Source: http://www.google.com/patents/US20090093731?dq=6233682
Timestamp: 2016-09-29 12:59:21
Document Index: 505004351

Matched Legal Cases: ['art 104', 'art 104', 'art 104', 'art 104', 'art 104', 'art 104', 'art 104', 'art 104', 'art 104', 'art 104', 'art 104']

Patent US20090093731 - Cardiac rhythm management system with noise detector - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsA system, method, or device determines whether noise is present on a sampled and/or digitized sensed intrinsic cardiac signal based on a moving count of turning/inflection points of the signal. If noise is detected, the manner in which the cardiac signal is acquired, or the manner in which the device...http://www.google.com/patents/US20090093731?utm_source=gb-gplus-sharePatent US20090093731 - Cardiac rhythm management system with noise detectorAdvanced Patent SearchTry the new Google Patents, with machine-classified Google Scholar results, and Japanese and South Korean patents.Publication numberUS20090093731 A1Publication typeApplicationApplication numberUS 12/333,008Publication dateApr 9, 2009Filing dateDec 11, 2008Priority dateOct 29, 2001Also published asUS6892092, US7467009, US20030083713, US20050192504Publication number12333008, 333008, US 2009/0093731 A1, US 2009/093731 A1, US 20090093731 A1, US 20090093731A1, US 2009093731 A1, US 2009093731A1, US-A1-20090093731, US-A1-2009093731, US2009/0093731A1, US2009/093731A1, US20090093731 A1, US20090093731A1, US2009093731 A1, US2009093731A1InventorsSurekha Palreddy, Carlos RicciOriginal AssigneeSurekha Palreddy, Carlos RicciExport CitationBiBTeX, EndNote, RefManPatent Citations (69), Referenced by (49), Classifications (7) External Links: USPTO, USPTO Assignment, EspacenetCardiac rhythm management system with noise detector
US 20090093731 A1Abstract
[0001] This application is a division of U.S. patent application Ser. No. 11/110,490, filed on Apr. 20, 2005, which is a division of U.S. patent application Ser. No. 10/046,650, filed on Oct. 29, 2001, now issued as U.S. Pat. No. 6,892,092, the specifications of which are incorporated by reference herein.
[0002] This document relates generally to cardiac rhythm management systems, devices, and methods, and particularly, but not by way of limitation, to a cardiac rhythm management system with a noise detector that reduces the likelihood that noise on a cardiac signal is erroneously sensed as a cardiac depolarization.
[0003] When functioning properly, the human heart maintains its own intrinsic rhythm. Its sinoatrial node generates intrinsic electrical cardiac signals that depolarize the atria, causing atrial heart contractions. Its atrioventricular node then passes the intrinsic cardiac signal to depolarize the ventricles, causing ventricular heart contractions. These intrinsic cardiac signals can be sensed on a surface electrocardiogram (ECG) obtained from electrodes placed on the patient's skin, or from electrodes implanted within the patient's body. The surface ECG waveform, for example, includes artifacts associated with atrial depolarizations (“P-waves”) and those associated with ventricular depolarizations (“QRS complexes”).
[0004] A normal heart is capable of pumping adequate blood throughout the body's circulatory system. However, some people have irregular cardiac rhythms, referred to as cardiac arrhythmias. Moreover, some patients have poorly spatially-coordinated heart contractions. In either case, diminished blood circulation may result. For such patients, a cardiac rhythm management system may be used to improve the rhythm and/or spatial coordination of heart contractions. Such systems are often implanted in the patient and deliver therapy to the heart.
[0005] Cardiac rhythm management systems include, among other things, pacemakers, also referred to as pacers. Pacers deliver timed sequences of low energy electrical stimuli, called pace pulses, to the heart, such as via an intravascular leadwire or catheter (referred to as a “lead”) having one or more electrodes disposed in or about the heart. Heart contractions are initiated in response to such pace pulses (this is referred to as “capturing” the heart). By properly timing the delivery of pace pulses, the heart can be induced to contract in proper rhythm, greatly improving its efficiency as a pump. Pacers are often used to treat patients with bradyarrhythmias, that is, hearts that beat too slowly, or irregularly. Such pacers may also coordinate atrial and ventricular contractions to improve pumping efficiency. Cardiac rhythm management systems also include cardiac resynchronization therapy (CRT) devices for coordinating the spatial nature of heart depolarizations for improving pumping efficiency. For example, a CRT device may deliver appropriately timed pace pulses to different locations of the same heart chamber to better coordinate the contraction of that heart chamber, or the CRT device may deliver appropriately timed pace pulses to different heart chambers to improve the manner in which these different heart chambers contract together.
[0006] Cardiac rhythm management systems also include defibrillators that are capable of delivering higher energy electrical stimuli to the heart. Such defibrillators include cardioverters, which synchronize the delivery of such stimuli to portions of sensed intrinsic heart activity signals. Defibrillators are often used to treat patients with tachyarrhythmias, that is, hearts that beat too quickly. Such too-fast heart rhythms also cause diminished blood circulation because the heart isn't allowed sufficient time to fill with blood before contracting to expel the blood. Such pumping by the heart is inefficient. A defibrillator is capable of delivering a high energy electrical stimulus that is sometimes referred to as a defibrillation countershock, also referred to simply as a “shock.” The countershock interrupts the tachyarrhythmia, allowing the heart to reestablish a normal rhythm for the efficient pumping of blood. In addition to pacers, CRT devices, and defibrillators, cardiac rhythm management systems also include devices that combine these functions, as well as monitors, drug delivery devices, and any other implantable or external systems or devices for diagnosing or treating the heart.
[0007] One problem faced by cardiac rhythm management devices is in detecting the atrial and/or ventricular depolarizations in the intrinsic electrical cardiac signals, since the delivery of therapy to the heart is typically based at least in part on the timing and/or morphology of such detected depolarizations. To detect a depolarization event, the cardiac signal may be amplified, filtered, and/or level-detected (e.g., to determine whether an artifact exceeds a particular threshold level associated with an atrial or ventricular depolarization). Depolarization detection is complicated, however, by the fact that the intrinsic cardiac signals may include noise unrelated to the heart depolarization. The noise may arise from a variety of sources, including, among other things: myopotentials associated with skeletal muscle contractions; a loose or fractured leadwire providing intermittent contact between the device and the heart; or, electromagnetic interference from AC power provided to nearby electrical equipment (e.g., 60 Hertz), from nearby switching power supplies, from a nearby electrosurgical tool, from communication equipment, or from electronic surveillance equipment. Noise erroneously detected as a heart depolarization may inappropriately inhibit bradyarrhythmia pacing therapy or cardiac resynchronization therapy, or may inappropriately trigger tachyarrhythmia shock therapy. For these reasons, the present inventor has recognized a need for detecting the presence of such noise, and using this information in such a way that the occurrence of such consequences can be reduced or avoided altogether.
[0008] This document discusses, among other things, a system, method, or device that determines whether noise is present on a sampled and/or digitized sensed intrinsic cardiac signal based on a moving count of turning/inflection points of the signal. If noise is detected, the manner in which the cardiac signal is acquired, or the manner in which the device operates in response to the acquired cardiac signal (or both) is altered to reduce the risk of erroneously detecting noise as a heart depolarization and, therefore, inappropriately triggering or withholding therapy.
[0009] In one example, this document discusses a method of determining whether a sampled cardiac signal is noisy. The method includes determining whether an evaluation sample of the cardiac signal is a turning point with respect to previous and subsequent samples. A number of the turning points is counted over a predetermined plurality of cardiac samples. A window that includes the predetermined plurality of cardiac samples is deemed to be noisy if the number of turning points exceeds a threshold value.
[0010] In another example, this document discusses a system. The system includes a first electrode associated with a heart. A cardiac signal detector is coupled to the first electrode. The cardiac signal detector includes a detector output providing a sampled cardiac signal. A signal processor circuit determines, over a predetermined plurality of cardiac signal samples, whether an evaluation sample of the cardiac signal is a turning point with respect to previous and subsequent samples. The signal processor circuit deems a portion of the cardiac signal to be noisy if a number of turning points exceeds a threshold value for the predetermined plurality of cardiac signal samples. Other aspects of the invention will be apparent on reading the following detailed description of the invention and viewing the drawings that form a part thereof.
BRIEF DESCRIPTION OF THE DRAWINGS [0011] In the drawings, which are offered by way of example, and not by way of limitation, and which are not necessarily drawn to scale, like numerals describe substantially similar components throughout the several views. Like numerals having different letter suffixes represent different instances of substantially similar components.
[0012] FIG. 1 is a block diagram illustrating generally portions of a cardiac rhythm management system and portions of an environment in which it is used.
[0013] FIG. 2 is a graph illustrating generally a relatively noise-free cardiac signal.
[0014] FIG. 3 is a graph illustrating generally a relatively noisy cardiac signal.
[0015] FIG. 4 is a flow chart illustrating generally one example of a noise detection technique.
[0016] FIG. 5 is a signal graph of a sampled cardiac signal, illustrating generally one technique for determining whether an evaluation sample is a turning/inflection point.
[0017] FIG. 6 is a signal graph of the sampled cardiac signal of FIG. 5, illustrating, among other things, that the turning/inflection point evaluation may be performed at a different frequency from that at which the cardiac signal was sampled.
[0018] FIG. 7 is a block diagram illustrating generally, by way of example, but not by way of limitation, several possible operational adjustments that may be performed in response to a noisy cardiac signal.
[0019] FIG. 8 is a block diagram illustrating an alternative example of a system including a second FIFO counter for performing the noise detection technique illustrated in the flow chart of FIG. 9.
[0020] FIG. 9 is a flow chart illustrating generally another example of a noise detection technique.
[0021] FIG. 10 is a schematic/block diagram illustrating generally one example of a turning point detector for operating upon an analog acquired cardiac signal x(t) and providing an indication of whether a particular sample of the acquired cardiac signal x(t) represents a turning point in the acquired cardiac signal x(t).
[0022] FIG. 11 is a schematic/block diagram illustrating generally another example of a turning point detector for operating upon an analog acquired cardiac signal x(t) and providing an indication of whether a particular sample of the acquired cardiac signal x(t) represents a turning point in the acquired cardiac signal x(t).
DETAILED DESCRIPTION [0023] In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that the embodiments may be combined, or that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.
[0024] FIG. 1 is a block diagram illustrating generally portions of a cardiac rhythm management system 100 and portions of an environment in which it is used. In this example, system 100 includes a cardiac rhythm management device 102 coupled to a heart 104 by one or more electrodes associated with heart 104, such as for sensing intrinsic cardiac signals and/or for delivering energy or other therapy to heart 104. System 100 also includes a programmer or other remote interface 106, which is wirelessly or otherwise communicatively coupled to a telemetry circuit 108 or other communication circuit in device 102. Device 102 includes a pacer, a defibrillator, a cardiac resynchronization therapy (CRT) device, a monitor, a device that combines more than one of these functions, or any other implantable or external device for diagnosing and/or treating the heart. In one example, device 102 is sized and shaped for being pectorally or abdominally implanted in a human patient. The electrode(s) coupling device 102 to heart 104 may include an intravascular electrode, an intracardiac electrode, an epicardial electrode, or a housing or a header electrode located on a housing of device 102 or a header attached thereto, or any combination of the above. In some configurations, such as where portion(s) of device 102 are external to the patient, the electrode(s) coupling device 102 to heart 104 may include a skin surface electrode external to the patient. The electrodes may be associated with the heart for bipolar (i.e., two electrodes that are relatively close together) or for unipolar (i.e., two electrodes that are farther apart) signal sensing or therapy energy delivery (e.g., pacing pulse or shocks).
[0025] In the example of FIG. 1, device 102 includes a cardiac signal detector 110 having an input coupled to heart 104 by electrodes associated with heart 104 in a suitable manner for sensing an intrinsic cardiac signal. Detector 110 need not actually extract heart depolarizations from the sensed intrinsic cardiac signal; such functions may be performed elsewhere in device 102. Detector 110 typically includes a sense amplifier for acquiring and amplifying the cardiac signal. Detector 110 may also include one or more continuous-time and/or discrete time (e.g., switched-capacitor) filter circuits, such as for selectively emphasizing the desired heart depolarization information relative to other acquired signal content. Detector 110 may also include an analog-to-digital converter (ADC) to convert continuous-time and/or discrete time samples into numerical representations of those samples. Detector 110 may also include one or more digital filters (or other digital signal processing circuitry) following the ADC, such as for selectively emphasizing the desired heart depolarization information relative to other acquired signal content. Detector 110 also includes an output providing a periodically sampled data cardiac signal x(n) to a cardiac signal processor module 112 of controller 114. Controller 114 is capable of sequencing through various control states such as, for example, by using a digital microprocessor having executable instructions stored in an associated instruction memory circuit, a microsequencer, or a state machine. In operation, by executing these instructions, controller 114 provides the functionality of cardiac signal processor module 112, as well as providing control signals to cardiac signal detector 110 and an energy output circuit 118. In one example, cardiac signal processor module 112 includes a first-in-first-out (FIFO) memory and counter 115 and a noise flag 116 (such as, for example, a bit in a register) to assist in the noise detection technique discussed herein. Energy output circuit 118 provides pacing or resynchronization pulses, defibrillation shocks, or other appropriate cardiac therapy to heart 104. Device 102 also includes a battery or other power source 120.
[0026] FIG. 2 is a graph illustrating generally a relatively noise-free cardiac signal 200 obtained from electrodes associated with heart 104. FIG. 3 is a graph illustrating generally a relatively noisy cardiac signal 300 similarly obtained from electrodes associated with heart 104. In the example of FIG. 3, the additional noise may make the underlying heart chamber depolarizations difficult to detect, since the noise may include frequencies within the passband of the depolarizations and may, therefore, erroneously be level-detected as an actual heart depolarization.
[0027] FIG. 4 is a flow chart illustrating generally one example of a noise detection technique performed by cardiac signal processor 112 on the sampled cardiac signal x(n) that is output by cardiac signal detector 110. At 400, FIFO counter 115 and noise flag 116 are initialized. In one example, FIFO counter 115 includes an N-bit shift register, which is initialized at 400 to all zeros, and also includes an associated counter that outputs a sum of the number of ones in the N-bit shift register. Noise flag 116 is also initialized to zero, indicating that noise has not yet been detected as being present on the cardiac signal x(n). At 402, a cardiac signal sample is obtained. At 404, a previously-obtained evaluation sample is considered as to whether it represents a turning point (also referred to as an inflection point), with respect to a cardiac signal sample previous to the evaluation sample, and with respect to a cardiac signal sample subsequent to the evaluation sample. If, at 404, the evaluation sample is deemed a turning point, then at 406, a logic “1” is shifted into the N-bit FIFO shift register, the earliest-stored bit in the shift register is discarded, and FIFO counter 115 is then updated to represent the new sum of the number of ones in the N-bit shift register. Otherwise, where the evaluation sample is not deemed a turning point, then at 408 a logic “0” is shifted into the N-bit shift register, the earliest stored bit in the shift register is discarded, and FIFO counter 115 is updated to represent the new sum of the number of ones in the N-bit shift register. After 406 or 408, at 410, the sum of the ones in the N-bit shift register provided by FIFO counter 115 is compared to a predetermined threshold value. If the sum exceeds the predetermined threshold value, then at 412 the noise flag is set to indicate that noise is present on the sampled cardiac signal x(n) obtained from cardiac signal detector 110. Otherwise, where the sum does not exceed the predetermined threshold value, then at 414 the noise flag is cleared to indicate that noise is not present on the sampled cardiac signal x(n) obtained from cardiac signal detector 110. After 412 or 414, at 416, the noise flag is evaluated to determine whether noise is present on the sampled cardiac signal x(n), as indicated by the noise flag being set. If the cardiac signal is noisy, then, at 418, one or more noise adjustment parameters and/or techniques is applied to the cardiac signal detection by cardiac signal detector 110 or to the response of device 102 to the acquired cardiac signal. Otherwise, where the cardiac signal is not noisy, then, at 420, one or more default parameters and/or techniques is applied to the cardiac signal detection by cardiac signal detector 110 or to the response of device 102 to the acquired cardiac signal. After 418 or 420, at 422, another cardiac signal sample is obtained by cardiac signal processor 112, so that another evaluation sample can be considered to determine whether the evaluation sample is a turning or inflection point, at 404. Additionally, device 102 may optionally communicate the state of the noise flag to an external programmer or other remote user interface 106 via telemetry circuit 108. Therefore, FIG. 4 illustrates, among other things, that a significant proportion of turning or inflection points in the sampled cardiac signal may indicate the presence of noise, which indication, in turn, may be used to modify the way in which the cardiac signal is obtained so as to reduce the likelihood that noise deflections are erroneously interpreted as heart depolarizations.
[0028] In the example FIG. 4, the counter may alternatively be compared to a multi-valued threshold, such as for providing hysteresis. In one such example, the threshold includes two distinct values: a majority threshold value and a quorum threshold value. The majority threshold value typically exceeds the quorum threshold value. At 400, the threshold is set to the higher majority value. At 412, upon setting the noise flag, the threshold is then set to the lower quorum value. At 414, upon clearing the noise flag, the threshold is then set to the higher majority value. In operation, once the counter exceeds the majority value, the threshold is then decreased to the quorum value. This effectively adds hysteresis to reduce or avoid chatter around the quorum threshold value.
[0029] FIG. 5 is a signal graph of a sampled cardiac signal 500, illustrating generally one technique for determining (such as performed at 404 of FIG. 4) whether an evaluation sample 502 is a turning or inflection point. In this example, the presence of noise is determined from: the evaluation sample 502, x(i); a previous sample 504, such as immediately preceding sample x(i−1); and a subsequent sample 506, such as immediately succeeding sample x(i+1). In this example, using the three samples, x(i), x(i−1), and x(i+1), the following equation is evaluated:
[0000] TP=sign{x(i)-x(i−1)}*sign{x(i+1)-x(i)} (1)
[0000] Equation 1 illustrates taking the sign of a first difference x(i)-x(i−1). A negative sign represents a negative-going signal excursion between the i sample and the (i−1) sample. A positive sign represents a positive-going signal excursion therebetween. Equation 1 also illustrates taking the sign of a second difference x(i+1)-x(i). A negative sign represents a negative going signal excursion between the (i+1) sample and the i sample. A positive sign represents a positive-going signal excursion therebetween. Thus, the product of the signs of the first and second differences, TP, will be −1 whenever the signal excursions on either side of the evaluation sample x(i) differ in direction or sense of their slopes, in which case the evaluation sample x(i) represents a turning/inflection point. Evaluation of the three samples then is shifted rightward on the signal illustration of FIG. 5, such as when another cardiac signal sample is obtained at 422 of FIG. 4, so that the number of turning/inflection points in a sliding window preceding the evaluation sample x(i) can be counted and compared to a threshold to determine whether a sufficient number of turning points has been detected to deem the cardiac signal to be noisy.
[0030] In the above example, choice of the x(i), x(i−1), and x(i+1) samples is simply a matter of convenience for ease of illustration of the above turning point noise detection technique. In particular, this example is not intended to imply a noncausal system. The above-discussed technique (or the other techniques discussed in this document) also applies to any other choice of sequential samples such as, for example, x(i), x(i−1), and x(i−2), or alternatively, x(i−1), x(i−2), and x(i−3), etc.
[0031] In a slightly modified example, a threshold requirement is added to the above technique for determining whether an evaluation sample 502 is a turning or inflection point. The threshold determines a noise floor below which the noise detection is substantially no longer sensitive. In one such example, a TP is evaluated according to Equation 1, but if |x(i)-x(i−1)|<TH1, or if |x(i+1)−x(i)|<TH2, then TP is set to a value different from −1 (e.g., set to 1) to indicate that evaluation sample 502 is not a turning point. TH1, and TH2 may take on the same, or different, threshold values. In one example, TH1=TH2=2 counts of an 8-bit A/D converter signal representing the sampled cardiac signal x(n). This suppresses excessive sensitivity to noise occurring at or beneath the level of 1 least significant bit (LSB). A similar threshold requirement may also be imposed on the other turning point evaluation techniques discussed in this document.
[0032] In one example, TP is a binary-valued signal that is high (“1”) if the evaluation sample 502 is a turning point, and low (“0”) otherwise. In another example, TP is a tri-state signal that is “-1” if the evaluation sample 502 is an inflection point, “0” if the slopes on either side of evaluation sample 502 are too small to determine whether evaluation sample 502 is an inflection point, and “1” if the slopes on either side of evaluation sample 502 are the same sign, such that evaluation sample 502 is not a turning point.
[0033] FIG. 6 is a signal graph of the sampled cardiac signal 500 of FIG. 5, illustrating that the turning/inflection point evaluation need not be performed at the same frequency at which the cardiac signal was sampled. In the example of FIG. 6, the turning/inflection point determination is based on the evaluation sample 502, x(i); a previous sample 504, such as preceding sample x(i−2); and a subsequent sample 506, such as succeeding sample x(i+2). Thus, Equation 1 can be expressed more generally as:
[0000] TP=sign{x(i)-x(i−K1)}*sign{x(i+K2)−x(i)} (2)
[0000] where K1 and K2 are integer offset constants which may, but need not, be the same value. Moreover, the turning point evaluation may be carried out repeatedly over different subsampling frequencies of the frequency at which the cardiac signal was sampled. In such a technique, a vector of TP values corresponding to the different subsampling frequencies may provide useful information about the frequency content of the noise, or may allow the noise detection to be tailored to noise having a particular frequency content. In one example, this is accomplished by varying K between different values, and, at the different values of K: (1) determining, for each sample, TP=sign{x(i)-x(i−K)}*sign{x(i+K)−x(i)}, in which x(i) is the ith sample of the sampled cardiac signal x(n), and in which K is an integer offset, and in which TP=−1 is used as at least one factor indicating that x(i) is a turning point; and (2) deeming the cardiac signal to be noisy if a number of turning points occurring during a fixed number of samples preceding x(i) exceeds a threshold value.
[0034] FIG. 7 is a block diagram illustrating generally, by way of example, but not by way of limitation, several possible operational adjustments that may be performed by device 102 at 418 of FIG. 4 in response to noise flag 116 being set as determined at 416 of FIG. 4. In one example, at 418A, a sense amplifier gain in cardiac signal detector 110 is adjusted (e.g., decreased) when noise is present to avoid erroneously detecting the noise as a heart depolarization. For example, in a switched-capacitor sense amplifier, controller 114 provides a control signal to cardiac signal detector 110 to use different gain-setting switched-capacitors. This noise-dependent gain adjustment effectively uses noise detection as input to an automatic gain control (AGC) feedback system. In an alternative example, at 418B, a frequency selectivity characteristic of the sense amplifier or other cardiac signal filter is adjusted when cardiac signal noise is present to increase the selectivity to the heart depolarization frequencies of interest and more aggressively discriminate against noise at nearby higher or lower frequencies. Alternatively, at 418C, a sensitivity is adjusted (e.g., decreased) in the presence of cardiac signal noise. This may be accomplished, for example, by raising a level-detector threshold for heart depolarizations. Alternatively, at 418D, a sensing electrode configuration is adjusted. For example, where first and second pairs of bipolar sensing electrodes are associated with the same heart chamber, and the first pair of sensing electrodes yields a noisy signal, cardiac signal detector 110 may be decoupled from the first pair of sensing electrodes and coupled instead to the second pair of sensing electrodes in order to try to obtain a less noisy signal. This may be effective, for example, for noise resulting from a fractured lead or other poor connection between the first pair of sensing electrodes and cardiac signal detector 110. In other examples, the sensing electrode configuration may be switched from unipolar sensing to bipolar sensing or vice-versa. In an alternative example, at 418E, noise present on a first electrode pair, for example, may trigger corroboration of heart depolarization detection with an independent second sensing channel that is coupled to a second heart electrode pair. In this example, a heart depolarization detected at the first electrode pair by a first cardiac signal detector would require verification as also having been detected at the second electrode pair by a second cardiac signal detector, thereby reducing the system's susceptibility to erroneously detecting noise as a heart depolarization and thereby inappropriately triggering or withholding therapy to heart 104.
[0035] The above noise detection techniques were tested on data acquired from a human heart from electrodes configured for bipolar sensing. The resulting intrinsic cardiac signal was amplified by a high input impedance continuous-time amplifier and a switched-capacitor discrete-time sense amplifier. Filtering was performed to remove frequencies outside of the range of about 20 Hz to about 130 Hz. The resulting sampled cardiac signal was provided at a sampling frequency of about 200 Hz. The above-described noise detection technique was used in which the turning/inflection points were determined from an evaluation sample, an immediately preceding sample, and an immediately succeeding sample. A moving window (e.g., FIFO shift-register length) of N=10 samples was used. A threshold value of 4 turning/inflection points in the N=10 samples was taken to indicate the presence of noise on the cardiac signal. The results showed good discrimination between the cardiac signal noise and a true fine ventricular fibrillation waveform, which should be sensed as true ventricular heart depolarizations rather than noise.
[0036] FIG. 8 is a block diagram illustrating an alternative example of a system 100 in which device 102 includes a second FIFO counter 800 for performing the noise detection technique illustrated in the flow chart of FIG. 9. In FIG. 9, which shares certain similarities with FIG. 4, first FIFO counter 115, a second FIFO counter 800, and noise flag 116 are initialized. In one example, first FIFO counter 115 includes an N-bit shift register, which is initialized at 400 to all zeros, and also includes an associated first counter that outputs a sum of the number of ones in the N-bit shift register. In this example, second FIFO counter 800 includes an M-bit shift register, which is initialized at 400 to all zeros, and also includes an associated second counter that outputs a sum of the number of ones in the M-bit shift register. Noise flag 116 is also initialized to zero, indicating that noise has not yet been detected as being present on the cardiac signal x(n).
[0037] At 402, a cardiac signal sample is obtained. At 404, a previously-obtained evaluation sample is considered as to whether it represents a turning point (also referred to as an inflection point), with respect to a cardiac signal sample previous to the evaluation sample, and with respect to a cardiac signal sample subsequent to the evaluation sample. If, at 404, the evaluation sample is deemed a turning point, then at 406, a logic “1” is shifted into the N-bit first FIFO shift register, the earliest-stored bit in the shift register is discarded, and first FIFO counter 115 is then updated to represent the new sum of the number of ones in the N-bit shift register. Otherwise, where the evaluation sample is not deemed a turning point, then at 408 a logic “0” is shifted into the N-bit shift register, the earliest stored bit in the shift register is discarded, and first FIFO counter 115 is updated to represent the new sum of the number of ones in the N-bit shift register.
[0038] After 406 or 408, at 410, the sum of the ones in the N-bit shift register provided by first FIFO counter 115 is compared to a first predetermined threshold value. If the sum exceeds the predetermined threshold value, then at 900 a logic “1” is shifted into the M-bit second FIFO shift register, the earliest-stored bit in the shift register is discarded, and second FIFO counter 800 is then updated to represent the new sum of the number of ones in the M-bit shift register. Otherwise, where the evaluation sample is not deemed a turning point, then at 905 a logic “0” is shifted into the M-bit shift register, the earliest stored bit in the shift register is discarded, and second FIFO counter 800 is updated to represent the new sum of the number of ones in the M-bit shift register. After 900 or 905, at 910, the sum of the ones in the M-bit shift register provided by second FIFO counter 800 is compared to a second predetermined threshold value, which may be different than the first predetermined threshold value. If the sum exceeds the second predetermined threshold value, then at 412 the noise flag is set to indicate that noise is present on the sampled cardiac signal x(n) obtained from cardiac signal detector 110. Otherwise, where the sum does not exceed the predetermined threshold value, then at 414 the noise flag is cleared to indicate that noise is not present on the sampled cardiac signal x(n) obtained from cardiac signal detector 110.
[0039] After 412 or 414, at 416, the noise flag is evaluated to determine whether noise is present on the sampled cardiac signal x(n), as indicated by the noise flag being set. If the cardiac signal is noisy, then, at 418, one or more noise adjustment parameters and/or techniques is applied to the cardiac signal detection by cardiac signal detector 110 or to the response of device 102 to the acquired cardiac signal. Otherwise, where the cardiac signal is not noisy, then, at 420, one or more default parameters and/or techniques is applied to the cardiac signal detection by cardiac signal detector 110 or to the response of device 102 to the acquired cardiac signal. After 418 or 420, at 422, another cardiac signal sample is obtained by cardiac signal processor 112, so that another evaluation sample can be considered to determine whether the evaluation sample is a turning or inflection point, at 404. Additionally, device 102 may optionally communicate the state of the noise flag to an external programmer or other remote user interface 106 via telemetry circuit 108. Therefore, FIG. 9 illustrates, among other things, an example in which the output of the N-bit shift register indicates whether a particular “window” is noisy, and the output of the M-bit shift register indicates whether a predetermined number of “windows” is noisy, such that the signal should be deemed noisy. FIGS. 4 and 9 illustrate the process of cascading additional windows, together with corresponding counters and thresholds. This process can be extended to cascading any number of additional windows, as needed.
[0040] As discussed above with respect to FIG. 4, the first and second counters may alternatively be compared to respective multi-valued thresholds, such as for providing hysteresis. In one such example, each of the first and second thresholds includes two distinct values: a majority threshold value and a quorum threshold value. The majority threshold value typically exceeds its corresponding quorum threshold value. At 400, the first threshold is set to its higher majority value, and the second threshold is likewise set to its higher majority value. At 900, if the first counter exceeds the first threshold, the first threshold is then set to its lower quorum value. At 905, if the first counter does not exceed the first threshold, then the first threshold is then set to the higher majority value. At 412, upon setting the noise flag, the second threshold is then set to its lower quorum value. At 414, upon clearing the noise flag, the second threshold is then set to its higher majority value. In operation, once each counter exceeds its majority value, its threshold is then decreased to its quorum value. This effectively adds hysteresis to reduce or avoid chatter around the respective quorum threshold values.
[0041] FIG. 10 is a schematic/block diagram illustrating generally one example of a turning point detector 1000, suitable for being included within cardiac signal detector 110, for operating upon an analog acquired cardiac signal x(t) at input node 1002 and providing an indication TP at output node 1004 of whether a particular sample of the acquired cardiac signal x(t) represents a turning point in the acquired cardiac signal x(t). In the example of FIG. 10, the acquired continuous time cardiac signal x(t) is input to a first sample-and-hold (S/H) circuit 1006, to create a delayed sample x(t-T1) output at node 1008. This, in turn is input to a second S/H 1010, to create a further delayed sample x(t-T2) at node 1012. The appropriate delay is obtained by clocking S/H circuits 1006 and 1010 by one or more appropriately timed clock signals, such as CL1 and CL2 received at clocking input nodes 1014 and 1016 of S/H 1006 and S/H 1010, respectively.
[0042] The samples x(t), x(t-T1), and x(t-T2) are received at inputs of differential amplifiers/buffers 1018A-B, which may provide gain greater than one, unity gain, or attenuation, as appropriate. In this example, x(t-T1) is received at a negative input of amplifier 1018A and at a positive input of amplifier 1018B, x(t) is received at a positive input of amplifier 1018A, and x(t-T2) is received at a negative input of amplifier 1018B. Amplifier 1018A provides an output representing the difference [x(t)-x(t-T1)] at node 1020A to first and second comparators 1022A-B. Amplifier 1018B provides an output representing the difference [x(t-T1)-x(t-T2)] at node 1020B to third and fourth comparators 1022C-D.
[0043] Each of comparators 1022A-D also receive a reference voltage input. For example, comparator 1022A receives at node 1024A a reference voltage VT1, comparator 1022B receives at node 1024B a reference voltage VT2, comparator 1022C receives at node 1024C a reference voltage VT3, and comparator 1022D receives at node 1024D a reference voltage VT4, In this example, VT1, VT3 are slightly negative voltages, and VT2, VT4 are slightly positive voltages.
[0044] In this example, comparator 1022A outputs a binary-valued signal Y1 at node 1026A that is high when the difference [x(t)-x(t-T1)]>VT1 and low otherwise, comparator 1022B outputs a binary-valued signal Y2 at node 1026B that is high when the difference [x(t)-x(t-T1)]>VT2 and low otherwise, comparator 1022C outputs a binary-valued signal Y3 at node 1026C that is high when the difference [x(t-T)-x(t-T2)]>VT3 and low otherwise, and comparator 1022D outputs a binary-valued signal Y4 at node 1026D that is high when the difference [x(t-T1)-x(t-T2)]>VT4 and low otherwise.
[0045] The signals Y1, Y2, Y3, and Y4 are input to digital logic circuit 1028, which outputs the binary valued signal TP at node 1004 that is high when x(t-T1) represents a turning point with respect to x(t) and x(t-T2). In one example, logic circuit 1028 is configured to implement functionality based on a double-bit signal S1, comprised of signals Y1 and Y2, and another double-bit signal S2, comprised of signals Y3 and Y4. The signal S1 includes information about the slope of the difference [x(t)-x(t-T1)], and the signal S2 includes information about the slope of the difference [x(t-T1)-x(t-T2)], as described more particularly below in Tables 1 and 2.
[0046] In Tables 1 and 2, A represents a negative slope, B represents a small absolute slope, C represents a positive slope, and D is not a valid state. The digital logic for providing the output TP is defined by Table 3. As seen in Table 3, TP is high when the difference [x(t)-x(t-T1)] represents a negative slope and the difference [x(t-T1)-x(t-T2)] represents a positive slope, or vice-versa, and is low otherwise (the “X” notation refers to invalid states, which may be considered as “don't care” for the purposes of logical minimization for realization of the logic circuit).
[0047] Although the configuration of comparators 1022A-D in FIG. 10 effectively implements a window comparator that will not yield a turning point if the slopes of either the difference [x(t)-x(t-T1)] or the difference [x(t-T1)-x(t-T2)] is of small magnitude, such a threshold requirement on the slopes is not required. For example, FIG. 11 is a schematic/block diagram illustrating generally an example in which these differences are each compared to 0V, by respective comparators 1100A-B. The respective comparator outputs at nodes 1105A-B are input to an exclusive-OR (XOR) gate 1110. XOR gate 1110 outputs TP, which is high when the sign of the difference [x(t)-x(t-T1)] is different from that of the difference [x(t-T1)-x(t-T2)].
[0048] It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-discussed embodiments may be used in combination with each other. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.”
Patent CitationsCited PatentFiling datePublication dateApplicantTitleUS4432362 *Mar 8, 1982Feb 21, 1984Cordis CorporationAtrial-based, atrial-ventricular sequential cardiac pacerUS4589420 *Jul 13, 1984May 20, 1986Spacelabs Inc.Method and apparatus for ECG rhythm analysisUS4679144 *Aug 21, 1984Jul 7, 1987Q-Med, Inc.Cardiac signal real time monitor and method of analysisUS4779617 *Oct 6, 1986Oct 25, 1988Telectronics N.V.Pacemaker noise rejection systemUS4913146 *Oct 13, 1987Apr 3, 1990Telectronics Pacing Systems Inc.Cardiac sense amplifier with pattern recognition capabilitiesUS4960123 *Mar 16, 1989Oct 2, 1990Telectronics N.V.Differentiating between arrhythmia and noise in an arrhythmia control systemUS5010887 *Nov 17, 1989Apr 30, 1991Siemens-Pacesetter, Inc.Noise discrimination in implantable pacemakersUS5095902 *Aug 27, 1990Mar 17, 1992Siemens AktiengesellschaftImplantable medical stimulation system optionally operable in a bipolar or a unipolar modeUS5188117 *Oct 25, 1991Feb 23, 1993Telectronics Pacing Systems, Inc.Notch filter noise rejection system in a cardiac control deviceUS5209237 *May 24, 1991May 11, 1993Felix RosenthalMethod and apparatus for detecting a signal from a noisy environment and fetal heartbeat obtaining methodUS5270124 *Jul 2, 1990Dec 14, 1993The Broken Hill Proprietary Co., Ltd.Composite rollUS5388578 *Apr 6, 1993Feb 14, 1995Incontrol, Inc.Electrode system for use with an implantable cardiac patient monitorUS5492128 *Oct 25, 1994Feb 20, 1996Telectronics Pacing Systems, Inc.Intracardiac electrogram sensing in an arrhythmia control systemUS5522857 *Sep 20, 1994Jun 4, 1996Vitatron Medical, B.V.Pacemaker with improved detection of and response to noiseUS5562713 *Jan 18, 1995Oct 8, 1996Pacesetter, Inc.Bidirectional telemetry apparatus and method for implantable deviceUS5564430 *Nov 16, 1994Oct 15, 1996Ela Medical S.A.Automatic control of the sensing threshold for monitoring cardiac rhythm in a implantable deviceUS5573550 *Apr 28, 1995Nov 12, 1996Pacesetter, Inc.Implantable stimulation device having a low noise, low power, precision amplifier for amplifying cardiac signalsUS5591214 *Nov 20, 1995Jan 7, 1997Telectronics Pacing Systems, Inc.Pacemaker with automatic blanking period functionUS5613495 *Jul 6, 1995Mar 25, 1997Instromedix, Inc.High functional density cardiac monitoring system for captured windowed ECG dataUS5647379 *Nov 22, 1994Jul 15, 1997Ventritex, Inc.Correlator based electromagnetic interference responsive control system useful in medical devicesUS5697958 *Jun 7, 1995Dec 16, 1997Intermedics, Inc.Electromagnetic noise detector for implantable medical devicesUS5702425 *Aug 13, 1996Dec 30, 1997Pacesetter, Inc.Apparatus and method of noise classification in an implantable cardiac deviceUS5702427 *Mar 28, 1996Dec 30, 1997Medtronic, Inc.Verification of capture using pressure waves transmitted through a pacing leadUS5709215 *Sep 6, 1995Jan 20, 1998Angeion CorporationR-wave detection method for implantable cardioverter defibrillatorsUS5755738 *Apr 22, 1997May 26, 1998Cardiac Pacemakers, Inc.Automatic sensing level adjustment for implantable cardiac rhythm management devicesUS5766227 *Mar 4, 1997Jun 16, 1998Nappholz; Tibor A.EMI detection in an implantable pacemaker and the likeUS5776168 *Apr 3, 1996Jul 7, 1998Medtronic, Inc.EGM recording system for implantable medical deviceUS5778881 *Dec 4, 1996Jul 14, 1998Medtronic, Inc.Method and apparatus for discriminating P and R wavesUS5782876 *Apr 15, 1996Jul 21, 1998Medtronic, Inc.Method and apparatus using windows and an index value for identifying cardic arrhythmiasUS5792212 *Mar 7, 1997Aug 11, 1998Medtronic, Inc.Nerve evoked potential measurement system using chaotic sequences for noise rejectionUS5817135 *May 2, 1997Oct 6, 1998Pacesetter, Inc.Rate-responsive pacemaker with noise-rejecting minute volume determinationUS5861008 *Feb 9, 1998Jan 19, 1999Pacesetter AbHeart stimulating device with stimulation energy responsive to detected noiseUS5865749 *Nov 7, 1996Feb 2, 1999Data Sciences International, Inc.Blood flow meter apparatus and method of useUS5867361 *Dec 18, 1997Feb 2, 1999Medtronic Inc.Adhesively-bonded capacitive filter feedthrough for implantable medical deviceUS5870272 *May 6, 1997Feb 9, 1999Medtronic Inc.Capacitive filter feedthrough for implantable medical deviceUS5871509 *Apr 2, 1998Feb 16, 1999Pacesetter AbMethod and apparatus to remove data outliers, produced by external disturbance, in internally measured signals in an implantable cardiac stimulatorUS5891171 *Oct 22, 1997Apr 6, 1999Pacesetter IncorporatedApparatus with noise classification in an implantable cardiac device by using an amplifier with a variable thresholdUS5897575 *Oct 24, 1997Apr 27, 1999Pacesetter, Inc.Arrhythmia classification system with reliability indication that allows for low quality input signals in pacemakersUS5957857 *May 7, 1998Sep 28, 1999Cardiac Pacemakers, Inc.Apparatus and method for automatic sensing threshold determination in cardiac pacemakersUS5978710 *Jan 23, 1998Nov 2, 1999Sulzer Intermedics Inc.Implantable cardiac stimulator with safe noise modeUS5999848 *Sep 12, 1997Dec 7, 1999Alfred E. Mann FoundationDaisy chainable sensors and stimulators for implantation in living tissueUS6029086 *Jun 15, 1998Feb 22, 2000Cardiac Pacemakers, Inc.Automatic threshold sensitivity adjustment for cardiac rhythm management devicesUS6031710 *Dec 18, 1997Feb 29, 2000Medtronic, Inc.Adhesively- and solder-bonded capacitive filter feedthrough for implantable medical devicesUS6063034 *Oct 26, 1998May 16, 2000Data Sciences International, Inc.Blood flow meter apparatus and method of useUS6068589 *Feb 14, 1997May 30, 2000Neukermans; Armand P.Biocompatible fully implantable hearing aid transducersUS6070097 *Dec 30, 1998May 30, 2000General Electric CompanyMethod for generating a gating signal for cardiac MRIUS6112119 *Oct 27, 1997Aug 29, 2000Medtronic, Inc.Method for automatically adjusting the sensitivity of cardiac sense amplifiersUS6195585 *Jun 25, 1999Feb 27, 2001Advanced Bionics CorporationRemote monitoring of implantable cochlear stimulatorUS6198968 *Jun 15, 1999Mar 6, 2001Intermedics Inc.Implantable cardiac stimulator with safe noise modeUS6201993 *Dec 9, 1998Mar 13, 2001Medtronic, Inc.Medical device telemetry receiver having improved noise discriminationUS6208900 *Mar 28, 1996Mar 27, 2001Medtronic, Inc.Method and apparatus for rate-responsive cardiac pacing using header mounted pressure wave transducerUS6223083 *Apr 16, 1999Apr 24, 2001Medtronic, Inc.Receiver employing digital filtering for use with an implantable medical deviceUS6230059 *Mar 17, 1999May 8, 2001Medtronic, Inc.Implantable monitorUS6236882 *Jul 14, 1999May 22, 2001Medtronic, Inc.Noise rejection for monitoring ECG'sUS6272381 *Jul 2, 1998Aug 7, 2001Pacesetter, Inc.Rate-responsive pacemaker with closed-loop controlUS6282446 *Aug 24, 1999Aug 28, 2001Cardiac Pacemakers, Inc.Automatic shock lead gain adjusterUS6321115 *Dec 3, 1999Nov 20, 2001Pacesetter, Inc.Noise detection system and method for use in an implantable medical deviceUS6421554 *Dec 30, 1999Jul 16, 2002Samsung Electronics Co., Ltd.Method and device for detecting fault of lead in electrocardiogram systemUS6505071 *Dec 15, 1999Jan 7, 2003Cardiac Pacemakers, Inc.Cardiac management device with capability of noise detection in automatic capture verificationUS6892092 *Oct 29, 2001May 10, 2005Cardiac Pacemakers, Inc.Cardiac rhythm management system with noise detector utilizing a hysteresis providing thresholdUS6917830 *Aug 19, 2003Jul 12, 2005Cardiac Pacemakers, Inc.Method and system for noise measurement in an implantable cardiac deviceUS7215993 *Aug 6, 2002May 8, 2007Cardiac Pacemakers, Inc.Cardiac rhythm management systems and methods for detecting or validating cardiac beats in the presence of noiseUS7233827 *Jun 9, 2004Jun 19, 2007Pacesetter, Inc.Implantable cardiac stimulation device with automatic evoked response sensing electrode configuration selection and methodUS7467009 *Apr 20, 2005Dec 16, 2008Cardiac Pacemakers, Inc.Cardiac rhythm management system with noise detectorUS20030082713 *Dec 11, 2000May 1, 2003Rutter Andrew JamesMonitoring oligonucleotide binding processes using chemiluminescence quenchingUS20040030256 *Aug 6, 2002Feb 12, 2004Yayun LinCardiac rhythm management systems and methods for detecting or validating cardiac beats in the presence of noiseUS20040106957 *Aug 19, 2003Jun 3, 2004Surekha PalreddyMethod and system for noise measurement in an implantable cardiac deviceUS20050192504 *Apr 20, 2005Sep 1, 2005Cardiac Pacemakers, Inc.Cardiac rhythm management system with noise detectorUS20070135722 *Jan 22, 2007Jun 14, 2007Yayun LinSystems and methods for detecting or validating signals in the presence of noise* Cited by examinerReferenced byCiting PatentFiling datePublication dateApplicantTitleUS7783340Jan 16, 2007Aug 24, 2010Cameron Health, Inc.Systems and methods for sensing vector selection in an implantable medical device using a polynomial approachUS8078272Dec 13, 2011Cardiac Pacemakers, Inc.Systems and methods for detecting or validating signals in the presence of noiseUS8079959Dec 20, 2011Cameron Health, Inc.Patient screening tools for implantable cardiac stimulus systemsUS8160686Mar 6, 2009Apr 17, 2012Cameron Health, Inc.Methods and devices for accurately classifying cardiac activityUS8160687Apr 17, 2012Cameron Health, Inc.Methods and devices for accurately classifying cardiac activityUS8200341Feb 7, 2007Jun 12, 2012Cameron Health, Inc.Sensing vector selection in a cardiac stimulus device with postural assessmentUS8265737Sep 11, 2012Cameron Health, Inc.Methods and devices for identifying overdetection of cardiac signalsUS8265749Dec 14, 2009Sep 11, 2012Cameron Health, Inc.Methods and devices for accurately classifying cardiac activityUS8494630Jan 16, 2009Jul 23, 2013Cameron Health, Inc.Data manipulation following delivery of a cardiac stimulus in an implantable cardiac stimulus deviceUS8521276Jan 11, 2011Aug 27, 2013Cardiac Pacemakers, Inc.Use of significant point methodology to prevent inappropriate therapyUS8548573Jan 18, 2010Oct 1, 2013Cameron Health, Inc.Dynamically filtered beat detection in an implantable cardiac deviceUS8565878Mar 6, 2009Oct 22, 2013Cameron Health, Inc.Accurate cardiac event detection in an implantable cardiac stimulus deviceUS8588896Sep 7, 2012Nov 19, 2013Cameron Health, Inc.Methods and devices for accurately classifying cardiac activityUS8600489Mar 30, 2012Dec 3, 2013Cameron Health, Inc.Methods and devices for accurately classifying cardiac activityUS8626280Mar 30, 2012Jan 7, 2014Cameron Health, Inc.Methods and devices for accurately classifying cardiac activityUS8700152May 21, 2013Apr 15, 2014Cameron Health, Inc.Data manipulation following delivery of a cardiac stimulus in an implantable cardiac stimulus deviceUS8712523Dec 11, 2009Apr 29, 2014Cameron Health Inc.Implantable defibrillator systems and methods with mitigations for saturation avoidance and accommodationUS8744555Oct 27, 2010Jun 3, 2014Cameron Health, Inc.Adaptive waveform appraisal in an implantable cardiac systemUS8744556Jan 24, 2012Jun 3, 2014Cardiac Pacemakers, Inc.Noise detection in implantable medical devicesUS8781602Jun 17, 2013Jul 15, 2014Cameron Health, Inc.Sensing vector selection in a cardiac stimulus device with postural assessmentUS8788023May 26, 2006Jul 22, 2014Cameron Health, Inc.Systems and methods for sensing vector selection in an implantable medical deviceUS8825157Jun 23, 2008Sep 2, 2014Cameron Health, Inc.Vector switching in an implantable cardiac stimulus systemUS8880161Oct 21, 2013Nov 4, 2014Cameron Health, Inc.Methods and devices for accurately classifying cardiac activityUS8929977Dec 4, 2013Jan 6, 2015Cameron Health, Inc.Methods and devices for accurately classifying cardiac activityUS8965491Apr 7, 2014Feb 24, 2015Cameron Health, Inc.Adaptive waveform appraisal in an implantable cardiac systemUS8965530Jun 18, 2014Feb 24, 2015Cameron Health, Inc.Implantable cardiac devices and methods using an x/y counterUS9079035Jun 6, 2013Jul 14, 2015Cameron Health, Inc.Electrode spacing in a subcutaneous implantable cardiac stimulus deviceUS9149637Jun 29, 2010Oct 6, 2015Cameron Health, Inc.Adaptive confirmation of treatable arrhythmia in implantable cardiac stimulus devicesUS9149645Mar 10, 2014Oct 6, 2015Cameron Health, Inc.Methods and devices implementing dual criteria for arrhythmia detectionUS9162074Nov 24, 2014Oct 20, 2015Cameron Health, Inc.Methods and devices for accurately classifying cardiac activityUS9242112Feb 20, 2014Jan 26, 2016Cameron Health, Inc.Data manipulation following delivery of a cardiac stimulus in an implantable cardiac stimulus deviceUS9265432May 23, 2014Feb 23, 2016Cameron Health, Inc.Methods and devices for accurately classifying cardiac activityUS9339662Oct 18, 2013May 17, 2016Cameron Health, Inc.Methods and devices for accurately classifying cardiac activityUS9345899Aug 6, 2014May 24, 2016Cameron Health, Inc.Vector switching in an implantable cardiac stimulus systemUS9357969Jul 29, 2015Jun 7, 2016Cameron Health, Inc.Sensing vector selection in a cardiac stimulus device with postural assessmentUS9364677Jun 13, 2014Jun 14, 2016Cameron Health, Inc.Systems and methods for sensing vector selection in an implantable medical deviceUS9380955Mar 6, 2015Jul 5, 2016Cameron Health, Inc.Patient screening tools for implantable cardiac stimulus systemsUS9421390Sep 11, 2015Aug 23, 2016Cameron Health Inc.Methods and devices implementing dual criteria for arrhythmia detectionUS20070135722 *Jan 22, 2007Jun 14, 2007Yayun LinSystems and methods for detecting or validating signals in the presence of noiseUS20070276445 *May 26, 2006Nov 29, 2007Cameron Health, Inc.Systems and methods for sensing vector selection in an implantable medical deviceUS20070276447 *May 26, 2006Nov 29, 2007Cameron Health, Inc.Implantable medical devices and programmers adapted for sensing vector selectionUS20070276452 *May 26, 2006Nov 29, 2007Cameron Health, Inc.Implantable medical device systems having initialization functions and methods of operationUS20080172100 *Jan 16, 2007Jul 17, 2008Cameron Health, Inc.Systems and methods for sensing vector selection in an implantable medical device using a polynomial approachUS20080188901 *Feb 7, 2007Aug 7, 2008Cameron Health, Inc.Sensing vector selection in a cardiac stimulus device with postural assessmentUS20080275521 *Jun 23, 2008Nov 6, 2008Cameron Health, Inc.Vector Switching in an Implantable Cardiac Stimulus SystemUS20090054796 *Aug 22, 2008Feb 26, 2009Cameron Health, Inc.Patient Screening Tools for Implantable Cardiac Stimulus SystemsUS20100094369 *Dec 14, 2009Apr 15, 2010Cameron Health, Inc.Methods and Devices for Accurately Classifying Cardiac ActivityUS20110098775 *Apr 28, 2011Cameron Health, Inc.Adaptive Waveform Appraisal in an Implantable Cardiac SystemUS20110172729 *Jul 14, 2011Sweeney Robert JUse of significant point methodology to prevent inappropriate therapy* Cited by examinerClassifications U.S. Classification600/509International ClassificationA61B5/0402, A61N1/37Cooperative ClassificationY10S128/901, A61N1/3718, A61N1/37European ClassificationA61N1/37RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services