Randomized trials for selective site pacing: do we know where we are going?

Clinical evidence is accumulating that pacing from traditional right-sided sites (right ventricular apex and right atrial appendage) may be associated with long-term detriment to left ventricular function and promotion of atrial arrhythmias. Large numbers of small studies, some randomized, have addressed the effects of pacing from nontraditional or alternate sites, but the studies have varied in design such that comparison of results is often difficult. Many studies show data from acute studies only, although more recently longer-term data have started to become available; definition and description of pacing site also varies, adding further to the difficulties in comparing data. This article attempts to examine the randomized studies available to date, and to consider how future studies may contribute to our understanding of the effects of pacing from traditional and selected, specific sites on the right side of the heart.