Source: http://www.google.com/patents/US6615083?dq=4168396
Timestamp: 2014-03-15 13:33:33
Document Index: 796665706

Matched Legal Cases: ['art 8', 'art 8', 'art 8', 'art 8', 'art 8', 'art 8']

Patent US6615083 - Implantable medical device system with sensor for hemodynamic stability and ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsAn implantable medical device system for regulating a heart of a patient. The system includes a first sensor, a second sensor, a processor, and a medical device. The first sensor is capable of sensing activity of a heart atrium. The second sensor is capable of sensing activity of a heart ventricle. The...http://www.google.com/patents/US6615083?utm_source=gb-gplus-sharePatent US6615083 - Implantable medical device system with sensor for hemodynamic stability and method of useAdvanced Patent SearchPublication numberUS6615083 B2Publication typeGrantApplication numberUS 09/842,877Publication dateSep 2, 2003Filing dateApr 27, 2001Priority dateApr 27, 2001Fee statusPaidAlso published asUS20030014083Publication number09842877, 842877, US 6615083 B2, US 6615083B2, US-B2-6615083, US6615083 B2, US6615083B2InventorsBernhard K�pperOriginal AssigneeMedtronic, Inc.Export CitationBiBTeX, EndNote, RefManPatent Citations (10), Referenced by (22), Classifications (7), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetImplantable medical device system with sensor for hemodynamic stability and method of useUS 6615083 B2Abstract An implantable medical device system for regulating a heart of a patient. The system includes a first sensor, a second sensor, a processor, and a medical device. The first sensor is capable of sensing activity of a heart atrium. The second sensor is capable of sensing activity of a heart ventricle. The processor is coupled to the first and second sensors and is capable of determining an atrial cycle time and a ventricular cycle time based upon signals from the first and second sensors. The processor is further capable of generating a hemodynamic baseline ratio based upon an atrial cycle time and a ventricular cycle time of a hemodynamic heartbeat, as well as an active ratio based upon an atrial cycle time and a ventricular cycle time of an active heartbeat. The processor is further capable of comparing the hemodynamic baseline ratio and the active ratio, and determining a corrective action based upon this comparison. The medical device is capable of supplying a therapy to the heart and is coupled to the processor. With this configuration, the processor is configured to control desired operation of the medical device based upon the determined corrective action.
What is claimed: 1. A system for evaluating functioning of a heart of a patient in conjunction with an implantable medical device, the system comprising:
a first sensor capable of sensing activity of a heart atrium; a second sensor capable of sensing activity of a heart ventricle; and a processor coupled to the first and second sensors, the processor configured for: determining an atrial cycle time and a ventricular cycle time for a heartbeat based upon signals from the first and second sensors, generating an active ratio based upon atrial cycle time and ventricular cycle time of an active heartbeat, comparing the active ratio to a hemodynamic baseline ratio, evaluating functioning of the heart based upon the comparison. 2. The system of claim 1, wherein the processor is further capable of establishing the hemodynamic baseline ratio based upon an atrial cycle time and a ventricular cycle time of a hemodynamic heartbeat.
3. The system of claim 2, wherein the processor is capable of analyzing a plurality of preliminary ratios, each based upon an atrial cycle time and a ventricular cycle time of a respective preliminary heartbeat, to establish the hemodynamic baseline ratio.
4. The system of claim 1, wherein the active ratio is atrial cycle time/ventricular cycle time for the active heartbeat.
5. The system of claim 1, wherein the processor is capable of determining an atrial depolarization period and an atrial repolarization period for the active heartbeat.
6. The system of claim 1, wherein the processor is capable of determining a ventricular depolarization period and a ventricular repolarization period for the active heartbeat.
7. The system of claim 1, wherein the processor is capable of determining a corrective therapy for the patient based upon the comparison of the active ratio and the hemodynamic baseline ratio.
8. The system of claim 1, wherein the processor is capable of generating a trend based upon a plurality of active ratios in comparison to the hemodynamic baseline ratio, and evaluating functioning of the heart based upon the trend.
9. An implantable medical device system for regulating a heart of a patient, the system comprising:
a first sensor capable of sensing activity of a heart atrium; a second sensor capable of sensing activity of a heart ventricle; a processor coupled to the first and second sensors, the processor configured for: determining an atrial cycle time and a ventricular cycle time based upon signals from the first and second sensors, generating a hemodynamic baseline ratio based upon an atrial cycle time and a ventricular cycle time of a hemodynamic heartbeat, generating an active ratio based upon an atrial cycle time and a ventricular cycle time of an active heart beat, comparing the hemodynamic baseline ratio and the active ratio, determining a corrective action based upon the comparison of the hemodynamic baseline ratio and the active ratio; and a medical device capable of delivering a therapy to the patient and coupled to the processor; wherein the processor is configured to prompt desired activation of the medical device based upon the determined corrective action. 10. The system of claim 9, wherein the medical device is a pacemaker.
11. The system of claim 10, wherein the pacemaker is a dual chamber pacemaker.
12. The system of claim 11, wherein the dual chamber pacemaker contains the processor.
13. The system of claim 9, wherein the medical device is a defibrillator.
14. The system of claim 9, wherein the medical device is a drug delivery system.
15. The system of claim 9, wherein the first sensor is a PT sensor.
16. The system of claim 9, wherein the second sensor is a QT sensor.
17. The system of claim 9, wherein the processor is a microprocessor.
18. The system of claim 9, wherein the hemodynamic baseline ratio is a ratio of atrial cycle time/ventricular cycle time of a hemodynamic heartbeat.
19. The system of claim 9, wherein the active ratio is a ratio of atrial cycle time/ventricular cycle time of an active heartbeat.
20. The system of claim 9, wherein the processor is capable of determining an atrial repolarization period, the atrial repolarization period being part of the atrial cycle time.
21. The system of claim 20, wherein the processor is further capable of determining an atrial depolarization period, the atrial depolarization period being part of the atrial cycle time.
22. The system of claim 9, wherein the processor is capable of determining a ventricular depolarization period, the ventricular depolarization period being part of the ventricular cycle time.
23. The system of claim 22, wherein the processor is capable of determining a ventricular repolarization period, the ventricular repolarization period being part of the ventricular cycle time.
24. The system of claim 9, wherein the processor is configured to perform digital signal processing.
25. The system of claim 9, wherein the processor is capable of predicting an arrhythmia based upon the comparison of the hemodynamic baseline ratio and the active ratio.
26. The system of claim 9, wherein the processor includes an algorithm for operating upon the comparison of the hemodynamic baseline ratio and the active ratio.
27. The system of claim 9, wherein the processor is capable of recording a plurality of active ratios each based upon atrial cycle times and ventricular cycle times of a plurality of heartbeats, respectively.
28. The system of claim 27, wherein the processor is capable of establishing an active ratio trend based upon the plurality of active ratios.
29. The system of claim 28, wherein the processor is capable of comparing the active ratio trend with the hemodynamic baseline ratio and determining a corresponding corrective action.
30. An implantable medical device system for regulating a heart of a patient, the system comprising:
first sensing means for sensing an atrial cycle time of a heartbeat; second sensing means for sensing a ventricular cycle time of a heartbeat; processing means for generating an active ratio based upon the sensed atrial cycle time and the sensed ventricular cycle time of an active heartbeat; comparing means for comparing the active ratio to a hemodynamic baseline ratio; analyzing means for determining a corrective action based upon a comparison of the active ratio and the hemodynamic baseline ratio; and heart therapy means for delivering a therapy to the patient based upon the determined corrective action. 31. The system of claim 30, wherein the heart therapy means comprises means for delivering electrical stimulation to the patient.
32. The system of claim 30, wherein the heart therapy means comprises means for delivering a drug to the patient.
33. The system of claim 30, wherein the first sensing means includes means for sensing an atrial repolarization period of a heartbeat.
34. The system of claim 33, wherein the first sensing means includes means for sensing an atrial depolarization period of a heartbeat.
35. The system of claim 34, wherein the first sensing means includes a PT sensor.
36. The system of claim 30, wherein the second sensing means includes means for sensing a ventricular depolarization period of a heartbeat.
37. The system of claim 36, wherein the second sensing means includes means for sensing a ventricular repolarization period of a heartbeat.
38. The system of claim 37, wherein the second sensing means includes a QT sensor.
39. The system of claim 30, wherein the first sensing means and the second sensing means include digital signal processing means.
40. The system of claim 30, wherein the analyzing means includes a microprocessor and an algorithm for evaluating the comparison of the active ratio and the hemodynamic baseline ratio.
41. The system of claim 38, further comprising:
determining means for determining the hemodynamic baseline ratio. 42. The system of claim 41, wherein the determining means includes means for establishing an atrial cycle time and a ventricular cycle time of a hemodynamic heartbeat.
43. The system of claim 42, wherein the determining means processes information from the first and second sensing means to determine the hemodynamic baseline ratio.
44. The system of claim 43, wherein the determining means includes means for analyzing a plurality of preliminary ratios each based upon a preliminary atrial cycle time and a preliminary ventricular cycle time for respective preliminary heartbeats.
45. The system of claim 30, wherein the active ratio is sensed atrial cycle time/sensed ventricular cycle time.
46. The system of claim 30, further comprising:
recording means for recording a plurality of active ratios. 47. The system of claim 46, further comprising:
correlating means for correlating the plurality of active ratios in comparison to the hemodynamic baseline ratio. 48. A method for applying therapy with an implantable medical device to a heart of a patient, the method comprising:
sensing an atrial cycle time for a first heartbeat; sensing a ventricular cycle time for the first heartbeat; generating an active ratio for the first heartbeat based upon the sensed atrial cycle time and the sensed ventricular cycle time; comparing the active ratio to a hemodynamic baseline ratio; determining a corrective action based upon the comparison; and applying a therapy to the heart to effectuate the determined corrective action. 49. The method of claim 48, wherein sensing an atrial cycle time includes sensing an atrial repolarization period for the first heartbeat.
50. The method of claim 49, wherein sensing the atrial repolarization period includes digitizing an ECG signal for the first heartbeat.
51. The method of claim 49, wherein sensing the atrial cycle time further includes sensing an atrial depolarization period for the first heartbeat.
52. The method of claim 51, wherein sensing the atrial cycle time includes determining a time period from initiation of the atrial depolarization period to termination of the atrial repolarization period.
53. The method of claim 48, wherein sensing a ventricular cycle time includes sensing a ventricular depolarization period for the first heartbeat.
54. The method of claim 53, wherein sensing a ventricular cycle time further includes sensing a ventricular repolarization period for the first heartbeat.
55. The method of claim 54, wherein sensing the ventricular cycle time includes determining a time period from initiation of the ventricular depolarization period to termination of the ventricular repolarization period.
56. The method of claim 48, wherein generating an active ratio includes determining a ratio of atrial cycle time/ventricular cycle time for the first heartbeat.
establishing the hemodynamic baseline ratio. 58. The method of claim 57, wherein establishing the hemodynamic baseline ratio includes:
determining an atrial cycle time for a hemodynamic heartbeat; and determining a ventricular cycle time for a hemodynamic heartbeat. 59. The method of claim 58, wherein determining an atrial cycle time for a hemodynamic heartbeat includes determining an atrial repolarization period for a hemodynamic heartbeat.
60. The method of claim 58, wherein establishing the hemodynamic baseline ratio further includes:
determining a ratio of atrial cycle time/ventricular cycle time for a hemodynamic heartbeat. 61. The method of claim 58, wherein establishing the hemodynamic baseline ratio further includes:
monitoring a plurality of preliminary heartbeats; determining an atrial cycle time for each of the preliminary heartbeats; determining a ventricular cycle time for each of the preliminary heartbeats; determining a preliminary ratio for each of the preliminary heartbeats, wherein each preliminary ratio is based upon the respective atrial and ventricular cycle times of the preliminary heartbeats; and correlating the preliminary ratios to establish the hemodynamic baseline ratio. 62. The method of claim 57, wherein the hemodynamic baseline ratio is a predetermined value.
63. The method of claim 48, wherein comparing the active ratio to the hemodynamic baseline ratio includes identifying an instability in an atrium of the patient.
64. The method of claim 48, wherein comparing the active ratio to a hemodynamic baseline ratio includes identifying an instability in a ventricle of the patient.
65. The method of claim 48, wherein comparing the active ratio to the hemodynamic baseline ratio includes identifying onset of an arrhythmia.
66. The method of claim 48, further comprising determining a plurality of active ratios based upon atrial cycle time and ventricular cycle time for a plurality of heartbeats, respectively.
67. The method of claim 66, further comprising formulating an activity trend for the heart based upon the plurality of active ratios.
68. The method of claim 67, further comprising determining an optimal lower rate limit for the heart based upon the activity trend.
69. The method of claim 48, wherein applying a therapy to the heart includes delivering an electrical stimulation to the patient.
70. The method of claim 48, wherein applying a therapy to the heart includes delivering a drug to the patient.
FIELD OF THE INVENTION The present invention relates generally to a system and method used in conjunction with an implantable medical device. More particularly, the present invention relates to a system and method for controlling an implantable medical device based upon sensed information indicative of hemodynamic stability.
BACKGROUND OF THE INVENTION Cardiac disease affects millions of people throughout the world. Cardiac disease may cause the excitatory and conductive systems of the heart to fail, resulting in an abnormal cardiac rhythm, usually referred to as arrhythmia. Some arrhythmias are very dangerous, and may lead to death of the patient. Other arrhythmias may be the origin of less threatening conditions, but for which medical treatment is nevertheless required. One of the possible treatments for patients suffering from arrhythmia is assistance by an implantable medical device (IMD).
Modern IMDs, such as pacemakers or defibrillators, are complicated electronic devices generally configured to deliver an electrical stimulation to the patient's heart. Alternatively, the IMD can be a drug delivery device, providing controlled distribution of an appropriate drug therapy. Regardless, IMDs are capable of providing assistance on demand, i.e., when the excitatory and conductive systems of the heart fail to operate normally. In order to accommodate specific patient needs, an IMD is normally part of an overall system that constantly monitors heart activity such that the resulting delivered therapy is optimal for the patient.
Overall IMD systems known in the art comprise several components, including the IMD, pacing and/or sensing leads, and a processor. For most applications, the IMD system is pre-programmed to effectuate a desired therapy routine. Often times, it is extremely useful to utilize feedback information from the patient's heart to alter and optimize the therapy routine. To this end, the sensing leads are available for sensing certain cardiac parameters and providing information relating to functioning of the heart, usually on a beat-by-beat basis. The processor analyzes these sensed activities and, based upon appropriate algorithms, determines an optimal therapy, both short-term and long-term. For most pacing applications, two sensing leads are typically provided, one deployed in a heart atrium and the other in a heart ventricle. With this arrangement, an electrocardiogram (ECG) signal is sensed and analyzed. As is well known, the ECG signal provides information indicative of atrial depolarization (P-wave), ventricular depolarization (QRS-wave), and ventricular repolarization (T-wave). Numerous efforts have been made to distinguish the various waves from one another, as well as to classify whether individual wave components indicate heart abnormalities.
For example, previous efforts have been made to utilize ventricular repolarization (ventricular T-wave) information to control a rate response, AV delay, and to predict arrhythmias. Examples of such applications are provided in Table 1 below:
5,330,511
4,228,803
All patents listed in Table 1 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 teachings of the present invention.
Noticeably absent from prior cardiac sensing and analyzing systems is information relating to atrial repolarization (atrial T-wave or atrial PT-wave). Due to the relatively small electrical activity associated with atrial repolarization and because atrial repolarization occurs during the predominant ventricular depolarization, it has previously been assumed that atrial repolarization is impossible to sense, as evidenced by the patents listed in Table 2.
5,772,604
Jun. 20, 1998
5,514,164
5,507,783
5,476,487
5,228,438
All patents listed in Table 2 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 2 may be modified advantageously by using the teachings of the present invention.
More recently, the ability to sense atrial repolarization has become possible. In particular, the advent of digital signal processing (DSP) has provided a tool that can be employed to effectively sense atrial repolarization. In this regard, Wolgemuth, U.S. Pat. No. 6,029,087, issued Feb. 22, 2000, the teachings of which are incorporated herein by reference, describes in detail DSP solution for sensing, processing, and classifying intracardiac signals so as to provide the IMD with reliable cardiac event data via DSP technology. Through the event classification based upon DSP information described by Wolgemuth, atrial repolarization, and thus total atrial cycle time for a heartbeat can now be sensed.
One disadvantage of prior art systems, including those listed in Tables 1 and 2 above, relates to the inability to utilize atrial repolarization information in controlling and/or optimally setting a specific IMD implanted in a specific patient. Therefore, there is a continuing need for a system and method that evaluates cardiac functioning utilizing atrial repolarization information for optimizing IMD therapy.
SUMMARY OF THE INVENTION The present invention overcomes the disadvantages of the prior art by providing a method of, and a system for, controlling an IMD based upon atrial cycle time, including atrial repolarization, information.
The present invention has certain objects. That is, the present invention provides solutions to certain problems existing in the prior art such as: (a) an inability to utilize the atrial repolarization portion of a cardiac signal to evaluate functioning of a heart; (b) an inability to utilize the atrial repolarization portion of a cardiac signal to control an implantable medical device; (c) an inability to predict short-term deviations from a hemodynamic situation; (d) an inability to control an implantable medical device to correct short-term deviations from a hemodynamic situation; (e) an inability to predict long-term deviations from a hemodynamic situation; (f) an inability to control an implantable medical device to correct long-term deviations from a hemodynamic situation; (g) an inability to evaluate heart operation based upon a correlation between atrial cycle time, including atrial repolarization, relative to ventricular cycle time; (h) an inability to control an implantable medical device based upon a correlation between atrial cycle time, including atrial repolarization, relative to ventricular cycle time.
The system and method of the present invention provides certain advantages including: (a) the ability to utilize the atrial repolarization portion of a cardiac signal to evaluate functioning of a heart; (b) the ability to utilize the atrial repolarization portion of a cardiac signal to control an implantable medical device; (c) the ability to predict short-term deviations from a hemodynamic situation; (d) the ability to control an implantable medical device to correct short-term deviations from a hemodynamic situation; (e) the ability to predict long-term deviations from a hemodynamic situation; (f) the ability to control an implantable medical device to correct long-term deviations from a hemodynamic situation; (g) the ability to evaluate heart operation based upon a correlation between atrial cycle time, including atrial repolarization, relative to ventricular cycle time; (h) the ability to control an implantable medical device based upon a correlation between atrial cycle time, including atrial repolarization, relative to ventricular cycle time.
The system and method of the present invention has certain features, including sensing atrial cycle time and ventricular cycle time for a particular heartbeat. The atrial cycle time includes the atrial repolarization period. A hemodynamic baseline ratio is generated based upon the atrial cycle time and the ventricular cycle time of an electrical heartbeat representing the hemodynamical cycle time of a heartbeat. Also, an active ratio is generated based upon an atrial cycle time and a ventricular cycle time of an active heartbeat. By comparing the hemodynamic baseline ratio and the active ratio, a corrective action can be determined. In this regard, a medical device is controlled to effectuate the determined corrective action. Essentially, then, electrical signals provided by the heart are sensed and then linked or correlated to a hemodynamical situation that results from the electromechanical coupling in each chamber of the heart.
FIG. 6 is an example of an enlarged electrocardiogram from a patient in a normal sinus rhythm.
FIG. 7 is a block diagram of an implantable medical device system in accordance with the present invention.
FIG. 8 is a flow chart illustrating a method of controlling an IMD in accordance with the present invention.
FIG. 9 is a flow chart illustrating establishing a hemodynamic baseline ratio in accordance with the present invention.
FIGS. 10A-10D are illustrative results of cardiac signal analyses performed in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a simplified schematic view of one embodiment of implantable medical device (�IMD�) 10 forming part of an implantable medical device system in accordance with 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 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 re-polarization of the heart 8, and further provide pacing pulses for causing depolarization of cardiac tissue in the vicinity of the distal ends thereof. 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 header 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 at the distal end of ventricular pacing lead 18 are located in the right ventricle. The leads 16, 18 can be tissue connected leads, floating leads, or a combination of tissue connected leads and floating leads.
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. In addition, microcomputer circuit 58 (or input/output circuit 54) preferably incorporates digital signal processing (DSP) technology, such as that described in U.S. Pat. No. 6,029,087 to Wolgemuth, the teachings of which are incorporated herein by reference.
The specific embodiments of input amplifier 88, output amplifier 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. More particularly, and as described in greater detail below, the sensed electrogram signal can be analyzed, via DSP technology, to determine atrial depolarization, atrial repolarization, ventricular depolarization, and ventricular repolarization.
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, ID 10 may operate in various rate-responsive, 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 only 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.
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 that carries three electrical connectors, each coupled to one of the coiled conductors. 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.
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 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. In addition, microprocessor 51 is capable of determining atrial repolarization (PT-wave) and ventricular repolarization (RT-wave or QT-wave).
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 29, which initiates charging of the 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 q cardiac pacing mode and awaits the next successive interrupt due to pacing or the occurrence of a sensed atrial or ventricular depolarization.
Continuing to refer to FIG. 5, delivery of cardioversion or defibrillation pulses is accomplished by output circuit 27 under the control of control circuitry 29 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 that 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, hereby incorporated by reference herein in its entirety.
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. Even further, IMD 10 can be a drug delivery system, as known in the art. The present invention is believed to find wide application to any form of implantable heart therapy device for use in conjunction with electrical leads.
The system and method of the present invention utilizes atrial cycle time to evaluate heart activity and determine appropriate corrective actions and/or therapies. In this regard FIG. 6 illustrates a typical surface electrocardiogram (ECG) wave form for a normal sinus rhythm or heartbeat and is characterized by a P-wave, corresponding with atrial depolarization and contraction of the atria, followed by the QRS complex (QRS-wave or R-wave) that corresponds generally with depolarization and contraction of the ventricles. A T-wave follows the QRS complex and corresponds with ventricular repolarization.
With the availability of DSP, it is now possible to effectively sense the atrial repolarization period, otherwise �hidden� within the QRS complex. FIG. 6 illustrates the initiation and termination of each depolarization and repolarization event during a cardiac cycle relative to the ECG waveform. Notably, while FIG. 6 relates to a surface ECG wave, the system and method of the present invention will preferably utilize intracardial signals to ascertain various components of the cardiac cycle. As is well known, these intracardial signals appear quite different from a surface ECG wave. However, the surface ECG wave conveniently illustrates the various cardiac cycle components being acted upon by the system and method of the present invention, such that FIG. 6 is provided to most clearly describe the present invention.
With the above explanation in mind, the time period of atrial depolarization (or P-wave) is illustrated as �a�, whereas the time period of atrial repolarization (PT-wave) is designated at �b�. Taken in combination, the total atrial cycle time is denoted as �c�, and reflects the time period from initiation of atrial depolarization a to termination of atrial repolarization b. Similarly, the ventricular depolarization period (QRS-wave or R-wave) is designated as �d�, whereas the ventricular repolarization period (T-wave or QT-wave) is designated as �e�. Taken in combination, the total ventricular cycle time is designated as �f�, and represents a time period from initiation of ventricular depolarization d to termination of ventricular repolarization e.
With the above designations in mind, the system and method of the present invention makes use of a correlation between total atrial cycle time c and total ventricular cycle time f to evaluate functioning of a patient's heart. In particular, and in a preferred embodiment, a processor, such as the microcomputer circuit 58 previously described with respect to FIG. 3, determines a ratio of atrial cycle time/ventricular cycle time, and then compares the ratio or resulting value relative to a hemodynamic baseline ratio or value. In general terms, the sensed and determined ratio will, according to the Frank-Starling Law remains stable so long as the heart remains in a stable situation. A change in the sensed ratio relative to the hemodynamic baseline ratio is indicative of abnormal cardiac activity.
With the above in mind, FIG. 7 illustrates in block form an IMD system 100 in accordance with the present invention. The system 100 includes an IMD 102, a processor 104, an atrium sensor 106, and a ventricle sensor 108. The IMD 102 can assume any of the forms previously described, such as a pacemaker, defibrillator, drug delivery system, etc. In one preferred embodiment, the IMD 102 is a dual chamber pacemaker. Similarly, the processor 104 can assume any of the forms previously described, and is preferably a microprocessor incorporating DSP technology. Finally, the atrium sensor 106 and the ventricle sensor 108 are also of types known in the art and previously described. In a preferred embodiment, the sensors 106, 108 are capable of sensing activity of a heart atrium and a heart ventricle, respectively. Taken in combination, the processor 104 is electrically coupled to the sensors 106, 108, and is configured to control the IMD 102. In a preferred embodiment, at least one of the sensors 106, 108 is a QT sensor available from Medtronic, Inc. The processor 104 is capable of determining an atrial cycle time and a ventricular cycle time based upon signals from the atrium sensor 106 and the ventricle sensor 108. As described in greater detail below, the processor 104 is further capable of generating a hemodynamic baseline ratio based upon an atrial cycle time and a ventricular cycle time of a hemodynamic heartbeat, as well as generating an active ratio based upon an atrial cycle time and a ventricular cycle time of an active heartbeat. The processor 104 is further capable of comparing the hemodynamic baseline ratio and the active ratio, and determining a necessary corrective action based upon this comparison. Finally, the processor 104 is capable of prompting and controlling the IMD 102 to effectuate the determined corrective action.
With further reference to the flow diagram of FIG. 8, operation of the system 100 begins at step 120 at which a hemodynamic baseline ratio is established. In a preferred embodiment, the hemodynamic baseline ratio is calculated according to the following equation: Atrial��Cycle��Time��for��Hemodynamic��Heartbeat Ventricular��Cycle��Time��for��Hemodynamic��Heartbeat The hemodynamic baseline ratio can be a predetermined value programmed by a user into the processor 104. Alternatively, as described in greater detail below, the processor 104 can establish the hemodynamic baseline ratio by analyzing a series of heartbeats.
Regardless of how the hemodynamic baseline ratio is established, at step 122, a cardiac signal associated with a patient's heartbeat is sensed via the sensors 106, 108. For purposes of clarification, and as used throughout the specification, reference to an �active heartbeat� relates to a particular heartbeat monitored by the system 100 following establishment of the hemodynamic baseline ratio. That is to say, heartbeats (or �preliminary heartbeats�) may be sensed and analyzed to arrive at the hemodynamic baseline ratio. Once established, however, the system continuously monitors subsequent or �active� heartbeats, and processes the information accordingly.
At step 124, the processor 104 determines an active ratio, preferably according to the following equation: Atrial��Cycle��Time��for��Active��Heartbeat Ventricular��Cycle��Time��for��Active��Heartbeat Once again, the atrial cycle time includes both atrial depolarization time period and atrial repolarization time period for the active heartbeat. The ventricular cycle time includes the ventricular depolarization period and the ventricular repolarization period for the active heartbeat.
The processor 104 then compares the active ratio to the hemodynamic baseline ratio at step 126. The processor 104 evaluates the implications of the comparison at step 128. To this end, the processor 104 preferably includes software having one or more algorithms configured to analyze the comparison between the hemodynamic baseline ratio and the active ratio. For example, in accordance with the Frank-Starling Law, an impairment between the atrial and the ventricular wall tension will be reflected in a deviation of the active ratio from the hemodynamic baseline ratio. Depending upon the magnitude and direction of the deviation (i.e., positive or negative), the algorithm will determine or predict the onset of an arrhythmia, as well as the likely cause, such as too long or too short AV conduction time or a ventricular iscaemia, frequency, tension of the muscular walls, myocardiatis, myocardium infarction, indocarditis, etc.
In response to the evaluation of step 128, the processor 104 then determines a corrective action at step 130. Again, the algorithm associated with the processor 104 generates a technical input that is used to determine an appropriate change, if necessary, in therapy being provided by the IMD 102. For example, where the IMD 102 is a pacemaker, the determined corrective action can be a change in the AV delay, lower rate limit, upper rate limit, preventative pacing, night rate drop, etc. Alternatively, where the IMD 102 is a drug delivery system, the corrective action can be an increase or decrease in drug dispersion frequency and/or volume. Regardless, at step 132, the processor 104 prompts the IMD 102 to effectuate the determined corrective action.
As previously described, the hemodynamic baseline ratio can be predetermined or can be generated by the system 100. For example, FIG. 9 provides a flow diagram illustrating one method of generating the hemodynamic baseline ratio. Beginning at step 150, a cardiac signal for a preliminary heartbeat is sensed. Once again, a �preliminary heartbeat� is relative to use of the system 100 prior to establishing the hemodynamic baseline ratio. At step 152, a preliminary ratio is determined for the preliminary heartbeat based upon the sensed signal. The preliminary ratio is preferably determined as follows: Atrial��Cycle��Time��for��Preliminary��Heartbeat Ventricular��Cycle��Time��for��Preliminary��Heartbeat Again, the atrial cycle time includes atrial depolarization and atrial repolarization time periods for a preliminary heartbeat, whereas the ventricular cycle time includes ventricular depolarization and ventricular repolarization time periods for a preliminary heartbeat. At step 154, the determined preliminary ratio is recorded within a memory of the processor 104.
As shown in FIG. 9, the same steps are repeated to generate plurality of preliminary ratios. At step 156, the plurality of preliminary ratios are correlated with one another, preferably via an appropriate algorithm. In this regard, other factors potentially influencing one or more of the preliminary ratios are accounted for to compensate for deviations in the variously recorded ratios. Effectively, the plurality of preliminary ratios serves as a learning period for the system 100. Finally, at step 158, the hemodynamic baseline ratio is established based upon the above-described analysis. Notably, once the hemodynamic baseline ratio has been established, the system 100 operates as a closed loop regulation circuit.
In addition to reacting to short-term deviations from a hemodynamic situation, the system and method of the present invention is preferably also configured to detect and compensate for long-term variations. In particular, the system can record a series of active ratios and/or comparative results (relative to the hemodynamic baseline ratio) over an extended period of time and then use a trend analysis to evaluate long-term cardiac inefficiencies. For example, an individual active ratio may deviate only slightly from the hemodynamic baseline ratio, such that the algorithm does not dictate a change in therapy. However, over time the trend analysis may establish that the atrial cycle time and ventricular cycle time are slowly changing (e.g., shortening), but at slightly different rates. The system and method of the present invention analyzes this long-term information to evaluate the propriety of the selected therapy routine. Alternatively or in addition, the same information can be provided to the patient's physician who performs his/her or own analyses. Regardless, based upon this long-term data relating to a plurality of active ratios, the particular therapy is then modified to optimize heart performance. Along these same lines, the system and method of the present invention can utilize long-term trend analysis to better estimate the destabilization process of the patient's heart. For example, the trend analysis may indicate that the atrial cycle time and the ventricular cycle time are both decreasing, but not at equal rates. In this case, the absolute deviation between a particular active ratio and the hemodynamic baseline ratio is less significant so that no short-term therapy modifications are required. However, the algorithms associated with the system and method of the present invention can correlate the long-term trend information and generate a multiplication factor to either the sensed atrial cycle time or the sensed ventricular cycle time to eliminate a medium-fast bias otherwise affecting faster changes in heart destabilization.
Yet another analysis technique made available with the system and method of the present invention is the ability to confirm the sufficiency of other parameters intended to optimize the hemodynamic performance of the heart. For example, the comparison of an active ratio with the hemodynamic baseline ratio for a particular heartbeat can be compared with other functions of the IMD (e.g., automatic AV-delay optimization, iscaemia detection, etc.), and then evaluate whether those other parameters are functioning as desired. Even further, the long-term trend analysis is available to indicate the necessity of other therapy compensations. For example, a continuous search for the hemodynamical optimal lower rate limit (LRL) can be guided by the active ratio, as the lowest LRL will exhibit the longest atrial cycle time and ventricular cycle time that still provides a stable active ratio. A graphical illustration of this analysis is provided in FIGS. 10A and 10B. In particular, FIG. 10A graphically illustrates data from a heartbeat designated as being hemodynamically stable. In particular, sensed portions of the hemodynamically stabile heartbeat of FIG. 10A exhibits an atrial cycle time (X1) accorded a value of �2�, and a ventricular cycle time (Y1) accorded a value of a �2.4�. The resulting hemodynamic baseline ratio, in accordance with one preferred correlation technique is thus 0.833 (i.e., 2/2.4).
FIG. 10B illustrates the optimal lower rate limit associated with the same patient, as determined by the system and method of the present invention, in which the sensed cardiac cycle has an atrial cycle time (X2) of �3�, and a ventricular cycle time (Y2) of �3.6�. The resulting ratio active of 0.833 (i.e., 3/3.6) is deemed to be hemodynamically stable, as it does not deviate from the hemodynamic baseline ratio previously described with respect to FIG. 10A. The system and method of the present invention, however, is able to identify this hemodynamically stable situation, in conjunction with the longest atrial cycle time and ventricular cycle time, and thus designate these times as the optimal LRL.
To further exemplify operation of the system and method of the present invention, FIG. 10C relates to the same patient as analyzed in FIG. 10A, and graphically illustrates a subsequently sensed cardiac signal. In particular, for the active signal analyzed by FIG. 10C, the atrial cycle time (X2) is accorded a value of �2�, and the ventricular cycle time (Y2) is accorded a value of �2�. The resulting active ratio is 1.0 (i.e., 2/2). A comparison of the active ratio of 1.0 to the hemodynamic baseline ratio of 0.833 causes the system and method of the present invention, via an internal algorithm, to identify the cardiac signal associated with the graph of FIG. 10C as being unstable. In particular, the active ratio of 1.0 is greater than the hemodynamic baseline ratio, with the system and method designating this instability as being an unstable ventricular activity. In this instance, the algorithm may call for a rise frequency corrective action.
A further exemplary analysis provided by the system and method of the present invention is graphically illustrated in FIG. 10D. Once again, the graph of FIG. 10D relates to a cardiac signal of the patient for which the hemodynamic baseline ratio of FIG. 10A was previously established. With respect to FIG. 10D, a sensed active cardiac signal has been determined to have an atrial cycle time (X2) value of �1.8�, and a ventricular cycle time (Y4) value of �2.4�. The resulting active ratio is 0.075 (i.e., 1.8/2.4). A comparison of this active ratio with the hemodynamic baseline ratio (0.833) reveals an unstable situation. In particular, a decrease of the active ratio relative to the hemodynamic baseline ratio indicates unstable atrial hemodynamics. As a result, the system and method of the present invention, may, via an internal algorithm, identify an AV/delay corrective action, for example.
The system and method of the present invention provides a marked improvement over previous implantable medical device system designs. In particular, by utilizing atrial cycle time, including atrial repolarization time, the system and method of the present invention provides a unique approach to atrial and ventricular management. Both short-term and long-term atrial or ventricular instabilities relative to hemodynamic functioning are consistently identified by the system and method of the present invention, and appropriate corrective action is provided.
In the claims section of this application, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. For example, although a nail and a screw may not be structurally equivalent in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wood parts, a nail and a screw are equivalent structures.
Although specific embodiments of the invention have been set forth herein in some detail, it is understood that this has been done for the purposes of illustration only and is not to be taken as a limitation on the scope of the invention as defined in the appended claims. It is to be understood that various alterations, substitutions, and modifications may be made to the embodiment described herein without departing from the spirit and scope of the appended claims. For example, while the preferred correlation between utilized to evaluate deviation from a hemodynamically stable situation has preferably been described as being the ratio of atrial cycle time/ventricular cycle time. Other correlations are also available. For example, the applied correlation can be a ratio of ventricular cycle time/atrial cycle time; atrial repolarization period/ventricular repolarization period; ventricular repolarization period/atrial repolarization period; atrial depolarization period/atrial repolarization period; ventricular depolarization period/ventricular repolarization period; etc.
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