients:

   • Immediate synchronized cardioversion

2. Hemodynamically stable patients:

   • First-line: Vagal maneuvers (Valsalva, carotid sinus massage)
   • Second-line: Adenosine IV (6mg rapid bolus, followed by 12mg if needed)
   • Third-line: IV calcium channel blockers (diltiazem, verapamil) or beta-blockers 1, 2

Long-term Management

1. Infrequent, well-tolerated episodes:

   • "Pill-in-pocket" approach with PRN oral medications
   • Lifestyle modifications (reducing caffeine, alcohol, stress)

2. Frequent, symptomatic episodes:

   • Definitive treatment: Catheter ablation (success rate >95%, low complication rate)
   • Alternative: Chronic pharmacotherapy with beta-blockers or calcium channel blockers 1, 2

Special Considerations

• Radiofrequency ablation vs. cryoablation: Cryoablation has lower risk of permanent AV block but higher recurrence rate compared to radiofrequency ablation 1

• Minimizing radiation exposure: Modern mapping systems allow for minimal or zero-fluoroscopy ablation procedures 1

• Monitoring for complications: Post-ablation patients should be monitored for:

  • AV block (rare with modern techniques)
  • Recurrence of arrhythmia (more common with cryoablation)
  • Development of other arrhythmias 1

Conclusion

The ECG diagnosis of AVNRT relies on recognizing its characteristic pattern of hidden or immediately post-QRS P waves creating distinctive pseudo S waves in inferior leads and pseudo R' in V1. Catheter ablation offers definitive treatment with high success rates, while medications provide effective symptom control for those who are not candidates for ablation.