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Patent Issued for Systems and Methods for Assessing Heart Failure and Controlling Cardiac Resynchronization Therapy Using Hybrid Impedance...

June 23, 2014

Patent Issued for Systems and Methods for Assessing Heart Failure and Controlling Cardiac Resynchronization Therapy Using Hybrid Impedance Measurement Configurations

By a News Reporter-Staff News Editor at Cardiovascular Week -- Pacesetter, Inc. (Sylmar, CA) has been issued patent number 8750981, according to news reporting originating out of Alexandria, Virginia, by NewsRx editors (see also Pacesetter, Inc.).

The patent's inventors are Bornzin, Gene A. (Simi Valley, CA); Min, Xiaoyi (Thousand Oaks, CA); Sloman, Laurence S. (West Hollywood, CA); Koh, Steve (South Pasadena, CA).

This patent was filed on August 25, 2011 and was published online on June 10, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Heart failure is a debilitating disease in which abnormal function of the heart leads to inadequate blood flow to fulfill the needs of the tissues and organs of the body. Typically, the heart loses propulsive power because the cardiac muscle loses capacity to stretch and contract. Often, the ventricles do not adequately fill with blood between heartbeats and the valves regulating blood flow become leaky, allowing regurgitation or back-flow of blood. The impairment of arterial circulation deprives vital organs of oxygen and nutrients. Fatigue, weakness and the inability to carry out daily tasks may result. Not all heart failure patients suffer debilitating symptoms immediately. Some may live actively for years. Yet, with few exceptions, the disease is relentlessly progressive. As heart failure progresses, it tends to become increasingly difficult to manage. Even the compensatory responses it triggers in the body may themselves eventually complicate the clinical prognosis. For example, when the heart attempts to compensate for reduced cardiac output, it adds cardiac muscle causing the ventricles to grow in volume in an attempt to pump more blood with each heartbeat, i.e. to increase the stroke volume. This places a still higher demand on the heart's oxygen supply. If the oxygen supply falls short of the growing demand, as it often does, further injury to the heart may result, typically in the form of myocardial ischemia or myocardial infarction. The additional muscle mass may also stiffen the heart walls to hamper rather than assist in providing cardiac output. A particularly severe form of heart failure is congestive heart failure (CHF) wherein the weak pumping of the heart leads to build-up of fluids in the lungs and other organs and tissues.

"In view of the potential severity of heart failure, it is highly desirable to detect its onset within a patient and to track its progression so that appropriate therapy can be provided. Many patients suffering heart failure already have pacemakers or ICDs implanted therein or are candidates for such devices. Accordingly, it is desirable to provide such devices with the capability to automatically detect and track heart failure and various techniques exploiting electrical impedance signals measured by an implantable device have been developed. Techniques exploiting impedance are presented, for example, in U.S. Pat. No. 7,505,814 to Bornzin et al., entitled 'System and Method for Evaluating Heart Failure based on Ventricular End-Diastolic Volume using an Implantable Medical Device' and in U.S. Pat. No. 7,272,443 to Min et al., entitled 'System and Method for Predicting a Heart Condition based on Impedance Values using an Implantable Medical Device.'

"More recently, techniques for measuring impedance using hybrid impedance vectors were described in U.S. patent application Ser. No. 13/023,408, filed Feb. 8, 2011, of Min et al., entitled 'Systems and Methods for Tracking Stroke Volume using Hybrid Impedance Configurations Employing a Multi-Pole Implantable Cardiac Lead', which is fully incorporated by reference herein. In one example described therein, current is injected between a large and stable reference electrode and a right ventricular (RV) ring electrode. The reference electrode may be, e.g., a coil electrode implanted within the superior vena cava (SVC) or the device case or 'can' electrode. Impedance values are then measured along a set of different sensing vectors between the reference electrode and the electrodes of a multi-pole left ventricular (LV) lead implanted via the coronary sinus (CS). These techniques are generally referred to as hybrid techniques since different vectors are employed for injecting current than for measuring the resulting impedance/voltage. More specifically, the techniques may be referred to as 'LV-based hybrid techniques' since LV electrodes are used to measure the impedance. The LV-based hybrid techniques advantageously allow impedance signals to be detected that exhibit significant variation throughout individual cardiac cycles to aid in the detection of stroke volume and related cardiac function parameters and to aid in the optimization of pacing delays for use with CRT.

"It would be desirable to provide hybrid impedance measurement techniques that additionally or alternatively exploit electrodes of a right atrial (RA) lead for measuring impedance values (based on current injected via the RV.) It is to these ends that various aspects of the present invention are directed."

Supplementing the background information on this patent, NewsRx reporters also obtained the inventors' summary information for this patent: "In an exemplary embodiment, a method is provided for use with an implantable medical device for implant within a patient having a lead system including an RV lead and an RA lead. Current is injected between a current injection reference electrode and an electrode in the RV, such as the RV ring or RV tip. The current injection reference electrode is preferably a relatively large and stable electrode (i.e., one that is relatively insensitive to patient motion artifacts and tissue property changes) such as the device can (or case) electrode or a coil electrode implanted within the SVC of the patient near the RA. Impedance values are then measured along a vector between a voltage sensing reference electrode and an electrode in or near the RA, such as an RA ring electrode. The voltage sensing reference electrode is also preferably a relatively large and stable electrode and can be the same reference electrode used for injecting current (e.g., the device can use the device case electrode both for injecting current in conjunction with an electrode in the RV and for then measuring impedance in conjunction with an electrode in or near the RA.) In this manner, a hybrid impedance detection configuration is exploited whereby an RV vector is used to inject current and an RA vector is used to measure impedance. At least one device function is then controlled based on the measured impedance values. The device function can comprise any function that can be performed or controlled by the device such as (a) detecting heart failure, interventricular dyssynchrony or other cardiac conditions based on the impedance values, (b) issuing warning signals in response to detection of such conditions, optimizing atrioventricular (AV) and interventricular (VV) pacing delays for use with CRT based on the impedance values or (d) recording impedance-based diagnostic information.

"In an illustrative example, the implantable device is a pacemaker, ICD or CRT device having an RA lead with a pair of tip and ring electrodes and an RV lead also having a pair of tip and ring electrodes. Both the RV and RA leads are implanted via the SVC. The RV lead also has an RV coil electrode positioned in the RV itself and a separate SVC coil electrode positioned in the SVC. Herein, the SVC coil is considered to be near the RA since the SVC is anatomically close to the RA. In the illustrative example, current is injected between either the device can electrode or the SVC electrode and at least one of the electrodes in the RV itself (i.e. the RV ring, RV tip or RV coil.) As such, the current injection vector exploits a relatively large and stable electrode, which generates a relatively wide electrical field for impedance measurement purposes. Note that the relatively wide field encompasses at least some non-cardiac thoracic fluids and tissues, as well as cardiac fluids and tissues, such that both intrathoracic and transthoracic (TTZ) impedance and intracardiac (ICZ) impedance are implicated. Insofar as the impedance measurement vector is concerned, in the illustrative example the device measures impedance between the RA tip or RA ring electrodes and the device can electrode (or the SVC coil electrode), thereby exploiting a different vector for impedance measurement as opposed to current injection. In other examples, instead of injecting current via the RV, current is injected RA ring to can or RA tip to can and then impedance is measured RA ring to can or RA tip to can.

"Herein, configurations that exploit electrodes in or near the RA for use in measuring impedance are referred to as 'RA-based impedance measurement configurations.' The impedance values (Z) measured using the RA-based configurations are referred to herein as Z.sub.RA values to distinguish from other impedance values measured using other measurement configurations.

"In at least some embodiments, the lead system also includes an LV lead implanted via the CS. In addition to measuring impedance (Z.sub.RA) using the electrodes of the RA lead, the device also measures impedance (Z.sub.LV) using electrodes of the LV lead. Herein, configurations that exploit electrodes on or near the LV for use in measuring impedance are referred to as 'LV-based impedance measurement configurations.' In an illustrative example, the LV lead is a quad-pole LV lead implanted via the CS with a distal tip electrode (D1), a proximal ring electrode (P4), and a pair of intermediate ring electrodes (M2 and M3). For convenience, the LV electrodes are identified herein by the index 'i' where i=1 refers to the D1 electrode, i=2 refers to the M2 electrode, i=3 refers to the M3 electrode and i=4 refers to the P4 electrode. Current is injected using any of the RV electrodes and either the SVC coil or the device can.

"The RA-based and LV-based impedance measurements are then used to detect heart failure or other conditions, optimize AV and VV delays for use with CRT, or to perform or control any other suitable functions. In some examples, at least some of these functions are performed by or in conjunction with an external system--such as a device programmer--in communication with the implanted device.

"In various examples described herein, impedance measurements are used but it should be understood that related electrical parameters might be detected and/or exploited instead such as admittance, conductance or immittance. Those skilled in the art can convert between these related parameters as needed. Herein, 'values representative of impedance' is intended to include related electrical parameters such as admittance, conductance and immittance.

"System and method implementations of the various exemplary embodiments are presented herein."

For the URL and additional information on this patent, see: Bornzin, Gene A.; Min, Xiaoyi; Sloman, Laurence S.; Koh, Steve. Systems and Methods for Assessing Heart Failure and Controlling Cardiac Resynchronization Therapy Using Hybrid Impedance Measurement Configurations. U.S. Patent Number 8750981, filed August 25, 2011, and published online on June 10, 2014. Patent URL:

Keywords for this news article include: Therapy, Cardiology, Heart Disease, Heart Failure, Pacesetter Inc., Cardiovascular Diseases.

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Source: Cardiovascular Week

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