News Column

Patent Issued for Closed-Loop Adaptive Adjustment of Pacing Therapy Based on Cardiogenic Impedance Signals Detected by an Implantable Medical Device

May 18, 2014

By a News Reporter-Staff News Editor at Heart Disease Weekly -- Pacesetter, Inc. (Sunnyvale, CA) has been issued patent number 8712519, according to news reporting originating out of Alexandria, Virginia, by NewsRx editors (see also Pacesetter, Inc.).

The patent's inventors are Panescu, Dorin (San Jose, CA); Yang, Weiqun (Cupertino, CA); Wong, Louis (Sunnyvale, CA); Holmstrom, Nils (Jarfalla, SE); Walker, Andre (Monte Sereno, CA).

This patent was filed on November 9, 2006 and was published online on April 29, 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.

"One particular technique for addressing heart failure is CRT, which seeks to normalize asynchronous cardiac electrical activation and the resultant asynchronous contractions by delivering synchronized pacing stimulus to the ventricles using pacemakers or ICDs equipped with biventricular pacing capability. The pacing stimulus is typically synchronized so as to help to improve overall cardiac function. This may have the additional beneficial effect of reducing the susceptibility to life-threatening tachyarrhythmias. With CRT, pacing pulses are selectively delivered to the left and right ventricles in an attempt to ensure that the ventricles contract more uniformly. CRT may also be employed for patients whose nerve conduction pathways are corrupted due, e.g., to right bundle branch block or due to other problems such as the development of scar tissue within the myocardium following a myocardial infarction. CRT and related therapies are discussed in, for example, U.S. Pat. No. 6,643,546 to Mathis, et al., entitled 'Multi-Electrode Apparatus And Method For Treatment Of Congestive Heart Failure'; U.S. Pat. No. 6,628,988 to Kramer, et al., entitled 'Apparatus And Method For Reversal Of Myocardial Remodeling With Electrical Stimulation'; and U.S. Pat. No. 6,512,952 to Stahmann, et al., entitled 'Method And Apparatus For Maintaining Synchronized Pacing'.

"Although CRT and related techniques have been found to be effective in mitigating problems arising due to heart failure or other conditions, considerable room for improvement remains. Typically, CRT is performed so as to improve some measure of cardiac performance such as cardiac output or stroke volume. Ideally, the CRT parameters would be adjusted in real-time so as to respond automatically to changes in cardiac performance. This however would typically require that cardiac performance be continuously evaluated, which is impractical. Accordingly, it would be desirable to provide more efficient techniques for automatically adjusting CRT pacing parameters or other pacing therapy parameters. It is to that end that the invention is primarily directed."

Supplementing the background information on this patent, NewsRx reporters also obtained the inventors' summary information for this patent: "In accordance with an exemplary embodiment, a method is provided for controlling therapy provided by an implantable cardiac stimulation device based on cardiogenic impedance. The method comprises detecting a cardiogenic impedance signal (Z.sub.C) and adjusting therapy provided by the device based on the cardiogenic impedance signal (Z.sub.C). A cardiogenic impedance signal (or intracardiac impedance signal) is an impedance signal representative of the beating of the heart of the patient in which the device is implanted. Typically, the cardiogenic impedance signal is sensed along a sensing vector passing through at least a portion of the heart so that the sensed impedance is affected by the mechanical beating of the heart along that sensing vector. Multiple cardiogenic impedance signals may be sensed using different sensing vectors each passing through different portions of the heart so as to be representative of the beating of different chambers of the heart or different portions of the myocardium. Typically, the therapy to be adjusted is pacing therapy. For example, pacing timing parameters such as the atrioventricular (AV) delay and the inter-ventricular (LV-RV) delay may be adjusted, wherein LV refers to the left ventricle and RV refers to the right ventricle. Within systems equipped to provide pacing at different locations within the same chamber, intra-ventricular (LV.sub.1-LV.sub.2) or intra-atrial (LA.sub.1-LA.sub.2) delay values may additionally or alternatively be adjusted. Preferably, the adjustments are adaptive, i.e. the adjustments are performed in a closed-loop so as to adapt the adjustments to changes in the cardiogenic impedance signal so as to optimize therapy.

"By adjusting pacing parameters based on one or more cardiogenic impedance signals, the parameters can be promptly adjusted to immediately respond to changes within the heart, such as any deterioration in mechanical synchrony arising due to CHF, conduction defects or other ailments such as myocardial infarction or acute cardiac ischemia. Moreover, by adaptively adjusting the pacing parameters based on cardiogenic impedance, the direction and/or magnitude of the adjustments need not be pre-determined. That is, it need not be known in advance whether a particular pacing parameter should be increased or decreased in response to a deterioration in inter-ventricular mechanical synchrony. Adaptive adjustment allows the direction and magnitude of any adjustments to the pacing parameters to be automatically optimized. Thus, if an initial increase in a particular pacing parameter causes a further deterioration in mechanical synchrony, the pacing parameter may then be automatically decreased in an attempt to improve synchrony. If neither an increase nor a decrease in a particular pacing parameter significantly affects mechanical synchrony, then a different pacing parameter may be selected for adaptive adjustment.

"In an illustrative embodiment, the device analyzes the cardiogenic impedance signal to derive some measure of cardiac function, such as a measure of intra-ventricular or inter-ventricular mechanical dyssynchrony, and adaptively adjusts one or more pacing timing parameters so as to improve cardiac function. In one particular implementation, the device analyzes the cardiogenic impedance signal to derive a fractionation index representative of the degree of fractionation of the cardiogenic impedance signal. Pacing parameters are adaptively adjusted so as to decrease the degree of fractionation. The fractionation index may be derived, e.g., by simply counting a number of 'notches' or 'troughs' appearing within those portions of the impedance signal that are representative of individual heartbeats. The notches often correspond to periods of time when chambers of the heart are not beating uniformly, i.e. the greater the number of notches, the greater the degree of mechanical dyssynchrony. Alternatively, the fractionation index may be derived by determining the frequencies associated with the cardiogenic impedance signal. The greater the number of notches and troughs within the cardiogenic impedance signal, the higher the frequencies of the signal, and the greater the mechanical dyssynchrony. In either case, adaptively adjusting pacing parameters so as to decrease the fractionation index also serves to improve mechanical synchrony within the heart. Thus, a computationally simple procedure for optimizing pacing parameters to improve mechanical synchrony is provided, which does not require the device to directly evaluate cardiac output or stroke volume or other cardiac performance parameters adversely affected by mechanical dyssynchrony. Preferably, adjustments to the pacing parameters are made substantially in real-time. Lossy or lossless data compression techniques may be employed to minimize the amount of actual cardiogenic impedance data that needs to be stored and processed at any given time. Trends in cardiac function within the patient may also be identified and tracked to detect, for example, progression of CHF as evidenced by an increasing fractionation of the cardiogenic impedance signal. Appropriate warnings may be generated for the patient, the physician, or both.

"The adaptive adjustment of pacing therapy using cardiogenic impedance signals may be performed in conjunction with one or more intracardiac electrogram (IEGM) signals. For example, a measure of electrical dyssynchrony may be derived from the IEGM signals while a measure of mechanical dyssynchrony is derived from the cardiogenic impedance signals, permitting both to be used in adjusting the pacing parameters. Still further, if the implanted device is equipped with a sensor to directly measure cardiac pressure (e.g., left atrial pressure (LAP) or LV end diastolic (LV.sub.END) pressure), such pressure measurements may be used in conjunction with the cardiogenic impedance signals to adjust pacing parameters so as to reduce cardiac pressure while also reducing mechanical dyssynchrony. In some implementations, the pacing parameters are adaptively adjusted only when the patient is in a certain predetermined states as determined by activity sensor, posture detectors, etc. In one particular example, adaptive adjustment is only performed if the patient is at rest and in a supine posture. Adaptive adjustment may be still further limited to times when the blood oxygen saturation (SO.sub.2) level of the patient is within a certain acceptable range. In implementations where multiple cardiogenic impedance signals are sensed along different sensing vectors, the implanted system may be equipped, e.g., with multiple electrodes per lead or with multiple leads per chamber. When using multiple electrodes on a given lead, it may be desirable to employ a helical lead configuration wherein proximal portions of the lead have a greater diameter than distal portions, so as to more readily accommodate the multiple electrodes."

For the URL and additional information on this patent, see: Panescu, Dorin; Yang, Weiqun; Wong, Louis; Holmstrom, Nils; Walker, Andre. Closed-Loop Adaptive Adjustment of Pacing Therapy Based on Cardiogenic Impedance Signals Detected by an Implantable Medical Device. U.S. Patent Number 8712519, filed November 9, 2006, and published online on April 29, 2014. Patent URL:

Keywords for this news article include: Therapy, Diagnosis, Cardiology, Chalcogens, Heart Attack, Hemodynamics, Cardio Device, Heart Disease, Stroke Volume, Cardiac Output, Medical Devices, Pacesetter Inc., Myocardial Ischemia, Heart Function Tests, Myocardial Infarction, Cardiovascular Diseases, Diagnostic Techniques and Procedures.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC

For more stories covering the world of technology, please see HispanicBusiness' Tech Channel

Source: Heart Disease Weekly