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Low cost implantable medical device

  • US 5,292,342 A
  • Filed: 05/01/1992
  • Issued: 03/08/1994
  • Est. Priority Date: 05/01/1992
  • Status: Expired due to Term
First Claim
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1. An implantable cardiac pacemaker programmable by application of a magnetic field means for generating a first external magnetic field having a first polarity and a second external magnetic field having a second polarity comprising:

  • a pulse generator for generating a cardiac stimulating pulse;

    voltage generation means coupled to said pulse generator for generating a first analog voltage and a second analog voltage;

    a first analog voltage storing device coupled to said voltage generation means for storing said first analog voltage;

    a first magnetic sensor circuit, having a first magnet signal generating means responsive to said first external magnetic field of said first polarity to produce a first magnet signal, and further having a second magnet signal generating means responsive to said second external magnetic field of said second polarity to produce a second magnet signal;

    a logic circuit, coupled to said magnetic sensor circuit and to said first analog voltage storing device, said logic circuit having a first increase signal generating means responsive to a first predetermined sequence of said first and second magnet signals to generate a first increase signal, and further having a first decrease signal generating means responsive to a second predetermined sequence of said first and second magnet signals to generate a first decrease signal, such that said first stored voltage is increased in response to said first predetermined sequence and decreased in response to said second predetermined sequence;

    a first reference current generating circuit, coupled to said first analog voltage storing device, for generating a first reference current proportional to said first stored analog voltage;

    sensing means, for sensing at least one cardiac event; and

    a base rate circuit, coupled to said pulse generator, said sensing means, and to said first reference current generating circuit, said base rate circuit having means for generating a trigger signal when a first time interval elapses following a previous cardiac event, wherein no new cardiac event occurs during said first time interval, and wherein said first time interval is proportional to said first reference current.

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