Cardiac monitoring method and apparatus

• US 5,022,404 A
• Filed: 10/16/1989
• Issued: 06/11/1991
• Est. Priority Date: 10/16/1989
• Status: Expired due to Term

• Current Assignee: Marquette Electronics (General Electric Company)
• Original Assignee: Marquette Electronics (General Electric Company)
• Inventors: Hafner, Curtis R.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): Getzow, Scott M.
• Application Number:
  US07/422,119
• Time in Patent Office: 603 Days
• Field of Search: 128/696, 128/699, 128/904, 364/413.06
• US Class Current: 600/508
• CPC Class Codes: A61B 5/0006 ECG or EEG signals
• CPC Class Codes: A61N 1/37211 Means for communicating with stimulators
• CPC Class Codes: A61N 1/3727 characterised by the modulation technique

Abstract

A patient monitoring system includes a plurality of leads adapted to be coupled to a patient for generating individual ECG data voltage signals. A switching matrix couples the leads to a plurality of differential circuits for coupling selected pairs of the ECG voltage signals to each of the differential circuits for generating differential ECG vector signals functionally related to the difference between selected pairs of the ECG voltage signals. A microprocessor is coupled to the leads and to the switching matrix and is operative to reset the switching matrix to uncouple one or more first leads from the differential circuits and for coupling one or more different ones of the ECG voltage signals to differential circuit formerly coupled to receive the voltage signal from the one or more first leads. An analog to digital converter is connected to the differential means for digitizing the ECG differential signals which are stored in the microprocessor and serially supplied to a modulator for phase modulating a carrier signal to be broadcast to a receiving and displaying unit. An LCD display indicates lead failure and a low battery condition.

Claims

1. A patient monitoring system including a patient monitor having at least four lead means adapted to be coupled to different locations on a patient for sensing individual ECG voltage signals, at least two differential means, switching means in circuit between said lead means and said differential means and operative for simultaneously coupling selected different groups of said ECT voltage signals to each of said differential means, each of said differential means being operative for simultaneously generating a differential signal functionally related to the difference between the preselected ones of said ECG voltage signals in said different groups sensed by the lead means connected thereto, control means coupled to said lead means and to said switching means and being responsive to a failure of one or more of said lead means for setting said switching means to couple different preselected groups of the ECT voltage signals to each of the differential means, the patient monitor including lead fail indicia, said control means being operative to activate the lead fail indicia upon the failure of one or more leads, transmitting means for transmitting RF signals to a display unit remote from the patient monitor, converter means connected to the differential means for receiving lead group signals therefrom, said converter means also being connected to said control means for providing modulating signals representative of the lead group signals, said control means providing said modulating signals to said transmitting means, said transmitting means including RF signal generating means for generating a carrier signal and modulating means connected to receive said carrier signal and said modulating signals and being operative to modulate the carrier signal with said modulating signals and for transmitting the same to said remote unit, whereby the remote display unit may continuously display all of the lead group differential signals, said control means being responsive to a failure in one or more of said lead means for actuating said switching means to disconnect the failed lead from any of the differential means to which it is connected and for connecting an unfailed lead to said differential means to form a different lead pair group with the other unfailed lead previously connected to the said differential means whereby at least two lead pair group differential signals can continuously be transmitted and displayed by the remote unit regardless of the occurrence of a failed lead.

2. The patient monitoring system set forth in claim 1 and including battery means for driving said differential means, said control means and said transmitting means, low voltage sensing means coupled to said battery means and to said control means, an LCD display coupled to said control means for receiving signals therefrom, said LCD display including indicia for indicating battery failure, said control means being operative upon the receipt of a low battery signal and an enabling signal to actuate the low battery indicia of the LCD display, and switch means operative to enable said control means.

3. The patient monitoring system set forth in claim 2 wherein said LCD display includes lead failure indicia for each of said lead means, said control means being operative to actuate said lead fail indicia upon the failure of one or more of said lead means, said switch means being operative to enable said control means for effecting the actuation of the LCD display to indicate lead means failure.

4. The patient monitoring system set forth in claim 1 wherein there are at least four lead means adapted to be connected respectively to the right arm/.the left .arm, the left leg and the chest, and first, second and third differential means, said switching means being operative to connect said first differential means to receive said left leg and right arm signals, said second differential means to receive said left leg and left arm signal, and said third differential means to receive said chest and right arm, left arm, left leg signals, said differential means being operative to provide ECG vector signals which are the differences between said signals received.

5. The patient monitoring system set forth in claim 1 and including means for detecting the existence of a pacemaker signal, said pacemaker signal detecting means being coupled to said control means, said transmitting means being operative to transmit said pacemaker signal to said remote unit.

6. The patient monitoring system set forth in claim 5 wherein said switching means includes switching matrix means having a plurality of input terminals and a plurality of output terminals and being operative upon the receipt of switching control signals to connect a selected pair of said input terminals to selected pairs of output terminals, circuit means connecting said input terminals to respectively receive different ones of said ECG data voltage signals, each of said differential means being connected to different pairs of said output terminals, said control means being operative to actuate said switching means for uncoupling the output terminals coupled to a failed lead and reconnecting the same to a different input terminal.

7. The patient monitoring system set forth in claim 1 wherein said transmitting means includes RF signal generating means for generating a carrier signal, modulating means connected to receive said carrier signal and said differential signals being operative to phase modulate the carrier signal with said digital signals and for transmitting the same to said remote unit.

8. The patient monitoring system set forth in claim 7 and including digital to analog converter means connected to the differential means for receiving analog signals therefrom, said analog to digital converter means also being connected to said control means for providing digital signals representative of the analog ECG signals, said control means providing said digital signals to said modulating means.

9. The patient monitoring system set forth in claim 8 wherein said digitizing means converts said analog signals into binary coded signals, said modulating means being operative to provide a 180°

phase shift with respect to said carrier signal and in response to a first binary digit received and a zero degree phase shift with respect to said carrier signal and in response to a different binary digit received.

10. The patient monitoring system set forth in claim 2 wherein there are at least four lead means adapted to be connected respectively to the right arm, the left arm, the left leg and the chest, and first, second and third differential means, said switching means being operative to connect said first differential means to receive said left leg and right arm signals, said second differential means to receive said left leg and left arm signal, and said third differential means to receive said chest and right arm, left arm, left leg signals, said differential means being operative to provide ECG vector signals which are the differences between said signals received.

11. The patient monitoring system set forth in claim 1 wherein said switching means includes switching matrix means having a plurality of input terminals and a plurality of output terminals and being operative upon the receipt of switching control signals to connect a selected pair of said input terminals to selected pairs of output terminals, circuit means connecting said input terminals to respectively receive different ones of said ECT data voltage signals, each of said differential means being connected to different pairs of said output terminals, said control means being operative to actuate said switching means for uncoupling the output terminals coupled to a failed lead and reconnecting the same to a different input terminal.

22. The patient monitoring system set forth in claim 2 wherein said switching means includes switching matrix means having a plurality of input terminals and a plurality of output terminals and being operative upon the receipt of switching control signals to connect a selected pair of said input terminals to selected pairs of output terminals, circuit means connecting said input terminals to respectively receive different ones of said ECG data voltage signals, each of said signal generating means being connected to different pairs of said output terminals, said control means being operative to actuate said switching means for uncoupling the output terminals coupled to a failed lead and reconnecting the same to a different input terminal.

23. The patient monitoring system set forth in claim 22 and including battery means for driving said signal generating means, low voltage sensing means coupled to said battery means and to said control means, an LCD display coupled to said control means for receiving signals therefrom, said LCD display including indicia for indicating battery failure, said control means being operative upon the receipt of a low battery signal and an enabling signal to actuate the low battery indicia of the LCD display, and switch means operative to enable said control means.

24. The patient monitoring system set forth in claim 23 wherein said LCD display includes lead failure indicia for each of said leads, said control means being operative to actuate one of said lead failure indicia upon the failure of one or more of said leads, and switch means being operative to enable said control means for effecting the actuation of the LCD display to indicate lead failure.

25. The patient monitoring system set forth in claim 24 and including analog to digital converter means connected to the signal generating means for receiving analog signals therefrom, said analog to digital converter means also being connected to said control means for providing digital signals representative of the analog ECG signals, said control means providing said digital signals to said modulating means.

26. The patient monitoring system set forth in claim 25 wherein said analog to digital converter means converts said analog signals into binary coded signals, said modulating means being operative to provide a 180°

phase shift in response to a first binary digit received and a zero degree phase shift with respect to said carrier signal and in response to a different binary digit received.

27. The patient monitoring system set forth in claim 26 wherein there are first, second and third signal gene and at least four lead means adapted to be connected respectively to the right arm, the left arm, the left leg and the chest, said switching means being operative to connect said first signal generating means to receive said left leg and right arm signals, said second signal generating means to receive said left leg and left arm signal, and said third signal generating means to receive said chest and right arm, left arm, left leg signals, said signal generating means being operative to provide ECG vector signals which are functionally related to the signals received.

28. The patient monitoring system set forth in claim 27 wherein said control means comprises a microprocessor, said microprocessor being operative to store said digital signals and for transmitting said digital signals serially to the modulating means.

32. The method set forth in claim 3 and including the step of providing battery means to provide power for generating and transmitting said signals and including the steps of sensing battery voltage and providing an output signal upon the occurrence of a low battery condition, and energizing indicia in an LCD display to indicate a low battery condition upon receipt of said output signal.

33. The method set forth in claim 3 and including the steps of sensing a lead fail condition and generating an electrical signal upon the occurrence thereof, providing a signal to an LCD display for energizing LCD indicia upon the occurrence of lead failure.

12. A patient monitoring system including at least four lead means adapted to be coupled to a patient located at a first location for sensing individual ECG voltage signals, at least two signal generating means, switching means in circuit between said lead means and said signal generating means and operative for simultaneously coupling a different selected pair of said ECG voltage signals to each of said signal generating means, said signal generating means being operative for generating at least two lead group signals functionally related to different selected pairs of said ECG voltage signals sensed by the lead means connected thereto, control means coupled to said lead means and to said switching means and being operative for setting said switching means to couple different preselected groups of the ECG voltage signals to each of the signal generating means, transmitting means, converter means connected to the differential means for receiving the lead group signals and for converting the same to modulating signals, said converter means also being connected to said control means for providing modulating signals representative of the lead group signals, said control means providing said modulating signals to said transmitting means, said transmitting means including RF signal generating means for generating a carrier signal and modulating means connected to receive said carrier signal and said modulating signals and being operative to modulate the carrier signal with said modulating signals, said transmitting means being operative to transmit the modulated carrier signal to a remote display unit whereby the remote display unit may simultaneously display all of the lead group differential signals, said control means being responsive to a failure in one or more of said lead means for actuating said switching means to disconnect the failed lead from any of the differential means to which it is connected and for connecting an unfailed lead to said differential means to form a different lead pair group with the other unfailed lead previously connected to the said signal generating means so that at least two lead pair group differential signals can continue to be converted to modulating signals for transmission and display at the remote unit regardless of the occurrence of a failed lead.

13. The patient monitoring system set forth in claim 12 wherein said switching means includes switching matrix means having a plurality of input terminals and a plurality of output terminals and being operative upon the receipt of switching control signals to connect a selected pair of said input terminals to a selected pairs of output terminals, circuit means connecting said input terminals to respectively receive different ones of said ECG data voltage signals, each of said signal generating means being connected to different pairs of said output terminals, said control means being operative to actuate said switching means for uncoupling the output terminals coupled to a failed lead and reconnecting the same to a different input terminal.

14. The patient monitoring system set forth in claim 12 and including battery means for driving said signal generating means, low voltage sensing means coupled to said battery means and to said control means, an LCD display coupled to said control means for receiving signals therefrom, said LCD display including indicia for indicating battery failure, said control means being operative upon the receipt of a low battery signal and an enabling signal to actuate the low battery indicia of the LCD display, and switch means operative to enable said control means.

15. The patient monitoring system set forth in claim 12 and including an LCD display having lead failure indicia for each of said leads, said control means being operative to actuate one of said lead fail indicia upon the failure of one or more of said leads, and switch means being operative to enable said control means for effecting the actuation of the LCD display to indicate lead failure.

16. The patient monitoring system set forth in claim 12 wherein there are three signal generating means and at least four lead means adapted to be coupled respectively to the right arm, the left arm, the left leg and the chest, and first, second and third differential means, said switching means being operative to connect said first signal generating means to receive said left leg and right arm signals, said second signal generating means to receive said left leg and left arm signal, and said third signal generating means to receive said chest and right arm, left arm, left leg signals, said signal generating means being operative to provide ECG vector signals which are functionally related to the signals received.

17. The patient monitoring system set forth in claim 12 and including means for detecting the existence of a pacemaker signal, said pacemaker signal detecting means being coupled to said control means, said transmitting means being operative to transmit said pacemaker signal to said remote unit.

18. A patient monitoring system including at least four lead means adapted to be coupled to a patient for sensing individual ECG voltage signals, at least two signal generating means, switching means in circuit between said lead means and said signal generating means and operative for simultaneously coupling a different selected pair of said ECG voltage signals to each of said signal generating means, said signal generating means being operative for generating at least two lead group signals functionally related to different selected pairs of said ECG voltage signals sensed by the lead means connected thereto, control means coupled to said lead means and to said switching means and being operative for setting said switching means to couple different preselected groups of the ECG voltage signals to each of the signal generating means and means for transmitting the lead group signals to a remote display unit whereby the remote display unit may display all of the lead group differential signals, digitizing means connected to the signal generating means for digitizing said lead group signals before the transmission thereof, said transmitting means including RF signal generating means for generating a carrier signal, modulating means connected to receive said carrier signal and said digitized lead group signals and being operative to phase modulate the carrier signal with said digital signals and for transmitting the same to said remote unit, said control means being responsive to a failure in one or more of said lead means for actuating said switching means to disconnect the failed lead from any of the differential means to which it is connected and for connecting an unfailed lead to said differential means to form a different lead pair group with the other unfailed lead previously connected to the said differential means whereby at least two lead pair group differential signals can continuously be transmitted regardless of the occurrence of a failed lead.

19. The patient monitoring system set forth in claim 18 and including analog to digital converter means connected to the signal generating means for receiving analog signals therefrom, said analog to digital converter means also being connected to said control means for providing digital signals representative of the analog ECG signals, said control means providing said digital signals to said modulating means.

20. The patient monitoring system set forth in claim 18 wherein said digitizing means converts said lead group signals into binary coded signals, said modulating means being operative to provide a 180°

phase shift with respect to said carrier signal in response to a first binary digit received and a zero degree phase shift with respect to said carrier signal in response to a different binary digit received.

21. A patient monitoring system including at least four lead means adapted to be coupled to a patient for sensing individual ECG voltage signals, at least two signal generating means, switching means in circuit between said lead means and said signal generating means and operative for simultaneously coupling a different selected pair of said ECG voltage signals to each of said signal generating means, said signal generating means being operative for generating at least two lead group signals functionally related to different selected pairs of said ECG voltage signals sensed by the lead means connected thereto, digitizing means connected to said signal generating means for digitizing said lead couple signals, control means coupled to said lead means and to said switching means and being operative for setting said switching means to couple different preselected groups of the ECG voltage signals to each of the signal generating means and transmitting means includes RF signal generating means for generating a carrier signal, modulating means connected to receive said carrier signal and said digitized lead couple signals and being operative to phase modulate the carrier signal with said digital signals and for transmitting the same to said remote display unit, means for detecting the existence of a pacemaker signal, said pacemaker signal detecting means being coupled to said control means, said transmitting means being operative to transmit said pacemaker signal to said remote unit whereby the remote display unit may display all of the lead group differential signals and said pacemaker signal, said control means being responsive to a failure in one or more of said lead means for actuating said switching means to disconnect the failed lead from any of the differential means to which it is connected and for connecting an unfailed lead to said differential means to form a different lead pair group with the other unfailed lead previously connected to the said differential means whereby at least two lead pair group differential signals can continue to be transmitted regardless of the occurrence of a failed lead.

29. A patient monitoring system including a plurality of lead means adapted to be coupled to a patient for sensing individual ECG voltage signals,

a plurality of signal generating means,

switching means in circuit between said lead means and said signal generating means and operative for coupling selected pairs of said ECG voltage signals to each of the signal generating means, said signal generating means being operative for generating lead couple signals functionally related to selected pairs of said ECG voltage signals,

control means coupled to said lead means and to said switching means and being operative for setting said switching means to coupled preselected ones of the ECG voltage signals to the signal generating means,

said control means being operative to sense the existence of a failed lead and being operative for resetting said switching means to uncouple the failed lead from the signal generating means and for coupling a different one of the ECG voltage signals to the signal generating means formerly coupled to receive the voltage signal from the failed lead,

said switching means including switching matrix means having a plurality of input terminals and a plurality of output terminals and being operative upon the receipt of switching control signals to connect selected pairs of said input terminals to selected pairs of said output terminals,

circuit means connecting said input terminals to receive different ones of said ECG data voltage signals,

each of said signal generating means being connected to different pairs of said output terminals,

said control means being operative to actuate said switching means for uncoupling the output terminals coupled to a failed lead and reconnecting the same to a different input terminal,

battery means for driving said signal generating means,

low voltage sensing means coupled to said battery means and to said control means,

an LCD display coupled to said control means for receiving signals therefrom, said LCD display including indicia for indicating battery failure,

said control means being operative upon the receipt of a low battery signal and an enabling signal to actuate the low battery indicia of the LCD display,

switch means operative to enable the control means,

said LCD display including lead failure indicia for each of said leads, said control means being operative to actuate one of said lead failure indicia upon the failure of one or more of said leads, said switch means being operative to enable said control means for effectuating the actuation of the LCD display to indicate lead failure,

transmitting means for transmitting RF signals to a remote display unit and including RF signal generating means for generating a carrier signal,

modulating means connected to receive the carrier signal and said lead couple signals and being operative to phase modulate the carrier signal and for transmitting the same to a remote unit,

digitizing means connected to the signal generating means for digitizing the lead couple signals before the transmission thereof, said digitizing means comprising analog to digital converter means connected to the signal generating means for receiving analog signals therefrom, said analog to digital converter means also being connected to said control means for providing digital signals representative of the analog ECG signals, said control means providing said digital signals to said modulating means,

said analog to digital converter means converting the analog signals to binary coded signals, said modulating means being operative to provide a 180°

phase shift with respect to said carrier signal in response to a first binary digit received and a zero degree phase shift with respect to said carrier signal in response to a different binary digit received,

and means for detecting the existence of a pacemaker signal, said pacemaker signal detecting means being operative to transmit said pacemaker signal to the remote unit.

30. The patient monitoring system set forth in claim 29 wherein said control means comprises a microprocessor, said microprocessor being operative to store said digital signals and for transmitting said digital signals serially to the modulating means.

31. In a method of cardiac monitoring from at least four voltage signals generated from individual patient leads applied to different selected body locations, comprising the steps of:

coupling at least two selected pairs of said signals to differentiating means, generating at least two ECG group signals from the differences between the selected pairs of said voltage signals, digitizing said ECG group signals, sensing lead failures in individual leads of said selected pairs of leads, disconnecting any failed lead from the lead group of which it formed a part and connecting a different one of said leads to said lead pair in place of the failed lead, and generating a carrier signal, phase modulating the carrier signal with the digitized ECG group signals and transmitting the phase modulated signals at RF frequency to a receiving unit for display.

34. The method set forth in claim 31 and including the steps of connecting patient leads respectively to the right arm, left arm, left leg and chest, generating a first voltage signal functionally related to the difference between said left leg, and right arm signals, generating a second voltage signal which is functionally related to the difference between the left leg and left arm signals and generating a third differential signal functionally related to the difference between the chest and the average of the right arm, left arm, left leg signals to comprise said differential voltages.

35. The method set forth in claim 31 including the steps of detecting the existence of a pacemaker signal, providing a digital signal upon the occurrence of a pacemaker signal and phase modulating the carrier signal with a digitized signal representative of the pacemaker signal.

36. The method set forth in claim 31 and including the steps of storing said digitized ECG and a pacemaker signals, and phase modulating the carrier signal with serialized digital signals representing said differential signals and said pacemaker signal.

37. The method set forth in claim 31 including the steps of detecting the existence of a pacemaker signal, providing a digital signal upon the occurrence of a pacemaker signal and phase modulating the carrier signal with a digitized signal representative of the pacemaker signal.

38. The method set forth in claim 37 and including the steps of storing said digitized ECG group and pacemaker signals, and phase modulating the carrier signal with serialized digital signals representing said ECG group signals and said pacemaker signal.

39. The method set forth in claim 38 and including the steps of converting the analog ECG group signals into binary signals, generating an RF carrier signal, phase modulating the carrier signal through a first phase angle in response to a binary 1 received and phase modulating the carrier signal through a second phase angle in response to a binary 0 received.

40. The method set forth in claim 39 and including the steps of connecting patient leads respectively to the right arm, left arm, left leg and chest, generating a first voltage signal functionally related to the difference between said left leg, and right arm signals, generating a second voltage signal which is functionally related to the difference between the left leg and left arm signals and generating a third differential signal functionally related to the difference between the chest and right arm, left arm, left leg signals to comprise said differential voltages.

52. The patient monitoring system set forth in claim 31 wherein said analog-to-digital converter means converts said analog signals into binary coded signals, said modulating means being operative to provide a 180°

phase shift with respect to said carrier signal in response to a first binary digit received and a zero degree phase shift with respect to said carrier signal in response to a different binary digit received.

53. The patient monitoring system set forth in claim 31 wherein said control means comprises a microprocessor, said microprocessor being operative to store said digital signals and for transmitting said digital signals serially to the modulating means.

41. In a method of cardiac monitoring from voltage signals generated from at least four patient leads applied to selected body locations of a patient located at a first location, comprising the steps of:

providing a plurality of differentiating means and switching means coupled to the differentiating means, coupling said patient leads to the switching means, providing a control programmed for controlling said switching means and for sensing a lead fail condition, providing control signals to said switching means from said control for setting said switching means for coupling at least two groups of said leads to each of the differentiating means, generating at least two preselected ECG lead group signals from lead couple differential voltages, converting said lead group signals to modulating signals, generating an RF carrier signal, modulating the carrier signal with the modulating signals and transmitting the modulated signals at RF frequency to a receiving unit at a second location remote from the first location for display, sensing a lead fail condition, providing control signals to said switching means for uncoupling a failed lead from the lead group to which it is connected and connecting an unfailed lead to said group so that at least two lead group differential signals can be transmitted.

42. The method set forth in claim 41 and including the step of providing battery means to provide power for generating and transmitting said signals and including the steps of sensing battery voltage and providing an output signal upon the occurrence of a low battery condition, and energizing indicia in an LCD display to indicate a low battery condition upon receipt of said output signal.

43. The method set forth in claim 41 and including the steps of sensing a lead fail condition and generating an electrical signal upon the occurrence thereof, providing a signal to an LCD display for energizing LCD indicia upon the occurrence of lead failure.

44. In a method of cardiac monitoring from at least four voltage signals generated from individual patient leads applied to different selected body locations, comprising the steps of:

coupling at least two selected pairs of said signals to differentiating means, generating at least tow ECG group signals from the differences between the selected pairs of said voltage signals, converting the analog ECG signals into binary signals, sensing lead failures in individual leads of said selected pairs of leads, disconnected any failed lead from the lead group of which it formed a part and connecting a different one of said leads to said lead pair in place of the failed lead, generating an RF carrier signal, phase modulating the carrier signal 180°

in response to a first binary digit received and phase modulating the carrier signal zero degrees in response to a different binary digit received, and transmitting the phase modulated carrier signal to a receiving unit for display.

45. In a method of cardiac monitoring from voltage signals generated from at least four patient leads applied to selected body locations, comprising the steps of:

providing a plurality of differentiating means and switching means coupled to the differentiating means, coupling said patient leads to the switching means, providing a microprocessor programmed for controlling said switching means and for sensing a lead fail condition, providing control signals to said switching means from said microprocessor for setting said switching means for coupling at least two groups of said leads to each of the differentiating means, generating at least two preselected ECG lead group signals from lead couple differential voltages, digitizing said lead group signals, generating a carrier signal, phase modulating the carrier signal with the digitized lead group signals and transmitting the phase modulated carrier signals at RF frequency to a remote receiving unit for display, providing control signals to said switching means from said microprocessor for setting said switching means for uncoupling a failed lead from the lead group to which it is connected and connecting an unfailed lead to said group so that at least two lead group differential signals can be transmitted.

46. The method set forth in claim 45 and including the steps of converting the lead group signals into binary signals, generating an RF carrier signal, and phase modulating the carrier signal through a first phase angle in response to a first binary digit received and phase modulating the carrier signal through a second phase angle in response to a different binary digit received.

47. The method set forth in claim 45 and including the steps of storing said digitized ECG an signals, and phase modulating the carrier signal with serialized digital signals representing said differential signals and said pacemaker signal.

48. The method set forth in claim 47 and including the steps of converting the analog ECG signals into binary signals, generating an RF carrier signal, and phase modulating the carrier signal through a first phase angle in response to a first binary digit received and phase modulating the carrier signal through a second phase angle in response to a different binary digit received.

49. A patient monitoring system including at least four lead means adapted to be coupled to different locations on a patient for sensing individual ECG voltage signals, at least two differential means, switching means in circuit between said lead means and said differential means and operative for simultaneously coupling selected different groups of said ECG voltage signals to each of said differential means, each of said differential means being operative for simultaneously generating a differential signal functionally related to the difference between the preselected ones of said ECG voltage signals in said different groups sensed by the lead means connected thereto, control means coupled to said lead means and to said switching means and being operative for setting said switching means to couple different preselected pairs of the ECG voltage signals to each of the differential means, and means for transmitting all of the differential signals to a remote display unit whereby the remote display unit may display all of the lead group differential signals, digitizing means connected to the differential means for digitizing said differential signals before the transmission thereof, said transmitting means including RF signal generating means for generating a carrier signal, modulating means connected to receive said carrier signal and said digitized differential signals and being operative to phase modulate the carrier signal with said digital signals and for transmitting the same to said remote unit.

50. A patient monitoring system including at least four lead means adapted to be connected respectively to the right arm, the left arm, the left leg and chest of a patient for sensing individual ECG voltage signals,

a plurality of differential means,

switching means in circuit between said lead means and said differential means and operative for coupling a first one of said differential means to receive said left leg and right arm signals and a second one of said differential means to receive said left leg and left arm signals and a third one of said differential means to receive said chest and right arm, left arm, and left leg signals, said differential means each being operative to provide ECG vector signals which are the differences between said signals received,

control means coupled to said lead means and to said switching means and being operative for setting said switching means to couple the preselected ones of the ECG voltage signals to the differential means respectively,

analog to digital converter means connected to the differential means for receiving analog signals therefrom, said analog to digital converter means being connected to said control means for providing digital signals representative of the analog ECG signals,

transmitting means including RF signal generating means for generating a carrier signal, modulating means connected to receive said carrier signal and said differential signals and being operative to phase modulate the carrier signal with said digital signals and for transmitting the same to a remote display unit,

said control means providing said digital signals to said modulating means,

said analog to digital converter means converting said analog signals into binary coded signals,

said modulating means being operative to provide a 180°

phase shift with respect to said carrier signal in response to a first binary digit received and a zero degree phase shift with respect to said carrier signal in response to a different binary digit receiving,

and means for detecting the existence of a pacemaker signal, said pacemaker signal detecting means being coupled to said control means,

said transmitting means being operative to transmit said pacemaker signal to the remote unit.

51. A patient monitoring system including at least four lead means adapted to be coupled to different locations on a patient for sensing individual ECG voltage signals, at least two differential means, switching means in circuit between said lead means and said differential means and operative for simultaneously coupling selected different groups of said ECG voltage signals to each of said differential means, each of said differential means being operative for simultaneously generating a differential signal functionally related to the difference between the preselected ones of said ECG voltage signals in said different groups sensed by the lead means connected thereto, control means coupled to said lead means and to said switching means and being operative for setting said switching means to couple different preselected pairs of the ECG voltage signals to each of the differential means, and transmitting means for transmitting all of the differential signals to a remote display unit, analog-to-digital converter means connected to the differential means for receiving analog signals therefrom, said analog-to-digital converter means also being connected to said control means for providing digital signals representative of the analog ECG signals, said control means providing said digital signals to said transmitting means, said transmitting means including RF signal generating means for generating a carrier signal, modulating means connected to receive said carrier signal and said digitized differential signals and being operative to phase modulate the carrier signal with said digital signals and for transmitting the same to said remote unit, whereby the remote display unit may display all of the lead group differential signals, said control means being responsive to a failure in one or more of said lead means for actuating said switching means to disconnect the failed lead from any of the differential means to which it is connected and for connecting an unfailed lead to said differential means to form a different lead pair group with the other unfailed lead previously connected to the said differential means whereby at least two lead pair group differential signals can continue to be transmitted regardless of the occurrence of a failed lead.

54. In a method of cardiac monitoring from voltage signals generated from at least four patient leads applied to selected body locations, comprising the steps of:

providing a plurality of differentiating means and switching means coupled to the differentiating means, coupling said patient leads to the switching means, providing a microprocessor programmed for controlling said switching means and for sensing a lead fail condition, providing control signals to said switching means from said microprocessor for setting said switching means for coupling at least two groups of said leads to each of the differentiating means, generating at least two preselected ECG lead group signals from lead couple differential voltages, detecting the existence of a pacemaker signal, providing a digital signal upon the occurrence of a pacemaker signal, generating a carrier signal, modulating the carrier signal with the ECG lead group differential signals, and phase modulating the carrier signal with a digitized signal representative of the pacemaker signal, and transmitting the phase modulated carrier signals to a remote receiving unit for display, providing control signals to said switching means from said microprocessor for setting said switching means for uncoupling a failed lead from the lead group to which it is connected and connecting an unfailed lead to said group so that at least two lead group differential signals can be transmitted.