Implantable cardiac stimulator wherein the atrial stimulation time interval is set dependent on the evoked response amplitude

Abstract

An implantable heart stimulating device with atrial overdrive capability has an atrial stimulation unit for stimulating the atrium via stimulation electrode(s), an atrial evoked response detector adapted to determine an atrial evoked response amplitude, and an atrial control unit to control an atrial timing unit to set an atrial stimulation time interval length between consecutively applied atrial stimulation pulses. The atrial stimulation time interval length is set in dependent on the determined atrial evoked response amplitude such that the next time interval length is a predetermined percentage of the present time interval length. If the ER signal amplitude decreases, the stimulating interval has to be decreased. The pacemaker can also try to increase the stimulating interval back to back until a decrease in ER signal amplitude is seen in order to avoid too high stimulating rate.

I claim as my invention:  
     
         1 . An implantable cardiac stimulator comprising: 
 an atrial pulse generator;    stimulation electrode(s) connected to the atrial pulse generator and adapted for interaction with the atrium to deliver pulses from the atrial pulse generator to the atrium;    an atrial evoked response detector connected to said stimulation electrode(s) for determining an atrial evoked response amplitude for at least one of said stimulation pulses; and    an atrial control unit connected to the atrial pulse generator and to the atrial evoked response detector, and having an atrial timer for setting an atrial stimulation time interval length between consecutive pulses from said atrial pulse generator, said control unit operating said atrial timer to set the atrial stimulation time interval length for a next time interval length, dependent on said atrial evoked response amplitude, as a predetermined percentage of a current time interval length.    
     
     
         2 . An implantable cardiac stimulator as claimed in  claim 1  wherein said control unit employs a predetermined percentage in a range between 85% and 95%.  
     
     
         3 . An implantable cardiac stimulator as claimed in  claim 1  for stimulating a heart having an intrinsic atrial time interval length, and wherein said control unit control said timer to set said time interval length for said next time interval to be as long as possible with respect to said intrinsic atrial time interval length.  
     
     
         4 . An implantable cardiac stimulator as claimed in  claim 1  wherein said atrial evoked response detector operates with a plurality of amplitude thresholds for identifying a decrease of said atrial evoked response amplitude, and wherein said control unit operates said atrial timer to decrease said atrial stimulation time interval length for said next time interval if a decreasing atrial evoked response amplitude is identified.  
     
     
         5 . An implantable cardiac stimulator as claimed in  claim 1  wherein said atrial evoked response detector determines if said atrial evoked response amplitude is less than a minimum evoked response amplitude threshold and, if so, said control unit operates said atrial timer to decrease said atrial stimulation time interval length for said next time interval by said predetermined percentage.  
     
     
         6 . An implantable cardiac stimulator as claimed in  claim 1  wherein said atrial evoked response detector operates with a plurality of amplitude thresholds to identify an increasing atrial evoked response amplitude, and wherein said control unit operates said atrial timer to increase said atrial stimulation time interval length for said next time interval length by said predetermined percentage if an increasing atrial evoked response amplitude is identified.  
     
     
         7 . An implantable cardiac stimulator as claimed in  claim 1  wherein said evoked response detector detects an electrical evoked response signal, and wherein said atrial evoked response amplitude is an amplitude of said electrical evoked response signal.  
     
     
         8 . An implantable cardiac stimulator as claimed in  claim 1  wherein said evoked response detector operates with amplitude thresholds to identify a decreasing atrial evoked response amplitude, and wherein said control unit operates said timer to decrease said atrial stimulation time interval length for said next time interval by said predetermined percentage if a decreasing evoked response amplitude is identified and, if said atrial stimulation time interval length for said next time interval was decreased in any of a predetermined number of preceding heart cycles, and if said atrial evoked response amplitude is above a predetermined threshold, said control unit operates said atrial timer to increase said atrial stimulation time interval length for said next time interval length.