Assessment of the echocardiograms will be performed by 2 investigators who are not blinded to the patient's treatment allocation. This is because the pacemaker lead is nearly always well visualised during echocardiographic studies making blinding impossible. However, the main outcomes of this study will be quantitative measures of TR and biventricular function derived from 3D echocardiography rather than qualitative measures used in previous studies and this will protect against bias that may be caused by the echocardiogram assessors knowing the allocation of the patients. The studies will also be assessed for interobserver and intraobserver variability to look for the likelihood of bias.