The invention more particularly relates to “multi-site” prostheses, in which electrodes are placed in a plurality of distinct respective sites comprising the two ventricular sites, right and left, and at least one atrial site. It can be a prosthesis of the “triple chamber” type (double ventricular stimulation and right atrial detection/stimulation) or the “quadruple chamber” type (double ventricular stimulation and double atrial detection/stimulation).
The majority of patients receiving such an implanted multi-site device are patients who usually present a normal atrio-ventricular conduction (each atrial event is followed by an associated ventricular depolarization) and who thus do not have a standard indication for implantation of a permanent pacemaker. The multi-site device is then indicated to treat the cardiac insufficiency so as to improve the general hemodynamic state of these patients, by joint and permanent stimulation of the left and right ventricles in order to re-synchronize them. This therapy makes it possible to observe often spectacular results for patients in class III cardiac insufficiency not improved by traditional treatments. These devices can operate in synchronous stimulation, i.e., the two ventricular sites of stimulation receive at the same time the depolarization impulse (no inter-ventricular delay), or as described in EP-A-1 108 446 and its counterpart, U.S. Pat. No. 6,556,866 (incorporated herein by reference), commonly assigned herewith to ELA Medical, with, between two ventricular stimulations, an inter-ventricular delay adjusted so as to re-synchronize contraction of the ventricles with a fine optimization of the hemodynamic state of the patient.
The starting point of the invention results from clinical observations carried out on patients having received such a device when a loss of capture appears on one of the two ventricular probes. The loss of capture is a situation in which the stimulation impulse applied to the electrode of the probe has an insufficient amplitude to cause depolarization of the ventricle. Such a loss of capture often follows a natural increase, over the long term, of the stimulation threshold. Because of this loss of capture, the stimulation of one of the ventricles will be without effect, and the patient will be in a state with a stimulation of only one of the two ventricles, either right or left. This stimulation of only one ventricle can be extremely noxious, if prolonged, because it can involve an increase in the inter-ventricular desynchronization. The inventors of the present invention noted that, in such a situation, to let express the spontaneous rhythm of the patient can prove to be an alternative less heavy in consequences than to continue stimulation of only one of the ventricles.