Late velocity vectors for the identification of slow-conducting anatomical isthmuses in tetralogy of Fallot: comparison with standard definition of slow conduction

Background Proactive radiofrequency catheter ablation (RFCA) in repaired tetralogy of Fallot (toF) before pulmonary valve replacement (PVR) relies on the identification of slow-conducting anatomical isthmuses (SCAI), achieved by collection of points by mapping catheter. Standard conduction velocity (CV) relies on linear measurement across a curved surface, providing only an average measure across anatomical isthmuses (AI). LAT velocity vectors (LVV) provide a local solution to CV, thus providing potentially more meaningful and geometrically coherent values. Data regarding their correlation, however, are scarce. Purpose To evaluate the correlation between standard CV measurement across anatomical isthmuses and CV measured with LVV in toF. Methods Among toF patients undergoing electrophysiological evaluation before PVR, right ventricular electroanatomical mapping (EAM) was performed. Simultaneous bipolar voltage, LAT and PASo mapping were acquired with 3.5 mm-tip mapping catheter. CV across AI was measured identifying nearest points with bipolar voltage >1.5 mV and measuring their linear distance and timing difference in local activation time (LAT); conduction velocity (CV) is defined as the ratio (space/time) between these two measures and SCAI are defined by a CV <0.5 m/s. LVV were evaluated by setting compression level=5 (maximal); CV was measured as the CV point were slow (thicker) LVV occurred across AI. Results Fourteen toF patient were enrolled (12 toF, 2 toF-related defects; 50% males, age 47±13 y, median age at repair 4 y, interquartile 2-11). AI 1 (ventriculotomy/transannular patch to tricuspid valve) was observed in all patients, AI2 (ventriculotomy/transannular patch to pulmonary valve) in 5 patients (36%), AI3 (ventricular septal defect to pulmonary valve) in 10 patients (71%), AI 4 in 2 patients (14%). SCAI 1 and SCAI 4 were never observed, while SCAI 2 in 2 patients (14%), SCAI 3 in 7 (50%). Relative SCAI/AI ratio were 40% and 70% for AI 2 and 3, respectively. Overall standard CV across isthmuses was 0.48±22 m/s, overall standard SCAI CV was 0.31±11 m/s; overall LVV CV was 0.27±14, overall LVV SCAI CV was 0.21±11. Linear regression model identified a linear correlation between standard CV and LVV CV (R=0.60, p 0.02). Bland-Altman plot showed an overall difference (standard CV-LVV CV) of +0.21 m/s, showing an overall underestimation of conduction velocities by LVV. Conclusions: In patients with repaired tetralogy of Fallot, LVV CV provides consistent values of conduction velocities into anatomical isthmuses, with a good correlation with standard linear measures across AIs and a tendency toward underestimation of CV. Whether this represents an intrinsic difference among measures or the capacity of LVV to highlight slower components of velocities into the AI remain to be evaluated, especially with the use of multipolar array-based mapping catheter.