Implantable medical device for stimulating a human or animal heart employing an automatic choice between different impedance measuring modes

Abstract

An implantable medical device for stimulating a human/animal heart having a stimulation unit which stimulates the His bundle and a detection unit which detects an electrical signal at the His bundle. The device performs: a) determining a first value of a parameter of a first measuring pulse measured between a first electrode pole and a housing; b) determining a second value of the same parameter of a second measuring pulse measured between the first electrode pole and a second electrode pole; c) comparing the first and second values; d) determining, based on the comparing step, whether the first or second measuring pulses enables a higher available level control range of the analog-to-digital converter; e) measuring an impedance in a unipolar manner between the first electrode pole and the housing or in a bipolar manner between the first electrode pole and the second electrode pole depending on the determining step.

Claims

1. Implantable medical device for stimulating a human or animal heart, comprising a housing, an analog-to-digital converter, a processor, a memory unit, a stimulation unit configured to stimulate the His bundle of a human or animal heart, and a detection unit configured to detect an electrical signal at the His bundle of the same heart, wherein the detection unit comprises an electrode having a first electrode pole and a second electrode pole, wherein the memory unit comprises a computer-readable program that causes the processor to perform the following steps when executed on the processor: a) determining, by the detection unit, a first value of at least one parameter of a first measuring pulse generated by the stimulation unit, the first value measured between the first electrode pole and the housing; b) determining, by the detection unit, a second value of the same at least one parameter of a second measuring pulse generated by the stimulation unit, the second value measured between the first electrode pole and the second electrode pole; c) comparing the first value of the at least one parameter of the first measuring pulse to the second value of the at least one parameter of the second measuring pulse; d) determining, based on the comparing of the preceding step, whether the first measuring pulse or the second measuring pulse enables a higher available level control range of the analog-to-digital converter; e) measuring an impedance in a unipolar manner between the first electrode pole and the housing when the first measuring pulse enables a higher available level control range of the analog-to-digital converter than the second measuring pulse; and measuring an impedance in a bipolar manner between the first electrode pole and the second electrode pole when the second measuring pulse enables a higher available level control range of the analog-to-digital converter than the first measuring pulse.

2. Implantable medical device according to claim 1, wherein the at least one parameter is chosen from the group consisting of an amplitude of a measuring current of the first and second measuring pulses and a measuring gain of the first and second measuring pulses.

3. Implantable medical device according to claim 2, wherein both the amplitude of the measuring current and the measuring gain are used as the at least one parameter.

4. Implantable medical device according to claim 1, wherein the computer-readable program causes the processor to classify the first value and the second value of the at least one parameter into a predefined class comprising a value range encompassing the respective value, wherein a numeric index is assigned to each class.

5. Implantable medical device according to claim 4, wherein the numeric index increases with increasing values of the value range.

6. Implantable medical device according to claim 4, wherein the computer-readable program causes the processor to accomplish the determining whether the first measuring pulse or the second measuring pulse enables a higher available level control range of the analog-to-digital converter by the following steps: a) determining whether the numeric index assigned to a single value of the at least one parameter of the first measuring pulse or the numeric index assigned to a single value of the at least one parameter of the second measuring pulse is lower when the value of exactly one parameter of the at least one parameter has been determined; and a′) calculating a first sum of numeric indices assigned to all values of the at least one parameter of the first measuring pulse and calculating a sum of numeric indices assigned to all values of the at least one parameter of the second measuring pulse when the values of more than one parameter of the at least one parameter have been determined and determining whether the first sum or the second sum is lower; and b) determining that the first measuring pulse enables a higher available level control range of the analog-to-digital converter when the numeric index assigned to a single value of the at least one parameter of the first measuring pulse is lower than the numeric index assigned to a single value of the at least one parameter of the second measuring pulse or when the first sum is lower than the second sum; and b′) determining that the second measuring pulse enables a higher available level control range of the analog-to-digital converter when the numeric index assigned to a single value of the at least one parameter of the second measuring pulse is lower than the numeric index assigned to a single value of the at least one parameter of the first measuring pulse or when the second sum is lower than the first sum.

7. Implantable medical device according to claim 1, wherein the at least one parameter of the first and second measuring pulses comprises at least two parameters, and wherein the computer-readable program causes the processor to determine the values of the at least two parameters of the first measuring pulse and the second measuring pulse and to classify the values into a predefined class comprising a value range encompassing the respective value, wherein a numeric index is assigned to each class.

8. Implantable medical device according to claim 1, wherein the stimulation unit is configured to provide stimulation pulses to the human or animal heart, and wherein the computer-readable program causes the processor to use the measured impedance as input value for adjusting at least one physical parameter of a stimulation pulse to be delivered by the stimulation unit to the His bundle of the heart.

9. Implantable medical device according to claim 1, wherein the first electrode pole is located in a tip region of the electrode and in that the second electrode pole is located proximally of the tip region of the electrode.

10. Implantable medical device according to claim 1, wherein the computer-readable program causes the processor to adjust a measuring gain of the first and second measuring pulses and to repeat steps a) to e) of claim 1.

11. Implantable medical device according to claim 10, wherein the computer-readable program causes the processor to measure the impedance using the measuring gain that resulted in the highest available level control range of the analog-to-digital converter.

12. Method for determining whether a cardiac impedance is to be measured in a unipolar manner or in a bipolar manner with an implantable medical device for stimulating a human or animal heart, wherein the implantable medical device comprises a housing, an analog-to-digital converter, a processor, a memory unit, a stimulation unit configured to stimulate the His bundle of a human or animal heart, and a detection unit configured to detect an electrical signal at the His bundle of the same heart, wherein the detection unit comprises an electrode having a first electrode pole and a second electrode pole, the method comprising the following steps: a) determining, with the detection unit configured to detect an electrical signal at the His bundle of the human or animal heart, a first value of at least one parameter of a first measuring pulse generated by the stimulation unit, the first value measured between first electrode pole of the electrode of the detection unit and the housing of the implantable medical device; b) determining, with the detection unit, a second value of the same at least one parameter of a second measuring pulse generated by the stimulation unit, the second value measured between the first electrode pole and the second electrode pole of the same electrode; c) comparing the first value of the at least one parameter of the first measuring pulse to the second value of the at least one parameter of the second measuring pulse; d) determining, based on the comparing of the preceding step, whether the first measuring pulse or the second measuring pulse enables a higher available level control range of an analog-to-digital converter of the implantable medical device; and e) measuring an impedance in a unipolar manner between the first electrode pole and the housing when the first measuring pulse enables a higher available level control range of the analog-to-digital converter than the second measuring pulse; and measuring an impedance in a bipolar manner between the first electrode pole and the second electrode pole when the second measuring pulse enables a higher available level control range of the analog-to-digital converter than the first measuring pulse.

13. Computer program product comprising non-transitory computer-readable code that causes a processor to perform the following steps when executed on the processor: a) determining, with a detection unit configured to detect an electrical signal at the His bundle of a human or animal heart, a first value of at least one parameter of a first measuring pulse generated by a stimulation unit, the first value measured between a first electrode pole of an electrode of the detection unit and a housing of an implantable medical device for stimulating a human or animal heart; b) determining, with the detection unit, a second value of the same at least one parameter of a second measuring pulse generated by the stimulation unit, the second value measured between the first electrode pole and a second electrode pole of the same electrode; c) comparing the first value of the at least one parameter of the first measuring pulse to the second value of the at least one parameter of the second measuring pulse; d) determining, based on the comparing of the preceding step, whether the first measuring pulse or the second measuring pulse enables a higher available level control range of an analog-to-digital converter of the implantable medical device; and e) configuring the detection unit to measure an impedance in a unipolar manner between the first electrode pole and the housing when the first measuring pulse enables a higher available level control range of the analog-to-digital converter than the second measuring pulse; and configuring the detection unit to measure an impedance in a bipolar manner between the first electrode pole and the second electrode pole when the second measuring pulse enables a higher available level control range of the analog-to-digital converter than the first measuring pulse.

14. Method of treatment of a human or animal patient in need of such treatment by means of an implantable medical device for stimulating a human or animal heart, wherein the implantable medical device comprises a housing, an analog-to-digital converter, a processor, a memory unit, a stimulation unit configured to stimulate the His bundle of a human or animal heart, and a detection unit configured to detect an electrical signal at the His bundle of the same heart, wherein the detection unit comprises an electrode having a first electrode pole and a second electrode pole, the method comprising the following steps: a) determining, with the detection unit, a first value of at least one parameter of a first measuring pulse generated by the stimulation unit, the first value measured between the first electrode pole and the housing; b) determining, with the detection unit, a second value of the same at least one parameter of a second measuring pulse generated by the stimulation unit, the second value measured between the first electrode pole and the second electrode pole; c) comparing the first value of the at least one parameter of the first measuring pulse to the second value of the at least one parameter of the second measuring pulse; d) determining, based on the comparing of the preceding step, whether the first measuring pulse or the second measuring pulse enables a higher available level control range of the analog-to-digital converter; e) measuring an impedance in a unipolar manner between the first electrode pole and the housing when the first measuring pulse enables a higher available level control range of the analog-to-digital converter than the second measuring pulse; and measuring an impedance in a bipolar manner between the first electrode pole and the second electrode pole when the second measuring pulse enables a higher available level control range of the analog-to-digital converter than the first measuring pulse; f) using the impedance as input value for adjusting at least one physical parameter of a stimulation pulse to be delivered by the stimulation unit to the His bundle of the heart; and g) delivering the stimulation pulse to the His bundle of the heart.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further details of aspects of the present invention will be described in the following making reference to exemplary embodiments and accompanying Figures. In the Figures:

(2) FIG. 1 shows a prior art setup for measuring an impedance in a unipolar manner; and

(3) FIG. 2 shows two possible ways of measuring an impedance with a His bundle electrode.

DETAILED DESCRIPTION

(4) FIG. 1 shows an implantable pulse generator 1 with a connected right ventricular electrode 2. This right ventricular electrode 2 is implanted in an apical region 3 of a human heart 4. The right ventricular electrode 2 comprises an electrode pole 5 at its tip. An impedance Z can be measured between the electrode pole 5 and a housing 6 of the implantable pulse generator 1 serving as counter electrode.

(5) FIG. 2 shows the situation in case of an implantable pulse generator 1 employing His bundle pacing as implantable medical device. Similar elements will be denoted with the same reference numerals as in FIG. 1.

(6) In case of His bundle pacing, typically no right ventricular electrode is present. Rather, a His bundle electrode 7 is connected to the implantable pulse generator 1. The His bundle electrode 7 is implanted at the His bundle 8 of the human heart 4. A first electrode pole 5 contacts the cardiac tissue at or nearby the His bundle 8 so as to be able to stimulate the His bundle 8 of the human heart 4. A second electrode pole 9 is located proximally the first electrode pole 5.

(7) It is now possible to measure an impedance in a unipolar manner between the first electrode pole 5 and a housing 6 of the implantable pulse generator 1. Such a measuring setup is similar to the measuring setup explained with respect to FIG. 1, but employs a different measuring path since the His bundle electrode 7 does not extend into the right ventricle of the human heart 4 as the right ventricular electrode 2 does (cf. FIG. 1).

(8) Another possibility to measure the impedance is to apply a bipolar measurement between the first electrode pole 5 and the second electrode pole 9. In such a case, the measuring path is significantly shorter than in case of the unipolar measurement. Depending on the contractility of the human heart 4, a bipolar measurement may thus result in higher measuring currents than a unipolar measurement. However, this strongly depends on the concrete site of implantation of the His bundle electrode 7 in the cardiac tissue around the His bundle 8.

(9) To decide whether a unipolar measurement or a bipolar measurement of the impedance is to be applied, a first measuring pulse is provided to the His bundle electrode 7, wherein both measuring gain and an amplitude of the measuring current are determined for this first measuring pulse. Subsequently, a second measuring pulse is applied to the His bundle electrode 7. Once again, the measuring gain and the amplitude of the measuring current are measured for this second measuring pulse. The first measuring pulse is applied between the first electrode pole 5 and the housing 6 of the implantable pulse generator 1, whereas the second measuring pulse is applied between the first electrode pole 5 and the second electrode pole 9.

(10) In an exemplary experiment, the unipolar measurement of the first measuring pulse resulted in an amplitude of the measuring current amounting to 200 μA. Furthermore, the gain was determined to be 50.0. In case of the bipolar measurement of the second measuring pulse, the amplitude of the measuring current was higher, namely at 400 μA. At the same time, the measuring gain was determined to be only 18.8. These values of the parameters of the first measuring pulse and of the second measuring pulse were then classified with the help of the following Tables:

(11) TABLE-US-00001 TABLE 1 Classes of amplitude ranges of measuring current. Amplitude of measuring Index.sub.C current/μA 0  0.1 to 50.0 1  50.1 to 100.0 2 100.1 to 200.0 3 200.1 to 300.0 4 300.1 to 400.0 5 400.1 to 500.0 6 >500

(12) TABLE-US-00002 TABLE 2 Classes of ranges of measuring gain. Index.sub.G Measuring Gain 0 .sub. 0 to 6.0 1  6.1 to 10.0 2 10.1 to 15.0 3 15.1 to 20.0 4 20.1 to 30.0 5 30.1 to 45.0 6 45.1 to 60.sub.  7 60.1 to 75.0 8  75.1 to 105.0 9 >105.0

(13) As can be seen from the preceding Table 1, each measuring current class covers a specific amplitude range of the measuring current and is assigned with a specific numeric index, called index.sub.C. Likewise, as can be seen from the preceding Table 2, each individual class of the measuring gain covers a specific again range and is also assigned with a specific numeric index, called index.sub.G.

(14) The measuring results for the first measuring pulse (a current amplitude of 200 μA and a gain of 50.0) resulted in an assignment of index.sub.C=2 and index.sub.G=6 to the first measuring pulse. Likewise, the measuring results for the second measuring pulse (a current amplitude of 400 μA and a gain of 18.8) resulted in an assignment of index.sub.C=4 and index.sub.G=3 to the second measuring pulse.

(15) Afterwards, index.sub.C and index.sub.G obtained for the first measuring pulse were added. Likewise, index.sub.C and index.sub.G obtained for the second measuring pulse were also added. The first sum for the first measuring pulse was 2+6=8. The second sum of the second measuring pulse 4+3=7.

(16) A lower sum is the equivalent of a higher available level control range of the analog-to-digital converter of the implantable medical device.

(17) Since 7 is lower than 8, a bipolar determination of the impedance was chosen as the method that enables a higher available level control range of the analog-to-digital converter of the implantable pulse generator 1. Therefore, subsequent impedance measurements were carried out by applying a bipolar determination of the impedance.

(18) It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points.