WO1999043381A1 - Implantable lead with switching means for switching between sensing and stimulating and medical device with such a lead - Google Patents

Implantable lead with switching means for switching between sensing and stimulating and medical device with such a lead Download PDF

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Publication number
WO1999043381A1
WO1999043381A1 PCT/SE1999/000243 SE9900243W WO9943381A1 WO 1999043381 A1 WO1999043381 A1 WO 1999043381A1 SE 9900243 W SE9900243 W SE 9900243W WO 9943381 A1 WO9943381 A1 WO 9943381A1
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WO
WIPO (PCT)
Prior art keywords
sensor
characterised
implantable lead
electrode
implantable
Prior art date
Application number
PCT/SE1999/000243
Other languages
French (fr)
Inventor
Johan Lidman
Charlotte Kjellman
Karin Ljungström
Åsa Uhrenius
Original Assignee
Pacesetter Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to SE9800566A priority Critical patent/SE9800566D0/en
Priority to SE9800566-3 priority
Application filed by Pacesetter Ab filed Critical Pacesetter Ab
Publication of WO1999043381A1 publication Critical patent/WO1999043381A1/en

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Classifications

    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61NELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00Electrotherapy; Circuits therefor
    • A61N1/02Details
    • A61N1/04Electrodes
    • A61N1/05Electrodes for implantation or insertion into the body, e.g. heart electrode
    • A61N1/056Transvascular endocardial electrode systems
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61NELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N1/00Electrotherapy; Circuits therefor
    • A61N1/18Applying electric currents by contact electrodes
    • A61N1/32Applying electric currents by contact electrodes alternating or intermittent currents
    • A61N1/36Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
    • A61N1/362Heart stimulators
    • A61N1/365Heart stimulators controlled by a physiological parameter, e.g. heart potential
    • A61N1/36514Heart stimulators controlled by a physiological parameter, e.g. heart potential controlled by a physiological quantity other than heart potential, e.g. blood pressure

Abstract

The implantable pacing lead comprises a tip electrode for stimulating heart events and a sensor for sensing a physiological parameter, said sensor outputting a sensor signal, whereby the sensor is electrically connected to said tip electrode and adapted to be electrically connected to said body tissue. The lead further comprises switching means which is electrically connected between said sensor and said tip electrode. The switching means function as a short-circuit when stimulating heart events and as a break when sensing said physiological parameter. It is the purpose of the switching means to prevent a short circuit between the sensor and the tip electrode when measuring the sensor output signal and this is achieved by letting the switching means implement a high impedance circuit between the sensor and the tip electrode for low voltages and a low impedance circuit for high voltages.

Description

IMPLANTABLE LEAD WITH SWITCHING MEANS FOR SWITCHING BETWEEN SENSING AND SΗMULATING AND MEDICAL DEVICE WITH SUCH A LEAD

Technical Field of the Invention

The invention relates generally to an implantable lead for implantable stimulation devices such as heart pacemakers. The invention relates further to implantable stimulation devices such as heart pacemakers comprising such an implantable lead. In particular, the invention relates to an implantable lead comprising a sensor for sensing a physiological parameter, e.g. the blood pressure.

Background of the Invention

For arrhythmia-treating implants, such as heart stimulators, pressure sensors for controlling the stimulator are ideal sensors in many respects. With a pressure sensor, heamodynamics can be measured in both tachy arrhythmias and brady arrhythmias. Heart contractions can be sensed and used for autocapture ® and atrial synchronisation. Furthermore, the time derivative dP/dt is a good rate response parameter.

For the applications in question, prior art pressure sensors normally contain a piezoelectric or piezoresistive pressure element. A pacemaker controlled with this type of sensor is previously known from e.g. US-A- 4 140 132 and US-A-4 600 017. One disadvantage of this type of sensor is that the sensor normally requires two additional electrical conductors. The implantable lead comprising the sensor must therefore contain relatively many conductors.

EP-A-0 632 992 solves this problem by providing an electrode system whereby the distance between the electrode conductors in a bipolar electrode system or between an electrode conductor and ambient electrolyte in a unipolar electrode system changes when the patient moves, thereby changing the capacitance between the electrode conductors and between the conductors and ambient electrolyte. The patient's heart movements will therefore be expressed as changes in capacitance. A disadvantage of this type of sensor is that the two conductors must not terminate in electrical poles in direct contact with one another via the electrolyte or the body fluid, since this would result in short-circuiting of the capacitance.

Swedish patent application having application no. 9603066-3 and filed on 23 August 1996 (corresponding to EP-A2-0,824,935, published 25 February 1998), relates to an implantable electrode lead whereby the tip electrode of the lead is covered with a piezoelectric material. When the heart contracts, the piezoelectric material will produce an output signal and consequently the tip electrode will be able to detect the mechanically evoked heart responses. However, the piezoelectric material acts as a capacitor and this capacitor will be in series with the stimulation electrode, i.e. the tip electrode. There may therefore be a problem of electrically stimulating the heart tissue with low voltages. So as to increase the possibility to stimulate the heart tissue with low voltages, a diode and resistor are connected in parallel with the piezoelectric material, such that the current for stimulating the heart tissue will pass through the diode and the resistor and not through the piezoelectric material. An alternative would be to only have the resistor. However, irrespective of which alternative is chosen, the diode and/or the resistor only fills a function when stimulating the body tissue and not when sensing evoked heart response.

Summary of the Invention

In the prior art there is a problem of needing additional conductors when providing an implantable electrode lead with a sensor and that the two conductors must not terminate in electrical poles in direct contact with one another via the electrolyte or the body fluid due to short-circuiting of the electrodes. These problems are solved by the invention as defined in independent claim 1, which relates to an implantable lead comprising a sensor for sensing a physiological parameter, and preferred embodiments thereof are defined in dependent claims 2 to 16. A medical device comprising an implantable lead according to anyone of claims 1 to 16 is defined in claims 17 and 18. An advantage of the implantable lead according to the invention is that it does not need any additional conductors than those needed for the tip and/or ring electrode. Furthermore, a very simple construction of the implantable lead is achieved. Moreover, the sensor and the electronic components which are needed are added to a standard unipolar or bipolar lead and consequently, no special connector to connect the lead to the pacemaker is needed.

Brief Description of the Drawings Fig. 1 is a schematic drawing of a heart pacemaker comprising an implantable lead in accordance with the invention; Fig. 2 is a schematic circuit diagram of an implantable lead in accordance with a first embodiment of the invention; Fig. 3 is a schematic circuit diagram of an implantable lead in accordance with a second embodiment of the invention;

Fig. 4 is a schematic drawing of an implantable lead in accordance with an embodiment of the invention; Fig. 5 is a schematic circuit diagram of a heart pacemaker and implantable unipolar lead in accordance with an embodiment of the invention; Fig. 6 is a schematic circuit diagram of a heart pacemaker and implantable bipolar lead in accordance with an embodiment of the invention.

Description of the preferred Embodiments

With reference now to the drawings, wherein like components are given the same reference signs, Fig. 1 shows the schematic drawing of a heart pacemaker 100 for tissue stimulation and a lead 11 according to a preferred embodiment of the invention. The heart pacemaker 100 comprises a stimulation pulse generator 120 that has its output side connected via the lead 11 to an electrode 10 applied in the ventricle of the heart for delivering stimulation pulses to the heart. The lead 11 may be a unipolar lead 1 or a bipolar lead 2. Of course, even if Fig. 1 shows the electrode 10 to be located in the ventricle, the invention also covers the electrode 10 being located in the atrium. The lead 11 further comprises a sensor 30 for sensing a physiological parameter. The stimulation pulse generator 120 can be activated to deliver a stimulation pulse via a control line, which is connected to a corresponding output of a control unit 130, e.g. a microprocessor. The stimulation pulse generated by the stimulation pulse generator 120 may be anyone of the stimulation pulses known to the skilled person. The duration of each stimulation pulse as well as the amplitude thereof are set by the control unit 130. In the illustrated preferred embodiment, the control unit 130 has access to a memory 140 wherein a program that execute all functions of the heart pacemaker 100 via the control unit 130 is stored. The pacemaker 100 comprises a telemetry unit 150 connected to the control unit 130 for programming and for monitoring the functions of the pacemaker 100 and of parameters acquired therewith on the basis of data exchange with an external programming and monitoring device (not shown).

In order to be able to acquire the reaction of the heart given a stimulation, the pacemaker 100 comprises a detector unit 110 which has an input side connected via the lead 11 to the sensor 30 for acquiring a signal corresponding to the physiological parameter of the heart.

The control unit 130 comprises means for evaluating the signal outputted from the sensor 30. The control unit 130 may e.g. determine the mechanical activity of the heart, if there has been capture or not, or evaluate the heart rate response.

In Fig. 2 there is shown a schematic circuit diagram of an implantable unipolar lead 1 for a heart pacemaker 100. The unipolar lead 1 comprises an inner conductor 3 which is connected to a tip electrode 10. The stimulation pulses from the heart pacemaker 100 are delivered to the tip electrode 10 via the inner conductor 3. The tip electrode 10 and the pulse generator case are electrically connected to each other by means of the body tissue 20 as is generally known in the art of unipolar leads. The lead 1 further comprises a sensor 30 for sensing a physiological parameter which is electrically connected to the inner conductor 3 and the body tissue 20. The inner conductor 3 comprises a switching means 40 which is electrically connected to the sensor 30 and the tip electrode 10.

The physiological parameter which is sensed by the sensor 30 may for example be blood pressure, blood flow, blood temperature or lead acceleration. Different types of sensors 30 may be used, for example piezoelectric, piezoresistive, resistive and capacitive sensors. The sensor 30 outputs a sensor signal, which may be a charge or voltage signal. However, a prerequisite for all of the sensor types which are used is that the voltage over the sensor 30 is low in comparison with the voltage of the stimulation pulse. The stimulation pulse voltage is usually in the range of 0.5 to 3 V. This voltage can be compared with the voltage Vout over the piezoelectric sensor which is approximately zero when detecting the charge by means of a charge amplifier (see below).

It is the purpose of the switching means 40 to prevent a short circuit between the sensor 30 and the tip electrode 10 when measuring the sensor output signal and this is achieved by letting the switching means 40 implement a high impedance circuit between the sensor 30 and the tip electrode 10 for low voltages and a low impedance circuit for high voltages. Consequently, the switching means 40 will function as a short circuit when stimulating the heart tissue and as a break when sensing the physiological parameter.

In Fig. 3 there is shown a schematic circuit diagram of an implantable bipolar lead 2 for a heart pacemaker 100. The bipolar lead 2 comprises an inner conductor 3 and an outer conductor 4 which are connected to a tip electrode 10 and a ring electrode 50 respectively. The stimulation pulses from the heart pacemaker 100 are delivered to the tip electrode 10 via the inner conductor 3. The tip electrode 10 and the ring electrode 50 are electrically connected to each other by means of the body tissue 20 6

as is generally known in the art of bipolar leads. The lead 2 further comprises a sensor 30 for sensing a physiological parameter which is electrically connected to the inner conductor 3 and the outer conductor 4. The inner conductor 3 comprises a switching means 40 which is electrically connected to the sensor 30 and the tip electrode 10. The sensor 30 and the switching means 40 are similar to those described in Fig. 2.

Fig. 4 is a schematic view of a bipolar lead according to a preferred embodiment of the invention and as described in more detail in Fig. 3. From Fig. 4 can be seen that the sensor 30 and the ring electrode 50 are integrated. This may for example be achieved in that the ring electrode 50 comprises an electrically conductive core which is covered by a piezoelectric material. The piezoelectric material is covered with an electrically conductive layer. The conductive layer is preferably porous for increasing the contact area between the electrode and the body tissue and it is furthermore biocompatible, e.g. vitreous carbon, porous titanium nitride, porous titanium carbide, platinum-black or oxidised iridium. The conductive layer may totally cover the piezoelectric material or only parts of it on the assumption that the remaining part of the piezoelectric material is covered by some other biocompatible material as e.g. silicon rubber. If, however, the piezoelectric material is biocompatible, there is no need to cover the remaining part thereof. Moreover, the sensor 30 would then function even when the protection layer constituting the conductive layer would be damaged.

In an alternative embodiment the sensor 30 and the ring electrode are physically separate but still electrically connected to one another, since they both are connected to the outer conductor 4. The sensor 30 would then either have to be embedded within the lead 1 or be covered by a biocompatible material. If the piezoelectric material is biocompatible the sensor 30 may be placed on the lead 11 such that it is in direct contact with the body tissue 20. That the sensor 30 is formed as a ring electrode is a preferred embodiment, but it may also be formed as is generally known in the art, cf. for example US-A-4 600 017

Fig. 5 shows a schematic circuit diagram of a heart pacemaker 100 and implantable unipolar lead 1 according to a preferred embodiment of the invention. The unipolar lead 1 is connected to the pacemaker 100 by means of a connector as is generally known in the art. In the preferred embodiment the sensor 30 is a piezoelectric sensor, which is characterised by a voltage source Vp and a capacitor Cp. The piezoelectric sensor 30 outputs a voltage Vou . The switching means 40 comprises a diode Dj and a resistor Rj in parallel to discharge the diode O\ after a stimulation pulse. An alternative to the resistor R\ for discharging the diode D^ could be a diode D2 (not shown). In accordance with the invention, the diode forward voltage Vj) would have to be larger than the output sensor voltage Vout such that the diode O\ functions as a short circuit when stimulating heart events and as a break when sensing the physiological parameter. Consequently, when having a piezoelectric sensor 30 which according to the preferred embodiment outputs a voltage Vout being approximately zero, a germanium diode having a forward voltage of V]} = 0.2 volts would be suitable, since it would fulfil the requirement that the germanium diode should function as a short circuit when stimulating heart events and as a break when sensing the physiological parameter.

The stimulation pulse generator 120 is depicted by means of a schematic equivalent circuit which is commonly used in the art. A capacitor C2 for generating a stimulating pulse is charged by means of a voltage source Vs and a switch S\. When the heart tissue is stimulated the capacitor C2 is discharged by means of a switch S4 and a capacitor C3. After stimulation the capacitor C3 is discharged by means of a switch S2-

The pacemaker 100 comprises a detector unit 110 which has an input side connected via a switch S3, the capacitor C3 and the lead 11 to the sensor 30 for acquiring a signal corresponding to the physiological parameter of the heart. The switch S3 is closed when detecting the signal outputted from the sensor 30 and otherwise is open. The detector unit 110 is a charge amplifier comprising an operational amplifier OP which negative input is connected to the switch S3. The output of the operational amplifier OP is via a capacitor Cl, a resistor R2 and a switch S5, which are connected in parallel, fed back to the negative input. The positive input is connected to ground.

As has already been mentioned, the piezoelectric sensor 30 can electrically be represented as a voltage source Vp in series with a capacitance Cp. The lead 1,2,11 can electrically be represented as a resistance Rlead- The piezoelectric sensor 30 is connected through the lead 1,2,11 to a charge amplifier 110, located inside the pacemaker. The capacitance Cp is normally in the order of nF and the resistance Rlead can be as low as 50 kΩ. These two quantities form a high-pass filter having a cut-off frequency in the order of kHz, in the worst situation approximately 3 kHz when a voltage amplifier is used. With the piezoelectric sensor 30 it is, however, desirable to measure pressure variations of frequencies down to about 0.2 Hz. Consequently, it is more suitable to connect the piezoelectric sensor 30 to a charge amplifier 110 than to a voltage amplifier, since the charge amplifier has a low input resistance for measuring the charge produced in the sensor when it is subjected to pressure variations. The amplification in this case is given by the ratio Cp / C\ and the cut-off frequency is equal to l/2π R2 C\ . As can be seen from Fig. 5 the piezoelectric sensor 30 will in practice be short-circuited by the input resistance of the charge amplifier 110.

In a preferred embodiment Rι=100 kΩ, R2=l GΩ, Cι=l nF, C2=10 U-F, C =10 M-F and Cp *1 nF. The resistance of the body tissue is approximately 500 .

Consequently, according to the preferred embodiment the heart beat may be divided into three stages: 1. Charge the capacitor C2 and measure the output of the sensor 30. Sι=closed; S2=open; S3=closed; S4=open; and S5=open.

2. Stimulate the heart. Sι=open; S2=open; S3=open; S4=closed; and S5=closed.

3. Discharge C3 and reset the charge amplifier 110. Sι=open; S2=closed; S3=open; S4=open; and S5=ιclosed.

State 2 lasts for approximately 1 ms and state 3 for approximately 10 ms. The rest of the time of the heart beat is state 1, normally in the order of 400 to 1000 ms.

Fig. 6 shows a schematic circuit diagram of a heart pacemaker 100 and implantable bipolar lead 2 according to an embodiment of the invention. The only difference to the embodiment as shown in Fig. 5 is that, since the lead 2 is bipolar, the signal outputted from the sensor 30 is sensed between the inner conductor 3 and the outer conductor 4 and not between the inner conductor 3 and the body tissue 20 as in the case of the unipolar lead 1.

As mentioned in conjunction with Fig. 2 and 3, the sensor 30 may also be e.g. a piezoresistive, resistive or a capacitive sensor. When using another sensor type than the one described in Fig. 5 and 6, the detector unit 110 would comprise another type of amplifier, e.g. a voltage amplifier. The most suitable combinations of the above- mentioned sensor types and amplifiers are generally known in the art. The switching means 40 need not comprise a diode but may instead comprise e.g. a transistor. Of course the switching means comprising a transistor would have to constructed in such a way that it does not need a conductor in addition to the conductor(s) used by the uni bipolar lead. How to control a transistor without adding a particular control conductor by using an already existing conductor is well known in the art, e.g. by means of a pulsed current. The importance is that the switching means 40 is chosen such that it will function as a short circuit when stimulating the heart tissue and as a break when sensing the physiological parameter.

Claims

10Claims
1. An implantable lead for stimulating body tissue comprising a conductor (3), a tip electrode (10) for stimulating body tissue and a sensor (30) for sensing a physiological parameter, said tip electrode (10) being electrically connected to said conductor (3), characterised in that said sensor (30) is electrically connected to said conductor (3), and said lead (1,2,11) further comprises switching means (40) which is electrically connected to said conductor (3) between said sensor (30) and said tip electrode (10).
2. An implantable lead according to claim 1, characterised in that said switching means (40) function as a short circuit when stimulating said body tissue and as a break when sensing said physiological parameter.
3. An implantable lead according to claims 1 or 2 , characterised in that said switching means (40) comprises a diode (Dj) which diode forward voltage (VQ) is larger than the voltage (Vout) sensed over the sensor (30) such that said diode (O\) functions as a short circuit when stimulating heart events and as a break when sensing said physiological parameter.
4. An implantable lead according to claim 3, characterised in that there are discharging means (R1-D2) connected in parallel to the diode (Dj) for discharging the diode (D\) after a stimulation pulse.
5. An implantable lead according to claim 4, characterised in that said discharging means (R1-D2) is a resistor (Ri).
6. An implantable lead according to claim 4, characterised in that said discharging means (K\ ,D_) is a diode (D2). 11
7. An implantable lead according to claims 1 or 2, characterised in that said switching means (40) comprises a transistor.
8. An implantable lead according to anyone of claims 1 to 7 characterised in that said sensor (30) is formed as a ring electrode on the lead (1,2,11).
9. An implantable lead according to anyone of claims 1 to 8, characterised in that said sensor (30) is a piezoelectric sensor comprising a first electrode electrically connected to said tip electrode, said first electrode being covered by a piezoelectric material, which is totally or partially covered by a second electrode adapted to be electrically connected to said body tissue.
10. An implantable lead according to claim 9, characterised in that said piezoelectric material is biocompatible.
11. An implantable lead according to anyone of claims 1 to 10, characterised in that said sensor (30) is a capacitive sensor.
12. An implantable lead according to anyone of claims 1 to 10, characterised in that said sensor (30) is a resistive sensor.
13. An implantable lead according to anyone of claims 1 to 12, characterised in that said lead (1) is a unipolar lead.
14. An implantable lead according to anyone of claims 1 to 12, characterised in that said lead (1) is a bipolar lead comprising an indifferent ring electrode (50).
15. An implantable lead according to claim 14 when dependent on claim 8, characterised in that said sensor (30) formed as a ring electrode is physically separated from said indifferent ring electrode (50). 12
16. An implantable lead according to claim 14 when dependent on claim 8, characterised in that said sensor (30) formed as a ring electrode and said indifferent ring electrode (50) are integrated with one another.
17. An implantable medical device for stimulating body tissue comprising a pulse generator (100) and an implantable lead (1,2,11) according to anyone of claims 1 to 16, said pulse generator (100) comprising means (120) for stimulating heart events by means of said tip electrode and further comprising a means (110) for detecting said output sensor signal.
18. An implantable medical device according to claim 17 when dependent on claim 9 or 10, characterised in that said detecting means (110) comprises a charge amplifier.
PCT/SE1999/000243 1998-02-25 1999-02-22 Implantable lead with switching means for switching between sensing and stimulating and medical device with such a lead WO1999043381A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
SE9800566A SE9800566D0 (en) 1998-02-25 1998-02-25 Implantable Lead and medical device
SE9800566-3 1998-02-25

Publications (1)

Publication Number Publication Date
WO1999043381A1 true WO1999043381A1 (en) 1999-09-02

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006036667A1 (en) * 2004-09-23 2006-04-06 Medtronic, Inc. Implantable medical lead
US7305270B1 (en) 2005-04-21 2007-12-04 Pacesetter, Inc. Cardiac pacing/sensing lead providing far-field signal rejection
WO2010071493A1 (en) * 2008-12-19 2010-06-24 St.Jude Medical Ab Implantable electrode lead with switching unit adapted for switching electrode lead between normal pacing mode and local pacing mode during mri
US7860581B2 (en) 2005-10-31 2010-12-28 St. Jude Medical Ab Implantable lead with a stimulating electrode and a mapping electrode that is electrically disconnectable

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4600017A (en) * 1984-07-19 1986-07-15 Cordis Corporation Pacing lead with sensor
GB2234908A (en) * 1989-08-16 1991-02-20 Cardiac Pacemakers Inc Combined defibrillator-pacer system utilising pacer tip lead switch
EP0585582A1 (en) * 1992-09-02 1994-03-09 Pacesetter AB Device for stimulating living tissue
US5709709A (en) * 1996-02-13 1998-01-20 Angeion Corporation ICD with rate-responsive pacing

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4600017A (en) * 1984-07-19 1986-07-15 Cordis Corporation Pacing lead with sensor
GB2234908A (en) * 1989-08-16 1991-02-20 Cardiac Pacemakers Inc Combined defibrillator-pacer system utilising pacer tip lead switch
EP0585582A1 (en) * 1992-09-02 1994-03-09 Pacesetter AB Device for stimulating living tissue
US5709709A (en) * 1996-02-13 1998-01-20 Angeion Corporation ICD with rate-responsive pacing

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006036667A1 (en) * 2004-09-23 2006-04-06 Medtronic, Inc. Implantable medical lead
US7493174B2 (en) * 2004-09-23 2009-02-17 Medtronic, Inc. Implantable medical lead
US8005551B2 (en) 2004-09-23 2011-08-23 Medtronic, Inc. Implantable medical lead
US7305270B1 (en) 2005-04-21 2007-12-04 Pacesetter, Inc. Cardiac pacing/sensing lead providing far-field signal rejection
US7860581B2 (en) 2005-10-31 2010-12-28 St. Jude Medical Ab Implantable lead with a stimulating electrode and a mapping electrode that is electrically disconnectable
WO2010071493A1 (en) * 2008-12-19 2010-06-24 St.Jude Medical Ab Implantable electrode lead with switching unit adapted for switching electrode lead between normal pacing mode and local pacing mode during mri
US8437863B2 (en) 2008-12-19 2013-05-07 St. Jude Medical Ab Electrode lead

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