Feasibility of SVCI in patients with CIEDs
Several previous reports have shown the histological and electrophysiological characteristics of the SVC. It has been microscopically confirmed by autopsy of human hearts that the myocardial sleeve of the SVC only extends approximately 1.5 cm from the RA15; however, many previous reports have demonstrated arrhythmogenicity of the SVC.16-18 In contrast, the electrical potential of the SVC has been recorded approximately 4 cm above the RA-SVC junction.19 Because breakthrough points from the RA to the SVC are limited, circumferential RF application is not always needed to achieve SVCI.20Therefore, RF applications to the site where the leads had been positioned could be avoided in most cases. Recently, conduction patterns between the SVC and the RA have been studied using ultra-high-resolution mapping. A spontaneous conduction block line was observed in 50% of the study patients, and the block line was mainly positioned from the lower lateral wall to the higher anterior wall or from the lower posterolateral wall to the higher mid-septal wall.19We confirmed that most of the leads passed through the lateral portion of the SVC. This might explain why most of the leads did not become obstacles for SVCI, which resulted in the high success rate for SVCI in the CIED group. Electrical reconnection between the SVC and the RA was observed in 9 of 12 patients who underwent the second session among the CIED group. The reconnection sites corresponded with the SVC wall contiguous to leads in all patients, which might have resulted from insufficient RF application at the site closest to the CIED leads. SVCI failed in 3 patients (8.8% of the study patients) after the final ablation procedure, which indicated that the target myocardial sleeve might have been in direct contact with CIED leads in these 3 patients. One patient in whom SVCI failed in the first ablation session had a dual-coil defibrillator lead. The SVC coil was located at the lateral wall of the SVC with a long adhering lesion, which might result in the electrical isolation failure of the SVC. (Figure 1A) Two patients in whom electrical re-isolation of the SVC failed in the second ablation session had leads with diameters of >2 mm. Therefore, leads with a large diameter were associated with a large contact area to target the myocardial sleeve of the SVC, which might result in SVCI failure.