Atrioventricular and interventricular delay optimization and response quantification in biventricular pacing: arrival of reliable clinical algorithms and research protocols, and how to distinguish them from unreliable counterparts.

In this issue of the journal, Bogaard et al. assess the achievable haemodynamic increment within individuals of optimizing atrioventricular (AV) and interventricular (VV) delays. Biventricular pacing, or cardiac resynchronization therapy (CRT), arguably the greatest advancement in the treatment of heart failure in the last decade, causes immediate increases in haemodynamics and then improvements in symptoms, exercise capacity, and reductions in hospitalization and mortality. The landmark endpoint studies included optimization of AV delay to give the most ideal appearance of transmitral Doppler. Subsequently, many studies, not always randomized and controlled, have assessed alternative optimization techniques including echocardiographic aortic velocity–time integral (VTI), mitral VTI, left ventricular (LV) end-systolic volume and ejection fraction, transmitral Doppler (E-A) duration, E-A truncation; thoracic electrical impedance; cardiac output by rebreathing techniques; blood pressure, plethysmography and pulse contour analysis; intracardiac electrogram and surface electrocardiogram, QRS morphology, QRS axis; heart sounds and phonocardiography; and LV pressure and pressure derivatives (dp/dtmax) and pressure–volume analysis.