Rechargeable demand inhibited cardiac pacer and tissue stimulator

• US 3,888,260 A
• Filed: 04/26/1974
• Issued: 06/10/1975
• Est. Priority Date: 06/28/1972
• Status: Expired due to Term

• Current Assignee: Robert E. Fischell
• Original Assignee: Robert E. Fischell
• Inventors: Fischell, Robert E.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US05/464,441
• Time in Patent Office: 410 Days
• Field of Search: 128/419EP,419PG,419PS,419S,421,422,2.1B,2.1R
• US Class Current: 607/36
• CPC Class Codes: A61N 1/365 controlled by a physiological parameter, e.g. heart potential evoked response A61N1/371
• CPC Class Codes: A61N 1/37512 Pacemakers
• CPC Class Codes: A61N 1/3787 from an external energy source

Abstract

An improved demand inhibited cardiac pacer or human tissue stimulator employs a rechargeable battery to furnish operating power to electronic pulse generating circuitry which generates output stimulating pulses. For the demand inhibited cardiac pacer these pulses are generated only when the patient'"'"''"'"'s heart stops beating properly at its own intrinsic rhythm as monitored by other circuitry in the pacer unit. A double hermetic sealing structure protects the electronic components of the pacer or tissue stimulator unit from exposure to corrosive fluids from the body and from the power source and additionally provides shielding against external electromagnetic interference, including protection of the electronic pulse generating circuitry from the alternating magnetic field that provides the recharging energy, but without significantly attenuating the inductive coupling of this recharging energy to the unit during the recharging operation. The demand inhibited pacer or tissue stimulator has an improved circuit design and provides accurate telemetry indication as to when such recharging of the unit'"'"''"'"'s battery is taking place. Moreover, the proposed demand inhibited pacer includes transistor switching circuitry which functions to electrically connect the output of the pulse generating circuitry to the patient'"'"''"'"'s heart only when an output pulse is being generated, in order to prevent the pulse generating circuitry from loading down the monitoring portion of the proposed pacer, and in certain configurations to reduce corrosion.

Claims

1. In a cardiac pacer and tissue stimulator adapted to be implanted in a patient'"'"''"'"'s body and including a rechargeable battery, means for coupling alternating magnetic input recharging energy to said battery from an external source, and electronic circuit means powered by said battery for generating stimulating pulses for application to the patient'"'"''"'"'s heart or other tissue, the improvement comprising, a first inner shield means disposed to shield said circuit means from said external source of alternating magnetic input recharging energy and sources of magnetic interference, said coupling means being disposed external to said first shield means, and a second outer shield means encompassing said coupling means, said battery, said first shield means and said electronic circuit means to form a hermetic shield against body fluids without substantially attenuating the recharging energy being coupled by said coupling means to said battery from said external source.

2. The cardiac pacer and tissue stimulator specified in claim 1 wherein said first shield means encompasses said electronic circuit means to form a second hermetic seal within the hermetic seal formed by said second outer shield means.

3. The cardiac pacer and tissue stimulator specified in claim 1 wherein said first inner shield means is constructed of a material characterized by relatively high magnetic permeablity and low electrical resistivity and said second outer shield means is constructed of a material characterized by relatively high electrical resistivity and low magnetic permeability.

4. The cardiac pacer and tissue stimulator specified in claim 3 wherein said first inner shield means is fabricated of nickel having a thickness greater than substantially 5 mils.

5. The cardiac pacer and tissue stimulator specified in claim 3 wherein said second outer shield means is fabricated of stainless steel having a thickness substantially within the range 3 to 20 mils.

6. The cardiac pacer and tissue stimulator specified in claim 3 wherein said second outer shield means is fabricated of titanium having a thickness substantially within the range 3 to 20 mils.

7. The cardiac pacer and tissue stimulator specified in claim 3 wherein said second outer shield means is fabricated of Haynes 25 alloy having a thickness substantially within the range 3 to 20 mils.

8. The cardiac pacer and tissue stimulator specified in claim 3 wherein said second outer shield means is glass.

9. The cardiac pacer and tissue stimulator specified in claim 3 wherein said second outer shield means is ceramic.

10. The cardiac pacer and tissue stimulator specified in claim 1 wherein said coupling means is an inductive coupling means.

11. The cardiac pacer and tissue stimulator specified in claim 10 wherein said inductive coupling means comprises a first winding means disposed within the patient'"'"''"'"'s body and adapted to inductively couple energy from said external source to said battery in order to recharge said battery.

12. The apparatus specified in claim 1 wherein said cardiac pacer is of the demand inhibited type including means for monitoring the heart beat of the patient and inhibiting said electronic circuit means in order to prevent the generation thereby of said heart stimulating pulse when said heart is beating naturally at an acceptable rate without application of said heart stimulating pulses.

13. The rechargeable demand inhibited cardiac pacer specified in claim 12 further including a coaxial catheter means having one end connected to said monitoring means and said electronic circuit means, and terminating at its opposite end in a pair of electrodes adapted to be disposed at a preselected location in the patient'"'"''"'"'s heart for applying the heart stimulating pulses generated by said electronic circuit means and for sensing the electrical R-wave signal emanating from the patient'"'"''"'"'s heart when the heart beats.

14. The cardiac pacer and tissue stimulator specified in claim 1 wherein, said first shield means is a substantially rectangular hollow metallic can having one end open to receive and have encapsulated therein said electronic circuit means, said second shield means is a substantially rectangular hollow metallic can having one end open to receive and have encapsulated therein, said rechargeable battery, said coupling means and said first metallic can, and further including a unitary end cap member attached to and covering the open end of each of said first and second can members.

15. The cardiac pacer and tissue stimulator specified in claim 14 wherein said end cap member is formed with first and second shoulder means mating with and sealing respectively the open end of said first and second metallic cans.

16. In a cardiac pacer and tissue stimulator adapted to be implanted in the body of a patient and including a rechargeable battery, means for coupling alternating magnetic input recharging energy to said battery from an external source, and electronic circuit means powered by said battery for generating stimulating pulses and applying them to the patient'"'"''"'"'s heart or other tissue, the improvement comprising, telemetrY means rendered effective when recharging energy is being coupled to said battery for providing an indication external of the patient'"'"''"'"'s body that said recharging is taking place, said telemetry means including a means operably connected to said coupling means to receive operating energy only during recharging of said battery for generating an output telemetry signal indicative that recharging of said battery is taking place, said output telemetry signal generating means being responsive to the magnitude of recharging current being applied to said battery to cause the output telemetry signal to indicate whether or not said battery is being recharged at an acceptable recharging current level.

17. The apparatus specified in claim 16 wherein said cardiac pacer is a demand inhibited type further including means for monitoring the beating of the patient'"'"''"'"'s heart for inhibiting said electronic pulse generating circuit means when said heart is beating naturally without the application of said stimulating pulse.

18. The cardiac pacer and tissue stimulator specified in claim 16 wherein the generating means included in said telemetry means is an electrical signal generating means rendered effective only when recharging of said battery is taking place to generate an output electrical telemetry signal capable of being received external of the patient'"'"''"'"'s body.

19. The cardiac pacer and tissue stimulator specified in claim 18 wherein said coupling means is an inductive coupling means comprising a core member and first and second winding means wound on said core member, said first winding inductively coupling energy from said external source to said battery in order to recharge said battery and wherein the output electrical telemetry signal from said signal generating means is connected to said second winding means on said core member for inductive coupling to receiving means external of the patient'"'"''"'"'s body.

20. The cardiac pacer and tissue stimulator specified in claim 16 wherein the generating means included in said telemetry means is an oscillator circuit means whose output signal frequency is proportional to the magnitude of recharging current being applied to said battery, said output frequency signal from said oscillator means being connected to said coupling means for transfer external of the patient'"'"''"'"'s body.

21. The cardiac pacer and tissue stimulator specified in claim 16 further including first shield means disposed to shield both said electronic circuit means and said telemetry signal generating means from said atternating magnetic input recharging energy and sources of magnetic interference, said coupling means being disposed external to said first shield means, and second shield means surrounding said first shield means, said electronic circuit means, said telemetry signal generating means, and said coupling means to form an outer hermetic seal for said pacer or stimulator without substantially attenuating the recharging energy being coupled by said coupling means to said battery from said external source.

22. The cardiac pacer and tissue stimulator specified in claim 21 wherein said first sheild means surrounds said electronic circuit means and said telemetry signal generating means to form a second inner hermetic seal for said pacer and stimulator.

23. In a demand inhibited cardiac pacer including a first electronic circuit means for generating output heart stimulating pulses for application to a patient'"'"''"'"'s heart and a second electronic circuit means for monitoring the patient'"'"''"'"'s heart beat and inhibiting the generation by said first electronic circuit means of said heart stimulating pulses in the presence of an acceptable natural heart beat rate, the improvement comprising, a step-up transformer included in said first electronic pulse generating circuit means and having primary and secondary windings for increasing the amplitude of each heart stimulating pulse prior to application thereof to the patient'"'"''"'"'s heart, catheter means having one end connected electrically to said second electronic circuit means and connectable electrically to the secondary winding of the step-up transformer of said first electronic pulse generating circuit means and terminating at its opposite end in electrode means adapted to be disposed at a preselected location in the patient'"'"''"'"'s heart for applying the heart stimulating pulses generated by said first electronic circuit means and for sensing the electrical R-wave signal emanating from the patient'"'"''"'"'s heart when the heart beats, and switching means for selectively connecting the secondary winding of the step-up transformer of said electronic pulse generating circuit means to said catheter means only when an output pulse is being generated by said pulse generating circuit means.

24. The demand inhibited cardiac pacer specified in claim 23 wherein said catheter means is a coaxial catheter and further including, a rechargeable battery for supplying operating voltage to said first and second electronic circuit means, and means for inductively coupling alternating magnetic recharging energy to said battery from an external source.

25. The rechargeable demand inhibited cardiac pacer specified in claim 24 further including, telemetry signal generating means connected to said inductive coupling means to receive operating power only during recharging of said battery for generating an output telemetry signal indicative that recharging of said battery is taking place, said output telemetry signal being connected to said inductive coupling means to be inductively coupled external of the patient'"'"''"'"'s body, first shield means disposed to shield both of said first and second electronic circuit means and said telemetry signal generating means from said alternating magnetic input recharging energy and sources of magnetic interference, and second shield means surrounding said first shield means, said first and second electronic circuit means, said telemetry signal generating means, and said inductive coupling means to form an outer hermetic seal for said pacer without substantially attenuating the recharging energy being coupled by said coupling means to said battery from said external source, said second shield means being constructed of a material effective to permit the coupling of recharging energy by said coupling means to said battery from said external source without substantial attenuation.

26. The rechargeable demand inhibited cardiac pacer specified in claim 25 wherein, said telemetry signal generating means is an oscillator circuit means operably connected to said inductive coupling means to receive operating voltage only during recharging of said battery for generating an output electrical signal whose existence provides an indication that recharging of said battery is taking place and whose frequency is proportional to the magnitude of recharging current being applied to said battery, said output frequency signal from said oscillator means being connected to said inductive coupling means to be inductively coupled external of the patient'"'"''"'"'s body, and said first shield means surrounds said first and second electronic circuit means and said oscillator means to form a second inner hermetic seal for said pacer unit.

27. The demand inhibited cardiac pacer specified in claim 26 wherein said switching means comprises a bi-polar transistor switching gate circuit connected electrically between said catheter means and the secondary winding of the step-up transformer of said pulse generating circuit means, said switching gate including transistor means rendered conductive by an output heart stimulating pulse from said pulse generating circuit means to said pulse generating circuit means only when an output heart stimulating pulse is being generated by said pulse generating circuit means.

28. The demand inhibited cardiac pacer specified in claim 23 wherein said switching means comprises a bipolar transistOr switching gate circuit connected electrically between the secondary winding of said output transformer and said catheter means, said switching gate including transistor means rendered conductive by an output heart stimulating pulse from said pulse generating circuit means to connect said catheter means to said output transformer only when an output heart stimulating pulse is being generated by said pulse generating circuit means and appears at the secondary winding of said output transformer.

29. The rechargeable demand inhibited cardiac pacer specified in claim 23 wherein said second electronic circuit means includes circuit means to prevent said first electronic circuit means from being inhibited by R-wave signals occurring at greater than a predetermined rate corresponding to a predetermined maximum acceptable natural heart rate.