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  Cardiac rhythm monitoring deviceRelated Patent Categories: Surgery, Diagnostic Testing, Cardiovascular, Heart, Detecting Heartbeat Electric Signal, Detecting ArrhythmiaThe Patent Description & Claims data below is from USPTO Patent Application 20060106323. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a continuation of application Ser. No. 10/156978, filed on May 29, 2002. BACKGROUND OF THE INVENTION [0002] Supraventricular arrhythmia is a particular type of electrical disturbance of the rhythm of the heart. It is an arrhythmia originating in the upper chambers of the heart, which can lead to an irregular, abnormal heartbeat. Supraventricular arrhythmia is a fairly common occurrence, and as people get older, their chance of experiencing supraventricular arrhythmia will typically increase. Supraventricular arrhythmia itself is not an immediately life-threatening condition. Current research, however, has revealed that supraventricular arrhythmia predisposes a patient to such life threatening conditions as stroke, cardiomyopathy, and congestive heart failure. Consequently, it is important for doctors to be able to detect supraventricular arrhythmia as early as possible, since the earlier that supraventricular arrhythmia is diagnosed and treated, the greater the chance that the arrhythmia or its dangerous side effects can be treated, reducing the risks of stroke, cardiomyopathy, and congestive heart failure. Furthermore, it is important to be able to monitor the arrhythmia over time, since duration is an important factor in evaluating the health risks associated with supraventricular arrhythmia and ongoing monitoring also allows doctors to regulate the amount of medication that patients take as treatment for supraventricular arrhythmia. [0003] Unfortunately, patients often will not even realize that they are experiencing supraventricular arrhythmia, since secondary symptoms may not appear or may be difficult to recognize. The standard technique for detecting arrhythmias employs an electrocardiogram ("ECG"), which uses several electrical leads attached to the patient's chest to monitor the patient's heart during a visit to the doctor's office (where the ECG machine is located). An ECG is a medical diagnostic device that produces a fairly detailed readout of the patient's heart rhythm, which a medical professional may interpret in order to evaluate how a patient's heart is functioning during the visit to the doctor's office. An ECG often does not monitor a patient's real-time beat-to-beat rhythm, however; instead, it may process the patient's heart rhythm over discrete time intervals (such as 5 seconds) to provide a "snapshot" heart rhythm output for interpretation by a medical expert. Consequently, it may be difficult for even medical professionals to detect supraventricular arrhythmia using an ECG. A real-time, beat-by-beat analysis of the patient's heart rhythm would allow for more accurate assessment of a patient's heart rhythm in order to detect the presence of an arrhythmia. [0004] Furthermore, supraventricular arrhythmia is often an intermittent, sporadic condition, such that the use of an ECG during a visit with a doctor may not reveal any irregularity in the heart rhythm, since the patient may not be experiencing the arrhythmia at that time. In such a case, regular (periodic) or continuous monitoring of the patient's heart rhythm would be better able to detect supraventricular arrhythmia. Once supraventricular arrhythmia has been detected, regular monitoring is also recommended in order to determine the duration of the arrhythmia, since sustained supraventricular arrhythmia lasting more than 24 to 48 hours greatly increases the chance of a blood clot forming that could cause a stroke in the patient. [0005] Regular monitoring would also allow for adjustment of the dosage of medications treating the supraventricular arrhythmia (or the secondary symptoms) based upon the patient's daily condition. Once an arrhythmia has been detected, doctors often prescribe blood-thinning drugs (anti-coagulants), such as Coumadin.RTM. (Warfarin Sodium), in order to reduce the chances of blood clot formation, or anti-arrhythmia medications, in order to stabilize the heart rate. Unfortunately, both the blood-thinning drugs and the anti-arrhythmia medications may have side effects, some of which can be medically serious. Therefore, doctors may prefer daily monitoring of the patient's heart rhythm for supraventricular arrhythmia, so that they may lower the dosage of drugs that the patient takes as the arrhythmia subsides (as opposed to the current practice of maintaining the same dosage level between doctor visits, which are typically spaced six months apart). This may reduce the side effects experienced by the patient. A device that a patient could use to monitor their heart rhythm, searching for signs of supraventricular arrhythmia, would address all of these needs. Since a patient would operate such a device, it should be simple, portable, convenient, low-cost, self-contained, non-invasive, and automatically assess the patient's likelihood of arrhythmia. [0006] The present invention of the Cardiac Rhythm Monitoring Device ("CRMD") is designed to perform all of these functions. It is not designed to be used exclusively by doctors as the primary device for sensing, detecting, diagnosing, or classifying arrhythmias. Rather, the CRMD allows for periodic monitoring of the rhythm of a patient's heart, warning the patient if it detects potential supraventricular arrhythmia activity. This can be useful when a doctor suspects that a patient has experienced intermittent supraventricular arrhythmia, but the ECG does not record any abnormal heart rhythms during the visit to the doctor's office. The CRMD can provide a preliminary warning of the possibility of a serious supraventricular arrhythmia, alerting the patient to see a doctor for a more thorough analysis of their rhythms. If the CRMD detects supraventricular arrhythmia for over a 24-hour period, for example, the patient has a greater need for medical attention than if the duration of the arrhythmia is shorter. And, the CRMD can be used in conjunction with blood-thinning medications or anti-arrhythmia medications to regulate the dosage according to the condition of the patient's heart rhythm. [0007] The CRMD may be used in a discrete, periodic manner, or it may be used to continuously monitor the patient's heart rhythm. In the first embodiment, the patient, as described above, would typically use the CRMD periodically. In the second embodiment, however, the CRMD could also be used continuously, which would be especially useful for detecting intermittent supraventricular arrhythmia. In that case, the patient would wear the CRMD continuously throughout the day. This would allow for continuous, uninterrupted monitoring of the patient's heart rhythm, such that the CRMD would be able to warn the patient immediately whenever it detects a potential supraventricular arrhythmia. The patient would then be able to seek prompt medical treatment from medical professionals, who could apply confirmatory tests to verify an arrhythmia and provide the appropriate level of treatment to the patient. For this type of continuous monitoring to be effective, however, the CRMD must not interfere substantially with patient's lifestyle (or else the patient will not wear it). Thus, convenience factors (such as small size, light-weight, and unobtrusive configuration) will be incorporated into the design of the device. SUMMARY OF THE INVENTION [0008] The Cardiac Rhythm Monitoring Device ("CRMD") is a simple, user-friendly medical device designed to be operated by a patient, without the need for extensive training. It monitors the patient's heart rhythm and determines if a patient is likely experiencing supraventricular arrhythmia. The CRMD may be used periodically, for regular checks of a patient's heart rhythm, or it may be used in a continuous, uninterrupted manner, for constant monitoring of a patient's heart rhythms. When used by a patient under the guidance and supervision of medical professionals, the CRMD can aid in the detection of intermittent supraventricular arrhythmia, can assist in determining the duration of the arrhythmia, and can assist in customizing the appropriate dosage of medication to fit the patient's specific needs. [0009] To effectively detect supraventricular arrhythmia, an analysis of the patient's beat-to-beat heart rate must be performed. The CRMD monitors a patient's beat-to-beat heart rate over a period of time, and analyzes the patient's heart rhythm to determine if it indicates that the patient is experiencing supraventricular arrhythmia. The CRMD is not designed to perform the extensive and detailed tests which would be required in order to develop a final diagnosis concerning the patient's heart rhythm (that would, for example, specifically classify the type of arrhythmia being experienced). Instead, the CRMD is designed to primarily serve a preliminary screening function. Thus, if the CRMD indicates that a patient may be experiencing supraventricular arrhythmia, the patient is directed to seek medical attention so that medical professionals may perform more extensive tests to diagnosis the specific problem and to develop an appropriate treatment regimen. [0010] The CRMD will often be used only periodically. For example, the CRMD may be used approximately once per day by the patient in order to check if the supraventricular arrhythmia lasts more than 24 hours. Arrhythmia is more dangerous if it lasts more than 24 hours, since prolonged arrhythmia encourages blood clotting which could, in turn, lead to stroke or other complications. Thus, if repeated, periodic uses of the CRMD indicated that the patient's arrhythmia has lasted more than 24 hours, the patient may need to seek immediate medical attention. [0011] Furthermore, once a patient has been diagnosed with supraventricular arrhythmia, the doctor will often prescribe blood-thinning medication, such as Coumadin.RTM. (Warfarin Sodium), in order to reduce the likelihood of blood clot formation, or anti-arrhythmia medications, in order to restore the patient's heart rate to a more normal rhythm. Unfortunately, these medications may have fairly dangerous side effects themselves, which could become life-threatening. For example, patients on blood-thinning medications are at an increased risk of bleeding. Therefore, it is preferable to use these blood-thinning medications only for as long as necessary (i.e. during supraventricular arrhythmia activity) and only in the lowest effective dosages, in order to limit the risk of bleeding to the patient. The CRMD may be used to monitor the patient's heart rhythm on a daily basis in order to allow for medical personnel to determine the appropriate dosage of medication to be used by the patient while the supraventricular arrhythmia continues, and to determine when the arrhythmia has ended and the drugs are no longer required. [0012] The CRMD device is essentially comprised of one or more sensors, which detect the R-R interval signal of the patient's heart rhythm (i.e. the actual beat-to-beat heart rate); a memory storage means, such as one or more computerized arrays, which stores the sensed beat-to-beat heart rhythm over a period of time in order to allow for proper analysis to determine if a warning regarding arrhythmia is warranted; and a processing unit, which executes an algorithm to analyze the sensed heart rhythm searching for indications of arrhythmia. [0013] The primary input (from the sensors) to the processing unit consists of the measured R-R interval of the patient's heart rhythm. This is a beat-to-beat input, indicating the amount of time between each individual heartbeat. Most commonly, the CRMD senses the R-R interval using two conductive electrodes, one contacting on the left side of the patient's body and one contacting on the right side of the patient's body, in order to sense the electrical current flow through the patient's heart. This is a non-invasive means for sensing the patient's beat-to-beat heart rhythm, making the CRMD user-friendly. When the patient's heart beats, the electrical impulse of the heart is transmitted throughout the patient's body. It is this very weak electrical signal, emanating from the patient's heart and indicating potential contraction of the heart as a beat, which becomes the primary input signal. The two electrodes of the CRMD receive this weak electrical signal from the patient's body. The signal is then typically amplified, digitized, and normalized before being transmitted to the processing unit for analysis. Although other sensing mechanisms (such as pulse oximeters, thermistors, optical electrodes, peak blood flow (pulse) and pressure sensors, capacitance/induction sensors, infrared/photoelectric sensors, and impedance sensors) could be used to measure the R-R interval, conductive electrode sensors provide an effective combination of ease-of-use, convenience, cost-effectiveness, and accuracy. [0014] The processing unit uses the input data from the sensors to determine if the patient is likely experiencing supraventricular arrhythmia by analyzing the regularity of the patient's heart rhythm. A heart rhythm will have some variation, even in a perfectly healthy, normal person. For a normal, healthy person, however, the variance is limited. So for instance, general population studies have indicated that the typical variance in time between heart beats for a healthy, normal heart is less than 125 milliseconds beat-to-beat. Extrapolating from this evidence, it stands to reason that if the signal from a patient indicates a variance outside of the normal range (i.e. more than a variance of 125 milliseconds between heart beats based on the example study), then there is a potential problem that could indicate arrhythmia. More specifically, the analysis performed by the processing unit would compare each R-R interval between heart beats to the average R-R interval for the patient. For a normal, healthy heart, the difference (i.e. variance) between each particular R-R interval and the calculated average R-R interval is less than or equal to 125 milliseconds; any variance greater than 125 milliseconds (above or below the average R-R interval calculated for the patient) would be indicative of a potential problem. Each such event is a potential irregular heart beat outside of the normal R-R interval variance range (based on general population studies). This type of analysis essentially uses a pre-constructed data table based on general population studies to determine the appropriate criteria for classifying individual heart beat intervals as irregular. Obviously, the precise criteria could vary depending upon the study used as the basis for comparison (and a variance of 125 milliseconds is merely an example). [0015] Alternatively, the processing unit could analyze the patient's sensor data for irregular heart beats using a statistical approach based upon normal distribution analysis of the patient's own heart rhythm. Again, the processor would be searching for irregular heart beats which are outside of the normal range of variance typically seen in human hearts, but this form of analysis effectively builds a data table to determine the appropriate criteria for classifying individual heart beat intervals as irregular instantaneously, using the patient's own individual heart rhythm to shape the criteria rather than basing the criteria on more general factors from studies of broader populations. Thus, this approach has the benefit of being customized to the particular patient. In this statistical approach, each sensed beat-to-beat heart beat interval is normalized using a standard normalization technique (such as dividing each interval by the average interval, for example). This allows normal distribution pattern analysis techniques to be utilized to identify heart beat intervals which are irregular and to indicate an unstable heart rhythm. Only normalized heart beat intervals at the extreme range of the normal distribution curve indicate irregularity, so for instance, those normalized values falling outside of the range of 0.95 to 1.05 might be classified as irregular. [0016] It is, however, fairly common for even healthy persons to experience an occasional variance in the interval between heartbeats which is slightly outside of the normal range. In other words, occasionally even a normal, healthy heart will produce an extra beat or skip a beat. One or more brief events outside a patient's normalized R-R interval variance range may not indicate supraventricular arrhythmia. Consequently, the CRMD will analyze the patient's beat-to-beat heart rhythm over some period of time, 10-60 seconds for example, or over a certain number of heart beats, with a sample data set typically ranging from 8 to 32 heart beats, to determine if there is a sustained irregularity that may indicate supraventricular arrhythmia. If the CRMD detects several irregular heartbeats with varying R-R intervals in the appropriate time frame (for example 3 or more within a minute) or a statistically significant number of normalized heartbeats indicating irregularity within a sensed data set, then that may be a strong indication of supraventricular arrhythmia. If the CRMD is used for an even longer period of time (greater than the base period), its analysis should become even more accurate, since the calculated R-R interval baseline will become more accurate as additional heart beats are factored into the calculations, allowing the CRMD software to more effectively identify irregular heart beats. [0017] In order to further improve the analysis performed by the CRMD, additional inputs related to the patient's beat-to-beat heart rate might optionally be used in addition to the primary sensor input. For example, the CRMD may optionally sense for peak blood flow, using a pulse pressure sensor, and/or for pulse oxygenation, using an optical sensor to monitor changes in the oxygenation of the patient's blood, in order to compare these mechanical/physiological indications of the patient's heart rhythm to the electrical R-R interval indication of the patient's heart rhythm. Such optional secondary inputs would serve as a check, verifying the accuracy of the electrical R-R interval input data and screening out false data (such as electromagnet noise from the environment around the patient). The secondary inputs would also provide more detailed information about the patient's heart rhythm for analysis, since the amount of lag time between the electrical signal (generated by the heart and sensed by the electrodes of the CRMD) and the mechanical/physiological (blood flow) responses also changes when a patient is experiencing supraventricular arrhythmia. The measured delay between the electrical signals and the mechanical signals can also assist in the detection of a patient experiencing arrhythmia. [0018] In addition to the required elements of one or more sensors for detecting the patient's beat-to-beat heart rhythm, a temporary memory block to store heart beat (R-R interval) data for the required duration needed to analyze the patient's heart rhythm, and a processing unit to analyze the data to determine if there are indications of supraventricular arrhythmia, there are also some additional features for the CRMD. First, the CRMD will require a power source to operate. While it could be plugged into a wall outlet to run off of centralized power, an independent, portable power source, such as one or more batteries, would be more convenient. A casing or housing, which could protect the processing unit from potentially damaging events and could protect the patient from electrical shock, would also make the CRMD a more durable and safe device. [0019] In addition, an output unit may be provided so that the patient may receive indication of the test results from the CRMD (although the CRMD may be designed so that it plugs into an external output device as well). For convenience, the output unit may be integrated into the CRMD device itself. For example, the output unit may indicate a warning by illuminating a red light when a problem is indicated. Or, a more sophisticated LCD-type screen could provide the patient with more detailed information concerning the test results and the recommended course of action. The output device need not be visual either. It could, for example, provide an audible alarm, or it could utilize a voice synthesizer to communicate with the patient. Further, the full output unit does not need to be incorporated within the CRMD. Instead, the CRMD could transmit its results to another, separate device for output to the patient or medical professionals. For example, the patient could download the results onto their personal computer, which would display the output in a form that the patient could understand. Or, the results from the processing unit could be transmitted over phone lines or over the Internet to the doctor's office, so that medical professionals may review the output results and discuss the information with the patient. [0020] Another optional element, which may be added to the CRMD, would be additional non-volatile memory storage space. Then, for example, the CRMD (used in a continuous monitoring format) could log a patient's heart rhythm over a longer period of time; say 24 hours, so that a doctor could review the actual beat-to-beat heart rhythm of the patient while diagnosing the patient's condition. Or, the CRMD (used in a periodic manner) could record the time and date of each test by the patient along with the results, so that a doctor could chart a patient's status over a longer period of time, in between monthly visits for example. Thus, the CRMD could be used as an additional source of information about the patient's heart rhythm as medical professionals diagnosis the patient's condition, develop an appropriate treatment regimen, and monitor the patient's progress under the treatment regimen. [0021] In the most typical arrangement of the CRMD configured for periodic testing, the CRMD would be housed in a casing with integrated handles. Each of the handles would have a conductive electrode to sense the patient's beat-to-beat (R-R interval) heart rhythm. Optionally, this version of the CRMD could also have secondary sensors incorporated within it. For example, besides the conductive electrodes in the handles, which directly sense the heart's electrical impulses, the handles could also have a finger pulse oximeter incorporated to measure the patient's mechanical/physiological (blood flow) responses. The sensor data would be transmitted to the processing unit, typically located in the housing between the two handles, and the results from the processing unit would be displayed on a LCD-type screen located atop the central portion of the housing, in between the two handles. Thus, the patient would grip the handles for a period of time, typically 10-60 seconds, and would then receive an indication concerning their heart rhythm. [0022] Alternatively, the CRMD could be configured for continuous usage by the patient. In the most typical arrangement of the CRMD configured for continuous monitoring, the patient would wear two sensor bands, on their wrists, for example. The sensor bands would contain the conductive electrodes for detecting the heart's electrical impulses, and could also incorporate a pulse pressure-sensing device to monitor the secondary, mechanical/physiological responses of the patient. This data would then be transmitted to the processing unit, which would typically be located in a housing worn on a belt in the manner of a Walkman.TM., for example. The housing would also usually include some sort of output device, such as a warning alarm and/or warning lights, to notify the patient when a problem has been detected. An LCD-type screen could also be included, to provide additional details to the patient after the initial warning. Furthermore, one of the sensor bands may also include the housing for the processor and other microelectronics, including an integrated output display device. Continue reading... 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