WO2004004560A1

WO2004004560A1 - Portable heart monitor

Info

Publication number: WO2004004560A1
Application number: PCT/GB2002/003278
Authority: WO
Inventors: Michael Vassallo; Savvas Sophocles Constantinides; Joseph Vassallo
Original assignee: Heart Detector Limited
Priority date: 2002-07-08
Filing date: 2002-07-08
Publication date: 2004-01-15
Also published as: AU2002317357A1

Abstract

A portable heart monitor has a housing with an electrode set for sensing a reference electrocardiogram (ECG) signal (48). A microprocessor receives the reference signal and stores a parameter of the signal in a memory (20). A comparator is provided for comparing the stored parameter with a parameter of a subsequent ECG signal and generating a response in dependence on the comparison.

Description

PORTABLE HEART MONITOR

One of the difficulties in dealing with patients who have a history of heart problems lies in detecting any serious abnormalities in the heart function quicldy enough to enable propermedical treatment to be given as early as possible. A heart attack usually brings about changes in the electrocardiogram (ECG) of apatient. Hitherto, where apatient suffers chest discomfort or pains the patient has to contact his doctor to have his heart checked, usually by way of an ECG. Often, where the symptoms relate to a temporary disorder of the heart, by the time the patient is examined by a doctor or cardiologist the symptoms have disappeared. This makes it extremely difficult for the doctor to recommend the appropriate treatment.

The present invention seeks to provide an improved portable heart monitor.

Accordingly, the present invention provides a portable heart monitor comprising: electrode means for sensing a reference electrocardiogram (ECG) signal; and a housing having: a microprocessor for receiving said reference signal and storing a parameter of said signal in a memory; and means for comparing said storedparameter with aparameter of a subsequent ECG signal and generating a response in dependence on the comparison.

The present invention is further described here and after, byway of example, with reference to the accompanying drawings, in which:

Figure 1 is a front elevation of one embodiment of a preferred form of heart monitor according to the present invention;

Figure 2 is a rear elevation of the monitor of Figure 1;

Figure 3 is a block diagram of the circuit of the heart monitor; Figure 4 is a waveforai representative of a single heart beat where the heart is functioning normally;

Figure 5 is a waveforai representative of a single heart beat where a heart attack has occurred;

Figure 6 is a waveforai representative of a single heart beat where an angina attack has occurred; and

Figure 7 is a side elevation of the monitor of Figure 1.

Referring firstly to Figures 1,2 and 7, these show the external appearance of apreferred form of heart monitor 10 according to the present invention.

Figure 1 shows a front elevation of the monitor which has an LCD display screen 12 which can be used to display an ECG signal or text instructions for the user.

A loudspeaker 14 may also be provided for audible signals such as alarm warnings.

Figure 2 shows a rear elevation of the monitor. Here the monitor is shown as having an electrode set in the form of three electrodes or electrode pads 16 which are placed against apatient's chest in order to pick up the ECG of the patient at aparticular site on the patient's chest. Ideally, two of the electrodes (the chest electrodes) could be used to contact the patient' s chest whilst the third (the hand electrode) contacts the patient' s hand which holds the monitor. The position of the electrodes can be varied but a preferred positioning is with the two chest electrodes vertically separated for contacting vertically separate positions onthepatient's chest. This arrangement would allow the shape of the monitor housing to be such as to facilitate the patient holding the monitor against the chest with the chest electrodes in contact with the chest and the hand electrode in contact with the p atient ' s hand. Figure 7 shows the slim nature of the monitor and would allow the chest electrodes to be placed vertically apart on one side wall 40 of the monitor housing as shown in dotted lines, with the hand electrode on the opposite side wall or on one of the other walls of the housing.

When the monitor is held against the patient's chest to take a reading the analogue signal (trace) monitored by the electrode set is converted to a digital signal by an analogue to digital converter 24 (Figure 3) which conveniently samples the ECG at a selected rate. The ECG trace normally runs at 25 m per second and is conveniently sampled at intervals of 1 mm i.e.25 tiι:„:s a second (every 40 ms) . The converter 24 is controlled by a microprocessor 18 which can vary the sampling rate or can be preprogrammed to apply a selected sampling rate.

The circuit of the monitor shown in Figure 3 also has a memory 20 in which the micro processor 18 stores either the ECG signal which has been detected or aparameter of the signal which is to be used for comparison purposes. The memory 20 can store anumber of different ECG signals. ********** comparator 40 is also provided for comparing two ECG signals or parameters.

The circuit also shows the LCD display 12 and audible alarm 14. It also has one or more light *********** emitting diodes (LED) 22 or other light sources which can be lit to indicate a particular problem or stages of operation of the monitor.

To use the monitor one must first record a normal ECG trace for comparison with future traces. In use, when the patient is preferably at rest, staiding or sitting, and is free of symptoms of angina or a heart attack, the patient holds the monitor against his chest with the chest electrodes in contact with the chest and the hand electrode in contact with the hand. The electrodes are preferably dry electrodes which do not use gel to ensure proper contact but in taking the initial, normal ECG gel maybeusedto ensure a clear signal. Ideally, the monitor is placed on the left side of the sternum.

The ECG is sampled by the converter 24 at the preselected rate which may be set or controlled by the microprocessor 18. The microprocessor then stores in the memory 20 the digitised form of the trace and additionally or alternatively one or more signals representing one or more selected parameters of the trace. Where the term "trace" is used in this description it will be appreciated that the description could equally apply to one or more parameters of the trace. The monitor can be provided with control switches 30 such as pressure sensitive buttons. These would include a "Record" button 32 for initiating recordal of the normal ECG and a "Cancel" button 34 to cancel the recordal. For recordal of an ECG for comparison with the normal ECG a separate "Compare" button 36 could be provided. However, to prevent the normal trace being inadvertently overwritten by a ' 'comparison" trace the Record button could be located remote from the Compε' button and be hidden by a protective cover or flap . Alternatively, the microprocessor could be programmed such that each successive trace is saved by the microprocessor in a separate location in the memory 20 and the microprocessor could then compare the normal trace with any selected trace. A keypad 44 on the housing could be used to select the number of the trace to be compared with the normal trace, or a button which cycles the microprocessor through the stored traces, comparing each one in turn with the normal trace.

The original normal trace maybe stored in a ROM. This could be effected by the patient' s doctor when the normal ECG is taken or could simply be electronically marked by the microprocessor as the normal ECG by pressing of a ' 'Reference" button to cause the microprocessor to store the ECG as the reference ECG against which subsequent recordings are to be compared.

Although only one ECG at one location on the chest maybe recorded, it is possible to repeat the recordal process at a number of locations on the patient's chest, typicallybetween four and six, with the results being stored in the memory 20 for comparison with future recordings. The traces could be monitored by the microprocessor to indicate a normal range of variation of parts of the ECG . A sep arate push button may provided for each location that is to be monitored or each trace could be stored separately when the Record button is pressed. Each stored signal is identified in memory with the relevant chest location.

Figure 4 is a trace 48 of a normal heart patient' s ECG. As can be seen, this has a QR rise, an RS fall, an ST segment aT wave and a J point. AnumberofdifferentparametersoftheECGcanbe measured and stored and compared with subsequent measurements to provide an indication of an abnormal heart trace and these are discussed below.

A first parameter is the Q-S time i.e. the time betweenpoints Q and S on the trace. Foratypically normal trace this time could be 120ms. Usually the range for a normal trace would be 110 ms to 130 ms but this would be determined by the recordal of the patient's normal ECG. If the time rises above or falls below the normal value (typically 120 ms) or rises or falls outside the : ge this can be indicative of myocardial injury. The microprocessor can be programmed to issue a warning if the value deviates from the normal value by more than, say, 10%.

The level of the J point indicated on Figure 4 can be monitored. The J point is defined as the point in the trace which occurs 1 mm (40 ms) after the beginning oftheS-T segment. Any variation up or down of the voltage level of this point in the trace would indicate a heart attack or an angina attack. Another option is to measure a point between the J point and the onset of the T wave, or the level of the trace at the onset of the T wave. A combination of two or more of the J point, a point between the J point and the onset of the T wave, and the onset of the T wave could be measured.

A further parameter is the time between specific points on adj acent heartbeats. For example, the time between successive J points could be measured and used to give an indication of heart problems. If the time increases above a set level or decreases below a set level it can trigger a warning. Other points on the trace can be chosen, such as the onset of the T wave.

It will be appreciated that some or all of the parameters can be monitored.

hi the simplest form of the monitor the microprocessor generates a parameter signal which is representative of the base line of the ECG of the patient and this parameter is stored in memory 20 for each of the traces and/or locations on the chest at which the ECG of the patient is sensed.

If the patient has symptoms of chest pain, the heart monitor can be used to record the patient's ECG and compare the whole trace with the stored normal ECG trace or compare one or more parameters of the monitored trace with the stored parameter values. The patient goes through the same process of placing the monitor on his chest in the same location as previously, pressing the relevant push button in order to cause the processor to process the ECG signal sensed by the sensors 16.

The microprocessor 18 compares the monitored parameter or parameters of the new ECG with the stored value and, in dependence on the results, will indicate the type of problem, if any, from which thepatient's heart is suffering. Where the comparison indicates that the patient is suffering from a heart attack or a serious angina attack men the alarm 14 can be sounded or a warning given on the LED display 22, or both.

The LED display 22 can b e set to display different symbols or text or a combination depending on the result of the comparison, to indicate the degree of seriousness, level of urgency and the like.

The monitor can be provided with a pressure sensitive switch 46 which is positioned such that when the monitor is pressed against the patient' s chest to record a trace for comparison with the normal ECG the switch is activated to begin recording. This can be indicated to the patient by the energising of a light (e.g. an LED) which goes out once recording is complete. An audible warning may also sound when the recording is complete. If the recording is not effected, the microprocessor can be programmed to illuminate a warning lamp or LED indicating a failed recording.

It will also be possible for the heart monitor to include a transmitter which could transmit a signal to the local hospital or emergency department to alert them of Hie patient's difficulties. The monitor could also transmit the initial, normal ECG trace to abase station which would be at the hospital or doctor's surgery. Subsequent recordings for comparison could also be transmitted for storing and inspection by the medical personnel. The microprocessor can also store each recording in a separate part of the memory 20 so that a history of the ECG measurements can be reviewed at a later date, for example by downloading onto a computer at a hospital or surgery.

The heart monitor is battery operated, hand held, light weight and portable and can be operated bythepatient. Itis self-contained with the electrodes being on or integral with the homing. There are thus no separate leads which need to be used as with conventional monitors and the monitor can be used at any time, whenever required.

The described heart monitor is aimed at identifying and alerting patients of an acute ischaemic episode (heart attack or angina).

Claims

1 A portable heart monitor comprising:

electrode means (16) for sensing a reference electrocardiogram (ECG) signal (48); and a housing having:

a microprocessor (18) for receiving said reference signal and storing a parameter of said signal in a memory (20);

and means (42) for comparing said stored parameter with a parameter of a subsequent ECG signal and generating a response in dependence on the comparison.

2 A portable heart monitor as claimed in claim 1 wherein said microprocessor is operable to store a plurality of parameters of said reference signal and saidmeans for comparing is operable to compare each said parameter of said reference signal with the equivalent parameter of said subsequent ECG signal.

3 A portable heart monitor as claimed in claim 1 wherein said parameter is the trace of a single heartbeat.

4 A portable heart monitor as claimed in claim 1 or 2 wherein the or one of the parameters is a value representative of the base line voltage level of the ECG.

5 A portable heart monitor as claimed in claim 1 , 2 or 4 wherein the or one of the parameters is a value representative of the J point of the ECG.

6 A portable heart monitor as claimed in claim 5 wherein said value is the voltage level of the J point. 7 A portable heart monitor as claimed in any of claims 1 , 2, or 4 to 6 wherein said parameter is a value representative of the Q-S time of the ECG.

8 A portable heart monitor as claimed in any of claims 1 , 2, or 4 to 7 wherein the or one of the parameters is a value representative of the onset of the T wave of the ECG.

9 A portable heart monitor as claimed in any of claims 1 , 2, or 4 to 8 wherein the or one of the parameters is a value representative of a point between the J point and the onset of the T wave of the ECG.

10 A portable heart monitor as claimed in any of the preceding claims wherein the electrode means (16) are mounted on said housing.

11 A portable heart monitor as claimed in any of the preceding claims wherein the electrode means (16) are integral with said housing.

12 A portable heart monitor as claimed in claim 10 or 11 wherein said electrode means comprises at least two spaced apart electrodes (16) on said housing.

13 A portable heart monitor as claimed in any of claims lOto 12 wherein said housing has a first, end wall (40) carrying said two spaced apart chest electrodes (16) and a further wall carrying a third electro de, the arrangement being s uch that when the monitor is pressed against the chest of a user with the chest electrodes in contact with the chest of the user, the third electrode is in contact with the user's hand.

14 A portable heart monitor as claimed in any of the preceding claims wherein said housing has apressure sensitive switch operable to cause said microprocessor to record said ECG, said switch being arranged on said housing so as to be actuated in response to pressurebeing applied to said electrode means. 15 A portable heart monitor as claimed in claims 13 and 14 wherein said switch is arranged on said housing so as to be actuated in response to pressure being applied to at least one of said electrodes.

16 A portable heart monitor as claimed in any of the preceding claims further comprising an analogue to digital converter (24) connected to said elecfrode means for converting s l signal into a digital signal.

17 A portable heart monitor as claimed in any of the preceding claims further comprising display means (12) for displaying indicia in response to said comparison.

18 A portable heart monitor as claimed in any of the preceding claims fiirther comprising sound generating means (12) for generating an audible warning in response to said comparison.