Method and apparatus for developing a vectorcardiograph in an implantable medical device

• US 6,766,190 B2
• Filed: 10/31/2001
• Issued: 07/20/2004
• Est. Priority Date: 10/31/2001
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Ferek-Petric, Bozidar
• Primary Examiner(s): LAYNO, CARL HERNANDZ
• Application Number:
  US10/003,547
• Publication Number:
  US 20030083587A1
• Time in Patent Office: 993 Days
• Field of Search: 600/509, 600/512, 600/515-518, 607/9, 607/14, 607/25
• US Class Current: 600/512
• CPC Class Codes: A61B 5/341 Vectorcardiography [VCG]
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia

Abstract

Implantable medical devices (IMDS) are adapted for developing a vectorcardiograph (VCG) from signals across pairs of electrodes. Sense amplifiers of the IMD are calibrated to correlate the signals to reference sagittal, horizontal and frontal planes of the body. Polar coordinate data is plotted over the time of occurrence of the sensed PQRST electrogram as at least one of an x-axis vector projected into the reference sagittal plane as a sagittal VCG, a y-axis vector projected into the reference horizontal plane as a horizontal VCG, a z-axis vector projected into the reference frontal plane as a frontal VCG, and an xyz-vector in 3-D space. The VCG loops plotted by each of the vectors can also be derived. Thresholding and template matching techniques determine one or more of the maximum vector magnitude and orientation, average axis vector magnitude and orientation, the loop shape, and the loop area representing a particular heart rhythm.

Claims

1. A method of developing a vectorcardiogram projected onto at least one of reference sagittal, horizontal, and frontal planes of the body employing an implantable medical device comprising:

implanting a pair of vectorcardiogram sense electrodes to define an internal lead vector in the body having a vector orientation in relation to the reference sagittal, horizontal, and frontal planes of the body;

coupling the pair of vectorcardiogram sense electrodes with the implantable medical device;

sensing the PQRST electrogram of the heart across the internal lead vector; and

deriving the orientation and magnitude of the wave front of at least one of the P-wave, QRS wave and T-wave of the sensed PQRST electrogram aver the fine of occurrence of the sensed PQRST electrogram as at least one of an x-axis vector projected into the reference sagittal plane as a sagittal vectorcardiogram, a y-axis vector projected into the reference horizontal plane as a horizontal vectorcardiogram, and a z-axis vector projected into the reference frontal plane as a frontal vectorcardiogram.

2. The method of claim 1, wherein the implanting step comprises implanting the pair of electrodes in selected locations within the right ventricle, the right atrium and the coronary sinus of the heart.

3. The method of claim 1, wherein the implanting step comprises implanting a first electrode of the pair of electrodes within one of the right ventricle, the right atrium and the coronary sinus of the heart and a second electrode of the pair of electrodes subcutaneously and remote from the heart.

4. The method of claim 1, further comprising the steps of:

deriving a gain factor that compensates for the angular deviation of the internal lead vector out of coplanar relation with the at least one of the reference sagittal, horizontal, and frontal planes of the body that the at least one of the sagittal vectorcardiogram, horizontal vectorcardiogram, and frontal vectorcardiogram is referenced to.

5. The method of claim 4, wherein the step of deriving a gain factor comprises:

delivering a known current to the patients'"'"' body in at least one of the reference signal, horizontal, and frontal planes of the body;

measuring the voltage induced by the delivered current across the internal lead vector in the body; and

calculating the gain factor as the dividing the induced voltage by the known current.

6. The method of claim 4, wherein the step of deriving a gain factor comprises:

delivering a known current to the patients'"'"' body through a pair of skin electrodes in at least one of the reference sagittal, horizontal, and frontal planes of the body;

within the implantable medical device, measuring the voltage induced by the delivered current across the internal lead vector in the body;

uplink telemetry transmitting the measured voltage to an external medical device in telemetry communication with the internal medical device;

within the external medical device, calculating the gain factor by dividing the induced voltage by the known current; and

downlink telemetry transmitting the calculated gain factor to the implantable medical device to be employed in the amplifying step.

7. The method of claim 4, wherein the step of deriving a gain factor comprises:

sensing the PQRST electrocardiogram of the heart across an external lead vector referenced to at least one of the reference sagittal, horizontal, and frontal planes of the body;

comparing the sensed PQRST electrocardiogram to the sensed PQRST electrogram to derive a difference between the sensed PQRST electrocardiogram to the sensed PQRST electrogram; and

calculating a gain factor that reduces the difference substantially to zero.

8. The method of claim 4, wherein the step of deriving a gain factor comprises:

sensing the PQRST electrocardiogram of the heart across an external lead vector referenced to at least one of the reference sagittal, horizontal, and frontal planes of the body;

uplink telemetry transmitting the sensed PQRST electrogram to an external medical device;

comparing the sensed PQRST electrocardiogram to the sensed PQRST electrogram, to derive a difference between the sensed PQRST electrocardiogram to the sensed PQRST electrogram;

calculating a gain factor that reduces the difference substantially to zero; and

downlink telemetry transmitting the calculated gain factor to the implantable medical device to be employed in the amplifying step.

9. The method of claim 1, further comprising the step of analyzing the one of the taxis vector, y-axis vector, and z-axis vector to ascertain the state of health of the heart.

10. The method of claim 1, further comprising the steps of:

analyzing the one of the x-axis vector, y-axis vector, and z-axis vector to ascertain the state of health of the heart; and

delivering a therapy to a head exhibiting, through the analysis of the one of the x-axis vector, y-axis vector, and z-axis vector, an abnormal state of health.

11. A method of developing a vectorcardiogram projected onto at least one of reference sagittal, horizontal, and frontal planes of the body employing a cardiac implantable medical device comprising:

implanting a first pair of vectorcardiogram sense electrodes in the body to define a first internal lead vector having a first vector orientation in relation to the reference sagittal, horizontal, and frontal planes of the body;

coupling the first pair of vectorcardiogram sense electrodes to the implantable medical device;

sensing a first PQRST electrogram of the heart across the first internal lead vector;

implanting a second pair of vectorcardiogram sense electrodes in the body to define a second internal lead vector having a second vector orientation in relation to the reference sagittal, horizontal, and frontal planes of the body;

coupling the second pair of vectorcardiogram sense electrodes to the implantable medical device;

sensing a second PQRST electrogram of the heart across the second internal lead sector;

deriving the orientation and magnitude of the wave front of at least one of the P-wave, QRS wave and T-wave over the time of occurrence of the first sensed PQRST electrogram as a first one of an x-axis vector projected into the reference sagittal plane as a sagittal vectorcardiogram, a y-axis vector projected into the reference horizontal plane as a horizontal vectorcardiogram, and a z-axis vector projected into the reference frontal plane as a frontal vectorcardiogram; and

deriving the orientation and magnitude of the wave front of at least one of the P-wave, QRS wave and T-wave over the time of occurrence of the second sensed PQRST electrogram as a second one of an x-axis vector projected into the reference sagittal plane as a sagittal vectorcardiogram, a

 

y-axis vector projected into the reference horizontal plane as a horizontal vectorcardiogram, and a z-axis vector projected into the reference frontal plane as a frontal vectorcardiogram.

12. The method of claim 11, wherein:

the step of sensing the first PQRST electrogram further comprises;

deriving a first gain factor that compensates for the angular deviation of the first internal lead vector out of coplanar relation with the first one of the reference sagittal, horizontal, and frontal planes of the body that the first one of the sagittal vectorcardiogram, horizontal vectorcardiogram, and frontal vectorcardiogram is traced into; and

amplifying the first sensed PQRST electrogram by the derived first gain factor; and

the step of sensing the second PQRST electrogram further comprises;

deriving a second gain factor that compensates for the angular deviation of the second internal lead vector out of coplanar relation with the second one of the reference sagittal, horizontal, and frontal planes of the body that the second one of the sagittal vectorcardiogram, horizontal vectorcardiogram, and frontal vectorcardiogram is traced into; and

amplifying the second sensed PQRST electrogram by the derived second gain factor.

13. The method of claim 11, wherein the implanting steps comprises implanting the first and second pairs of electrodes at selected locations within the right ventricle, the right atrium, and the coronary sinus of the heart.

14. The method of claim 11, wherein the implanting steps comprise implanting the first and second pair of electrodes at selected locations within the right ventricle, the right atrium, and the coronary sinus of the heart and subcutaneously and remote from the heart.

15. A method of developing an xyz-vectorcardiogram projected into three dimensional space in spatial reference to at least one of reference sagittal, horizontal, and frontal planes of the body employing an implantable medical device, comprising:

implanting a pair of vectorcardiogram sense electrodes in the body to define an internal lead vector having a vector orientation in relation to the reference sagittal, horizontal, and frontal planes of the body;

coupling the a pair of vectorcardiogram sense electrodes to the implantable medical device;

sensing the PQRST electrogram of the heart across the internal lead vector; and

deriving the orientation and magnitude of the wave front of at least one of the P-wave, QRS wave and T-wave of the sensed PQRST electrogram over the time of occurrence of the sensed PQRST electrogram as an xyz-vectorcardiogram projected into three-dimensional space in reference to at least one of reference sagittal, horizontal, and frontal planes of the body.

16. The method of claim 15, further comprising the step of deriving the orientation and magnitude of the wave front of at least one of the P-wave, QRS wave and T-wave of the sensed PQRST electrogram over the time of occurrence of the sensed PQRST electrogram as at least one of an x-axis vector projected into the reference sagittal plane as a sagittal vectorcardiogram, a y-axis vector projected into the reference horizontal plane as a horizontal vectorcardiogram, and a z-axis vector projected into the reference frontal plane as a frontal vectorcardiogram.

17. The method of claim 16, wherein the sensing step further comprises:

deriving a gain factor that compensates for the angular deviation of the internal lead vector out of coplanar relation with the at least one of the reference sagittal, horizontal, and frontal planes of the body that the at least one of the sagittal vectorcardiogram, horizontal vectorcardiogram, and frontal vectorcardiogram is traced into; and

amplifying the sensed PQRST electrogram by the derived gain factor.

18. The method of claim 15, wherein the sensing step further comprises:

deriving a gain factor that compensates for the angular deviation of the internal lead vector out of coplanar relation with the at least one of the reference sagittal, horizontal, and frontal planes of the body that the xyz-vectorcardiogram is misted to; and

amplifying the sensed PQRST electrogram by the derived gain factor.

19. The method of claim 15, wherein the implanting step comprises implanting the pair of electrodes in selected locations within the right ventricle, the right atrium and the coronary sinus of the heart.

20. The method of claim 15, wherein the implanting step comprises implanting a first electrode of the pair of electrodes within one of the right ventricle, the right atrium and the coronary sinus of the heart and a second electrode;

of the pair of electrodes subcutaneously and remote from the heart.

21. A cardiac implantable medical device that develops a vectorcardiogram projected onto at least one of reference sagittal, horizontal, and frontal planes of the body comprising:

a pair of vectorcardiogram sense electrodes adapted to be implanted in the body to define an internal lead vector having a vector orientation In relation to the reference sagittal, horizontal, and frontal planes of the body;

means for sensing the PQRST electrogram of the heart across the internal lead vector; and

means for deriving the orientation and magnitude of the wave front of at least one of the P-wave;

QRS wave and T-wave of the sensed PQRST electrogram over the time of occurrence of the sensed PQRST electrogram as at least one of an x-axis vector projected into;

the reference sagittal plane as a sagittal vectorcardiogram, a y-axis vector projected into the reference horizontal plane as a horizontal vectorcardiogram, and a z-axis vector projected into the reference frontal plane as a frontal vectorcardiogram.

22. The implantable medical device of claim 21, wherein the pair of vectorcardiogram sense electrodes are at locations selected from the right ventricle, the right atrium and the coronary sinus of the heart.

23. The implantable medical device of claim 21, wherein the pair of vectorcardiogram sense electrodes comprises a first electrode within one of the right ventricle, the right atrium and the coronary sinus of the heart and a second electrode implanted subcutaneously and remote from the head.

24. The implantable medical device of claim 21, further comprising:

means for deriving a gain factor that compensates for the angular deviation of the internal lead vector out of coplanar relation with the at least one of the reference sagittal horizontal, and frontal planes of the body that the at least one of the sagittal vectorcardiogram, horizontal vectorcardiogram, and frontal vectorcardiogram is traced into; and

wherein the sensing means further comprises;

means for amplifying the sensed PQRST electrogram by the derived gain factor.

25. The implantable medical device of claim 24, wherein the means for deriving a gain factor comprises:

means for delivering a known current to the patients'"'"' body in at least one of the reference sagittal, horizontal, and frontal planes of the body;

means for measuring the voltage induced by the delivered current across the internal lead vector in the body; and

means for calculating the gain factor as the dividing the induced voltage by the known current.

26. The implantable medical device of claim 24, wherein the means for deriving a gain factor comprises:

means for delivering a known current to the patients'"'"' body through a pair of skin electrodes in at least one of the reference sagittal, horizontal, and frontal planes of the body;

means within the implantable medical device for measuring the voltage induced by the delivered current across the internal lead vector in the body;

means within the implantable medical device for uplink telemetry transmitting the measured voltage to an external medical device in telemetry communication with the internal medical device;

means within the external medical device for calculating the gain factor by dividing the induced voltage by the known current; and

means within the external medical device for downlink telemetry transmitting the calculated gain factor to the implantable medical device to be employed in the amplifying step.

27. The implantable medical device of claim 24, wherein the means for deriving a gain factor comprises:

means for sensing the PQRST electrocardiogram of the heart across an external lead vector referenced to at least one of the reference sagittal, horizontal, and frontal planes of the body;

means for comparing the sensed PQRST electrocardiogram to the sensed PQRST electrogram to derive a difference between the sensed PQRST electrocardiogram to the sensed PQRST electrogram; and

means for calculating a gain factor that reduces the difference substantially to zero.

28. The implantable medical device of claim 24, wherein the means for deriving a gain factor comprises:

means for sensing the PQRST electrocardiogram of the heart across an external lead vector referenced to at least one of the reference sagittal, horizontal, and frontal planes of the body;

means within the implantable medical device for uplink telemetry transmitting the sensed PQRST electrogram to an external medical device;

means within the external medical device for comparing the sensed PQRST electrocardiogram to the sensed PQRST electrogram to derive a difference between the sensed PQRST electrocardiogram to the sensed PQRST electrogram;

means within the external medical device for calculating a gain factor that reduces the difference substantially to zero; and

means within the external medical device for downlink telemetry transmitting the calculated gain factor to the implantable medical device to be employed in the amplifying stop.

29. The implantable medical device of claim 21, further comprising means for analyzing the one of the x-axis vector, y-axis vector, and z-axis vector to ascertain the state of health of the heart.

30. The implantable medical device of claim 21, further comprising:

means for analyzing the one of the x-axis vector, y-axis vector, and z-axis vector to ascertain the state of health of the head; and

means for delivering a therapy to a head exhibiting, through the analysis of the one of the x-axis vector, y-axis vector, and z-axis vector, an abnormal state of health.

31. A cardiac implantable medical device that develops a vectorcardiogram projected onto at least one of reference sagittal, horizontal, and frontal planes of the body comprising:

a first pair of vectorcardiogram sense electrodes adapted to be implanted within the body defining a first internal lead vector having a first vector orientation in relation to the reference sagittal, horizontal, and frontal planes of the body;

first sensing means for sensing a first PQRST electrogram of the heart across the first internal lead vector;

a second pair of vectorcardiogram sense electrodes adapted to be implanted within the body defining a second internal lead vector having a second vector orientation in relation to the reference sagittal, horizontal, and frontal planes of the body;

second sensing means for sensing a second PQRST electrogram of the heart across the second internal lead vector;

means for deriving the orientation and magnitude of the wave front of at least one of the P-wave, ORS wave and T-wave over the time of occurrence of the first sense PQRST electrogram a first one of an x-axis vector projected Into the reference sagittal plane as a sagittal vectorcardiogram, a y-axis vector projected into the reference horizontal plane as a horizontal vectorcardiogram, and a z-axis vector projected into the reference frontal plane as a frontal vectorcardiogram; and

means for deriving the orientation and magnitude of the wave front of at least one of the P-wave, QRS wave and T-wave over the time of occurrence of the second sensed PQRST electrogram as a second one of an x-axis vector projected into the reference sagittal plane as a sagittal vectorcardiogram, a y-axis vector projected into the reference horizontal plane as a horizontal vectorcardiogram, and a z-axis vector projected into the reference frontal plane as a frontal vectorcardiogram.

32. The implantable medical device of claim 31, wherein:

the first sensing means further comprises;

means for deriving a first gain factor that compensates for the angular deviation of the first internal lead vector out of coplanar relation with the first one of the reference sagittal, horizontal, and frontal planes of the body that the first one of the sagittal vectorcardiogram, horizontal vectorcardiogram, and frontal vectorcardiogram is traced into; and

means for amplifying the first sensed PQRST electrogram by the derived first gain factor; and

the second sensing means further comprises;

deriving a second gain factor that compensates for the angular deviation of the second internal lead vector out of coplanar relation with the second one of the reference sagittal, horizontal, and frontal planes of the body that the second one of the sagittal vectorcardiogram, horizontal vectorcardiogram, and frontal vectorcardiogram is traced into; and

amplifying the second sensed PQRST electrogram by the derived second gain factor.

33. The implantable medical device of claim 31, wherein the first and second pairs of electrodes are at selected locations of the right ventricle, the right atrium, and the coronary sinus of the heart.

34. The implantable medical device of claim 31, wherein the first and second pair of electrodes are at selected locations of the right ventricle, the right atrium, the coronary sinus of the heart, and subcutaneously and remote from the heart.

35. A cardiac implantable medical device that develops an xyz vectorcardiogram projected into three dimensional space in spatial reference to at least one of reference sagittal, horizontal, and frontal planes of the body comprising:

a pair of vectorcardiogram sense electrodes adapted to be implanted in the body to define an internal lead vector having a vector orientation in relation to the reference sagittal, horizontal, and frontal planes of the body;

means for sensing the PQRST electrogram of the heart across the internal lead vectors and means for deriving the orientation and magnitude of the wave front of at least one of the P-wave, QRS wave and T-wave of the sensed PQRST electrogram over the time of occurrence of the sensed PQRST electrogram as an xyz-vectoroardiogram projected into three dimensional space in reference to at least one of reference sagittal, horizontal, and frontal planes of the body.

36. The implantable medical device of claim 35, further comprising

means for deriving the orientation and magnitude of the wave front of at least one of the P-wave, QRS wave and T-wave of the sensed PQRST electrogram over the time of occurrence of the sensed PQRST electrogram as at least one of an x-axis vector projected into the reference sagittal plane as a sagittal vectorcardiogram, a y-axis vector projected into the reference horizontal plane as a horizontal vectorcardiogram, and a z-axis vector projected into the reference frontal plane as a frontal vectorcardiogram.

37. The implantable medical device of claim 36, wherein the sensing means further comprises:

means for deriving a gain factor that compensates for the angular deviation of the internal lead vector out of coplanar relation with the at least one of the reference sagittal, horizontal, and frontal planes of the body that the at least one of the sagittal vectorcardiogram;

horizontal vectorcardiogram, and frontal vectorcardiogram is traced into; and

means for amplifying the sensed PQRST electrogram by the derived gain factor.

38. The implantable medical device of claim 35, wherein the sensing means further comprises:

means for deriving a gain factor that compensates for the angular deviation of the internal lead vector out of coplanar relation with the at least one of the reference sagittal, horizontal, and frontal planes of the body that the xyz-vectorcardiogram is related to; and

means for amplifying the sensed PQRST electrogram by the derived gain factor.

39. The implantable medical device of claim 35, wherein the electrodes of the pair of electrodes are adapted to be implanted in selected locations within the right ventricle, the right atrium and the coronary sinus of the heart.

40. The implantable medical device of claim 35, wherein a first electrode of the pair of electrodes is adapted to be implanted within one of the right ventricle, the right atrium and the coronary sinus of the heart and a second electrode of me pair of electrodes is adapted to be implanted subcutaneously and remote from the heart.

41. A system for developing an xyz-vector vectorcardiogram of electrical signals of the heart accompanying depolarization and re-polarization of the muscle cells of the heart during a PQRST cardiac cycle employing an implantable medical device comprising:

an atrial electrode implanted in relation to the one of the right atrium and left atrium;

a right ventricular electrode implanted in relation to the right ventricle;

a left ventricular electrode implanted in relation to the left ventricle;

first sensing means selectively coupled to the atrial electrode and the right ventricular electrode for sensing the electrical signals of the heart along a first internal lead vector and providing a first vector signal;

second sensing means selectively coupled to the atrial electrode and the left ventricular electrode for sensing the electrical signals of the heart along a second internal lead vector and providing a second vector signal;

third sensing means selectively coupled to the left ventricular electrode and the right ventricular electrode for sensing the electrical signals of the heart along a third internal lead vector and providing a third vector signal;

means for developing an xyz-vector of a vectorcardiogram that is related to reference sagittal, horizontal, and frontal planes of the body from one or more of the first, second and third internal lead vector signals; and

means for deriving the orientation and magnitude of a wave front of at least one of the P-wave, QRS wave and T-wave of the sensed PQRST electrogram over the time of occurrence of a sensed PQRST electrogram as at least one of an x-axis vector protected into the reference sagittal plane as a sagittal vectorcardiogram a y-axis vector protected into the reference horizontal plane as a horizontal vectorcardiogram, and a z-axis vector projected into the reference frontal plane as a frontal vectorcardiogram.

42. The system of claim 41, wherein:

the first sensing means further comprises;

means for deriving a first gain factor that compensates for the angular deviation of the first internal lead vector out of coplanar relation with the at least one of the reference sagittal, horizontal, and frontal planes of the body that the xyz-vectorcardiogram is related to; and

means for amplifying the sensed PQRST electrogram by the derived gain factor to provide the first vector signal;

the second sensing means further comprises;

means for deriving a second gain factor that compensates for the angular deviation of the second internal lead vector out of coplanar relation with the at least one of the reference sagittal, horizontal, and frontal planes of the body that the xyz-vectorcardiogram is related to; and

means for amplifying the sensed PQRST electrogram by the derived gain factor to provide the second vector signal; and

the third sensing means further comprises;

means for deriving a third gain factor that compensates for the angular deviation of the third internal lead vector out of coplanar relation with the at least one of the reference sagittal, horizontal, and frontal planes of the body that the xyz-vectorcardiogram is related to; and

means for amplifying the sensed PQRST electrogram by the derived gain factor to provide the third vector signal.

43. A method of developing an xyz-vector vectorcardiogram of electoral signals of the heart accompanying depolarization and re-polarization of the muscle cells of the heart during a PQRST cardiac cycle employing an implantable medical device comprising:

implanting an atrial electrode in relation to the one of the right atrium and left atrium;

implanting a right ventricular electrode in relation to the right ventricle;

implanting a left ventricular electrode in relation to the left ventricle;

sensing the electrical signals of the heart along a first internal lead vector between the atrial electrode and the right ventricular electrode and providing a first internal lead vector signal;

sensing the electrical signals of the heart along a second internal lead vector between the atrial electrode and the left ventricular electrode and providing a second internal lead vector signal;

sensing the electrical signals of the heart along a third internal lead vector between the left ventricular electrode and the right ventricular electrode for and providing a third internal lead vector signal;

developing an xyz-vector of a vectorcardiogram mat is related to reference sagittal, horizontal, and frontal planes of the body from one or mare of the first, second and third internal lead vector signals; and

developing the orientation and magnitude of the wave front of at least one of the P-wave, QRS wave and T-wave of the sensed PQRST electrogram over the time of occurrence of the sensed PQRST electrogram as at least one of an x-axis vector projected into the reference sagittal plane as a sagittal vectorcardiogram, a y-axis vector projected into the reference horizontal plane as a horizontal vectorcardiogram, and a z-axis vector projected into the reference frontal plane as a frontal vectorcardiogram.

44. The method of claim 43, wherein:

the step of sensing and providing the first internal lead vector signal further comprises;

deriving a first gain factor that compensates for the angular deviation of the first internal lead vector out of coplanar relation with the at least one of the reference sagittal, horizontal, and frontal planes of the body that the xyz-vectorcardiogram is related to; and

amplifying the sensed PQRST electrogram by the derived gain factor to provide the first vector signal;

the step of sensing and providing the second internal lead vector signal further comprises;

deriving a second gain factor that compensates for the angular deviation of the second internal lead vector out of coplanar relation with the at least one of the reference sagittal, horizontal, and frontal planes of the body that the xyz-vectorcardiogram is related to; and

amplifying the sensed PQRST electrogram by the derived gain factor to providing the second vector signal; and

the, step of sensing and providing the third internal lead vector signal further comprises;

deriving a third gain factor that compensates for the angular deviation of the third internal lead vector out of coplanar relation with the at least one of the reference sagittal, horizontal, and frontal planes of the body that the xyz-vectorcardiogram is related to; and

amplifying the sensed PQRST electrogram by the derived gain factor to provide the third vector signal.

45. A system for developing an internal X_p-vector, Y_p-vector and

Z_p-vector electrical signals of the heart accompanying depolarization and re-polarization of the muscle cells of the heart during a cardiac cycle in an implantable medical device capable of communicating with an external medical device, the external medical device capable of developing a reference X_E-vector signal, a reference Y_E-vector signal, and a reference

Z_E-vector signal within a set of orthogonal reference planes defined by a reference X_E-vector, a reference _E-vector, and a reference Z_E-vector, the system comprising:

first, second, and third electrodes implanted in relation to the heart separated apart from one another such that a first internal lead vector is defined between the first and second electrodes, a second internal lead vector is defined between the first and third electrodes, and a third internal lead vector is defined between the second and third electrodes;

first sensing means selectively coupled to the first electrode and the second electrode for sensing and amplifying the electrical signals of the heart along the first internal lead vector at a first gain and providing a first vector signal;

second sensing means selectively coupled to the first electrode and the third electrode for sensing and amplifying the electrical signals of the heart along the second internal lead vector at a second gain and providing a second vector signal;

third sensing means selectively coupled to the second electrode and the third electrode for sensing and amplifying the electrical signals of the heart along the third internal lead vector at a third gain and providing a third vector signal;

means for adjusting the first gain to normalize the first vector signal to the reference X_E-vector signal to provide the X_p-vector signal;

means for adjusting the second gain to normalize the second vector signal to the reference Y_E-vector signal to provide the Y_p-vector signal; and

means for adjusting the third gain to normalize the third vector signal to the reference Z_E-vector signal to provide the Z_p-vector signal.

46. The system of claim 45, further comprising means for developing an xyz-vector within three dimensional space referenced to the set of orthogonal reference planes defined by the reference X_E-vector, the reference Y_E-vector, and the reference Z_E-vector from the internal X_p-vector, Y_p-vector and Z_p-vector signals.