Permanent Cardiac Pacing in Adults with High Grade Atriovetricular Block and Preserved Left Ventricular Function: Optimal Mode and Site of Pacing

Abstract

Cardiac pacing is the only effective treatment for patients with sick sinus syndrome and atrioventricular conduction disorders. In permanently paced patients, cardiac performance and exercise capacity depend on 3 main parameters: the quality of chronotropic function, atrioventricular synchrony, and the ventricular activation sequence. Dual chamber pacing is believed to have an advantage over single chamber ventricular pacing in that it resembles cardiac physiology more closely by maintaining atrioventricular (AV) synchrony and dominance of the sinus node, which in turn may reduce cardiovascular morbidity and mortality thus contributing to patient survival and quality of life. However, the prospective studies designed with the objective of analyzing the impact of maintaining AV synchrony on mortality were disappointing. The PASE (Lamas et al, 1998), CTOPP (Connolly et al, 2000), MOST (Lamas et al, 2002) and UKPACE (Toff et al, 2005) studies demonstrated only secondary benefits, such as the decrease in the incidence of atrial fibrillation and improved quality of life, but without any effect on mortality. It has been proposed that the probable deleterious effects of right ventricular stimulation leading to dyssynchrony can annul the benefits obtained with the atrioventricular synchronism. At the same time, there is increasing evidence that conventional pacing from the right ventricular apex was associated with dyssynchronous activation of the left ventricle, resulting in impaired haemodynamic function (Leclercq et al,1995;Wilkoff et al,2002; Schmidt et al, 2007; Tops et al, 2006; Tops et al, 2007). The detrimental effects of ventricular apical pacing on left ventricular (LV) haemodynamics were demonstrated as early as 1925 by Wiggers (Wiggers, 1925). However, it was not until recently that it became abundantly clear that the time has come to seek alternative ways to minimize or avert the adverse clinical outcomes resulting from the asynchronous contraction pattern that RVA stimulation induces (Wilkoff et al, 2002; Tops et al, 2007, Sweeney et al,2003). In this Chapter, we attempt to discuss in patients with high grade atrioventricular block and preserved LV function, 1) the optimal mode of pacing (VVI(R)= single chamber, ventricular pacing in the inhibited mode vs DDD=dual chamber pacing and sensing, both triggered and inhibited mode) particularly in elderly patients, 2) the effectiveness and safety of alternative