What are the baseline ECG (electrocardiogram) predictors of atrioventricular (AV) reentry or supraventricular tachycardia (SVT)?

Baseline ECG Predictors of AV Reentry or SVT

The most definitive baseline ECG predictor of AV reentry is the presence of a pre-excitation pattern, characterized by a short PR interval and delta wave, which indicates a manifest accessory pathway that can participate in AVRT. 1

Key Baseline ECG Predictors

For Accessory Pathway-Mediated Tachycardias (AVRT)

• Pre-excitation pattern on baseline ECG:

  • Short PR interval (<120 ms)
  • Slurred initial upstroke of QRS complex (delta wave)
  • Widened QRS complex
  • These findings indicate a manifest accessory pathway (Wolff-Parkinson-White syndrome when associated with symptoms) 1

• Concealed accessory pathways:

  • Normal baseline ECG (no pre-excitation)
  • These pathways conduct only retrogradely and don't affect ECG during sinus rhythm
  • Can still participate in orthodromic AVRT 1

For AV Nodal Reentrant Tachycardia (AVNRT)

• Baseline ECG is typically normal
• No specific baseline ECG predictors exist for AVNRT
• Diagnosis often made during tachycardia or electrophysiological study 1, 2

Differentiating Features During Tachycardia

While not baseline predictors, these ECG features during tachycardia help identify the mechanism:

AVNRT Features

• Regular narrow QRS tachycardia (150-250 bpm)
• P waves often hidden within QRS complex or visible at terminal portion of QRS
• Short RP interval (RP < PR) in typical AVNRT 3, 4

AVRT Features

• Regular narrow QRS tachycardia (150-250 bpm)
• P waves visible in early ST segment
• RP interval typically >70 ms 4
• Wide QRS with maximal pre-excitation in antidromic AVRT 1, 5

Clinical Considerations

Age and Gender Distribution

• AVNRT is more common in middle-aged and older individuals
• AVNRT is more common in females
• AVRT is more prevalent in younger patients (adolescents)
• WPW pattern incidence in general population is 0.1-0.3% 1

Diagnostic Challenges

• Concealed accessory pathways show no ECG abnormalities during sinus rhythm but can still participate in AVRT
• Intermittent pre-excitation may be missed on a single ECG
• Some accessory pathways with anterograde conduction may show minimal pre-excitation that is difficult to detect 1

Diagnostic Approach for Suspected SVT

1. Obtain 12-lead ECG during sinus rhythm:

   • Look for pre-excitation pattern (short PR, delta wave)
   • Assess for other structural abnormalities

2. If pre-excitation is present:

   • High likelihood of potential AVRT
   • Consider referral to electrophysiologist 2

3. If baseline ECG is normal:

   • Could be AVNRT or concealed accessory pathway
   • Capture ECG during symptoms if possible
   • Consider electrophysiologic study for definitive diagnosis 6

Important Pitfalls to Avoid

• Missing subtle pre-excitation: Some accessory pathways produce minimal pre-excitation that can be overlooked
• Assuming normal ECG rules out AVRT: Concealed accessory pathways show normal baseline ECG but can still participate in orthodromic AVRT
• Misdiagnosing wide-complex tachycardia: Always consider ventricular tachycardia in the differential diagnosis of wide-complex tachycardia before assuming SVT with aberrancy 2
• Relying solely on rate: Both AVNRT and AVRT typically present with heart rates between 150-250 bpm, so rate alone cannot differentiate between them 4

Remember that definitive diagnosis often requires electrophysiologic study, especially when baseline ECG is normal or when the mechanism of arrhythmia remains uncertain despite ECG documentation during tachycardia.