Whether unidirectional conduction block (UB) can be observed after creation of a radiofrequency (RF) line is still a subject of debate. Previous study reported a prevalence of 9% of UB, but the assessment was performed using a point-by-point recording across the line, which may have artificially increased this UB percentage.

To prospectively assess bidirectional block using ultra-high-resolution (UHR) system after RF line creation.

Prospective patients admitted for an RF ablation procedure were included in this study. UHR maps were performed by pacing on both sides of the line created.

A total of 18 maps were created in 8 patients (5 men, mean age 71.5±10) by pacing (mean cycle length 600±80ms) from both sides of the line after a mean waiting time of 60±18min: 2 left atrial roof and 7 cavotricuspid isthmus lines; mean number of 4863±3982 electrograms (381±651 beats) acquired during 10±9min; mean right or left atrial volume 81±82mL. The RF lines were all unambiguously blocked bidirectionally. After a mean follow-up of 12±4 months, no patient experienced any arrhythmia recurrence (Fig. 1).

UHR mapping confirmed that the presence of a conduction block along a RF line is always associated with a block in the opposite direction.