Electrophysiologic evidence of epicardial connections between low right atrium and remote right atrial region or coronary sinus musculature: Relevance for catheter ablation of typical atrial flutter

Electrophysiological evidence of right atrial epicardial connections in a case with recurrent common atrial flutter

The majority of the cavotricuspid isthmus (CTI) region consists of discretely arranged muscle bundles separated by connective tissue. Heterogeneity in the anatomic arrangement of the muscle bundles results in differences in the endocardial and epicardial activation patterns. We present a case of recurrent atrial flutter (AFL) despite the presence of a complete endocardial CTI block. We found epicardial-endocardial breakthrough (EEB) sites on the right atrial high septum. In addition, the epicardial excitation confirmed by endocardial activation mapping was detected as far-field potentials. Radiofrequency ablation was performed at the EEB site. No AFL has recurred for 12 months after the present procedure.

Diversity and complexity of the cavotricuspid isthmus in rabbits: A novel scheme for classification and geometrical transformation of anatomical structures

The aim of this study was to describe the morphology of the cavotricuspid isthmus (CTI) in detail and introduce a comprehensive scheme to describe the topology of this region based on functional considerations. This may lead to a better understanding of isthmus-dependent flutter and fibrillation and to improved intervention strategies. We used images of the cavotricuspid isthmus from 52 rabbits of both sexes with a median weight of 3.40 ± 0.93 kg. The area of the CTI was 124.25 ± 42.14 mm² with 53.28 ± 21.13 mm² covered by pectinate muscles connecting the terminal crest and the vestibule. Isthmus length decreased from inferolateral (13.09 ±2.14 mm) to central (9.85 ± 2.14 mm) to paraseptal (4.88 ± 1.96 mm) resembling the overall human geometry. Ramification sites of pectinate muscles were identified and six levels dividing the CTI from posterior to anterior were introduced. This allowed the classification of pectinate muscle segments based on the connected ramification level. To account for the high inter-individual variations in size and shape, the CTI was projected onto a normalized reference frame using bilinear transformation. Furthermore, two measures of complexity were introduced: (i) the ramification index, which reflects the total number of muscle segments connected to a ramification site and (ii) the complexity index, which reflects the type of ramification (branching or merging site). Topological analysis showed that the complexity of the pectinate muscle network decreases from inferolateral to paraseptal and that the number of electrically uncoupled parallel pathways increases in the central section between the terminal crest and the vestibule which introduces potential reentry pathways.

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.