Is the left ventricle the preferred pacing site in all children with atrioventricular block?

Abstract

This editorial refers to ‘Preserved cardiac synchrony and function with single-site left ventricular epicardial pacing during mid-term follow-up in paediatric patients’ by M. Tomaske et al., on page 1168 Cardiac pacing for the treatment of bradycardia has been applied in children of all age groups for many years. In the paediatric population, the most common indications for cardiac pacing are auto-immune-mediated congenital atrioventricular block (CAVB) and acquired CAVB after congenital heart surgery. Traditionally, the right ventricular (RV) apex has been used for transvenous ventricular pacing leads because it is easily accessible and allows a stable position and low pacing thresholds. In young children, many centres prefer to place epicardial ventricular pacing leads, which are usually attached to either the RV apex or the RV free wall. Although thousands of children have profited from pacing the RV, there is increasing evidence that long-term RV apical pacing (RVP) eventually can result in LV failure. In animal studies, it has been demonstrated that chronic RVP leads to decreased LV function, dilatation, and asymmetric septal hypertrophy. 1 Clinical studies in adults have demonstrated that RVP is associated with increased mortality and morbidity related to heart failure. 2 Reports in children have also shown that long-term RVP causes LV mechanical dyssynchrony, which is associated with decreased LV function. 3,4 The deleterious effect of permanent RV pacing has become an important topic in cardiac pacing in the paediatric population, since this group requires pacemaker therapy over many decades. This young pacemaker population also includes a significant number of children with complex congenital heart disease at high risk for future heart failure. Literature data indicate that in children with normal cardiac anatomy, long-term RVP will lead to LV failure in 7%. 4 A very recent study by Gebauer et al. 5 reported even higher percentage (13%) of LV dilatation in a retrospective cohort of 82 patients after a mean pacing period of 7.4 years. In this study, children with epicardial RV free wall pacing had a higher risk of LV dilatation and LV dysfunction compared with those with RVP. 5 Furthermore, small case series has demonstrated that children with congenital CAVB who developed RV pacing-associated cardiomyopathy showed impressive improvement of LV function after cardiac resynchronization therapy (CRT). These findings indicate that mechanical dyssynchrony induced by RV pacing appeared to be the key factor in the development of heart failure in this group of congenital CAVB. Also, the CRT data in children and patients with congenital heart disease from three large studies have shown that 45‐70% of children undergoing CRT for heart failure had pacing-induced ventricular dyssynchrony. 6 So, if the RV apex appears inappropriate for long-term ventricular pacing, what then should we use as an alternative? In the RV, selective pacing sites at the high RV septum and RV outflow tract region may produce more synchronous contraction patterns and better haemodynamics. Therefore, RV septal pacing could decrease the long-term detrimental effects of RV pacing. Advanced tools and lead technology nowadays allow for pacing these specific RV sites, also in paediatric patients. However, to date, long-term clinical studies have been conflicting, and large randomized trials are now expected to demonstrate the significance of selective site RV pacing in the protection of LV function. 7 LV pacing appears to be less harmful than RVP as shown in acute haemodynamic studies in patients with normal LV function. 8 Animal studies as well as an acute haemodynamic study in children have suggested that the LV apex is the optimal pacing site in the LV. 9 Trials in adult patients have shown that single-site LV free wall pacing (LVP), comparable with biventricular pacing, has beneficial haemodynamic effects in patients with heart failure and left bundle branch block. 10 Also, a small study in children with LV dysfunction and RVP or intrinsic left bundle branch block has demonstrated improvement of LV function 1 month after single-site LVP. 11