Optimization of the atrioventricular delay in sequential and biventricular pacing: physiological bases, critical review, and new purposes.

Atrioventricular (AV) delay optimization in sequential and biventricular (BiV) pacing, although widely recommended, is often poorly performed in clinical practice as an improper setting can reduce the success of the stimulation. Despite the several methods proposed, the AV delay is frequently programmed in an empirical way or left to a predefined value (usually the manufacturer's setting), without considering the different variables involved in this context, concerning the intra- and interindividual variability of the electromechanical events, the peculiarities of the several cardiopathies, the spontaneous interatrial and AV conduction, the pharmacological therapy, and the pacing mode. The manuscript illustrates the physiological bases of the optimization, describes why and how to programme the best AV delay at rest and during daily activities and discusses critically all methods proposed, divided into three groups: predefined formulas, iterative attempts, and automatic settings. The manuscript is not only a review because it tries to clarify this complex topic, stating the fundamental concept in BiV pacing; the optimal AV delay should be short enough to have always a pre-exitated stimulation and contemporary an optimal left ventricular filling. The paper suggests new purposes and new solutions for this goal, it shows the limits of the actual guidelines and the disappointing results obtained in several studies by automatic methods, goading to find new algorithms.