Background Ultra-high-density mapping enables detailed mechanistic analysis of atrial reentrant tachycardia but has yet to be used to assess circuit conduction velocity (CV) patterns in adults with congenital heart disease. Methods and Results Circuit pathways and central isthmus CVs were calculated from consecutive ultra-high-density isochronal maps at 2 tertiary centers over a 3-year period. Circuits using anatomic versus surgical obstacles were considered separately and pathway length <50th percentile identified small circuits. CV analysis was used to derive a novel index for prediction of postablation conduction block. A total of 136 supraventricular tachycardias were studied (60% intra-atrial reentrant, 14% multiple loop). Circuits with anatomic versus surgical obstacles featured longer pathway length (119 mm; interquartile range [IQR], 80-150 versus 78 mm; IQR, 63-95; P<0.001), faster central isthmus CV (0.1 m/s; IQR, 0.06-0.25 versus 0.07 m/s; IQR, 0.05-0.10; P=0.016), faster non-isthmus CV (0.52 m/s; IQR, 0.33-0.71 versus 0.38 m/s; IQR, 0.27-0.46; P=0.009), and fewer slow isochrones (4; IQR, 2.3-6.8 versus 6; IQR 5-7; P=0.008). Both central isthmus (R2=0.45; P<0.001) and non-isthmus CV (R2=0.71; P<0.001) correlated with pathway length, whereas central isthmus CV <0.15 m/s was ubiquitous for small circuits. Non-isthmus CV in tachycardia correlated with CV during block validation (R2=0.94; P<0.001) and a validation map to tachycardia conduction time ratio >85% predicted isthmus block in all cases. Over >1 year of follow-up, arrhythmia-free survival was better for homogeneous CV patterns (90% versus 57%; P=0.04). Conclusions Ultra-high-density mapping-guided CV analysis distinguishes atrial reentrant patterns in adults with congenital heart disease with surgical obstacles producing slower and smaller circuits. Very slow central isthmus CV may be essential for atrial tachycardia maintenance in small circuits, and non-isthmus conduction time in tachycardia appears to be useful for rapid assessment of postablation conduction block.
Keywords: adult congenital heart disease; catheter ablation; conduction velocity; high‐density mapping; intra‐atrial reentrant tachycardia.