Cardiac resynchronization therapy (CRT) is limited by a high proportion of non-responders. Pacing activation from multiple separated left ventricular (LV) sites might improve the depolarization pattern, thereby promoting more physiological activation. To explore the effect of MPP on cardiac neuro-hormonal activity, the investigators will enroll approximately 30 patients who already underwent CRT-D implantation with a quadripolar LV lead connected to a device capable of MPP.