Controlled and modulated high power racing combined with intracardiac pressure monitoring feedback system utilizing the chronicle implantable hemodynamic monitoring (IHM) and calculated EPAD Number:7,386,346 from the United States Patent and Trademark Office (PTO) owispatent

Title: Controlled and modulated high power racing combined with intracardiac pressure monitoring feedback system utilizing the chronicle implantable hemodynamic monitoring (IHM) and calculated EPAD

Abstract: Techniques for pacing the heart of a patient as a function of a pressure value make use of a pressure monitor that receives a signal from a pressure sensor in the heart. The pressure monitor measures a pressure value. The pressure monitor may, for example, estimate the pulmonary artery diastolic pressure if the pressure sensor is located in the right ventricle, or calculate the mean central venous pressure if pressure sensor is located in the right atrium. The energy level of the pacing pulses delivered to the patient's heart by a pacemaker is modulated as a function of the pressure value. Modulating the energy level of the pacing pulses modulates the cardiac output of the patient's heart.

Patent Number: 7,386,346 Issued on 06/10/2008 to Struble

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Inventors:	Struble; Chester (Eijsden, NL)
Assignee:	Medtronic, Inc. (Minneapolis, MN)
Appl. No.:	10/126,858
Filed:	April 22, 2002

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Current U.S. Class:	607/17
Field of Search:	600/373,374,513,393,508,509,519,521 607/4-9,11,17,18,23,116,119,122,123,126,127

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References Cited [Referenced By]

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U.S. Patent Documents

4316472	February 1982	Mirowski et al.
4375817	March 1983	Engle et al.
4379459	April 1983	Stein
4384585	May 1983	Zipes
4476868	October 1984	Thompson
4485813	December 1984	Anderson et al.
4556063	December 1985	Thompson et al.
4727877	March 1988	Kallok
4800883	January 1989	Winstrom
4821723	April 1989	Baker et al.
4949719	August 1990	Pless et al.
4953551	September 1990	Mehra et al.
5099838	March 1992	Bardy
5117824	June 1992	Keimel
5131388	July 1992	Pless
5144949	September 1992	Olson
5158078	October 1992	Bennett et al.
5163427	November 1992	Keimel
5188105	February 1993	Keimel
5199428	April 1993	Obel et al.
5207218	May 1993	Carpentier et al.
5269298	December 1993	Adams et al.
5312453	May 1994	Shelton et al.
5314430	May 1994	Bardy
5320643	June 1994	Roline et al.
5324327	June 1994	Cohen
5330507	July 1994	Schwartz
5331966	July 1994	Bennett et al.
5354316	October 1994	Keimel
5368040	November 1994	Carney
5545186	August 1996	Olson
5564434	October 1996	Halperin et al.
5626623	May 1997	Kieval et al.
5690686	November 1997	Min et al.
5800464	September 1998	Kieval
5891176	April 1999	Bornzin
6314323	November 2001	Elkwall
6371922	April 2002	Baumann et al.

Other References

"High Output Ventricular Pacing Increased the Cardiac Output", 550 59/3, Cardiostim 96 Eur.J.C.P.E., vol. 6 No. 1, Jun. 96, p. 138. cited by other.

Primary Examiner: Layno; Carl
Assistant Examiner: Oropeza; Frances P.
Attorney, Agent or Firm: McDowall; Paul H. Bauer; Steve

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Claims

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The invention claimed is:

1. An implantable medical device, comprising: a pressure sensor that generates a pressure signal as a function of a pressure in a heart, said pressure developed solely as a result of application of supra-threshold cardiac pacing therapy delivery delivered when the heart tissue is non-refractory; a pressure monitor that identifies a pressure value at a point of maximum slope in the pressure signal; means for identifying a need for increased cardiac output (CO) for a patient and providing an increase-CO signal related thereto; and a processor coupled to the means for identifying and adapted to increase the energy level of the supra-threshold pacing therapy delivered to the heart in a substantially non-linear manner in response to receipt of the increase-CO signal and as a function of the pressure value.

2. The device of claim 1, wherein the processor is further configured to generate a control signal as a function of the pressure value, wherein the pacemaker is configured to receive the control signal and adjust the energy level of pacing pulses of the supra-threshold pacing therapy as a function of the control signal.

3. The device of claim 1, wherein the amplitude of the pacing pulse delivered by the pacemaker is a function of the pressure value.

4. The device of claim 3, wherein the pulse amplitude is within a range from approximately 0.5 volts to approximately 5.0 volts.

5. The device of claim 1, wherein the pulse width of the pacing pulse delivered by the pacemaker is a function of the pressure value.

6. The device of claim 5, wherein the pulse width is within a range from approximately 0.05 ms to approximately 1.5 ms.

7. The device of claim 1, wherein the pressure sensor includes one of a capacitive absolute pressure sensor, a piezoelectric crystal transducer and a piezoresistive pressure transducer.

8. The device of claim 1, wherein the pressure monitor comprises a differentiating circuit, the differentiating circuit configured to generate a differential signal that is representative of a second derivative of the pressure signal, wherein the pressure monitor identifies the pressure value corresponding to a zero crossing point on the differential signal.

9. The device of claim 1, further comprising an input/output device coupled to the processor, the input/output device configured to exchange information between a person and the processor.

10. The device of claim 1, wherein the device is adapted to be implanted in the upper chest of a patient.

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Description

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FIELD OF THE INVENTION

The present invention relates generally to cardiac pacemakers and cardiac monitoring, and more particularly to cardiac pacemakers that work in cooperation with pressure monitors.

BACKGROUND

Heart failure refers to the heart's inability to keep up with the demands made upon it. Congestive heart failure refers to an inability of the heart to pump an adequate amount of blood to the body tissues. Because the heart is unable to pump an adequate amount of blood, blood returning to the heart becomes congested in the venous system.

In a healthy heart, the heart pumps all of the blood that returns to it, according to the Frank-Starling law. Increased venous return leads to increased end diastolic volume, which causes increased strength of contraction and increased stroke volume. In addition to intrinsic control according to the Frank-Starling law, a healthy heart is subject to extrinsic control, such as stimulation by the sympathetic nervous system to enhance contractility.

In a patient experiencing congestive heart failure, intrinsic and extrinsic control mechanisms may not function properly, and consequently the heart may fail to pump an adequate amount of blood. A condition known as cardiac decompensation is used to describe heart failure that results in a failure of adequate circulation.

Failure of the left side of the heart is generally more serious than the failure of the right side. On the left side of the heart, blood returns from the pulmonary system and is pumped to the rest of the body. When the left side of the heart fails, there are consequences to both the pulmonary system and to the rest of the body. A patient with congestive heart failure may be unable to pump enough blood forward to provide an adequate flow of blood to his kidneys, for example, causing him to retain excess water and salt. His heart may also be unable to handle the blood returning from his pulmonary system, resulting in a damming of the blood in the lungs and increasing his risk of developing pulmonary edema.

Causing more blood to be expelled from the heart, i.e., increasing cardiac output would reduce the damming of blood in the lungs and the congestion of blood in the venous system caused by heart failure. In addition to pharmacological therapies to increase cardiac output, some patients with congestive heart failure benefit from an implanted pacemaker. A pacemaker rhythmically generates pacing pulses that spread throughout the heart to drive the atria and ventricles. A typical pacemaker monitors the electrical activity of the patient's heart and provides pacing pulses to cause the heart to beat at a desired rate, such as sixty beats per minute. Because cardiac output depends in part on heart rate, increasing the pacing rate of a pacemaker has been used as a method of increasing cardiac output.

Existing methods for increasing or optimizing cardiac output may involve modulation of a variety of parameters associated with a pacing program other than the pacing rate. For example, some existing methods modulate atrial escape interval, atrioventricular (A-V) delay, sequential mode of operation, refractory period, pacing pulse energy, pulse amplitude, or pulse width, which is sometime referred to as pulse duration. The energy level of a pacing pulse is a function of several parameters, including pulse amplitude and pulse width.

For example, Nakayama, et. al., "High Output Ventricular Pacing Increased the Cardiac Output," EUR.J.C.P.E., Vol. 6, No. 1, June 1996, reported that high voltage amplitude ventricular pacing increased cardiac output as measured by Doppler echocardiogram and cardio-thoracic ratio. Cardiac output was higher when paced at high voltage amplitude, 4.2 or 5.0 volts, than at low voltage amplitude, 2.5 volts. Nakayama, et. al., concluded that the increase in cardiac output was due to the synchronous contraction of the ventricle caused by a larger field stimulation area due to high voltage pacing.

Because the condition of a patient may change between visits to a physician, and because the patients need for increased cardiac output may also vary as a result of the demand caused by the patient's activity, it is desirable to monitor the patient's need for increased cardiac output continuously. Some existing methods use implanted devices that can estimate cardiac output and control a pacemaker to modulate pacing parameters to maximize cardiac output in a feedback mechanism. For example, U.S. Pat. No. 5,891,176, issued to Bornzin, discloses measuring mixed venous oxygen saturation, blood flow, or ventricular pressure as an estimate of cardiac output, and modulating pacing parameters such as atrial escape interval, A-V delay, and sequential mode of operation to maximize mixed venous oxygen saturation, blood flow, or ventricular pressure. U.S. Pat. No. 6,314,323, issued to Elkwall, discloses integrating a measured ventricular pressure curve during systole, using the integration result as an estimate of cardiac output, and modulating pacing parameters such as A-V delay, stimulation rate, refractory period, stimulation pulse energy, duration and amplitude to maximize the integrated value. These existing methods, however, may not accurately estimate the need for increased cardiac output, or may require complicated devices and methods to estimate the need for increased cardiac output. These problems may cause less effective treatment of the symptoms of cardiac decompensation, or may increase complexity, expense, and power consumption of an implantable device.

Examples of the above referenced existing techniques and/or devices may be found in the issued U.S. Patents listed in Table 1 below.

TABLE-US-00001 TABLE 1 U.S. Pat. No. Inventor Issue Date 6,314,323 Elkwall Nov. 6, 2001 5,891,176 Bornzin Apr. 6, 1999 5,626,623 Kieval et al. May 6, 1997 5,368,040 Carney Nov. 29, 1994

All patents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the techniques of the present invention.

SUMMARY OF THE INVENTION

The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art with respect to treatment of cardiac decompensation utilizing a pacemaker. Such problems may include, for example, the inaccuracy or complexity of existing systems and methods for identifying a need for increased cardiac output and modulating pacing parameters to increase cardiac output to meet this need. It is an object of the present invention to provide a more accurate and less complicated system and method for identifying a need for increased cardiac output and modulating pacing parameters to increase cardiac output to meet this need. In particular, it is an object of the present invention to treat cardiac decompensation by modulating the energy level of pacing pulses delivered by a pacemaker with a signal based upon intra-cardiac pressures.

The present invention has certain features. In particular, various embodiments of the present invention may include a pacemaker that can deliver pacing pulses to the heart at a variety of different energy levels, and that is responsive to a control signal to modulate the energy level of pacing pulses. The energy level of a pacing pulse is a function of several parameters, including pulse amplitude and pulse width. Therefore, in some embodiments of the present invention, the energy level of pacing pulses delivered by the pacemaker may be modulated by varying, among other things, the amplitude or width of the pacing pulses.

Various embodiments of the present invention may also include a pressure sensor that detects pressure within the heart, and a pressure monitor that receives a pressure signal from the pressure sensor. In some embodiments of the present invention, the pressure monitor processes the pressure signal, and measures a pressure value that is indicative of a need for increased cardiac output. In particular, in some embodiments, the pressure monitor may differentiate a pressure signal to, for example, estimate the pressure in the right ventricle that causes the pulmonary valve to open. In some embodiments, the pressure monitor may receive pressure signals from the atria to, for example, calculate the beat-to-beat mean central venous pressure (CVP). In some embodiments, the measured pressure value is then used to cause the pacemaker to adjust the energy level parameters of pacing pulses delivered to the patient's heart.

Various embodiments of the invention, therefore, may include a processor that receives a signal from the pressure monitor that indicates the measured pressure value, and generates a control signal to control the pacemaker to adjust the energy level parameters of pacing pulses delivered to the patient's heart as a function of the measured pressure value. In some embodiments, the processor may select one or more energy level parameter values by comparing the measured pressure value to a look-up table of pressure values and associated parameter values. In other embodiments, the processor might select the energy level parameter values by applying one or more equations that relate pressure values to parameters. The look-up table or equations may be stored in memory. The look-up table or equations may, for example, be received via remote distribution link or RF telemetry.

In some embodiments, the processor may receive programming from a physician via remote distribution link, RF telemetry, or otherwise via an external programmer. In this manner, the patient's physician may customize the treatment for the patient. The patient's physician may specify, for example, suitable pacing pulse energy parameter values for particular pressures. The present invention presents techniques whereby the patient's physician can relate the pacing of the patient's heart to the monitored pressures.

In various embodiments of the present invention, the pressure monitor and processor function together to continuously monitor a pressure in a patient's heart and modulate the energy level of pacing pulses delivered to the heart by a pacemaker as a function of the pressure.

The present invention has certain advantages. That is, in comparison to known implementations for identifying a need for increased cardiac output and modulating pacing parameters to increase cardiac output to meet this need, various embodiments of the present invention may provide one or more advantages. Such advantages may include, for example, more accurate and less complex determination of need for increased cardiac output.

For example, the system and method of the present invention accurately determines whether there is a need for increased cardiac output by processing a pressure signal that represents pressure in the heart to measure a pressure value indicative of whether an increase in cardiac output is needed. By more directly and accurately measuring the symptoms of cardiac decompensation as reflected in the pressure value, the present invention more effectively treats them. Further, measuring the pressure value in accordance with the present invention requires a less complicated system and method than existing systems and methods for determining whether there is a need for increased cardiac output. Consequently, implementing the present invention requires a less expensive device that consumes less power than existing methods. Also, the system and method of the present invention effectively increase the cardiac output as needed by increasing the energy level of pacing pulses delivered to the heart by a pacemaker.

The above summary of the present invention is not intended to describe each embodiment or every embodiment of the present invention or each and every feature of the invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an implantable medical device.

FIG. 2 shows the implantable medical device located in and near a heart.

FIG. 3 is a block diagram illustrating the constituent components of an implantable medical device.

FIG. 4 shows a pacemaker-cardioverter-defibrillator located in and near a heart.

FIG. 5 is a functional schematic diagram of one embodiment of an implantable medical device.

FIG. 6 is a diagram of a system including a pressure monitor and a pacemaker.

FIG. 7 is a graph of voltage amplitude as a function of time, showing pacing pulses of varying energy levels.

FIG. 8 is a diagram of a human heart, with a pressure sensor and a lead.

FIG. 9 is a timing diagram showing an electrocardiogram signal, a signal indicative of right ventricular pressure, and the first and second derivatives of the right ventricular pressure signal.

FIG. 10 is a timing diagram showing an electrocardiogram signal and a signal indicative of the central venous pressure.

FIG. 11 is a flow diagram illustrating techniques of the invention.

FIG. 12 is a graph showing voltage amplitudes of pacing pulses as a function of an estimated pulmonary artery diastolic pressure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

FIG. 1 is a simplified schematic view of one embodiment of implantable medical device ("IMD") 10 of the present invention. IMD 10 shown in FIG. 1 is a pacemaker comprising at least one of pacing and sensing leads 16 and 18 attached to connector module 12 of hermetically sealed enclosure 14 and implanted near human or mammalian heart 8. Pacing and sensing leads 16 and 18 sense electrical signals attendant to the depolarization and repolarization of the heart 8, and further provide pacing pulses for causing depolarization of cardiac tissue in the vicinity of the distal ends thereof. The pacing pulses delivered to the heart each have a particular energy level. The energy level of a pacing pulse is a function of several parameters, including pulse amplitude and pulse width. Leads 16 and 18 may have unipolar or bipolar electrodes disposed thereon, as is well known in the art. Examples of IMD 10 include implantable cardiac pacemakers disclosed in U.S. Pat. No. 5,158,078 to Bennett et al., U.S. Pat. No. 5,312,453 to Shelton et al., or U.S. Pat. No. 5,144,949 to Olson, all hereby incorporated by reference herein, each in its respective entirety.

FIG. 2 shows connector module 12 and hermetically sealed enclosure 14 of IMD 10 located in and near human or mammalian heart 8. Atrial and ventricular pacing leads 16 and 18 extend from connector module 12 to the right atrium and ventricle, respectively, of heart 8. Atrial electrodes 20 and 21 disposed at the distal end of atrial pacing lead 16 are located in the right atrium. Ventricular electrodes 28 and 29 disposed at the distal end of ventricular pacing lead 18 are located in the right ventricle.

FIG. 3 shows a block diagram illustrating the constituent components of IMD 10 in accordance with one embodiment of the present invention, where IMD 10 is a pacemaker having a microprocessor-based architecture. IMD 10 is shown as including activity sensor or accelerometer 11, which is preferably a piezoceramic accelerometer bonded to a hybrid circuit located inside enclosure 14 (shown in FIGS. 1 and 2). Activity sensor 11 typically (although not necessarily) provides a sensor output that varies as a function of a measured parameter relating to a patient's metabolic requirements. For the sake of convenience, IMD 10 in FIG. 3 is shown with lead 18 only connected thereto. However, it is understood that similar circuitry and connections not explicitly shown in FIG. 3 apply to lead 16 (shown in FIGS. 1 and 2).

IMD 10 in FIG. 3 is most preferably programmable by means of an external programming unit (not shown in the figures). One such programmer is the commercially available Medtronic Model 9790 programmer, which is microprocessor-based and provides a series of encoded signals to IMD 10, typically through a programming head which transmits or telemeters radio-frequency (RF) encoded signals to IMD 10. Such a telemetry system is described in U.S. Pat. No. 5,312,453 to Wyborny et al., hereby incorporated by reference herein in its entirety. The programming methodology disclosed in Wyborny et al.'s '453 patent is identified herein for illustrative purposes only. Any of a number of suitable programming and telemetry methodologies known in the art may be employed so long as the desired information is transmitted to and from the pacemaker.

As shown in FIG. 3, lead 18 is coupled to node 50 in IMD 10 through input capacitor 52. Activity sensor or accelerometer 11 is most preferably attached to a hybrid circuit located inside hermetically sealed enclosure 14 of IMD 10. The output signal provided by activity sensor 11 is coupled to input/output circuit 54. Input/output circuit 54 contains analog circuits for interfacing with heart 8, activity sensor 11, antenna 56 and circuits for the application of stimulating pulses to heart 8. The rate of heart 8 is controlled by software-implemented algorithms stored within microcomputer circuit 58.

Microcomputer circuit 58 preferably comprises on-board circuit 60 and off-board circuit 62. Circuit 58 may correspond to a microcomputer circuit disclosed in U.S. Pat. No. 5,312,453 to Shelton et al., hereby incorporated by reference herein in its entirety. On-board circuit 60 preferably includes microprocessor 64, system clock circuit 66 and on-board RAM 68 and ROM 70. Off-board circuit 62 preferably comprises a RAM/ROM unit. On-board circuit 60 and off-board circuit 62 are each coupled by data communication bus 72 to digital controller/timer circuit 74. Microcomputer circuit 58 may comprise a custom integrated circuit device augmented by standard RAM/ROM components.

Electrical components shown in FIG. 3 are powered by an appropriate implantable battery power source 76 in accordance with common practice in the art. For the sake of clarity, the coupling of battery power to the various components of IMD 10 is not shown in the Figures.

Antenna 56 is connected to input/output circuit 54 to permit uplink/downlink telemetry through RF transmitter and receiver telemetry unit 78. By way of example, telemetry unit 78 may correspond to that disclosed in U.S. Pat. No. 4,566,063 issued to Thompson et al., hereby incorporated by reference herein in its entirety, or to that disclosed in the above-referenced '453 patent to Wyborny et al. It is generally preferred that the particular programming and telemetry scheme selected permit the entry and storage of cardiac rate-response parameters. The specific embodiments of antenna 56, input/output circuit 54 and telemetry unit 78 presented herein are shown for illustrative purposes only, and are not intended to limit the scope of the present invention.

Continuing to refer to FIG. 3, VREF and bias circuit 82 most preferably generates stable voltage reference and bias currents for analog circuits included in input/output circuit 54. Analog-to-digital converter (ADC) and multiplexer unit 84 digitizes analog signals and voltages to provide "real-time" telemetry intracardiac signals and battery end-of-life (EOL) replacement functions. Operating commands for controlling the timing of IMD 10 are coupled from microprocessor 64 via data bus 72 to digital controller/timer circuit 74, where digital timers and counters establish the overall escape interval of the IMD 10 as well as various refractory, blanking and other timing windows for controlling the operation of peripheral components disposed within input/output circuit 54.

Digital controller/timer circuit 74 is preferably coupled to sensing circuitry, including sense amplifier 88, peak sense and threshold measurement unit 90 and comparator/threshold detector 92. Circuit 74 is further preferably coupled to electrogram (EGM) amplifier 94 for receiving amplified and processed signals sensed by lead 18. Sense amplifier 88 amplifies sensed electrical cardiac signals and provides an amplified signal to peak sense and threshold measurement circuitry 90, which in turn provides an indication of peak sensed voltages and measured sense amplifier threshold voltages on multiple conductor signal path 67 to digital controller/timer circuit 74. An amplified sense amplifier signal is also provided to comparator/threshold detector 92. By way of example, sense amplifier 88 may correspond to that disclosed in U.S. Pat. No. 4,379,459 to Stein, hereby incorporated by reference herein in its entirety.

The electrogram signal provided by EGM amplifier 94 is employed when IMD 10 is being interrogated by an external programmer to transmit a representation of a cardiac analog electrogram. See, for example, U.S. Pat. No. 4,556,063 to Thompson et al., hereby incorporated by reference herein in its entirety.

Output pulse generator 96 provides amplified pacing stimuli to patient's heart 8 through coupling capacitor 98 in response to a pacing trigger signal provided by digital controller/timer circuit 74 each time either (a) the escape interval times out, (b) an externally transmitted pacing command is received, or (c) in response to other stored commands as is well known in the pacing art. By way of example, output pulse generator 96 may correspond generally to an output amplifier disclosed in U.S. Pat. No. 4,476,868 to Thompson, hereby incorporated by reference herein in its entirety.

As mentioned above, output pulse generator 96 provides each pacing pulse at a particular energy level. The energy level of a pacing pulse is a function of several parameters, including pulse amplitude and pulse width. As will be described below, the energy level of the pacing pulses provided by output pulse generator 96 can be varied by varying parameters such as amplitude or width of the pulses. One or more of the components of the microcomputer circuit 58 or controller/timer circuit 74 may control the amplitude and width values for the pulses to be generated by pulse generator 96.

The specific embodiments of sense amplifier 88, output pulse generator 96 and EGM amplifier 94 identified herein are presented for illustrative purposes only, and are not intended to be limiting in respect of the scope of the present invention. The specific embodiments of such circuits may not be critical to practicing some embodiments of the present invention so long as they provide means for generating a stimulating pulse and are capable of providing signals indicative of natural or stimulated contractions of heart 8.

In some preferred embodiments of the present invention, IMD 10 may operate in various non-rate-responsive modes, including, but not limited to, DDD, DDI, VVI, VOO and VVT modes. In other preferred embodiments of the present invention, IMD 10 may operate in various rate-responsive modes, including, but not limited to, DDDR, DDIR, VVIR, VOOR and VVTR modes. Some embodiments of the present invention are capable of operating in both non-rate-responsive and rate responsive modes. Moreover, in various embodiments of the present invention IMD 10 may be programmably configured to operate so that it varies the rate at which it delivers stimulating pulses to heart 8 in response to one or more selected sensor outputs being generated. Numerous pacemaker features and functions not explicitly mentioned herein may be incorporated into IMD 10 while remaining within the scope of the present invention.

The present invention is not limited in scope to single-sensor or dual-sensor pacemakers, and is not limited to IMD's comprising activity or pressure sensors only. Nor is the present invention limited in scope to single-chamber pacemakers, single-chamber leads for pacemakers or single-sensor or dual-sensor leads for pacemakers. Thus, various embodiments of the present invention may be practiced in conjunction with one or more leads or with multiple-chamber pacemakers, for example. At least some embodiments of the present invention may be applied equally well in the contexts of single-, dual-, triple- or quadruple-chamber pacemakers or other types of IMD's. See, for example, U.S. Pat. No. 5,800,465 to Thompson et al., hereby incorporated by reference herein in its entirety, as are all U.S. Patents referenced therein.

IMD 10 may also be a pacemaker-cardioverter-defibrillator ("PCD") corresponding to any of numerous commercially available implantable PCD's. Various embodiments of the present invention may be practiced in conjunction with PCD's such as those disclosed in U.S. Pat. No. 5,545,186 to Olson et al., U.S. Pat. No. 5,354,316 to Keimel, U.S. Pat. No. 5,314,430 to Bardy, U.S. Pat. No. 5,131,388 to Pless, and U.S. Pat. No. 4,821,723 to Baker et al., all hereby incorporated by reference herein, each in its respective entirety.

FIGS. 4 and 5 illustrate one embodiment of IMD 10 and a corresponding lead set of the present invention, where IMD 10 is a PCD. In FIG. 4, the ventricular lead takes the form of leads disclosed in U.S. Pat. Nos. 5,099,838 and 5,314,430 to Bardy, and includes an elongated insulative lead body 1 carrying three concentric coiled conductors separated from one another by tubular insulative sheaths. Located adjacent the distal end of lead 1 are ring electrode 2, extendable helix electrode 3 mounted retractably within insulative electrode head 4 and elongated coil electrode 5. Each of the electrodes is coupled to one of the coiled conductors within lead body 1. Electrodes 2 and 3 are employed for cardiac pacing and for sensing ventricular depolarizations. At the proximal end of the lead is bifurcated connector 6 which carries three electrical connectors, each coupled to one of the coiled conductors. Elongated coil electrode 5, which is a defibrillation electrode 5, may be fabricated from platinum, platinum alloy or other materials known to be usable in implantable defibrillation electrodes and may be about 5 cm in length.

The atrial/SVC lead shown in FIG. 4 includes elongated insulative lead body 7 carrying three concentric coiled conductors separated from one another by tubular insulative sheaths corresponding to the structure of the ventricular lead. Located adjacent the J-shaped distal end of the lead are ring electrode 9 and extendable helix electrode 13 mounted retractably within an insulative electrode head 15. Each of the electrodes is coupled to one of the coiled conductors within lead body 7. Electrodes 13 and 9 are employed for atrial pacing and for sensing atrial depolarizations. Elongated coil electrode 19 is provided proximal to electrode 9 and coupled to the third conductor within lead body 7. Electrode 19 preferably is 10 cm in length or greater and is configured to extend from the SVC toward the tricuspid valve. In one embodiment of the present invention, approximately 5 cm of the right atrium/SVC electrode is located in the right atrium with the remaining 5 cm located in the SVC. At the proximal end of the lead is bifurcated connector 17 carrying three electrical connectors, each coupled to one of the coiled conductors.

The coronary sinus lead shown in FIG. 4 assumes the form of a coronary sinus lead disclosed in the above cited '838 patent issued to Bardy, and includes elongated insulative lead body 41 carrying one coiled conductor coupled to an elongated coiled defibrillation electrode 21. Electrode 21, illustrated in broken outline in FIG. 4, is located within the coronary sinus and great vein of the heart. At the proximal end of the lead is connector plug 23 carrying an electrical connector coupled to the coiled conductor. Elongated coil defibrillation electrode 41 may be about 5 cm in length.

IMD 10 is shown in FIG. 4 in combination with leads 1, 7 and 41, and lead connector assemblies 23, 17 and 6 inserted into connector module 12. Optionally, insulation of the outward facing portion of housing 14 of IMD 10 may be provided using a plastic coating such as parylene or silicone rubber, as is employed in some unipolar cardiac pacemakers. The outward facing portion, however, may be left uninsulated or some other division between insulated and uninsulated portions may be employed. The uninsulated portion of housing 14 serves as a subcutaneous defibrillation electrode to defibrillate either the atria or ventricles. Lead configurations other that those shown in FIG. 4 may be practiced in conjunction with the present invention, such as those shown in U.S. Pat. No. 5,690,686 to Min et al., hereby incorporated by reference herein in its entirety.

FIG. 5 is a functional schematic diagram of one embodiment of IMD 10 of the present invention. This diagram should be taken as exemplary of the type of device in which various embodiments of the present invention may be embodied, and not as limiting, as it is believed that the invention may be practiced in a wide variety of device implementations, including cardioverter and defibrillators which do not provide anti-tachycardia pacing therapies.

IMD 10 is provided with an electrode system. If the electrode configuration of FIG. 4 is employed, the correspondence to the illustrated electrodes is as follows. Electrode 25 in FIG. 5 includes the uninsulated portion of the housing of IMD 10. Electrodes 25, 15, 21 and 5 are coupled to high voltage output circuit 27, which includes high voltage switches controlled by CV/defib control logic 79 via control bus 31. Switches disposed within circuit 27 determine which electrodes are employed and which electrodes are coupled to the positive and negative terminals of a capacitor bank (which includes capacitors 33 and 35) during delivery of defibrillation pulses.

Electrodes 2 and 3 are located on or in the ventricle of the patient and are coupled to the R-wave amplifier 37, which preferably takes the form of an automatic gain controlled amplifier providing an adjustable sensing threshold as a function of the measured R-wave amplitude. A signal is generated on R-out line 39 whenever the signal sensed between electrodes 2 and 3 exceeds the present sensing threshold.

Electrodes 9 and 13 are located on or in the atrium of the patient and are coupled to the P-wave amplifier 43, which preferably also takes the form of an automatic gain controlled amplifier providing an adjustable sensing threshold as a function of the measured P-wave amplitude. A signal is generated on P-out line 45 whenever the signal sensed between electrodes 9 and 13 exceeds the present sensing threshold. The general operation of R-wave and P-wave amplifiers 37 and 43 may correspond to that disclosed in U.S. Pat. No. 5,117,824 to Keimel et al., hereby incorporated by reference herein in its entirety.

Switch matrix 47 is used to select which of the available electrodes are coupled to wide band (0.5-200 Hz) amplifier 49 for use in digital signal analysis. Selection of electrodes is controlled by microprocessor 51 via data/address bus 53, which selections may be varied as desired. Signals from the electrodes selected for coupling to bandpass amplifier 49 are provided to multiplexer 55, and thereafter converted to multi-bit digital signals by A/D converter 57, for storage in random access memory 59 under control of direct memory access circuit 61. Microprocessor 51 may employ digital signal analysis techniques to characterize the digitized signals stored in random access memory 59 to recognize and classify the patient's heart rhythm employing any of the numerous signal processing methodologies known to the art.

The remainder of the circuitry is dedicated to the provision of cardiac pacing, cardioversion and defibrillation therapies, and, for purposes of the present invention may correspond to circuitry known to those skilled in the art. The following exemplary apparatus is disclosed for accomplishing pacing, cardioversion and defibrillation functions. Pacer timing/control circuitry 63 preferably includes programmable digital counters which control the basic time intervals associated with DDD, VVI, DVI, VDD, AAI, DDI and other modes of single and dual chamber pacing well known to the art. Circuitry 63 also preferably controls escape intervals associated with anti-tachyarrhythmia pacing in both the atrium and the ventricle, employing any anti-tachyarrhythmia pacing therapies known to the art.

Intervals defined by pacing circuitry 63 include atrial and ventricular pacing escape intervals, the refractory periods during which sensed P-waves and R-waves are ineffective to restart timing of the escape intervals and the pulse widths of the pacing pulses. The durations of these intervals are determined by microprocessor 51, in response to stored data in memory 59 and are communicated to pacing circuitry 63 via address/data bus 53. Pacer circuitry 63 also determines the amplitude and pulse width of the cardiac pacing pulses under control of microprocessor 51. By controlling the amplitude and pulse width, IMD 10 controls the energy level of the delivered pacing pulses.

During pacing, escape interval counters within pacer timing/control circuitry 63 are reset upon sensing of R-waves and P-waves as indicated by a signals on lines 39 and 45, and in accordance with the selected mode of pacing on time-out trigger generation of pacing pulses by pacer output circuitry 65 and 67, which are coupled to electrodes 9, 13, 2 and 3. Escape interval counters are also reset on generation of pacing pulses and thereby control the basic timing of cardiac pacing functions, including anti-tachyarrhythmia pacing. The durations of the intervals defined by escape interval timers are determined by microprocessor 51 via data/address bus 53. The value of the count present in the escape interval counters when reset by sensed R-waves and P-waves may be used to measure the durations of R-R intervals, P-P intervals, P-R intervals and R-P intervals, which measurements are stored in memory 59 and used to detect the presence of tachyarrhythmias.

Microprocessor 51 most preferably operates as an interrupt driven device, and is responsive to interrupts from pacer timing/control circuitry 63 corresponding to the occurrence of sensed P-waves and R-waves and corresponding to the generation of cardiac pacing pulses. Those interrupts are provided via data/address bus 53. Any necessary mathematical calculations to be performed by microprocessor 51 and any updating of the values or intervals controlled by pacer timing/control circuitry 63 take place following such interrupts.

Detection of atrial or ventricular tachyarrhythmias, as employed in the present invention, may correspond to tachyarrhythmia detection algorithms known in the art. For example, the presence of an atrial or ventricular tachyarrhythmia may be confirmed by detecting a sustained series of short R-R or P-P intervals of an average rate indicative of tachyarrhythmia or an unbroken series of short R-R or P-P intervals. The rate of onset of the detected high rates, the stability of the high rates, and a number of other factors known in the art may also be measured at this time. Appropriate ventricular tachyarrhythmia detection methodologies measuring such factors are described in U.S. Pat. No. 4,726,380 issued to Vollmann, U.S. Pat. No. 4,880,005 issued to Pless et al., and U.S. Pat. No. 4,830,006 issued to Haluska et al., all incorporated by reference herein, each in its respective entirety. An additional set of tachycardia recognition methodologies is disclosed in the article "Onset and Stability for Ventricular Tachyarrhythmia Detection in an Implantable Pacer-Cardioverter-Defibrillator" by Olson et al., published in Computers in Cardiology, Oct. 7-10, 1986, IEEE Computer Society Press, pages 167-170, also incorporated by reference herein in its entirety. Atrial fibrillation detection methodologies are disclosed in Published PCT Application Ser. No. US92/02829, Publication No. WO92/8198, by Adams et al., and in the article "Automatic Tachycardia Recognition," by Arzbaecher et al., published in PACE, May-June, 1984, pp. 541-547, both of which are incorporated by reference herein in their entireties.

In the event an atrial or ventricular tachyarrhythmia is detected and an anti-tachyarrhythmia pacing regimen is desired, appropriate timing intervals for controlling generation of anti-tachyarrhythmia pacing therapies are loaded from microprocessor 51 into the pacer timing and control circuitry 63, to control the operation of the escape interval counters therein and to define refractory periods during which detection of R-waves and P-waves is ineffective to restart the escape interval counters.

Alternatively, circuitry for controlling the timing and generation of anti-tachycardia pacing pulses as described in U.S. Pat. No. 4,577,633, issued to Berkovits et al., U.S. Pat. No. 4,880,005, issued to Pless et al., U.S. Pat. No. 4,726,380, issued to Vollmann et al., and U.S. Pat. No. 4,587,970, issued to Holley et al., all of which are incorporated herein by reference in their entireties, may also be employed.

In the event that generation of a cardioversion or defibrillation pulse is required, microprocessor 51 may employ an escape interval counter to control timing of such cardioversion and defibrillation pulses, as well as associated refractory periods. In response to the detection of atrial or ventricular fibrillation or tachyarrhythmia requiring a cardioversion pulse, microprocessor 51 activates cardioversion/defibrillation control circuitry 79, which initiates charging of high voltage capacitors 33 and 35 via charging circuit 69, under the control of high voltage charging control line 71. The voltage on the high voltage capacitors is monitored via VCAP line 73, which is passed through multiplexer 55 and in response to reaching a predetermined value set by microprocessor 51, results in generation of a logic signal on Cap Full (CF) line 77 to terminate charging. Thereafter, timing of the delivery of the defibrillation or cardioversion pulse is controlled by pacer timing/control circuitry 63. Following delivery of the fibrillation or tachycardia therapy microprocessor 51 returns the device to cardiac pacing mode and awaits the next successive interrupt due to pacing or the occurrence of a sensed atrial or ventricular depolarization.

Several embodiments of appropriate systems for the delivery and synchronization of ventricular cardioversion and defibrillation pulses and for controlling the timing functions related to them are disclosed in U.S. Pat. No. 5,188,105 to Keimel, U.S. Pat. No. 5,269,298 to Adams et al., and U.S. Pat. No. 4,316,472 to Mirowski et al., hereby incorporated by reference herein, each in its respective entirety. Any known cardioversion or defibrillation pulse control circuitry is believed to be usable in conjunction with various embodiments of the present invention, however. For example, circuitry controlling the timing and generation of cardioversion and defibrillation pulses such as that disclosed in U.S. Pat. No. 4,384,585 to Zipes, U.S. Pat. No. 4,949,719 to Pless et al., or U.S. Pat. No. 4,375,817 to Engle et al., all hereby incorporated by reference herein in their entireties, may also be employed.

Continuing to refer to FIG. 5, delivery of cardioversion or defibrillation pulses is accomplished by output circuit 27 under the control of control circuitry 79 via control bus 31. Output circuit 27 determines whether a monophasic or biphasic pulse is delivered, the polarity of the electrodes and which electrodes are involved in delivery of the pulse. Output circuit 27 also includes high voltage switches which control whether electrodes are coupled together during delivery of the pulse. Alternatively, electrodes intended to be coupled together during the pulse may simply be permanently coupled to one another, either exterior to or interior of the device housing, and polarity may similarly be pre-set, as in current implantable defibrillators. An example of output circuitry for delivery of biphasic pulse regimens to multiple electrode systems may be found in the above-cited patent issued to Mehra and in U.S. Pat. No. 4,727,877 to Kallok, hereby incorporated by reference herein in its entirety.

An example of circuitry which may be used to control delivery of monophasic pulses is disclosed in U.S. Pat. No. 5,163,427 to Keimel, also incorporated by reference herein in its entirety. Output control circuitry similar to that disclosed in U.S. Pat. No. 4,953,551 to Mehra et al. or U.S. Pat. No. 4,800,883 to Winstrom, both incorporated by reference herein in their entireties, may also be used in conjunction with various embodiments of the present invention to deliver biphasic pulses.

Alternatively, IMD 10 may be an implantable nerve stimulator or muscle stimulator such as that disclosed in U.S. Pat. No. 5,199,428 to Obel et al., U.S. Pat. No. 5,207,218 to Carpentier et al., or U.S. Pat. No. 5,330,507 to Schwartz, or an implantable monitoring device such as that disclosed in U.S. Pat. No. 5,331,966 issued to Bennet et al., all of which are hereby incorporated by reference herein, each in its respective entirety. The present invention is believed to find wide application to any form of implantable electrical device for use in conjunction with electrical leads.

FIG. 6 shows a system 100 illustrating an embodiment of the invention in which pressure is used to modulate the energy level of pacing pulses delivered by a pacemaker. System 100, or any of its constituent components, could be implanted in a human being or a mammal. System 100 includes pacemaker 114, which paces heart 8. Pacemaker 114 is coupled to atrial lead 116 and ventricular lead 120. Electrodes 118 and 122 disposed on leads 116 and 120 may serve to sense electrical signals and to pace heart 8. Pacemaker 114 may further be coupled to lead 124, which includes defibrillation coil electrode 126. Alternatively, defibrillation coil electrode 126 may be coupled to lead 116 or 120. Pacemaker 114 may be one of the many forms of implantable medical devices 10 described above, or may be an external pacemaker. Atrial electrode 118 may correspond to any of electrodes 9, 13, 20 or 21 described above, ventricular electrode 122 may correspond to any of electrodes 2, 3, 28 and 29 described above, and defibrillation coil electrode 126 may correspond to elongated coil electrode 5 described above.

Pacemaker 114 can deliver pacing pulses to the heart 8 via electrodes 118 and 122 at a variety of different energy levels. The energy level of a pacing pulse is, in part, a function of the pulse amplitude and pulse width. Therefore, in some embodiments of the present invention, the energy level of pacing pulses delivered by pacemaker 114 may be changed by varying, among other things, the amplitude or width of the pacing pulses.

Many commercially available pacemakers can produce pulses with amplitudes within the range from 0.5 to 5.0 volts, and widths within the range from 0.05 to 1.5 ms. Some pacemakers can produce pulses with amplitudes as high as 10 volts and widths as wide as 2.0 ms. The size of the amplitude and width ranges of pacemaker 114 are less important to the practice of the present invention, and may be subject to variation, so long as there is some amplitude or width range within which the pacing pulse energy level may be varied for effectiveness.

FIG. 7 shows examples of three pacing pulses, 140, 142 and 144, that might be delivered by pacemaker 114. FIG. 7 is provided to further illustrate that the energy level of a pacing pulse can be varied in at least two ways in accordance with the present invention. Both pulses, 142 and 144, have a higher energy level than pulse 140. Pulse 142 delivers more energy to the heart 8 than pulse 140 because of a greater amplitude. Pulse 144 delivers more energy to the heart 8 than pulse 140 because of a greater pulse width.

Pacemaker 114 may also include a microcomputer circuit 58, controller/timer circuit 74, microprocessor 51, pacer timing and control circuit 63, or an equivalent device that may control the amplitude, pulse width and other energy parameters of the pulses to be delivered to heart 8. The microcomputer circuit 58, controller/timer circuit 74, microprocessor 51, pacer timing and control circuit 63, or other device can receive control signals, signals from other components and/or programming, and set the amplitude, pulse width and other parameters accordingly.

The present invention presents techniques for adjusting the energy level of pacing pulses based on the pressure of the blood flowing inside the patient's heart 8. System 100, as shown in FIG. 6, includes pressure monitor 102, which is coupled to pressure sensor 106 by lead 104. Pressure sensor 106 responds to the absolute pressure inside heart 8.

FIG. 8 is a diagram of a human heart, including a pressure sensor and a lead. Pressure sensor 106 may, as shown in FIG. 8, be placed inside right ventricle 152 of heart 8. Sensor 106 is coupled to lead 104, which extends from right ventricle 152, through right atrioventricular valve 164, and through superior vena cava 176. Lead 104 extends further through the patient's circulatory system, eventually exiting the circulatory system and coupling to implanted pressure monitor 102 (not shown in FIG. 8). Pressure monitor 102 may be implanted in the patient's upper chest near pacemaker 114, or in the patient's abdomen. Alternatively, pressure monitor 102, processor 110 and pacemaker 114 may form a single device implanted in the patient's upper chest.

Sensor 106 may generate pressure signals itself or may modulate pressure signals conducted through lead 104 along wires 172 and 174. The pressure signals are a function of the fluid pressure in right ventricle 152. Pressure monitor 102 receives, monitors and analyzes the pressure signals, as will be described in more detail below. An example of pressure monitor 102 that may be used with this embodiment of the present invention is the Chronicle.TM. Implantable Hemodynamic Monitor manufactured by and commercially available from Medtronic, Inc.

Pressure sensor 106 may be one of many forms of pressure sensors. One form of pressure sensor that is useful for measuring blood pressure inside a human heart is a capacitive absolute pressure sensor, as described in U.S. Pat. No. 5,564,434 to Halperin, et al., hereby incorporated by reference herein in its entirety. Pressure sensor 106 may also be a piezoelectric crystal or piezoresistive pressure transducer. The invention is not limited to any particular kind of pressure sensor.

As will be described below, pressure monitor 102 processes the pressure signals received from pressure sensor 106. Pressure monitor 102 may, in some embodiments, identify or calculate a pressure value that is of significance in patient monitoring. As shown in FIG. 6, processor 110 receives a signal 108 from pressure monitor 102. Signal 108 may indicate the pressure value identified or calculated by pressure monitor 102.

Processor 110 may select a value for one or more pacing pulse energy parameters, such as pulse amplitude and width, as a function of signal 108. If signal 108 indicates a pressure value, processor 110 may select the parameter values by comparing the pressure value to a look-up table of pressure values and associated parameter values. As an alternative, processor 110 may select the parameter values by applying equations that relate pressure values to the parameters. The look-up table or equations may be stored in memory 132. The look-up table or equations may, for example, be received via remote distribution link 128, RF telemetry 130, or from an external programmer.

Processor 110 may, as shown in FIG. 6, generate a control signal 112. Based on control signal 112, processor 110 may control pacemaker 114 to adjust the value of one or more pacing pulse energy param