Implantable Medical Device

• US 20080125665A1
• Filed: 11/27/2006
• Published: 05/29/2008
• Est. Priority Date: 11/27/2006
• Status: Active Grant

• Current Assignee: Biotronik SE & Company KG
• Original Assignee: Biotronik VI Patent AG (Biotronik SE & Company KG)
• Inventors: Nigam, Indra B.
• Granted Patent: US 7,657,305 B2
• Time in Patent Office: Days
• US Class Current: 600/509
• CPC Class Codes: A61B 5/0006 ECG or EEG signals
• CPC Class Codes: A61B 5/319 Circuits for simulating ECG signals
• CPC Class Codes: A61B 5/7232 involving compression of the physiological signal, e.g. to extend the signal recording period
• CPC Class Codes: A61N 1/368 comprising more than one electrode co-operating with different heart regions A61N1/3622, A61N1/3627 take precedence
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control

Abstract

An implantable medical device provides for improved storage of recorded IEGMs. A sensing stage is connected to an electrode for picking up electric potentials from inside a heart, the time course of said electric potentials representing a heart signal, a control unit connected to said sensing stage is adapted to process a sequence of data points that each represent an amplitude or magnitude A of a time-varying signal at equidistant points of time t, wherein end points of data segments are determined by processing of the sequence of data points. The control unit is adapted to identify end points of data segments by processing of the sequence of data points.

Claims

1. An implantable medical device comprising:

at least a sensing stage connected or being connectable to an electrode for picking up electric potentials from inside a heart, the time course of said electric potentials representing a heart signal, said heart signal being sampled in constant sampling intervals

and

a control unit

that is connected to said sensing stage and

that is adapted to process a sequence of data points that each represent a magnitude A of a time-varying signal at equidistant points of time t, said processing of the sequence of data points includes;

determining end points of data segments by

a) determination of a first difference quotient D₁=(A_n−

A<sub>n−

1</sub>)/(t_n−

t<sub>n−

1</sub>) with respect to an actual data point An at tn and an immediately preceding, second last data point A<sub>n−

1</sub> at t<sub>n−

1</sub>,

b) determination of a second difference quotient D₂=(A_n−

A_e)/(t_n−

t_e) or D₂=(A<sub>n−

1</sub>−

A_e)/(t<sub>n−

1</sub>−

t_e) with respect to an actual data point A_n at t_n or a second last data point A<sub>n−

1</sub> and t<sub>n−

1</sub>, respectively, and a last end point A_e at t_e, said last end point A_e being a previously determined end point or a first data point of said sequence of data points, wherein t_e represents the point of time belonging to said end point A_e,

c) selecting the second last data point A<sub>n−

1</sub> as a new end point, if the magnitude of the difference between the two difference quotients D_D=D₁−

D₂ exceeds a predetermined first threshold value T, D_D>

T, and

determining a data segment length L=t_n−

t_e between the point of time t_n of an actual data point A_n and the point of time t_e of a last end point A_e,

and selecting A<sub>n−

1</sub> as a new end point, if said data segment length L exceeds a predetermined maximum length L_max,

and storing said selected end points in association with a segment length between each stored endpoint and an immediately preceding end point as a compressed data representation of said time varying signal.

2. The implantable medical device of claim 1, wherein the control unit is further adapted to:

determine whether said first and said second difference quotient are of opposite sign and

select the second last data point A<sub>n−

1</sub> as a new end point, if the magnitude of the difference between the two difference quotients D_D=D₁−

D₂ exceeds a predetermined second threshold value T2.

3. The implantable medical device of claim 1 or 2, wherein the control unit is further adapted to:

determine whether a data segment length L=t_n−

t_e between the point of time t_n of an actual data point A_n and the point of time t_e of a last end point A_e exceeds a predetermined threshold length L1 and whether the magnitude of the difference between the two difference quotients D_D=D₁−

D₂ exceeds a predetermined third threshold value T3, and to select the second last data point A<sub>n−

1</sub> as a new end point, if said two conditions are met.

4. The implantable medical device of one of claims 1 to 3, wherein the control unit is adapted to determine the first, and, if applicable, the second and the third threshold value as a predetermined fraction of a peak amplitude value of said time-varying signal.

5. The implantable medical device of claim 4, wherein the control unit is adapted to redetermine the first, and, if applicable, the second and the third threshold value if a moving average of said peak amplitude value of said time-varying signal changes.

6. The implantable medical device of claim 1, said implantable medical device having two sensing stages for picking-up and sampling of two heart signals, thus generating two data sequences each representing the time course of a heart signal, wherein the control unit is adapted to select endpoints of both data sequences and to store every selected endpoint of any of the data sequences together with a corresponding data point of the respective other data sequence and the segment length between two consecutive endpoints irrespective the data sequence the endpoints belong to.

7. The implantable medical device of claim 1, wherein the control unit is adapted to transform each magnitude value into a transformed magnitude value prior to storing a selected end point, wherein the transformation is nonlinear such that endpoint values with lower magnitudes are encoded with greater precision, while endpoint values with higher magnitudes are encoded with lesser precision.

8. The implantable medical device of claim 1, wherein the control unit is adapted to downsample an original data sequence in order to generate a data sequence comprising less data points than the original data sequence, wherein a data point of the original data sequence that has the largest magnitude among a number of data points eligible for being dropped is retained and the others are dropped.

9. A method of deriving a compressed data representation of said time varying signal form a sequence of data points that each represent an amplitude A of a time-varying signal at equidistant points of time t, said method comprising the steps of:

determining end points of data segments by

a) determination of a first difference quotient D₁=(A_n−

A<sub>n−

1</sub>)/(t_n−

t<sub>n−

1</sub>) with respect to an actual data point An at tn and an immediately preceding, second last data point A<sub>n−

1</sub> at t<sub>n−

1</sub>,

b) determination of a second difference quotient D₂=(A_n−

A_e)/(t_n−

t_e) or D₂=(A<sub>n−

1</sub>−

A_e)/(t<sub>n−

1</sub>−

t_e) with respect to an actual data point An at t_n or a second last data point A<sub>n−

1</sub> and t<sub>n−

1</sub>, respectively, and a last end point A_e at t_e, said last end point A_e being a previously determined end point or a first data point of said sequence of data points, wherein t_e represents the point of time belonging to said end point A_e,

c) selecting the second last data point A<sub>n−

1</sub> as a new end point, if the difference between the first and the second difference quotients D_D=D₁−

D₂ exceeds a predetermined threshold value T, D_D>

T, and

determining a data segment length L=t_n−

t_e between the point of time t_n of an actual data point A_n and the point of time t_e of a last end point A_e,

and selecting A<sub>n−

1</sub> as a new end point, if said data segment length L exceeds a predetermined maximum length Lmax,

and storing all selected end points in association with a segment length between each stored endpoint and an immediately preceding end point as a compressed data representation of said time varying signal.

10. The method of claim 9, wherein the method further comprises the steps of:

determining whether said first and said second difference quotient are of opposite sign and

selecting the second last data point A<sub>n−

1</sub> as a new end point, if the magnitude of the difference between the two difference quotients D_D=D₁−

D₂ exceeds a predetermined second threshold value T2.

11. The method according to claim 9 or 10, wherein the method further comprises the steps of:

determining whether a data segment length L=t_n−

t_e between the point of time t_n of an actual data point A_n and the point of time t_e of a last end point A_e exceeds a predetermined threshold length L1 and whether the magnitude of the difference between the two difference quotients D_D=D₁−

D₂ exceeds a predetermined third threshold value T3,

and selecting the second last data point A<sub>n−

1</sub> as a new end point, if said two conditions are met.

12. The method according to one of claims 9 to 11, wherein the method further comprises the step of determining the first, and, if applicable, the second and the third threshold value as a predetermined fraction of a peak amplitude value of said time-varying signal.

13. The method of claim 12, wherein the method further comprises the step of redetermining the first, and, if applicable, the second and the third threshold value if a moving average of said peak amplitude value of said time-varying signal changes.

14. The method according to claim 9, said method being adapted to process two or more data sequences each representing the time course of a heart signal, wherein the method comprises the steps of selecting endpoints in any of the data sequences and storing every selected endpoint of anyone of the data sequences together with corresponding data points of the other data sequences and the segment length between two consecutive endpoints irrespective the data sequence the endpoints belong to.

15. The method of claim 9, wherein the method comprises a step of value-to-code transformation that is carried out prior to storing an endpoint or another data point representing a signal amplitude value, wherein each magnitude value is nonlinearly transformed into a transformed magnitude code such that endpoint values with lower magnitudes are encoded with greater precision, while endpoint values with higher magnitudes are encoded with lesser precision.

16. The method of claim 9, wherein the method comprises the step of downsampling an original data sequence in order to generate a downsampled data sequence comprising less data points than the original data sequence, wherein a data point of the original data sequence that has the largest magnitude among a number of data points eligible for being dropped is retained and the others are dropped.