ACHD
Characteristics of the Device and Conduction Disturbances in Transcatheter Device Closure of Perimembranous Ventricular Septal Defects
2024 Volume 88 Issue 9 Pages 1380-1382
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2024 Volume 88 Issue 9 Pages 1380-1382
Perimembranous ventricular septal defects (VSD) are the most common subtype of VSD. In perimembranous VSD, conduction disturbances have been an inherent complication of transcatheter closure due to the anatomical characteristics of the conduction system, which is commonly situated posteroinferior to the defects (Figure 1).1 Devices are positioned by the radial force of their waist and the gripping force of their double disks (Figure 2A). To securely position devices, appropriate radial and gripping forces are required; however, radial and gripping forces also become the external forces applied to the conduction system (Figure 2B). This is strongly related to the design of the device, as well as clinical practice, especially the selection of the size of the device. Oversizing of the device, which may reduce the risk of device embolization, is known to be a risk factor for conduction disturbances. The presence of the right-side disk of double-disk devices may contribute to fixing the device in position, which helps minimize the radial force. However, it can also lead to other problems, such as the production of crimping force and interference with the tricuspid valve. Due to the high incidence of complete heart block reported in the 2000s,2 and the satisfactory surgical closure of VSDs, the device has not been approved by the US Food and Drug Administration.2 Meanwhile, many types of devices have been developed worldwide, providing modifications to reduce the external forces applied to the conduction system. In recent reports, the incidence of complete heart block decreased to approximately 0.2–0.3%,3,4 which is comparable to the surgical risk.5 Although the risk of complete heart block has been addressed, left bundle branch block (LBBB), another conduction disturbance, is now coming into focus. Moreover, the clinical impact of device-induced LBBB is more prominent, because it can lead to progressive ventricular dysfunction due to interventricular dyssynchrony. This may necessitate not only surgical removal of the device, but also cardiac resynchronization therapy.6–10
Morphology of the perimembranous ventricular septal defect and the conduction system. Arrowheads indicate the ventricular septal defect. Dotted line and arrows indicate the conduction bundle. RVOT, right ventricular out-flow tract; TV, tricuspid valve; RV, right ventricle.
External forces by a device applied to the surrounding tissues. (A) Radial force and gripping force due to the device. (B) Relationship between a device positioned in a perimembranous ventricular septal defect and the conduction bundle. AS, atrial septum; MV, mitral valve; PB, penetration bundle; TV, tricuspid valve; VS, ventricular septum.
Article p 1372
Modified double-disk symmetrical devices, which are used in this issue of the Journal by Jiang et al, are the devices that have been commonly used in China recently.11 These devices were manufactured by some industries including SHAMA (Shanghai Shape Memory Alloy; Shanghai, China), Starway Medical (Beijing, China), and Lifetech Scientific (Shenzhen, China). Bai et al reported the incidence of complete heart block in a retrospective study of a consecutive series with 1,046 patients.9 In that study, modified double-disk symmetrical devices were used for 431 patients, whereas asymmetrical devices were used for 354 patients, a thin-waist device was used for 246 patients, and a duct occluder was used for 9 patients. Complete heart block was identified in 6 cases (17 patients in total, including the other types of devices), and 2 (0.46%) patients underwent permanent pacemaker implantation. In this cohort, there was no significant difference in the incidence of complete heart block according to type of device. Interestingly, both the patients who underwent permanent pacemaker implantation had a recurrence of complete heart block, one at 2,417 and the other 1,175 days after implantation. This result may suggest that the mechanism of heart block was fibrosis associated with chronic inflammation. In this study, the data for LBBB were not shown, probably because they were absent. Tang et al reported the incidence of a device-induced complete LBBB in a retrospective study of large cohort with 2,349 patients.10 In that study, all patients were treated with modified double-disk symmetrical devices. Complete heart block and complete LBBB were identified in 13 (0.6%) and 57 (2.7%) patients, respectively. Among the patients with complete LBBB, 53 patients developed within 1 week, and 2 developed within 2 weeks after the procedure. Late-onset complete LBBB was noticed in 2 patients (2 months and 2 years after the procedure), and 8 patients developed persistent complete LBBB. Of the 8 patients with persistent complete LBBB, 1 patient underwent cardiac resynchronization therapy. The larger diameter of the delivery sheath and oversizing of the device were identified as risk factors for complete LBBB. Late onset and recurrence might be related to the persistence of complete LBBB.
The current study by Jiang et al contains valuable analysis data comparing the risks of complications based on differences in the waist length of the device: 3 and 4 mm.11 As the authors mentioned, from the point of external forces applied to the conduction system by the gripping force, the device with a 3-mm waist length could have a higher risk of conduction disturbance. The outcome of this study was almost comparable with previous studies; however, the sample size may have been too small to evaluate the risk of heart block or LBBB due to their low incidence. Of the 395 patients treated with the modified double-disk symmetrical devices, 6 (1.5%) patients developed complete LBBB and no patients developed complete heart block. All the 6 patients who developed complete LBBB did so within 5 days after the procedure. Five cases recovered to a normal rhythm (1 converted to right bundle branch block) with 3 patients recovered after surgical device removal in. Interestingly, although not statistically significant, complete LBBB was identified more commonly in patients treated with a 4-mm waist device, one patient (0.5%) with a 3-mm waist device (n=208) and in 5 patients (2.9%) with a 4-mm waist device (n=172).
The mechanism behind device-related conduction disturbances has not yet been clearly elucidated, and the results of this study may raise questions about the speculated pathophysiology thus far. Although the incidence of this complication has decreased significantly over time, it has not been eliminated entirely. For the wider adoption of transcatheter device closure of perimembranous VSD, it is crucial to reduce the incidence to below that of surgical closure and strive to approach “zero”. Urgent efforts are needed to clarify the mechanism of conduction disturbances and develop an “ideal” device design, and to improve procedures based on this understanding.
