Implantable cardiac stimulator wherein AV-delay adjustment is limited during dynamic atrial overdrive

An implantable cardiac stimulator comprising:

• a housing adapted for implantation in a subject;
• an atrial lead adapted for interaction with an atrium of the subject;
• a ventricular lead adapted for interaction with a ventricle of said subject;
• stimulating pulse generating circuitry in said housing, connected to said atrial lead and to said ventricular lead, for generating stimulating pulses which are conveyed to the atrium and the ventricle, respectively, via said atrial lead and said ventricular lead;
• sensing circuitry in said housing connected to said atrial lead and to said ventricular lead for sensing depolarizations in the atrium and the ventricle via said atrial lead and said ventricular lead, respectively;
• a control circuit connected to said stimulating pulse generating circuitry and to said detector circuitry for adjusting sensed and stimulated AV/PV delays and for operating said stimulating pulse generating circuitry to produce physiologically optimal AV/PV delays at different paced and sensed heart rates;
• and
• said control circuit operating said stimulating pulse generating circuitry in a mode for dynamic overdrive of the atrium upon a sensing of a predetermined atrial condition by said sensing circuitry and for limiting adjustment of the AV delay when operating said stimulating pulse generating circuitry in said mode.