Hello yoanne, thanks for your interest in my history, it is a bit lengthy and complex. I received the original Medtronic's pacemaker defibrillator in 2001. It is configured as you described, i.e. one lead in the atrium, the other in the ventricular chamber. The defibrillator portion is programmed to deliver a shock if the pacing of the heart exceeds the set parameters established by the doctors technicians. In 2015 the old device was replaced by a Bi ventricular pacemaker defibrillator, identified as a Medtronic's Viva Quad XT CRT. The original wires in the right atrium and right ventricle remained in place and were connected to the new device. A third lead was attached to the left ventricle and connected to the device to assist with the pumping efficiency of the lower chamber. This modification was done in a surgical procedure while I was totally sedated. The decision to install the Bi V device was made to improve the low ejection fraction. Hopefully this explanation provides the information you were asking about. Thanks again for your interest.