Atrial overdrive pacing in non-atrial tracking mode while maintaining AV synchrony

A heart stimulator for stimulating at least an atrium and a ventricle of a heart, the heart stimulator comprising:

• electrode leads comprising electrodes configured
• to pick up electric potentials inside at least one atrium and at least one ventricle of a heart, and/or,
• to deliver electric stimulation pulses to said at least one atrium and said at least one ventricle of said heart;
• at least one sensing stage connected to said electrode leads, wherein said at least one sensing stage is configured to sense an excitation or a contraction of a heart chamber;
• at least one stimulation pulse generator configured to generate the electric stimulation pulses and connected to said electrode leads;
• a control unit, which is connected to said at least one sensing stage and to said at least one stimulation pulse generator and which is configured
• to trigger the electrical stimulation pulses that are generated by said at least one stimulation pulse generator and that are to be delivered via said electrode leads comprising said electrodes;
• to perform at least a mode of pacing
• wherein an atrial or a ventricular stimulation pulse is triggered in an atrium asynchronous manner when a respective atrial or ventricular escape interval times out because no intrinsic atrial or ventricular contraction is sensed during said respective atrial or ventricular escape interval, respectively;
• wherein a trigger of the atrial or a ventricular stimulation pulse is inhibited, when the intrinsic atrial or ventricular contraction, respectively, is sensed prior to time out of the respective atrial or ventricular escape interval;
• and wherein the atrial and the ventricular escape interval corresponds to an overdrive stimulation rate, that is higher than an intrinsic heart rate;
• and,
• to resynchronize atrial stimulation and ventricular stimulation after an atrial sense event As or an atrial refractory sense event Ars is sensed during an atrial escape interval and is followed by a ventricular sense Vs or a ventricular pace Vp event, wherein said control unit is further configured to recalculate a ventricular escape interval and said atrial escape interval based on an AsV-Interval AsVI, which begins with said atrial sense event As or said atrial refractory sense event Ars and which ends with a following ventricular sense event Vs or ventricular pace event Vp so that an interval from the atrial sense event As or the atrial refractory sense event Ars to a next atrial stimulation pulse corresponds to the overdrive stimulation rate, and a next ventricular stimulation pulse is synchronized to a next atrial stimulation pulse such that the ventricular escape interval for resynchronization VVresync equals:
• VVresync=max(ODI−AsVI+AVD, URL)
• wherein ODI is an overdrive interval that corresponds to the overdrive stimulation rate and
• wherein AVD is a predetermined atrioventricular delay interval and
• wherein URL is a shortest possible ventricular pacing interval that corresponds to a preset maximum stimulation rate and
• and said atrial escape interval for resynchronization VAresync equals:
• VAresync=VVresync−AVD=max(ODI−AsVI, URL−AVD).