Discussion
This is the first case-series reporting on the safety and feasibility of CSP in unselected patients with a wide range of CHD subtypes. Of note, 95% of patients included in our series had moderate or complex forms of CHD. Our results show that physiological pacing is feasible and safe in this subset of patients with a successful implant rate of 100% when considering both HBP and LBBAP, and 75% (15/20) when using strict criteria for LBBP. In the remaining 5 patients LVSP pacing with significant QRS narrowing could also be achieved. Of note, the systemic ventricle systolic function and NYHA class significantly improved during follow-up. Electrical parameters remained stable at last follow-up and only 1 patient required lead revision due to acute pacing threshold rise 4 days post-implant.
In recent years, CSP has emerged as the cornerstone of physiological pacing1-5. Several studies have demonstrated that HBP can reduce heart failure hospitalizations and can improve LVEF1. This potential benefit is greater for those patients with higher percentage of ventricular pacing and those with impaired LVEF at baseline; particularly, younger patients with a high burden of ventricular pacing18. In a series of 238 patients with CHD, the mean age at pacemaker implantation was 26 years IQR (13;42)19. Moreover, patients with CHD and chronic right ventricular pacing are at particularly increased risk of developing pacemaker induced cardiomyopathy. Recently, HBP has been shown to improve LVEF in chronically paced patients and pacing induced cardiomyopathy5. Our results show that CSP is feasible in chronically paced CHD patients with longstanding AV block and thus should be considered as a potential pacing strategy for this subset of patients with pacing induced cardiomyopathy.
Pacemaker implantation in patients with CHD can be challenging due to the baseline anatomical distortion and also due to the presence of prostethic materials introduced during the surgical corrections8-11. As a consequence, implant duration was prolonged with higher radiation exposure. As a reference, in one of the largest series of HBP published so far, mean implant duration was 70±34 min for single or dual chamber pacemakers thus reflecting the complexity of the implant technique in patients with CHD1. The use of multiple sheaths in 50% of the cases also reflects the complex anatomy and the absence of tailored tools available. Moore et al.12 have recently reported the safety and feasibility of CSP in 15 patients with cc-TGA showing an acute implant success rate of 85% with a median procedure time of 146 minutes (IQR 112– 212) and use of multiples sheaths in 27%. In comparison, our series with unselected CHD patients including more complex anatomies, shows that CSP is still feasible in a wide range of CHD defects.
Localization of the proximal conduction system in our cohort poses a challenge. Although simple defects are usually associated with minor variations, moderate and severe defects have characteristically significant variations in the conduction system disposition20. Electroanatomical mapping of the conduction system during implant in those patients with spontaneous intrinsic rhythm should be considered, especially in patients with complex anatomy and previous surgery. In patients with D-TGA and a prior atrial switch operation, only the left conduction system is usually accessible. In our 2 patients with D-TGA and a Senning correction we unsuccessfully tried to reach the proximal left bundle within the interventricular septum but ultimately accepted the distal portion of the left conduction system (left anterior fascicle)(Figures 3 and 5). Additional landmarks may be useful to localize the conduction system such as a calcified VSD patch from a previous membranous septum VSD closure (patient #4, cc-TGA + perimembranous VSD + dextrocardia), (Figure 6 and Supplementary video 2).
It is of interest that LBBP could be successfully achieved in the 2 patients with a D-TGA and previous atrial switch operation. A significant percentage of patients with an atrial switch operation are likely to develop future systemic RV dysfunction and may also need permanent ventricular pacing. Although biventricular pacing has been attempted in different CHD scenarios, the CS ostium is not usually accesible from the systemic venous atrium in these patients and thus the only chance for CRT in this setting is the surgical implantation of an epicardial lead in the systemic RV. Our 2 cases show that CSP can potentially be achieved after the atrial switch operation accesing the subpulmonic ventricle via the systemic venous atrium. In fact, this particular anatomic disposition allows direct access to the left conduction system as the subpulmonic ventricle is morphologically a left ventricle. In these 2 patients, we were able to clearly record and capture a left bundle potential (Figures 3 and 5). However, the effect of LBBAP on systemic ventricular synchrony requires further data as it relies on activation of the right bundle as well.
In conclusion, HBP and LBBAP are safe and feasible in patients with CHD and a permanent pacing indication despite challenging anatomy and advanced conduction system disease.