Source: http://www.google.fr/patents/US7376463
Timestamp: 2013-05-24 22:24:03
Document Index: 776218873

Matched Legal Cases: ['art 105', 'art 105', 'art 105', 'art 105', 'art 105', 'art 615', 'art 615', 'art 615']

Brevet US7376463 - Therapy control based on the rate of change of intracardiac impedance - Google�BrevetsRecherche Images Maps Play YouTube Actualit�s Gmail Drive Plus » Recherche avanc�e dans les brevets | Historique Web | Connexion Recherche avanc�e dans les brevets BrevetsA system comprising a medical device that includes an impedance measurement circuit adapted to be coupled to implantable electrodes to obtain an intracardiac impedance signal between electrodes, a therapy circuit operable to deliver a therapy to a subject, and a controller circuit coupled to the impedance...http://www.google.fr/patents/US7376463?utm_source=gb-gplus-shareBrevet US7376463 - Therapy control based on the rate of change of intracardiac impedance Num�ro de publicationUS7376463 B2Type de publicationOctroi Num�ro de demande11/169,339 Date de publication20 mai 2008 Date de d�p�t29 juin 2005 Date de priorit�29 juin 2005Autre r�f�rence de publicationUS7953485US20070005114US20080249583 InventeursJesse W. HartleyJoseph M. PastoreRodney W. SaloJeffrey E. Stahmann Cessionnaire d'origineCardiac Pacemakers, Inc. Classification aux �tats-Unis607/17 Classification internationaleA61N1/00 Classification coop�rativeA61N1/30A61N1/36521 Classification europ�enneA61N1/365B2R�f�rencesCitations de brevets (6) R�f�renc� par (8)Liens externesUSPTO Cession USPTO EspacenetTherapy control based on the rate of change of intracardiac impedanceUS 7376463 B2 R�sum� A system comprising a medical device that includes an impedance measurement circuit adapted to be coupled to implantable electrodes to obtain an intracardiac impedance signal between electrodes, a therapy circuit operable to deliver a therapy to a subject, and a controller circuit coupled to the impedance measurement circuit and the therapy circuit. The controller circuit determines a time rate of change of the intracardiac impedance signal and adjusts at least one parameter related to therapy in a manner that alters the rate of change.
TECHNICAL FIELD The field generally relates to implantable medical devices and, in particular, but not by way of limitation, to systems and methods for detecting events related to cardiac activity through monitoring intracardiac impedance.
BACKGROUND Implantable medical devices (IMDs) are devices designed to be implanted into a patient. Some examples of these devices include cardiac function management (CFM) devices. CFMs include implantable pacemakers, implantable cardioverter defibrillators (ICDs), and devices that include a combination of pacing and defibrillation including cardiac resynchronization therapy. The devices are typically used to treat patients using electrical therapy and to aid a physician or caregiver in patient diagnosis through internal monitoring of a patient's condition. The devices may include electrical leads in communication with sense amplifiers to monitor electrical heart activity within a patient, and often include sensors to monitor other internal patient parameters. Other examples of implantable medical devices include implantable insulin pumps or devices implanted to administer drugs to a patient.
SUMMARY This document discusses, among other things, systems and methods for detecting events related to cardiac activity. A system embodiment includes a medical device. The medical device includes an impedance measurement circuit adapted to be coupled to implantable electrodes to obtain an intracardiac impedance signal between electrodes, a therapy circuit operable to deliver a therapy to a subject, and a controller circuit coupled to the impedance measurement circuit and the therapy circuit. The controller circuit determines a time rate of change of the intracardiac impedance signal and adjusts at least one parameter related to therapy in a manner that alters the rate of change.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates an embodiment of portions of a system including an implantable medical device.
This document discusses systems and methods for controlling cardiac therapy using sensed intracardiac impedance. The various regions of an asynchronous left ventricle typically do not contract simultaneously. Instead, myocytes of the different regions typically shorten and lengthen asynchronously with respect to each other. This results in a prolonged contraction. The prolonged contraction requires more time to create a useful pressure to begin ejection of blood from heart chambers and more time from the beginning to the end of the contraction. As a result, the ejection force in an asynchronous left ventricle is lessened along with corresponding decreases in the peak value of a rate of volume change with respect to time (dV/dt) and the peak value of a rate of pressure change with respect to time (dP/dt). When the left ventricle is re-coordinated, the peak values are increased and maximum synchrony of contraction will result in a maximum left ventricle dV/dt or dP/dt. A measure of dV/dt in the left ventricle is directly related to the peak blood flow through the aorta and is thus a measure of left ventricle contraction strength. Rate of pressure change dP/dt is an after-load independent measure of left ventricular contraction strength or �contractility� independent of dV/dt. Both peak positive dV/dt and dP/dt are measures of contraction strength that occur at different times during the contraction. However, it is impractical to measure dP/dt in the left ventricle using a sensor such as a pressure transducer because placing the sensor in the left ventricle increases a potential for thrombosis and creates a possibility of a resulting stroke.
V = ρ ⁢ ⁢ L 2 Z , where ρ is blood resistivity and L is the distance between impedance measuring electrodes. Therefore, for a change of intracardiac impedance that is much less than the value of the intracardiac impedance itself (i.e., dZ<<Z), a measured rate of change of blood volume can be determined from a measured negative rate of change of intracardiac impedance (dV=−dZ).
The intracardiac impedance is measured using a medical device. The impedance is measured between implantable electrodes placed in or near the heart chamber of interest. Alternatively, the impedance is measured between implantable electrodes placed within the thorax such that a component of the resulting impedance represents cardiac impedance. Information about the rate of change of blood volume can be determined either by converting the impedance to volume or by using the measured unprocessed, or �raw,� impedance signal.
Cardiac lead 108 includes a proximal end that is coupled to DME 110 and a distal end, coupled by an electrode or electrodes to one or more portions of a heart 105. The electrodes typically deliver cardioversion, defibrillation, pacing, or resynchronization therapy, or combinations thereof to at least one chamber of the heart 105. The electronics unit of the IMD 110 typically includes components that are enclosed in a hermetically-sealed canister or �can.� Other electrodes may be located on the can, or on an insulating header extending from the can, or on other portions of IMD 110, such as for providing pacing energy, defibrillation energy, or both, in conjunction with the electrodes disposed on or around a heart 105. The lead 108 or leads and electrodes may also typically be used for sensing electrical activity of the heart 105.
Other forms of electrodes include meshes and patches which may be applied to portions of heart 105 or which may be implanted in other areas of the body to help �steer� electrical currents produced by IMD 110. In one embodiment, one of atrial lead 108A or ventricular lead 108B is omitted, i.e., a �single chamber� device is provided, rather than the dual chamber device illustrated in FIG. 2. In another embodiment, additional leads are provided for coupling the IMD 110 to other heart chambers and/or other locations in the same heart chamber as one or more of leads 108A-B. The present methods and systems will work in a variety of configurations and with a variety of electrical contacts or �electrodes.� Sensing among different sets of electrodes often provides directional information regarding the propagation of cardiac signals and is often referred to as sensing among different vectors. For example, sensing from an electrode placed proximal to the right atrium 200A to an electrode placed proximal to the right ventricle 205A would be one vector, sensing from the right atrium 200A to the left atrium 200B would be a second vector, and sensing from the right ventricle 205A to a can electrode 250, or a header electrode 255, would be a third vector.
Similarly, a biphasic current waveform can be used to promote charge balance. It is important to maintain a DC current level as low as possible to limit corrosion in metal electrodes. The current leakage levels to limit corrosion are typically lower than the leakage limits for patient safety. Common practice to limit DC current is to capacitively couple the system/electrode interface. Using a biphasic waveform to promote charge balance further limits the corrosion. An additional reason that biphasic or symmetric waveforms are desirable is that they cause less interference with the internal sense-amps or with external sensing equipment, such as ECG machines. Descriptions of systems and methods using biphasic or symmetric waveforms to measure impedance are found in Hartley et al., U.S. Pat. No. 6,076,015, entitled, �Rate Adaptive Cardiac Rhythm Management Device Using Transthoracic Impedance,� which is incorporated herein by reference.
FIG. 4A shows a waveform that represents a typical signal Z(t) obtained from the impedance measurement circuit 310. The peak to peak amplitude of the waveform is labeled �A.� FIG. 4B shows a waveform that represents the first derivative of the signal
ⅆ Z ⁡ ( t ) ⅆ t . The peak positive amplitude of the derivative, or the peak value of the rate of change, is labeled �B.� The peak negative amplitude of the derivative is labeled �C.�
According to some examples, the system 300 includes a plurality of implantable electrodes adaptable to sense electrical signals of a heart of a subject. In some examples, referring to FIG. 2, electrodes are placed in a coronary vein 220 and a right ventricle 205A. The impedance measurement circuit 310 measures intracardiac impedance between the coronary vein 220 and the right ventricle 205A using the electrodes to obtain an intracardiac impedance signal for the left ventricle 205B. In some examples, electrodes are placed in a right atrium 200A and a right ventricle 205A. The impedance measurement circuit 310 obtains an intracardiac impedance signal for the right ventricle 205A from between the electrodes placed in the right atrium 200A and the right ventricle 205A. In some examples, the electrodes are placed in a right ventricle 205A and on a left side lateral wall or free wall of the heart, such as by placement in the left anterior descending artery or by placement through the coronary sinus into a coronary vein. The impedance circuit 310 obtains an intracardiac impedance signal from between electrodes at the right ventricle 205A and the left ventricle lateral wall. Descriptions of systems and methods for multi-site impedance sensing are found in Salo et al., U.S. Pat. No. 6,278,894, entitled �Multi-Site Impedance Sensor Using Coronary Sinus/Vein Electrodes,� which is incorporated herein by reference. As another example, a lead containing at least two electrodes is placed in a coronary vein 220. The impedance circuit 310 obtains an intracardiac impedance signal from between the two electrodes placed in the coronary vein. The impedance measurement will be affected by the change in ventricular wall thickness due to cardiac cycles of systole and diastole. Thus, the intracardiac impedance measurement can be used to derive the time to peak wall thickness change for the left ventricle free wall as measured from the beginning of a cardiac cycle, such as from a sensed occurrence of depolarization of atrial cells (a P-wave) for example.
According to some examples, cardiac electrodes placed in or around the heart (e.g., the right ventricle) and an electrode on the IMD (e.g., the IMD �can� electrode) are used to measure impedance. The impedance measurement circuit 310 measures the intrathoracic impedance of the heart and lungs between the cardiac electrodes and the IMD electrode. Impedance measurement circuit 310 includes a filter circuit to remove any pulmonary component of the measurement while retaining the cardiac component of the measurement.
In some examples, the system 300 is included in a neural stimulation device such as a vagal stimulation device. As an example application, a vagal stimulation device is used to control heart activity by decreasing heart contractility during a period of recovery of a patient that has suffered myocardial infarction. One possible result of myocardial infarction is a physiological compensation that increases diastolic filling pressure, i.e. backward failure. An increase in preload causes an increase in stroke volume during systole, a phenomena known as the Frank-Starling principle. Thus, heart failure can be at least partially compensated by this mechanism but at the expense of possible pulmonary and/or systemic congestion. The contractility of the heart is decreased to reduce the effect of ventricle remodeling from the increased pressure that can ultimately lead to more heart congestion. Descriptions of systems and methods to reduce or prevent the effects of ventricle remodeling through reduction of ventricular wall stress are found in Pastore et al., U.S. patent application Ser. No. 10/700,368, entitled �Multi-Site Ventricular Pacing Therapy with Parasympathetic Stimulation,� filed Nov. 3, 2003, and which is incorporated herein by reference. In an example of a vagal stimulation device, the controller circuit 320 adjusts parameters related to parasympathetic nerve stimulation to optimize the peak value of the rate of change of intracardiac impedance. In some examples, the system 300 monitors the impact of reduced contractility. In some examples, the controller circuit 320 adjusts parameters to maintain the peak value of the rate of change of intracardiac impedance within a predetermined range of values.
FIG. 6 is an illustration of portions of another example of a system 600 to control cardiac therapy using sensed intracardiac impedance. In this example, the system 600 includes an IMD 605 that is a cardiac rhythm management device. The IMD 605 is coupled to heart 615 by cardiac leads 610 that include lead tip and ring electrodes 620, 622, 625, 627. The cardiac leads 610 are connected to the MD at header 640. The IMD 605 includes components that are enclosed in a hermetically-sealed canister or �can� 630. A therapy circuit 670 is used to provide cardiac function management therapy such as pacing and/or defibrillation energy in conjunction with the electrodes disposed in or around heart 615. The leads 610 and lead electrodes 620, 622, 625, 627 are used in conjunction with sense amplifiers 675 for sensing electrical activity of a heart 615.
Citations de brevets Brevet cit� Date de d�p�t Date de publication D�posant TitreUS45482096 f�vr. 198422 oct. 1985Medtronic, Inc.Energy converter for implantable cardioverterUS473366711 ao�t 198629 mars 1988Cardiac Pacemakers, Inc.Closed loop control of cardiac stimulator utilizing rate of change of impedanceUS57828845 nov. 199621 juil. 1998Sulzer Intermedics Inc.Rate responsive cardiac pacemaker with peak impedance detection for rate controlUS627889421 juin 199921 ao�t 2001Cardiac Pacemakers, Inc.Multi-site impedance sensor using coronary sinus/vein electrodesUS714620825 mars 20035 d�c. 2006St. Jude Medical AbSystolic function monitoring utilizing slope of measured impedanceUS717125825 juin 200330 janv. 2007Cardiac Pacemakers, Inc.Method and apparatus for trending a physiological cardiac parameter R�f�renc� par Brevet citant Date de d�p�t Date de publication D�posant TitreUS795348517 avr. 200831 mai 2011Cardiac Pacemakers, Inc.Therapy control based on the rate of change of intracardiac impedanceUS797469121 sept. 20055 juil. 2011Cardiac Pacemakers, Inc.Method and apparatus for controlling cardiac resynchronization therapy using cardiac impedanceUS812654818 janv. 200828 f�vr. 2012Cardiac Pacemakers, Inc.Closed loop impedance-based cardiac resynchronization therapy systems, devices, and methodsUS826576931 janv. 200711 sept. 2012Medtronic, Inc.Chopper-stabilized instrumentation amplifier for wireless telemetryUS829592720 oct. 200823 oct. 2012Cardiac Pacemakers, Inc.Closed loop impedance-based cardiac resynchronization therapy systems, devices, and methodsUS832101613 juin 200727 nov. 2012St. Jude Medical AbImplantable medical device and a method comprising means for detecting and classifying ventricular tachyarrhythmiasUS83548812 d�c. 201015 janv. 2013Medtronic, Inc.Chopper-stabilized instrumentation amplifierUS2010017941113 juin 200715 juil. 2010St. Jude Medical AB a, corporationIMPLANTABLE MEDICAL DEVICE AND A METHOD COMPRISING MEANS FOR DETECTING AND CLASSIFYING VENTRICULAR TACHYARRHYTMIAS (As Amended)Faire pivoterImage d'origineAccueil Google - Plan du site - T�l�chargements par lot sur l'USPTO - R�gles de confidentialit� - Conditions d'utilisation - � propos de Google�Brevets - Envoyer des commentairesDonn�es fournies par IFI CLAIMS Patent Services©2012 Google