Excerpt

The implantation of the first internal cardiac pacemaker in 1958 heralded the era of implantable cardiac devices1. The subsequent evolution of the cardiac pacemaker through stages of progressive sophistication reflects still extant efforts to mimic the physiology of native conduction. The right ventricular (RV) apex has traditionally been used as the preferred site of pacing due to the relative ease of access and the favorable logistics of securing the pacemaker lead in the trabeculae. Single-chamber RV pacing was followed by dual-chamber pacing to maintain atrioventricular synchrony. However, studies have demonstrated deleterious effects of RV apical pacing on left ventricular (LV) function due to mechanical dyssynchrony resulting from the spread of the activation wavefront through the myocardium rather than specialized conduction tissue2. The iatrogenic wide-QRS left bundle branch block (LBBB) produced by RV apical pacing results in an extreme degree of LV intraventricular dyssynchrony. Progressive deterioration of LV systolic function after RV apical pacing is a well-recognized phenomenon and has spurred the practice of pre-emptive biventricular pacing in patients with LV systolic dysfunction who are expected to be dependent on a substantial burden of paced beats. Quite remarkably, however, despite evidence of better-preserved LV systolic function3 there have been relatively few efforts to substantiate the notion of less mechanical dyssynchrony with biventricular compared to RV pacing. Continuing efforts to optimize the physiology of cardiac pacing have resulted in proposals for RV septal pacing and His-bundle pacing.4,5 The latter approach, although theoretically the most physiological, is fraught with the technical challenges of lead stability and increasing pacing thresholds over time.6 More recently, left bundle branch (LBB) pacing has been proposed7 as an alternative to His-bundle pacing with the hope of overcoming some of these shortcomings with potential improved long-term stability and thresholds allowing maximal battery life. Unique downsides to LBB pacing are the possibility of septal perforation and potential coronary injury in addition to injury to the His-Purkinje system with repositioning, all of which need to be evaluated in larger studies. …