Patent Application
20110028821
The present invention relates to the field of medical electronics, more precisely to the field of instruments for measuring and recording bioelectric signals, such as electrocardiographs (ECGs).
The concept of a system for urgent cardiac diagnostics, in which measurements for ECG determination are obtained from the patient and sent to a remote diagnostic center for possible intervention, is known. Such systems rely on measurements taken by the patient, and then, on the basis of these and a conversation with the patient, a cardiologist at a remote location can decide: a) whether an urgent intervention is needed, b) whether the intervention can be performed by the patient himself, or c) whether the patient's state requires urgent medical intervention, and acts accordingly. It is very important that the most critical period, from the occurrence of the first symptoms until the medical treatment, be minimized (Lenfant C. et al.: Considerations for a national heart attack alert program, Clin. Cardiol. 1990 Aug.; 13 (8 Suppl 8): VIII9-11). There is a number of patents and products which, within the concept of urgent cardiological diagnostics, offer different solutions for recording and transmitting the ECG signal: U.S. Pat. No. 4,889,134 Greenwold, et al., 1989; U.S. Pat. No. 5,226,431 Bible, et al. 1993; U.S. Pat. No. 5,321,618 Gessman, 1994; U.S. Pat. No. 5,966,692 Langer, et al., 1999; PCT WO 01/70105 A2, B. Bojovie 2001; “Instant Memory Recorder” of the company TELESCAN MEDICAL SYSTEMS (TELESCAN MEDICAL SYSTEMS 26424 Table Meadow Road, Auburn, Calif. 9560); “CardioCall Event Recorder” by REYNOLDS MEDICAL (REYNOLDS MEDICAL LTD, John Tate Road, Hertford SG13 7NW United Kingdom) and “Heartwiev P-12” by AEROTEL (AEROTEL LTD. 5 Hazoref st. Holon 58856 Israel). The solutions can be divided into three groups:
1) The first group comprises solutions for sending the recording of one or two standard ECG leads. The mobile recorders of this group can be very small and with integrated electrodes (no cables are needed), which is the advantage of the group. The recording is performed by simple holding of the device on the patient's chest or by positioning the fingers on the integrated electrodes. This is a quick and simple way for a patient to record one or two leads of his ECG. However, recording one or two ECG signals limits the application of these devices to the patients with rhythm disorders, which is about 20% of the patient population with heart diseases. Typical device of this group is “CardioCall Event Recorder” by REYNOLDS MEDICAL.
2) The second group consists of solutions that enable direct recording and transmission of standard 12-lead ECG, thus including their application to the patients with the diagnoses of coronary artery diseases. Namely, in such patients, the complete standard 12-lead ECG is necessary for urgent diagnostics. Some of these devices are equipped with the full set of electrodes and cables for recording all 12 standard ECG leads (usually 10 electrodes, that is cables), which a patient himself attaches onto his body during recording. The typical representative of this group is “12 Lead Memory ECG Recorder” by TELESCAN MEDICAL SYSTEMS. The other method is the use of a reduced number of electrodes that are moved during the recording. For example, if four electrodes are used, three are positioned at the locations of standard ECG leads I, II, and III (arms and legs of the patient), while the fourth electrode has to be moved during recording to each of the six chest positions for recording chest leads V1-V6 (U.S. Pat. No. 4,889,134, Greenwold et al., 1989). The method that uses three cable connected electrodes and four button-shaped integrated electrodes can be found in the device “Heartwiev P-12” by AEROTEL. The recording of 12 leads is performed in three steps: leads DI, D2, D3, aVR, aVL, aVF, V1, and V2 are recorded in the first step, V3 and V4 in the second, and V5 and V6 in the third step. The common disadvantage of the whole group is rather complicated and long-lasting recording procedure, which makes them very inconvenient for self-application, especially for the patients suffering a heart attack. Significant errors are, however, possible, due to imprecise positioning of the electrodes.
3) The third group includes the solutions in which a reduced number of special leads is recorded, and later, on the basis of this recording, all 12 standard ECG leads are reconstructed computationally. The method for the reconstruction of 12 standard ECG leads and/or x,y,z leads of a vectorcardiogram based on the recorded special leads obtained with four electrodes is explained in U.S. Pat. No. 4,850,370, G. E. Dower 1989. The method is based on the dipole approximation of the electrical heart activity and uses the universal tranformation matrix T, with dimensions 3×12, and with the matrix coefficients determined experimentally. A similar solution is given in EASI system method (http://www.healthcare.philips.com/main/products/patient_monitoring/products/ecg/index.wpd).
The conventional ECG leads V (I, II, III, aVR, aVL, aVF, V1, V2, V3, V4, V5, V6) are obtained by multiplying the transformation matrix T with the recorded signals at the special leads Vs(Vs1, Vs2, Vs3). The universal transformation matrix for all patients does not contain information about individual characteristics of a patient, which results in major errors in the reconstruction of the standard ECG lead signals. In this setup, the quality of signal reconstruction is highly dependent on the proper positioning of special leads electrodes.
An improvement of this method by introducing the individual transformation matrix is given in the paper by Scherer, J. A. et al., Journal of Electrocardiology, v 22 Suppl, pp. 128, 1989, and applied in the U.S. Pat. No. 5,058,598 (J. M. Niklas et al., 1993), wherein the implementation of the individual transformation matrix for each patient, with the segment calculation of the transformation matrix coefficients, was suggested (ECG signal is divided into segments and the coefficients for each segment are calculated individually). The reconstruction of the standard ECG lead signals by the individual transformation matrix means that it is necessary to perform the basic (calibrating) recording for each patient, which will be used for the matrix coefficient calculation. The errors in this approach are significantly reduced compared to the method using the universal transformation matrix. The major drawback of both of these methods is the need to use cables for recording with the suggested arrangement of electrodes, which is very inconvenient for self-application, especially in patients suffering a heart attack. The method in which the reconstruction of standard ECG leads is also done with the individual transformation matrix (Scherer, J. A. et al., Journal of Electrocardiology, v 22 Suppl, pp. 128, 1989), but with the mobile ECG device with integrated electrodes, i.e. with no cables used, is presented in the patent PCT WO 01/70105 A2, B. Bojovic 2001. The device enables quick and easy recording of the special ECG leads and reconstruction of all 12 standard ECG leads with the individual transformation matrix. However, the limitations in the arrangement of the electrodes, due to the use of the integrated ones, disable the optimal arrangement of electrodes on the patient's body, which can result in errors in the signal reconstruction.
An additional problem present in all three groups is the occurrence of the base line wandering of the ECG signal during recording. The effect is especially undesirable for the third group of the devices because the base line wandering during the recording of special leads brings about major diagnostic errors in the procedure of the reconstruction of 12 standard ECG leads.
As described herein, a wearable device is configured to generate special ECG signals for constructing a 12-lead ECG, the special ECG signals numbering less than twelve and being combinable with a calibration matrix in order to construct the 12-lead ECG. The wearable device includes a belt having one or more belt electrodes, a waistband having one or more waistband electrodes, the belt and waistband electrodes configured to contact the skin of a wearer and obtain electrical signals therefrom, and a host unit in electrical communication with the belt and waistband electrodes, the host unit including circuitry for generating the special ECG signals from one or more of the acquired electrical signals and circuitry for transmitting information based on the special ECG signals to a location remote from the wearable device.
Also as described herein is a system for monitoring a cardiac condition of a patient that includes a diagnostic center configured to construct a 12-lead ECG of a patient using a special ECG signals numbering less than twelve by combining the special ECG signals with a transformation matrix, and a wearable device configured to generate the special ECG signal. The wearable device includes a belt having one or more belt electrodes, a waistband having one or more waistband electrodes, the belt and waistband electrodes configured to contact the skin of the patient and obtain electrical signals therefrom, and a host unit in electrical communication with the belt and waistband electrodes, the host unit including circuitry for generating the special ECG signals from one or more of the acquired electrical signals and circuitry for transmitting information based on the special ECG signals to a location remote from the wearable device.
Also described herein is a method for generating a 12-lead ECG of a patient. The method includes using belt-mounted electrodes to obtain electrical signals from the patient, using waistband-mounted electrodes to obtain electrical signals from the patient, using a host unit to generate special ECG signals from the electrical signals obtained from the belt-mounted and waistband-mounted electrodes, and to transmit information based on the special ECG signals to a diagnostic center, the special ECG signals numbering less than 12, and constructing a 12-lead ECG by combining the special ECG signals with a transformation matrix.
Also described herein is a wearable device configured to generate special ECG signals for constructing a 12-lead ECG, the special ECG signals numbering less than twelve and being combinable with a calibration matrix in order to construct the 12-lead ECG, the wearable device including: a first wearable component having one or more electrodes configured to contact the skin of a wearer and obtain electrical signals therefrom; and a host unit in electrical communication with the first wearable component, the host unit including circuitry for generating the special ECG signals from one or more of the acquired electrical signals and circuitry for transmitting information based on the special ECG signals to a location remote from the wearable device.
The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more examples of embodiments and, together with the description of example embodiments, serve to explain the principles and implementations of the embodiments.
In the drawings:
Example embodiments are described herein in the context of a bedside cardiac monitoring system and method using an orthogonal electrode pattern. Those of ordinary skill in the art will realize that the following description is illustrative only and is not intended to be in any way limiting. Other embodiments will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the example embodiments as illustrated in the accompanying drawings. The same reference indicators will be used to the extent possible throughout the drawings and the following description to refer to the same or like items.
In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.
A system and method are described herein for reliably and comfortably monitoring patient ECG over a period of interest, and is particularly useful for patients who have undergone cardiac related procedures such as angioplasty, stenting, bypass surgery and the like and need to be monitored for a period of time following the procedure, or for patients who are known to be at risk for cardiac events such as heart attacks and need to be continuously monitored as part of bedside care.
A system such as that shown in
In a hospital setting, the patient (not shown) wearing the wearable device 102 can be in one location, such as a private or shared room, while the diagnostic center 104 can be at a different location or room. The ECG generated at the diagnostic center 104 can be displayed and monitored there, or at a remote location 106 on or off the hospital premises and in communication with the diagnostic center. It will be appreciated that while a single wearable device 102 is depicted, it is possible for diagnostic center 104 to be in communication with multiple such devices so that a plurality of patients can be monitored simultaneously by the single diagnostic center. Of course in that case, when individualized transformation matrices are used, the diagnostic center 104 would contain multiple individualized transformation matrices each associated with a specific patient so that the individual patient's ECG can be reconstructed.
Also shown in
Different schemes for the electrodes (a-e) can be utilized, with the scheme shown in
It should be noted that while the wearable components of the wearable device 102 are in the form of a “belt” and a “waistband,” other expedients such as harnesses, bands and straps can be used in lieu of or in conjunction with one or both the belt and waistband, and can be associated with parts of the body of the patient other than the waist and chest. For example, either or both the belt and waistband can be replaced with patches that abut the skin of the patient, bringing it into contact with electrodes disposed on the patches. Such patches can be adhered to the skin using an appropriate adhesive, or they can be sewn or otherwise affixed to the interior of a special garment worn by the patient, or they can be strapped to the patient's body through any suitable means.
All the electrodes (a-e) are connected to host unit 202 and provide electrical signals derived from the body of the patient to the host unit. Electrodes a-c provide special lead signals, electrode d provides a common signal, and electrode e provides a ground signal for the ECG reconstruction procedure as further explained below. The common signal from electrode d is used to efficiently provide a common reference point against which the potentials at electrodes a, b and c are measured. Alternatively, each of the electrodes a, b and c can be associated with its own reference point against which the potential is determined.
As mentioned above, some or all of the electrodes a-e can communicate wirelessly with the host unit. A general schematic of such wireless communication between two electrodes in this example and the host unit is shown in
The signals from transmitter modules 2121 and 2122 are received by a counterpart electrode receiver module 220 at the host unit 202. The receiver module 220 includes an antenna 222 and an RF demodulator 224. It is also contemplated that some or all the circuitry and components of transceiver 306, antenna 312 and controller, discussed in detail below, can be used to receive and process the signals from the wireless electrodes ei in lieu of or in addition to the circuits and components of receiver module 220.
Details of host unit 202/202b are shown schematically in
The amplifiers 310a-310c amplify the signals from special leads 318a-318c and pass them to controller 304, which is optional and which can be used to provide management and control functions for the other components of the host unit 202 and wearable device 102. For instance, the operation of the amplifier module 310 can be monitored using controller 304 and feedback to the wearer or caretaker indicative of proper operation can be provided. As an example, the controller 304 can check for appropriate voltage levels received from the amplifiers, and if these are below predetermined thresholds, an indication that a lead is not properly positioned on the body of the patient can be provided, in the form of an acoustic tone or flashing LED (not shown), for instance. Conversely, proper connection and operation can be indicated by a different tone or an uninterrupted LED emission, or other indication. These indications can be provided at the wearable device 102, and/or at the diagnostic center 104 with which it is in communication. The indications can also be provided to guide the patient and/or caretaker during the calibration process detailed below, to for instance indicate successful or unsuccessful calibration, recording in-progress, and so on.
Other functions of the controller 304 can be to condition the signals received from the amplifier module 310 for transmission by transceiver 306 and antenna 312. Conditioning may include appropriately modulating a carrier wave for RF transmission, in accordance with any known protocol. Other components to facilitate transmission can be used, such as a modem, as is known, and any of myriad types of wireless or wired schemes for communication between wearable device 102 and diagnostic center 104 may be employed. Moreover, two-way communication is contemplated, such that antenna 312 and transceiver 306 can be configured to receive signals from diagnostic center 104 and/or other devices to pass on to controller 304. These signals can be for performance of a handshaking procedure for proper connection, an authentication procedure, or they can be command signals for controller 304, for example to recalibrate, or to provide a failure signal or indication at the wearable device 102.
The signals from amplifier module 310 can also be stored for subsequent downloading, and memory 314 is provided for this purpose. Memory 314 is preferably a persistent type device, such that information remains stored even after power-down. Power to the various components is provided by power supply 302, which can take the form of a rechargeable or disposable battery pack.
Using the above arrangement, it is possible to precisely reconstruct all 12 signals of standard ECG leads with only signals from the three special leads 201a-201c. This is performed by combining the special leads signals by a pre-generated transformation matrix, preferably one that is individualized for the particular patient. The reconstruction is conducted in real time, preferably at the diagnostic center 104, which contains computing resources that include hardware and/or software to perform the combining, generate the ECG therefrom, display it to the operator, and possibly conduct intelligent automated monitoring and signal any alarm conditions.
As explained above, the information obtained from the electrodes e-c can be transmitted to diagnostic center 204 in real time, or it can be stored, for example in memory 314, for subsequent transmission, at prescribed intervals or in a single burst. Alternatively, the information can be retained in the memory 314 for subsequent downloading at the diagnostic center, using a dedicated connection such as a cable, cradle, or wirelessly (BlueTooth™, etc.). Since the data used is from three special leads (and reference and/or ground), rather than the conventional 12 leads, the amount of information that needs to be stored is reduced and the memory requirements are similarly reduced. The information itself can be in raw form, or it can have undergone partial or complete processing in the host unit 202 to render an ECG for presentation to the caregiver or physician. Processed data is derived by combining the raw data with the personalized or general transformation matrix, for instance, which in this example would take place in the wearable device itself, and specifically in the host unit thereof. Alternatively, the 12-lead reconstruction could take place at the diagnostic center.
The process for monitoring a patient with the system 100 is explained with reference to
Actual monitoring occurs after the calibration step, and is illustrated at 404 in
The accuracy in the reconstruction of 12 standard ECG leads using the recordings of three special leads is achieved using the arrangement of integrated electrodes as described herein. The reconstruction algorithm is based on the assumption that diffused electrical activity of the heart muscle can be approximated by a time-changing electrical dipole (heart dipole) immersed in a low conducting environment. Heart dipole is a vector defined by three non-coplanar projections, so that it can be determined on the basis of recording of electric potential in at least four points that correspond to three non-coplanar directions—that is, three ECG leads not lying on the same plane, with the fourth providing a reference, that may be common to all three (or it may be in the form of a separate electrode associated with each of the three special leads). Once the heart vector is determined, it is possible to calculate the electric potentials in any point, meaning the 12 standard ECG leads as well. The calculation of heart dipole is not necessary; the direct connection between the recorded special leads and standard ECG leads can be established instead, so that standard ECG leads are obtained as linear combinations of the recorded special leads and coefficients by which the transformation matrix is defined. However, direct application of this approach is facilitated by a detailed analysis of the error sources and an attempt to reduce them. Based on this analysis, it has been shown that there are two dominant error sources that should be taken into consideration.
The system of reconstruction of the standard ECG leads on the basis of recording of three special leads is based on the dipole representation of heart electrical activity. However, the heart dipole is only the first term in the multipole expansion of diffused heart electrical activity and this approximation is valid only for recording points at the sufficient distance from the heart. In the points near the heart, the potential is significantly affected by the non-dipole content created due to the presence of higher order terms in multipole expansion.
Practical calculation of transformation matrix T is conducted by the simultaneous recording of 12 standard ECG leads V(D1, D2, D3, aVR, aVL, aVF, V1, V2, V3, V4, V5, V6) and three special leads Vs(Vs1, Vs2, Vs3), followed by numerical solving of the equation V=T·Vs, by the least-squares method. The errors in recording the electric potentials introduce the errors in the calculation of transformation matrix coefficients. The analysis has shown that the errors can be minimized if the vectors of special leads recording points are orthogonal.
Finally, having in mind the model errors (a) and the transformation matrix calculation errors (b), two requirements are imposed concerning the arrangement of the electrodes for special leads recording, in order to minimize the total error. The first one is to position the electrodes of the special leads as far as possible from the heart; the second one is to arrange the electrodes in such a way that the vectors of recording points' positions are close to orthogonal as much as possible. By arranging the electrode positions as described herein, and choosing the common point, the optimal minimization of the model errors (a) and transformation matrix calculation errors (b) can be achieved. It should be noted that in this arrangement, the accurate positioning of the special leads is not critically important, provided that the initial positioning used in calibrations are maintained during monitoring. Furthermore, if the arrangement is to be re-applied by the patient, the application is more easy to be correctly repeated by the patient, compared to prior art.
An additional problem in signal recording of special as well as of standard ECG leads is the effect of the base line wandering of the recorded signals. The problem occurs during the recording of ECG signals with all kinds of ECG devices, but is more prominent with mobile ECG devices due to the more difficult recording conditions. When systems which obtain standard ECG leads by the reconstruction of recorded special leads are concerned, the elimination of the base line wandering problem during recording of special leads is important for the proper functioning of the system. The controller 304 can be used to establish control of the base line wandering during recording of special leads by managing the process of recording automatically. From the moment of putting the device into the recording position until the moment when the base line of a signal fits into the previously specified range, a characteristic sound signal can be emitted. During the next period defined by the signal relaxation time, another characteristic sound signal can be being emitted, indicating that the recording will start soon. The recording itself is indicated by the third characteristic sound signal. If the significant base line wandering occurs in any phase of the procedure, the procedure will be repeated from the beginning. Doing so enables generation and sending of high-quality recording of special leads, which makes possible the accurate reconstruction of standard ECG leads.
The arrangement of integrated electrodes described above, their positioning, the way of recording, and described system for eliminating the base line wandering of recorded signals minimize the errors in the reconstruction of standard ECG leads, making the accuracy of recording similar to the standard ECG devices.
While embodiments and applications have been shown and described, it would be apparent to those skilled in the art having the benefit of this disclosure that many more modifications than mentioned above are possible without departing from the inventive concepts disclosed herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.
This application may be considered related to U.S. patent application Ser. No. 10/568,868 filed Feb. 21, 2006, which claims priority to the International Application No. PCT/YU04/00020 filed Aug. 19, 2004.
