Effect of Site of Right Ventricular (RV) Pacing on RV Function, Left Ventricular (LV) Dyssynchrony and Contraction Efficiency

Permanent pacing with right ventricular stimulation is the standard method used in patients with bradyarrhythmia, and recommended by current international guidelines because it is associated with improved clinical outcomes. The extent of right ventricular pacing (RVP) varies between patients and many individuals tolerate a high proportion of RVP without complications. However, chronic RVP may cause electrical and mechanical dyssynchrony that may lead to impaired left ventricular ejection fraction (LVEF). Dyssynchronous ventricles require more oxygen to generate the same amount of mechanical work and the consequence is a decline in the efficieny of myocardial contraction. RV septal pacing (RVS) is thought to allow more physiological LV depolarisation, than RV apical pacing (RVA) with preservation of LV function. However, there are conflicting data on its benefits, and the recently completed Protect-Pace (The protection of LV function during RV pacing) study showed both RVA and non-RVA pacing to have a small adverse effect on EF in patients with preserved LV function, but no difference between the methods. The effect of RV pacing on RV function has not been evaluated systematically, with most studies focusing on tricuspid regurgitation (TR) as the outcome of interest. Echocardiographic assessment of LV dyssynchrony has been extensively used because it is noninvasive, widely available, and has no known risk or side effect. Speckle tracking echocardiography is a novel echocardiographic technique without the angle dependence of an ultrasound beam and is able to measure regional deformation in any direction in the LV and RV, that can detect subtle myocardial dysfunction because it is more sensitive compared with conventional parameters, Furthermore, strain imaging can display the timing and extent of myocardial thickening and stretching so that it is well suited to estimate the amount of inefficient dyssynchronous contraction. Global Longitudinal Strain (GLS) and LV mechanical function and dyssynchrony assessment by speckle-tracking echocardiography (STE) enables us to detect subclinical LV dysfunction. And also a very attractive clinical tool for the assessment of right ventricular (RV) systolic performance, providing incremental diagnostic and prognostic information over the traditional indices of RV function, Among various imaging modalities, echocardiography is currently the method of choice for clinical assessment of RV longitudinal strain (RVLS). The methodology of speckle-tracking echocardiography to obtain RVLS has been recently standardized and demonstrated to be feasible, accurate, and robust for clinical use. Inter-technique and inter-vendor comparability and reliability of RVLS are improving. RVLS is advantageous because it is more sensitive to subtle changes in myocardial function than conventional parameters used to assess RV function (i.e. tricuspid annular plane systolic excursion, tissue Doppler systolic velocity, fractional area change, or RV ejection fraction) representing a sensitive tool for the long-term follow-up of patients.