The first pacemakers were provided with a single electrode, which was implanted on one or two ventricles of the heart of the sick patient, and epicardial stimulation was only performed on the ventricle to which said electrode was connected in those pathological cases in which the heart did not contract on its own or did not adequately contract. The implants were performed with a thoracotomy or subxiphoid approach. In 1967, pacemaker implantation became endocardial, i.e. the stimulating electrode was inserted transvenously into the right ventricle; the intervention is considerably less invasive.
In a subsequent development phase, greater clinical knowledge, improved implantation techniques, significant evolution of the pacemakers both from a stoichiometric and circuital point of view, and significant improvement of the stimulating electrodes, it was also proposed to place only one electrode in the atrium, as an alternative to connecting the electrode to the ventricle alone, a much more physiological solution in the case of particular clinical pictures.
In a subsequent phase pacemakers 1, which had two electrodes 3 and 4, were also developed and in this case an electrode 4 was positioned in the right ventricle and the other electrode 3 was positioned in the right atrium, cf. FIG. 1. The surgical operation for implantation of these pacemakers, known as dual-chamber or sequential pacemakers, was more complicated given the presence of two electrodes, thus they were only preferred in those heart conditions that justified the increased risk. Subsequently, with the progress of implantation techniques and the progress of the electrode technology, there was an increasing choice of dual-chamber pacemakers; since 1995, implanting a pacemaker means implanting a dual-chamber pacemaker unless there are clinical contraindications.
Given their clinical conditions, some patients require particular, more complex stimulations than the sequential, right atrium-ventricle stimulation. Such patients have serious conditions, i.e. they have an ejection fraction of less than 35% and are in NYHA class III or IV. So as to improve the clinical picture, i.e. to improve stroke volume and cardiac output, in addition to the atrial electrode 5 in the right atrium RA and the right ventricular electrode 6 in the right ventricle RV, in these patients there is also inserted a third electrode 7 in the left ventricle LV to also stimulate this part of the heart 20 with programmed times compared to the stimulation of the right ventricle, cf. FIG. 2. In such patients, depending on the clinical picture, there can be implanted a defibrillator 2 instead of a pacemaker; it should be borne in mind that a defibrillator also performs the functions of a pacemaker and that such functions are suitably controlled by the control programme of the pacemaker-defibrillator device.
For these patients, for whom it is necessary to implant a third electrode in the left ventricle in addition to the two electrodes in the right ventricle and atrium, there is nevertheless envisaged an implantation surgical operation that is often particularly lengthy and therefore very dangerous due to the very fact that it is performed on patients whose heart is particularly weakened, with risk to their life in the course of the operation. The difficulty of such an operation results from the need to make the third electrode cross the coronary sinus to reach the affixing position above the left ventricle inside the great cardiac vein. There are sometimes particular difficulties that advise against implanting the third electrode adapted to stimulate the left ventricle, and that are generally linked to the clinical conditions of the patient.