THE R’’ WAVE IN V1 AND THE NEGATIVE TERMINAL QRS VECTOR IN AVF COMBINE TO A NOVEL 12-LEAD ECG ALGORITHM TO IDENTIFY SLOW CONDUCTING ANATOMICAL ISTHMUS 3 IN PATIENTS WITH TETRALOGY OF FALLOT

Aims: Patients with repaired tetralogy of Fallot (rTOF) have an increased risk of ventricular tachycardia (VT), with slow conducting anatomical isthmus (SCAI) 3 as dominant VT substrate. In patients with right bundle branch block (RBBB), SCAI 3 leads to local activation delay with a shift of terminal RV activation towards the lateral RVOT which may be detected by terminal QRS vector changes on sinus rhythm ECG.
Methods and results: Consecutive rTOF patients aged ≥16 years with RBBB who underwent electroanatomical mapping at our institution between 2017-2022 and 2010-2016, comprised the derivation and validation cohort, respectively. Forty-six patients were included in the derivation cohort (aged 40±15 years, QRS duration 165±23ms). Among patients with SCAI 3 (n=31, 67%), 17 (55%) had an R’’ in V1, 18 (58%) a negative terminal QRS portion (NTP) ≥80ms in aVF, and 12 (39%) had both ECG characteristics, compared to only 1 (7%), 1 (7%), and 0 patient without SCAI, respectively.
Combining R’’ in V1 and/or NTP ≥80ms in aVF into a diagnostic algorithm resulted in a sensitivity of 74% and specificity of 87% in detecting SCAI 3. The interobserver agreement for the diagnostic algorithm was 0.875. In the validation cohort (n=33, 18 (55%) with SCAI 3) the diagnostic algorithm had a sensitivity of 83% and specificity of 80% for identifying SCAI 3.
Conclusion: A sinus rhythm ECG based algorithm including R’’ in V1 and/or NTP ≥80ms in aVF can identify rTOF patients with a SCAI 3 and may contribute to non-invasive risk stratification for VT.