What are the ECG predictors of AV reentry or SVT?

ECG Predictors of AV Reentry or SVT

The most reliable ECG predictors of AV reentry or SVT include the presence of a narrow QRS complex tachycardia with hidden or retrograde P waves, specific RP interval patterns, and abrupt onset/termination characteristics. 1

Key ECG Features of AVNRT (AV Nodal Reentrant Tachycardia)

Typical (Slow-Fast) AVNRT:

• Regular narrow QRS tachycardia (QRS <120 ms)
• Heart rate typically 150-250 bpm
• P waves often hidden within or immediately after the QRS complex
• Characteristic "pseudo S wave" in inferior leads (II, III, aVF)
• "Pseudo R'" pattern in lead V1
• Short RP interval (RP < PR)
• RP interval typically <90 ms 1, 2

Atypical (Fast-Slow) AVNRT:

• Retrograde P waves with negative polarity in inferior leads
• Long RP interval (RP > PR)
• Can be difficult to distinguish from PJRT or low septal atrial tachycardia 1

Key ECG Features of AVRT (AV Reentrant Tachycardia)

Orthodromic AVRT:

• Regular narrow QRS tachycardia
• P waves visible in early part of ST-T segment
• Short RP interval (RP < PR)
• RP interval typically >90 ms (longer than typical AVNRT) 1

Antidromic AVRT:

• Wide QRS complex tachycardia (can mimic ventricular tachycardia)
• Occurs in <5% of patients with WPW syndrome
• Pre-excitation pattern during sinus rhythm (delta wave, short PR, wide QRS) 3

Distinguishing Features from Other Arrhythmias

SVT vs. VT in Wide-Complex Tachycardia:

• Lack of any R-S complexes in leads V1-V6 suggests VT
• R-S interval >100 ms in any precordial lead suggests VT
• Initial R wave in aVR suggests VT
• AV dissociation strongly suggests VT
• QRS concordance (all positive or all negative) in precordial leads suggests VT 1

SVT with Aberrancy vs. VT:

• QRS in tachycardia identical to sinus rhythm suggests SVT
• R-wave peak time ≥50 ms in lead II suggests VT 1

Clinical Context and Response Patterns

• Abrupt onset and termination strongly suggests reentrant mechanism (AVNRT or AVRT)
• Termination with vagal maneuvers or adenosine suggests AV node involvement (AVNRT or AVRT)
• Regular RR intervals are typical of AVNRT and AVRT
• Polyuria may occur during episodes due to atrial natriuretic peptide release 1

Diagnostic Algorithm for Narrow QRS Tachycardia

1. First, determine if regular or irregular:

   • Regular → Consider AVNRT, AVRT, atrial flutter, AT
   • Irregular → Consider AF, atrial flutter/AT with variable AV conduction, MAT

2. For regular tachycardia, assess P waves:

   • P waves not visible → Likely AVNRT
   • P waves visible → Assess RP interval

3. Analyze RP interval:

   • Short RP (RP < PR):
     • RP <90 ms → Typical AVNRT
     • RP >90 ms → Orthodromic AVRT
   • Long RP (RP > PR):
     • Atypical AVNRT, AT, or PJRT 1

Common Pitfalls in ECG Diagnosis

• Misdiagnosing wide-complex tachycardia as SVT when it could be VT (potentially life-threatening)
• Overlooking subtle P waves that may be hidden in the QRS or T wave
• Failing to obtain a 12-lead ECG during tachycardia (single-lead monitoring may miss critical P wave morphology)
• Misinterpreting artifact as P waves or vice versa
• Confusing junctional rhythm with AVNRT (junctional rhythm typically has slower rate and AV dissociation) 2

Key Diagnostic Considerations

• Always obtain a 12-lead ECG during tachycardia when possible
• Consider esophageal pill electrodes to help reveal P waves when not visible
• Response to adenosine or vagal maneuvers can provide diagnostic clues
• Pre-excitation pattern during sinus rhythm suggests potential for AVRT 1, 2

By systematically analyzing these ECG characteristics, clinicians can accurately diagnose the mechanism of SVT, which is crucial for appropriate treatment selection and long-term management.