ECG Predictors for AV Reentry Rhythm in Youth
The most reliable ECG predictors for atrioventricular (AV) reentry rhythm in youth include ventricular pre-excitation with a short PR interval (<120 ms) and delta wave, QRS alternans during tachycardia, and visible P waves with RP intervals ≥100 ms. 1, 2
Key ECG Findings for AV Reentry Tachycardia (AVRT)
Pre-excitation Pattern (WPW)
- Short PR interval (<120 ms)
- Delta wave (slurred upstroke in QRS complex)
- Wide QRS (≥120 ms)
- This pattern indicates an accessory pathway capable of anterograde conduction 1
During Tachycardia (Orthodromic AVRT)
- Visible P waves in 74% of cases (sensitivity 92%, specificity 64%) 2
- RP intervals ≥100 ms in 91% of cases (sensitivity 84%, specificity 91%) 2
- QRS alternans (sensitivity 50%, specificity 89%) 3
- ST-segment depression ≥2 mm (sensitivity 52%, specificity 82%) 2
- ST-segment elevation in lead aVR (sensitivity 94%, specificity 58%) 3
Differentiating AVRT from AVNRT
AVRT must be distinguished from AVNRT, which is another common cause of SVT in youth. The following ECG findings help differentiate between these mechanisms:
AVNRT-Specific Findings
- Pseudo r' wave in lead V1 (specificity 100%) 2
- Pseudo S waves in inferior leads (specificity 100%) 2
- When P waves are visible, RP interval ≤90 ms favors AVNRT 3
- P waves often hidden within or immediately after QRS complex 4
AVRT-Specific Findings
- ST-segment depression (odds ratio: 12.67) 3
- QRS alternans (odds ratio: 9.43) 3
- Visible P waves with longer RP intervals 2
Age Considerations in Youth
- In adolescents, the prevalence may be balanced between AVRT and AVNRT, or AVRT may be more prevalent 1
- Mean age of symptom onset for AVRT is around 8 years in pediatric populations, versus 11 years for AVNRT 1
- Ectopic atrial rhythm on baseline ECG is a predictor of AVNRT with a positive predictive value of 82% 5
Clinical Correlations
- The incidence of manifest pre-excitation (WPW pattern) on ECG in the general population is 0.1% to 0.3% 1
- Not all patients with ventricular pre-excitation develop symptomatic tachycardia 1
- In a study of patients <21 years with WPW pattern, 64% had symptoms at presentation, with documented SVT in 38% 1
Pitfalls and Caveats
- 12-lead ECG during tachycardia is essential for accurate diagnosis, as single-lead monitoring may miss critical P wave morphology 4
- Misdiagnosis can occur if P waves are overlooked or misinterpreted as artifact 4
- Wide-complex tachycardia should not be automatically assumed to be SVT with aberrancy, as it could be ventricular tachycardia 4
- Holter/event recorder tracings (1-3 channel) are inadequate for differentiating SVT mechanisms, with 55% resulting in incorrect diagnosis 2
- In asymptomatic children with ventricular pre-excitation, electrophysiological evaluation remains the gold standard for assessing risk of life-threatening arrhythmias 6
By carefully analyzing these ECG features, clinicians can more accurately identify AV reentry rhythms in youth and distinguish them from other supraventricular tachycardias, allowing for appropriate management and treatment decisions.