Does Unidirectional Block Exist after a Radiofrequency Line Creation? Insights from Ultra-High-Density Mapping (The UNIBLOCK Study)

Background: Whether unidirectional conduction block (UB) can be observed after creation of a radiofrequency (RF) line is still debated. Previous studies reported a prevalence of 9 to 33% of UB, but the assessment was performed using a point-by-point recording across the line. Ultra-high-density (UHD) system may bring some new insights on the exact prevalence of UB. Purpose: A prospective study was conducted to assess the prevalence of UB and bidirectional block (BB) using UHD system after RF line creation. Methods: Patients referred for atrial RF ablation procedure were included in this multicenter prospective study. UHD maps were performed by pacing both sides of the created line. Results: A total of 80 maps were created in 40 patients (67 ± 12 years, 70% male) by pacing (mean cycle length 600 ± 57 ms) from both sides of the cavotricuspid isthmus line. After a 47 ± 17 min waiting time after the last RF application, UHD maps (mean number of 4842 ± 5010 electrograms, acquired during 6 ± 5 min) showed that BB was unambiguously confirmed on all of them. UB was not observed in any map. After a mean follow-up of 12 ± 4 months, 6 (14%) patients experienced an arrhythmia recurrence. Conclusion: After creation of an RF line, no case of UB was observed using UHD mapping, suggesting that the presence of a conduction block along a RF line is always associated with a block in the opposite direction.

Effects of Short-Term Memory on Electrical Behaviors of Postextrasystolic Beats

Cardiac short-term memory which reflects the influence of pacing history is an intrinsic property of paced myocardium. It has been observed that premature ventricular contractions (PVCs) facilitate initiation of reentrant tachyarrhythmias. However, little is known about effects of pacing history on electrical behaviors of postextrasystolic beats. In the paper, by incorporating endo-, mid-, and epi-cardial myocytes, we developed a one-dimensional heterogeneous fiber to examine effects of the number of regular stimulations before PVCs on postextrasystolic depolarizations (PEDs). OpenMP parallel algorithm was performed on a four-core personal computer to accelerate the calculation. The results showed that for any type of myocytes, APDs for PEDs became longer for 500 than for 100 regular driven beats. The calculated ECGs reflected that repolarisation of the tissue was also lengthened for the fast long time pacing. Therefore, it was suggested that because of accumulation of memory, prolonged APDs and repolarisation after PVCs could provide sites for unidirectional block in the tissue and increase the risk of reentrant arrhythmias.