the following group describes the effects of the left ventricular stimulation involving a dipole of two electrodes located inside a suitable vessel branch of the coronary sinus (CS). Standard BIV pacing modality can be achieved by either a quadripolar electrode implanted in the CS, of which only two poles will be used for cardiac resynchronization therapy, or by a bipolar electrode equipped with just two electrodes. The latter describes the old technology, requiring a change into typology of generator which has to display an IS-1 connection (due to different distal terminal of the electrode itself), instead of the new one IS-4 connection that has been developed for quadripolar electrodes.

Such modality of left ventricular stimulation requires a dynamic use of the four electrodes located in the proximal segment of the electrocatheter that allows the recruitment of a vast area of the left ventricle. It is limited by the presence of scars on left ventricle surface, or phrenic nerve inadvertent stimulation.

Implanted CRT-D devices settings will be programmed based on the best acute hemodynamic response assessed non-invasively

change in dP/dtmax, expressed in mmHg/s, assessed through photoplethysmography. This assessment represents in a non-invasive fashion, the rise in pressure (P) developed inside left ventricle during contraction over time.

change in global longitudinal strain, assessed through echocardiography. This assessment elucidates longitudinal shortening of the left ventricle as a percentage (change in length as a proportion to baseline length). GLS is derived from speckle tracking, and analyzed by post-processing of apical images of the left ventricle.

change in GLS. Participants will investigate whether left ventricular remodeling upon "patient-tailored" biventricular stimulation will behave differentially according to type of stimulation; the total amount of CRT-responder patients will be therefore considered