Pacemaker with adaptive sensing means for use with unipolar or bipolar leads

Claim 1

In a cardiac pacer system of the type having electrical lead means comprising one or more distally disposed electrodes coupled by one or more elongated conductors to spaced and electrically isolated contact areas on a proximal connector pin, an implantable pulse generator means, resettable timing means coupled to said pulse generator means for causing said pulse generator means to produce electrical stimulating pulses at predetermined intervals unless said timing means is reset prior to the end of said predetermined intervals, sensing means coupled to said resettable timing means, said pulse generator means, said resettable timing means and said sensing means being housed in a moisture-proof container made at least in part from a conductive material which, when said housing is implanted in a living body, is in contact with tissue and body fluids, said container having terminal means for receiving said proximal connector pin, said terminal means having first and second spaced contacts for conductively engaging said spaced and electrically isolated contact areas on said proximal connector pin, an improved sensing means comprising: (a) a sense amplifier exhibiting a predetermined input impedance characteristic between a pair of input terminals thereof, said sense amplifier having an output terminal coupled to said resettable timing means; (b) first and second impedance elements, each of an impedance value which is at least ten times greater than the impedance of animal tissue and body fluids proximate the location of said distally disposed electrodes but less than ten percent of said predetermined input impedance of said sensing amplifiers; (c) means coupling said first and second impedance elements between said conductive material of said housing and a first and a second of said pair of input terminals of said sense amplifier, respectively; (d) means coupling said first spaced contact of said terminal means of said container to said first input terminal of said pair of input terminals of said sense amplifier means; and (e) means coupling said second spaced contact of said terminal means of said container to said second input terminal of said pair of input terminals of said sense amplifier means, said first and second spaced contacts in said terminal means of said container mating with said spaced and electrically isolated contact areas on said connector pin of said lead means.