Patent ID: 7761156

Claim:
A method for operating an implantable cardiac stimulator having an atrial pulse generator, comprising the steps of: operating said pulse generator in a pacing regimen and, in said pacing regimen, delivering stimulation pulses in vivo from the atrial pulse generator to an atrium of a heart with a set, current stimulation time interval length between consecutive stimulation pulses; measuring a degree of atrial fusion in the atrium of the heart by making an in vivo measurement of an amplitude of an atrial evoked response for at least one of the delivered stimulation pulses, thereby obtaining a measured amplitude; in a processor, automatically comparing said measured amplitude to an amplitude threshold to determine whether said measured amplitude has a relation to said amplitude threshold that deviates from a predetermined relationship that is indicative of atrial fusion not being present; when said relationship of said measured amplitude to said amplitude threshold deviates from said predetermined relationship, using the deviation as an indication that atrial fusion exists and automatically changing operation of said atrial pulse generator from said pacing regimen to emit consecutive stimulation pulses in an overdrive regimen and, in said overdrive regimen, automatically re-setting the atrial stimulation time interval length to a length that prevents said atrial fusion, dependent on said deviation from said predetermined relationship, as a predetermined percentage of said current time interval length; and from said processor, maintaining said atrial pulse generator as operating in said overdrive regimen until said measured amplitude and said threshold amplitude no longer exhibit said deviation from said predetermined relationship.