Reducing Ventricular Pacing Frequency in Patients With Atrioventricular Block

With aging of the general population, an increased incidence of conduction disease will result in an increased need for permanent pacemaker therapy. According to the 2015 European Heart Rhythm Association (EHRA) White Book, in the 56 member countries of the European Society of Cardiology (ESC), the pacemaker implantation rate has increased from a mean implantation rate of 614 per million inhabitants in 2010 to 641 in 2014, thus growing at a rate of about 0.4% to 0.6% per year. Much has been learned from clinical studies to identify optimal device mode selection and device programming for an individual patient to maximize the benefits of cardiac implantable electronic device therapy, as well as to minimize any potential adverse outcomes caused by ventricular pacing (VP). Several clinical studies have reported that chronic right ventricular (RV) pacing has detrimental effects on cardiovascular outcomes, including adverse cardiac remodeling, atrial fibrillation (AF), congestive heart failure (HF), and mortality. The potential mechanism(s) by which RV pacing increases the risk for HF and AF are not completely elucidated, but are likely caused by both electric and mechanical dyssynchrony, disruption of sympathetic/parasympathetic balance that alters myocardial activation pattern and contraction sequence, thereby modifying myocardial strain resulting in less efficient contraction. These changes lead to chamber enlargement, functional mitral regurgitation, reduction of parasympathetic/ sympathetic balance in response to reduced ventricular output, and contribute to the development of HF and AF. Notably, not all patients paced in the RV experience adverse outcomes; these detrimental effects seem to be dependent on a high cumulative percentage of RV pacing, generally indicated by >40%. Furthermore, the increased risk of HF has been more frequently observed in those with pre-existing left ventricular (LV) systolic dysfunction. A recent review by Gillis2 has covered the optimal pacing mode for RV and biventricular devices. It is clear that the abnormal ventricular activation sequence generated by spontaneous left bundle branch block (LBBB) or by RV pacing itself triggers a remodeling process. In the presence of HF and LBBB, simultaneous RV and LV pacing or LV pacing by restoring mechanical synchrony has profound effects at the genome, proteome, transcriptome, metabolome, cellular, and phenome level. However, full reversal of maladaptive remodeling process at all levels (from subcellular to organ level) induced by biventricular pacing is strongly related to the percentage of continuous biventricular pacing, which shall be as close as to 100% and in any case higher than 95% to maximize the effect. The American Heart Association (AHA)/American College of Cardiology (ACC)/Heart Rhythm Society (HRS) and ESC/EHRA guidelines recommend the use of pacing algorithms to reduce the percentage of VP. This recommendation is the result of 2 decades of clinical trials that led to the deconvolution of the complex electromechanical interaction and effects of pacing on cardiac function and arrhythmias. However, the vast majority of clinical trials tested algorithms, which reduce VP primarily in patients with sick sinus syndrome. Because the most common indication for permanent pacing is intermittent or persistent complete atrioventricular block (AVB) (Web Table 3-ESC GDL 2013); the value of reducing VP has not been tested adequately in this patient group until recently (Table 1). New studies have evaluated the use of an algorithm limiting the frequency of VP in patients with advanced or complete AVB (Table 1). The purpose of the present review is to report the recent apparently contradictory data suggesting more aggressively adopting algorithms that reduce the frequency of ventricular pacing in patients with AVB—a population for whom we have typically programmed continuous and uninterrupted ventricular pacing.