WO1985005547A1

WO1985005547A1 - Apparatus for and method of ambulatory electrocardiography

Info

Publication number: WO1985005547A1
Application number: PCT/US1984/000825
Authority: WO
Inventors: Ricardo G. Kortas
Original assignee: Kortas Ricardo G
Priority date: 1984-05-29
Filing date: 1984-05-29
Publication date: 1985-12-19
Also published as: EP0182782A1

Abstract

The technical field of the invention concerns the medical field of cardiology and more particularly the field of continuous ambulatory electrocardiographic monitoring employing a 16 electrode precordial map for recording episodes of myocardial ischemia. The present invention is an ambulatory recorder system (10) which comprises cable assemblies (58) and (64) and an electrode signal switching recorder which includes an electronic switching circuit (76) as enclosed in an housing (74) to which the cable assemblies (58) and (64) are connected, a dual channel electrocardiocorder (80), and a multi-conductor cable (78) interconnecting the electronic switching circuit (76) and the electrocardiocorder (80). The electronic switching circuit (76) automatically and repetitively switches sequentially through the signals transmitted from a plurality of electrodes (11) through (26) attached to an individual. This repetitive switching successively through these signals applies each successive signal continuously to the electrocardiocorder (80) respective inputs for approximately seven heart beats. Since each electrode's signal is recorded for such an interval once every minute it is virtually impossible to miss detecting an episode of myocardial ischemia since such episodes most frequently last longer than one minute.

Description

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THE DESCRIPTION

APPARATUS FOR AND METHOD OF AMBULATORY

ELECTROCARDIOGRAPHY

I

Technical Field

This invention relates generally to the technical field of devices used in the practice of cardiology and more particularly to such devices especially useful for am¬ bulatory electrocardiography.

Background Art "Ischemia" is a term used by physicians to describe a physiological state in which the rate at which oxygen is supplied to any organ of the body is less than that at which the organ is consuming oxygen. That is, ischemia is a physiological state in which an organ's oxygen consumption exceeds its oxygen supply. Thus the term ischemia may be applied to describe an episode during which an organ in¬ creases its metabolism thereby increasing its use of oxygen such as may occur in skeletal muscles during physical exer¬ cise. "Myocardial ischemia" is a term used by physicians, and more particularly cardiologists, to describe the particular physiological state in which the heart's oxygen consumption exceeds its oxygen supply. Thus an episode of myocardial ischemia may occur as a natural consequence of physical exercise or it may occur as a consequence of a diseased state of the heart in which insufficient blood is supplied to that organ. Consequently, myocardial ischemia occurs during a myocardial infarction (heart attack) when the blood supplied to the heart is temporarily reduced or stopped. However, even in a resting or ambulatory individual it appears that episodes of myocardial ischemia occur more frequently than do myocardial infarctions. Electrocardiog¬ raphy is the most readily available method to detect ///

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episodes of myocardial ischemia because during such an episode transitory changes occur in S-T segment of an 5 electrocardiogram. Thus, even in the absence of pain or any other subjective symptom such transitory changes in the S-T segment can be considered an objective indication of is¬ chemia.

"Silent (painless) myocardial ischemia" is a term used

-j_Q by cardiologists to identify a physiological condition in which an individual exhibits clinically observable indica¬ tions of abnormal heart function but in which the individual experiences no physical symptoms, angina pectoris, or pain of a myocardial infarction. Episodes of silent myocardial

15 ischemia generally occur randomly and last for intervals of between one and ten minutes. In an introductory article entitled "Seminar on Asymptomatic Coronary Artery Disease" published during 1983 in volume 1(3) of the Journal of the American College of Cardiology at page 922, Peter F. Cohen

20 estimates that 5% of the middle-aged population exhibits silent myocardial ischemia and that 20 to 30% of the in¬ dividuals who have a myocardial infarction subsequently exhibit silent myocardial ischemia. Thus, it is believed that significant improvements in treating coronary artery

25 disease could be achieved if individuals exhibiting silent myocardial ischemia could be identified before they ex¬ perience a nonfatal myocardial infarction as its first manifestation. However, the difficulties of identifying individuals exhibiting silent myocardial ischemia and/or or

3_Q identifying individuals experiencing true angina pectoris through the usual electrocardiographic testing procedures and the associated expense of those procedures makes general population screening controversial because of the cost/benefit ratio associated with searching for a disease

35 that has a small prevalence in the general population.

Observing individuals with known coronary artery dis¬ ease has revealed that silent myocardial ischemia appears in electrocardiographic testing during exercise stress testing /// -3-

and during continuous ambulatory electrocardiographic monitoring. Kim M. Fox, Andrew P. Selwyn, and John P. Shil- lingford in a technical article entitled "A Method for Praecordial Surface Mapping of the Exercise Electrocar¬ diogram" published in 1978 at page 1339 of volume 40 of the British Heart Journal ("the '78 Fox Article"), describe a precordial surface mapping technique useful in diagnosing and assessing medical and surgical treatments for patients with ischemic heart disease. The '78 Fox Article reports that difficulties in performing this surface mapping electrocardiogram centered around the time taken to perform the test and the lack of an adequate electrode system which is stable even during severe exertion. In taking a surface electrocardiogram according to the method described in the '78 Fox Article, 16 electrodes are located at the vertices of a four-by-four matrix whose vertical columns begin at an individual's side under his left arm and extend horizontally almost completely across his chest toward his right arm. The electrodes are then secured in those locations using ad¬ hesive tape sufficiently tight to stabilize them.

To allow using a conventional, four channel electrocar¬ diograph for recording the electrical signals from these 16 electrodes, the ^' '78 Fox Article mentions a specially designed, manually operated switching box for successively selecting groups of four signals from among the 16 trans¬ mitted by the electrodes for recording with the standard, four channel electrocardiograph. In a subsequent article by Kim M. Fox, Andrew P. Selwyn, David Oakley, and John P. Shillingford entitled "Relation Between the Precordial Projection of ST Segment Changes After Exercise and Coronary Angiographic Findings" published in the November 1979 issue of the American Journal of Cardiology, volume 44, at page 1068, the authors report a significant improvement in iden¬ tifying individuals with disease in a single coronary ves¬ sel, i.e. mild coronary artery disease, by detecting myocar¬ dial ischemia using this 16 electrode precordial surface

mapping technique in comparison with a modified 12 lead electrocardiogram. In a more recent article by Kim M. Fox, J. Deanfield, P Ribero, D. England and E. Wright entitled "Projection of ST Segment Changes on to the Front of the Chest, Practical Implications for Exercise Testing and Ambulatory Monitoring" published during 1982 in volume 48 of the British Heart Journal at page 555 reporting on the design of a 12 lead precordial matrix (locations at which the 12 electrodes may be positioned on an individuals chest), the authors report that:

"failure to record ST segment changes using am- bulatory monitoring in patients complaining of chest pain[, i.e. non-silent myocardial ischemia,] may mean that the wrong site was selected for placing the exploring electrode. Moving one or both of the exploring electrodes to other posi- tions of the precordial matrix in subsequent recordings may then provide diagnostic information that otherwise would have been missed."

Consequently, to have a high probability of success any procedure attempting to identify individuals experiencing episodes of myocardial ischemia appears to require using at least a 16 electrode precordial surface mapping technique described in The '78 Fox Article. Further, it appears that such testing requires using either an exercise stress test or continuous ambulatory electrocardiographic monitoring to successfully identify such individuals. Since continuous ambulatory electrocardiographic monitoring is capable of recording the signals from an individual's heart during his usual daily activity and does not require special, dedicated test facilities such as those required for exercise stress testing with their attendant cost, it appears that con¬ tinuous ambulatory electrocardiographic monitoring may be a preferred way of testing for silent myocardial ischemia. In

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addition, Steven H. Kunkes, Agusto D. Pichard, Harry Smith, Jr., Richard Gorlin, Michael V. Herman, and Joel Kupersmith 5 in a technical article entitled "Silent ST Segment Devia¬ tions and Extent of Coronary Artery Disease" published in the December 1980 issue of the American Heart Journal, volume 100, number 6, part 1 at page 813 report that "it is not the presence of ST segment deviations, but rather the 0 total duration of ST segment deviations over 24 hours which correlates with more severe degrees of coronary disease".

Ambulatory electrocardiographic monitoring was first introduced by a engineer, Norman J. Holter, during the 1950's. In an article entitled "New Method for Heart Studies 5 Continuous Electrocardiography of Active Subjects" published during 1961 in volume 134 of Science at page 1214, Doctor Holter reported transmitting the heart's signal from an exercising individual to a nearby radio receiver using a cumbersome, heavy (85 lb) radio transmitter. Doctor Holter 0 subsequently developed a "electrocardiocorder" which would record up to a 10 hour, two electrode, electrocardiogram using a portable magnetic tape recorder worn by the in¬ dividual being monitored. In an article by Shlomo Stern entitled "The History and Development of Ambulatory Monitor- 5 ing of the Electrocardiogram" published in 1978 at page 1 of a monograph which he edited entitled Ambulatory ECG Monitor¬ ing ("the Stern Monograph"), the author states:

"Today, about 15 years after the first steps in long-term continuous ECG recording were made, 0 the basic idea and technical solutions forwarded by Doctor Holter and associates remain largely unchanged.

* * * * * * * * *

Most commercially available systems, record two 5 simultaneous channels of ECG, usually one resem¬ bling V and the other at V [ , standard locations

1 5 at which electrodes may be positioned on an in¬ dividuals chest]. The former provides a better P

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and QRS morphology and easier arrhythmia recogni¬ tion, and the latter gives an ST-T configuration, which is the most sensitive to ischemic alterations."

Presently there are various distinct categories of electrocardiocorder. For example there are continuous or "Holter" recorders which continuously record signals from two electrodes onto a magnetic tape for 24 hours. A varia¬ tion of these continuous electrocardiocorders are real-time analysis systems which analyze the signal received by the electrocardiocorder and store only certain parameters of the data and/or only a few periods of the electrocardiogram. Yet another type of electrocardiocorder only records signals intermittently perhaps at preselected intervals or if cer¬ tain predefined events are detected. Frequently, the re¬ corders of the various types allow the patient to manually activate recording if symptoms occur.

While there are various types of electrocardiocorders available from several manufacturers, none are suitable for recording the signals from a 16 electrode precordial map apparently so necessary to reliably identifying an episode of silent myocardial ischemia. For example, present con¬ tinuous electrocardiocorders such as the model 445B manufac¬ tured by Del Mar Avionics of Irvine, California, even though approximately ten times more expensive than a comparable audio tape recorder, is capable of simultaneously recording signals from only two electrodes. A significant factor contributing to the cost of such present electrocardiocor¬ ders is that the signals, which may be recorded either on reel mounted tape or on tape stored in a standard audio cassette, must be recorded with an essentially flat (3db down) frequency response over the interval of 0.05 to 100 Hz to meet the American Heart Association standard for electro¬ cardiocorders. In particular, because electrode voltage changes slowly during the ST segment of an electrocar- ///

OMPI -7-

diographic signal, a recorder having good low frequency recording characteristics is critical to preserving a record 5 of episodes of silent myocardial ischemia. This frequency response criterion in combination with the need to record signals continuously during a 24 hour interval establish a demanding technical performance criterion for an electroca¬ rdiocorder. The preceding economic and technical considera- o tions conclusively demonstrate the impracticality of simply and directly extending present electrocardiocorder technol¬ ogy to record the 16 signals from the electrodes of a precordial map.

Further, even if a 16 channel electrocardiocorder 5 capable of simultaneously recording signals from 16 electrodes were technologically and economically practical, difficulties associated with present techniques for positioning and attaching the electrodes to a patient, connecting them to the electrocardiocorder, and maintaining o that attachment and connection during a 24 hour recording interval could be so great as to prevent its routine use. In an article by Leonard S. Gettes and Sherry R. Winternitz entitled "The Use of Ambulatory ECG Monitoring to Detect 'Silent' Ischemia" published at page 93 of the Stern 5 Monograph which describes results achieved with conven¬ tional, two channel continuous ambulatory electrocar¬ diographic monitoring, the authors state that:

"Although electrode placement is not of critical importance when arrhythmia detection is the goal, 0 i is critical when seeking information about the S-T segment. It must be remembered that the signal recorded from the ambulatory monitor is bipolar and reflects the position of both the negative and positive leads. 5 * * * * * * * * *

The problem of lead placement is perhaps the greatest obstacle to accurate monitoring of S-T segment changes". /// -8-

Presently electrical signals generated at the electrodes attached to an individual's chest are coupled to an electrocardiocorder for continuous ambulatory electrocar¬ diographic monitoring by a cable made up of two separate sections. The first section of such a cable, one end of which attaches to the individual electrodes, consists of a plurality of individual wires adapted to clip onto in- dividual electrodes. Individual jacks are attached at the other ends of this section's wires to plug into mating sockets of a multi-wire connector located at one end of the cable's second section. The other end of this second section plugs directly into an electrocardiocorder which is secured to an individual's body. Presently, cardiologists attempt to minimize the possibility of generating electrical noise at the junction between the electrode and the cable by forming circularly shaped "stress loops" in each of the cable's individual wires immediately adjacent to the electrode to which it is connected. Each such stress loop is then in¬ dividually taped to the body by two pieces of adhesive tape arranged in an X-shape across the stress loop's diameter. Further, adhesive tape is also used to secure the individual jacks into the multi-wire connector, and to secure the connector itself to the body about the navel. However, the use of the preceding techniques does not eliminate excessive electrical noise pickup in continuous ambulatory electrocar¬ diographic monitoring. Besides being ineffective for preventing the generation of electrical noise, the area on an individual's chest occupied by the stress loops and tape significantly reduces the maximum number of electrodes which may be secured to an individual's chest.

Disclosure of the Invention An object of the present invention is to enhance the technology of continuous ambulatory electrocardiographic monitoring and improve the techniques for its use. /// ///

OMPI Another ob ect of the present invention is to make continuous ambulatory electrocardiographic monitoring a practical technique for reliably detecting changes in the S- T segment of an electrocardiogram.

Another object of the present: invention is to make continuous ambulatory electrocardiographic monitoring a practical technique for reliably detecting silent myocardial ischemia.

Another object of the present invention is to allow recording a 16 electrode, continuous ambulatory electrocar¬ diogram for detecting myocardial ischemia with a conven¬ tional, two channel electrocardiocorder. Another object of the present invention is to provide a device for electrically interconnecting an electrocardiocor¬ der and the electrocardiographic electrodes which allows reliably recording the S-T segment of an electrocardiogram throughout entire duration of continuous ambulatory electrocardiographic monitoring.

Briefly, the present invention is a electrocardiocorder system which includes a electrocardiocorder having a switch¬ ing means for automatically and repetitively switching sequentially through the signals transmitted from a plurality of electrodes attached to an individual. This switching means successively couples signals from electrodes to the input of the electrocardiocorder. This repetitive switching successively through the electrodes signals ap¬ plies each successive signal continuously to the electroca- rdiocorder's respective inputs for an interval several times longer than the period of the physiological signal being recorded before switching from that signal to the next successive signal.

In the particular instance of recording a 16 electrode precordial map for detecting myocardial ischemia, a suitable length of time for recording the signal from an individual electrode is approximately 7.5 seconds. Thus in recording the signals from 16 electrodes in this manner using a dual

///

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channel electrocardiocorder, during any one minute time interval the signal from each of the 16 electrodes will be 5 individually and continuously recorded for a 7.5 second interval, approximately the duration of seven heartbeats. Further, each electrode's signal will 'be recorded for such a 7.5 second interval once every minute. Since a myocardial ischemia episode most frequently lasts longer than one 0 minute, it is virtually impossible to miss such an episode while making this recording.

The continuous application of the electrodes' signals to the electrocardiocorder's inputs for an interval which, on the average, is at least several times longer than the

15 period of the physiological signal being recorded distin¬ guishes the present invention from a conventional sampling multiplexing technique. With a conventional sampling multi¬ plexing technique, the electrodes' signals would be repeti¬ tively applied to the electrocardiocorder's input for a very

20 short interval of time so the signals from all 16 electrodes could be successively recorded many times over during the duration of a single heartbeat. In accordance with the Nyquist Sampling Theorem, such a multiplexing technique would have to sample the data at a rate no less than twice

25 as fast as the highest frequency to be recorded. Therefore to accurately record electrocardiogram signals having sig¬ nificant frequency components up to 100 Hz, the signal from each electrode would have to be sampled at a frequency of 200 Hz. Consequently each input of a electrocardiocorder

30 would have to be switched among the signals from eight of the electrodes at a frequency of 1600 Hz (8 x 200 Hz). Thus if a conventional multiplexing technique were employed, each signal would be successively applied to an input of the electrocardiocorder for an interval which could not exceed

35 625 microseconds as distinguished from the 7.5 second inter¬ val of the present invention. ///

In addition to an electrocardiocorder having a switch¬ ing means which automatically and repetitively switches sequentially through the signals transmitted by a plurality of electrodes attached to an individual, the electrocardio- corder system of the present invention further includes an improved cable assembly for interconnecting numerous electrodes secured to an individual and such an electroca- rdiocorder. This improved cable assembly reduces noise in the electrode signal recorded by the electrocardiocorder by collecting the plurality of individual wires into a unitary assembly extending between the electrodes and the electroca¬ rdiocorder. Further, the cable assembly of the present invention eliminates the need for stress loops by mechani¬ cally securing the cable's individual wires in a trunk portion of the cable immediately adjacent to the electrode to which an individual wire connects. This trunk is itself mechanically secured to the individual at its end adjacent to the electrodes to support the cable assembly's weight and to maintain the spatial relationship between this end of the cable assembly's trunk and the electrodes attached to the individual. By thus securing this cable assembly to the individual, forming stress loops in the individual wires immediately adjacent to the electrodes becomes unnecessary because stress in the individual wires projecting outward from the cable assembly's trunk to the electrodes and in the connection to the electrodes is greatly reduced. Further, eliminating such stress loops provides an additional benefit in allowing convenient placement of an increased number of electrodes on an individual. Lastly, using this cable as¬ sembly greatly reduces relative motion at the junction between the electrodes and the connector secured to the cable's individual wires. An advantage of the present invention is that it en¬ hances the technology of continuous ambulatory electrocar¬ diographic monitoring and improves the techniques for its use.

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Another advantage of the present invention is that it makes continuous ambulatory electrocardiographic monitoring a practical technique for reliably detecting changes in the S-T segment of an electrocardiogram.

Another advantage of the present ^*invention is that it makes continuous ambulatory electrocardiographic monitoring a practical technique for reliably detecting silent myocar- dial ischemia.

Another advantage of the present invention is that it allows recording a 16 electrode continuous ambulatory electrocardiogram for detecting myocardial ischemia with a conventional, two channel electrocardiocorder. Another advantage of the present invention is that it provides a-device for electrically interconnecting an elec¬ trocardiocorder and the electrocardiographic electrodes which allows reliably recording the S-T segment of an electrocardiogram throughout entire duration of continuous ambulatory electrocardiographic monitoring.

These and other features, objects and advantages will either be discussed or will, no doubt, become apparent to those of ordinary skill in the art after having read the following detailed description of the best modes for carry- ing out the invention as illustrated in the various drawing figures.

Brief Description of the Drawings

Fig. 1 is a diagramatic plan view of a human torso depicting an ambulatory recorder system including cable assemblies and an electrode signal switching recorder in accordance with the present invention which shows the place¬ ment of a plurality of electrodes on the torso for recording a 16 electrode precordial map as taught in The '78 Fox Article;

Fig. 2 is a diagramatic representation depicting one period of an electrical signal as is transmitted via the cable assembly from an electrode of Fig. 1 to the input of ///

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the electrode signal switching recorder showing various features of an electrocardiographic signal; 5 Fig. 3 is a diagramatic functional-type block diagram of an electronic switching circuit included in the electrode signal switching recorder of Fig. 1 for switching among the various electrode signals applied thereto via the cable assemblies; and

■_{j Q} Fig. 4 is a diagramatic timing chart depicting a plurality of electrical signals transmitted from a plurality of the electrodes shown in Fig. 1 and also depicting an output signal from the electronic switching circuit of Fig. 3 as may be preserved by recording it with an electrocardio-

-I5 corder included in the electrode signal switching recorder.

Best Mode for Carrying Out the Invention

Referring now to Fig. 1 , depicted there is a human torso 8 to which is attached ambulatory recorder system in _Q accordance with the present invention referred to by the general reference character 10. The ambulatory recorder system 10 as depicted in Fig. 1 is adapted for recording a precordial map in according with the teaching of The '78 Fox Article. The ambulatory recorder system 10 includes a 5 plurality of electrodes 11 through 26 fixed to the human torso 8 which generate 16 electrocardiographic signals needed to record the precordial map. Also fixed to the lower right hand side of the human torso 8 below and to one side of the vertical column of electrodes 11 through 14 is a 0 ground electrode 28. Analogously, a negative reference electrode 30 is fixed to the upper left hand side of the human torso 8 above and approximately between vertical columns of electrodes 15 through 18 and 19 through 22. The particular type of electrodes 11 through 26, 28, and 30 used ₅ in the ambulatory recorder system 10 may be chosen from among those marketed by various manufacturers such as the model Offset Dx manufactured by Graphic Controls Corp. of Buffalo, New York. /// .

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Referring now to Fig. 2, depicted there a single period of an electrocardiographic signal referred to by the general 5 reference character 32 as may be transmitted from electrode 17 during a single heart beat. Cardiologists routinely employ various names to identify particular locations and or features on this electrocardiographic signal 32. Thus during the period of each heart beat cardiologists identify a "P

10 wave" 34, a "Q wave" 36, a "R wave" 38, a "S wave" 40, and a "T wave" 42. That segment of the electrocardiographic signal 32 joining the S wave 40 and the T wave 42, depicted by a plurality of dashed curves in Fig. 2, is referred to as the "S-T segment" 44. The point at which the S-T segment 44

15 commences, immediately adjacent to the S wave 40, is iden¬ tified as a "J point" 46. In Fig. 2 , the S-T segment 44 is depicted with a plurality of dashed curves to indicate that its morphology (shape) may change depending upon the state of the individual, e.g. resting versus exercising, and/or

20 upon the condition of ^" their heart, e.g. healthy versus diseased. Thus the dashed curves of Fig. 2 depict possible alternative shapes for the S-T segment 44. It is changes in the morphology of the S-T segment 44 which^" cardiologists now believe may be interpreted as an objective manifestation of

25 myocardial ischemia.

Referring again to Fig. 1, the ambulatory recorder system 10 also includes a plurality of connectors 52 which mate with and attach to the equal plurality of electrodes 11 through 26, 28 and 30. Each connector 52 is also secured to

30 one terminal end of a electrode signal wire 54 to which it couples the electrical signals respectively transmitted by the electrodes 11 through 26, 28, and 30. The electrode signal wires 54 coupled to the electrodes 11 through 18 and to the ground electrode 28 by the connectors 52 are gathered

35 along a substantial portion of their length into a trunk 56 of a cable assembly 58. Similarly, the electrode signal wires 54 coupled to the electrodes 19 through 26 and to the negative reference electrode 30 by the connectors 52 are

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gathered along a substantial portion of their length into a trunk 62 of a cable assembly 64. 5 Attached respectively along the length of the trunks 56 and 62 about their terminal ends from which the electrode signal wires 54 extend to reach the connectors 52 are a pair of adhesive foam pads 68 that will adhere to the skin of an individual. Either electrodes such as the Offset Dx iden- o tified above or simply foamed material coated with adhesive may be used for the adhesive foam pads 68. Each pair of adhesive foam pads 68 respectively secured to the cable assemblies 58 and 64 is longitudinally separated along the length of their respective trunks 56 and 62. Thus when the 5 adhesive foam pads 68 adhere to the skin of an individual they support the weight of the cable assemblies 58 and 64. Further, the separated locations for the adhesive foam pads 68 along the lengths of the trunks 56 and 62 and the exten¬ sion of the electrode signal wire 54 therefrom are selected 0 to maintain the spatial relationship between the trunk 56 and the electrodes 11 through 18 and 28, and between the trunk 62 and the electrodes 19 through 26 and 30. This secure attachment of the trunks 56 and 62 of the cable assemblies 58 and 64 to the human torso 8 eliminates the 5 need for the stress loops as taught in the prior art. Fur¬ ther, this attachment of the cable assemblies 58 and 64 to the human torso 8. strictly controls lead placement necessary to accurately monitor the S-T segment 44 of the electrocar¬ diographic signals 32. 0 Secured to the opposite end of the trunks 56 and 62 of each of the cable assemblies 58 and 64 furthest from the adhesive foam pads 68 is one-half of a multi-pin connector 72. The mating half of each multi-pin connector 72 is mounted on a housing 74 which encloses an electronic switch- 5 ing circuit referred to by the general reference character 76 as depicted in Fig. 3. Each of the electrode signal wires 54 in each of the cable assemblies 58 and 64 is respectively connected to an individual pin of the multi-pin connector 72

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for applying the signals transmitted by the electrodes 11 through 26, 28, and 30 to the electronic switching circuit 76. Also depicted in Fig. 1 is a multi-conductor cable 78 which couples the output signals of the electronic switching circuit 76 to the various inputs of 'a standard, continuous "Holter" type electrocardiocorder 80 such as a Del Mar Avionics model 445B dual channel electrocardiocorder. The combined electronic switching circuit 76 as enclosed in the housing 74, the multi-conductor cable 78, and the electroca¬ rdiocorder 80 together constitute an electrode signal switching recorder adapted to preserve representation of an electrocardiogram. Referring now to Fig. 3, the electronic switching circuit 76 includes two integrated circuit, analog signal multiplexers 82, each multiplexer 82 having eight switched signal inputs 83. Digital control signals applied to three control signal inputs 84 cause each multiplexer 82 to couple one of the signals from its switched signal inputs 83 to a switched signal output 85. The signal transmitted from the switched signal output 85 of each multiplexer 82 is coupled via a multiplexer output signal line 86 tσ a non-inverting input 87 of a buffer amplifier 88 associated with each multiplexer 82. Thus, depending upon the particular digital control signals applied to the control signal inputs 84, each multiplexer 82 selects one particular input signal applied to its eight switched signal inputs 83 and then applies that selected signal to the non-inverting input 87 of its associated buffer amplifier 88.

Because the signals which the electronic switching circuit 76 receives from the various electrodes 11 through 26 have differing direct current ("DC") offset voltages measuring between 10 and 300 millivolts while the alternat- ing current ("AC") voltage of the electrocardiogram signals such as that depicted in Fig. 2 measures only several mil¬ livolts, it is necessary to remove this DC offset before the signals may be applied to the inputs of the electrocardio- ///

OMPI corder 80. Thus the signals from electrodes 11 through 18 are applied through separate, identical high-pass filters 89 to the eight switched signal inputs 83 of one multiplexer 82 while the signals from electrodes 19 through 26 are applied through separate identical high-pass filters 89 to the eight switched signal inputs 83 of the other multiplexer 82. A diagram depicting one of the identical electronic circuits used in each of the high-pass filters 89 interposed between each switched signal input 83 of the multiplexers 82 and the signals from the electrodes 11 through 26 is shown in Fig. 3 as receiving the signal from electrode 25. The electronic circuit of each high-pass filter 89 consists of a capacitor 90 connected in series between a switched signal input 83 of the multiplexer 82 and the signal received by the electronic switching circuit 76 from one of the electrodes 11 through 26 combined with a resistor 91 connected between the switched signal input 83 of the multiplexer 82 and circuit ground of the electronic switching circuit 76. To obtain, a low frequency cut-off below 0.05 Hz for the high-pass fil¬ ters 89, the capacitor 90 of each high-pass filter 89 has a value of approximately 33 microfarads and its resistor 91 has a value of one megohm. To properly switch among such a plurality of low voltage AC signals measuring only several millivolts, the multiplexers 82 may be selected from various commercial types of integrated circuits such as the type CD4051BM analog multiplexer/demultiplexer marketed by Na¬ tional Semiconductor of Santa Clara, California. Conversely from the signals of the electrodes 11 through 26 which are applied to the inputs of the multi¬ plexer 82 to allow selecting among them, the signals trans¬ mitted by the ground electrode 28 and the negative reference electrode 30 are not applied to inputs of a multiplexer 82. Rather, within the housing 74 the signal received from the ground electrode 28 is connected directly to the circuit ground of the electronic switching circuit 76 while the signal from the negative reference electrode 30 passes

/// _directly through housing 74 to the multi-conductor cable 78. The multiplexers 82 require certain control signals to 5 repetitively switch among the various electrode's signals applied to their switched signal inputs 83 and thus to sequentially select one particular input signal to be trans¬ mitted to the non-inverting input 87 of the corresponding buffer amplifier 88. These control signals are provided by o combining an integrated circuit clock 96 and counter 98. Connected between a pair of timing circuit inputs 100 to the clock 96 is a capacitor 102 and an adjustable resistor 104 connected in series. The capacitor 102 and the adjustable resistor 104 establish a time interval for a periodic clock 5 signal transmitted from the clock 96 to the counter 98 over the clock line 106. In response to this periodic signal from the clock 96, the counter 98 operates as a three binary digit counter the output signals of which repetitively increment through their possible binary values (000 through 0 111) during successive periods of the clock signal. These three binary digit output signals are transmitted from the counter 98 over binary digit lines 108 to the control signal inputs 84 of the multiplexers 82.

During each successive period of the signal transmitted 5 from the clock 96 to the counter 98, the counter 98 main¬ tains output signals representing a particular three digit binary number on the binary digit lines 108. The multiplexer 82, responding to the digital control signals which it receives from the counter 98 via the binary digit lines 108, 0 couples one of the signals from its switched signal inputs 83 to its switched signal output 85. At the beginning of the next successive time interval of the output signal trans¬ mitted from the clock 96 to the counter 98, the counter 98 increments to the next successive binary digit. Responding 5 to the new binary digit signals present on the binary digit lines 108, the multiplexers 82 couple the next successive signal from their respective switched signal inputs 83 to their respective switched signal output 85. After the ///

lA . ^"V counter 98 reaches the largest binary digit which it can represent (111), at the beginning of the next successive time interval of the periodic signal transmitted by the clock 96, the counter 98 returns to the smallest binary digit which it can represent (000). THus because the counter 98 repetitively counts through all possible three digit binary numbers in response to signals transmitted by the clock 96, the multiplexers 82, responding to the control signals represented by those numbers, each repetitively couple a sequence of signals present on their eight switched signal inputs 83 to their switched signal output 85.

In the particular instance of recording a 16 electrode precordial map for detecting myocardial ischemia in which signals from eight electrodes 11 through 18 are applied to the switched signal inputs 83 of one multiplexer 82 while the signals from the remaining eight electrodes 19 through 26 are applied to the switched signal inputs 83 other multi- plexer 82, as described previously, a suitable length of time for recording successive signals from individual electrodes is approximately 7.5 seconds. If the type of integrated circuit used for the clock 96^' is a CD4047BM multivibrator marketed by National Semiconductor of Santa Clara, California, then a capacitor 102 having a value of 20 microfarads and an adjustable resistor 104 having a value of 1 megohm may be used to establish such a periodic clock signal time interval. The output signal from the CD4047BM integrated circuit used for the clock 96 is suitable for driving a MM74C93 binary counter marketed by National Semi¬ conductor of Santa Clara, California as the counter 98 which transmits digital control signals to the control signal inputs 84 of the multiplexer 82.

Thus, when electric power is supplied to the multi- plexers 82, the buffer amplifiers 88, the clock 96, and the counter 98 via a positive voltage supply line 112 and a negative voltage supply line 114 from 9 volt batteries 116, the clock 96 immediately commences transmitting periodic /// -20- . .

signals to the counter 98 over the clock line 106. Respond¬ ing to these periodic clock signals, the counter 98 operates as a three binary digit counter which repetitively incre¬ ments through the successive three digit binary values during successive periods of the clock signal to transmit digital control signals via the binary digit lines 108 to the control signal input 84 of the multiplexer 82. Respond¬

1 0 ing to these digital control signals, the multiplexer 82 couples one of the signals present at its switched signal inputs 83 to its switched signal output 85.

Referring now to Fig. 4, depicted there are a plurality of electrocardiographic signals, similar to the electrocar-

1 diographic signal 32 of Fig. 2, as may be transmitted by electrodes 11 through 18 to the input of the multiplexer 82 during a continuous one minute time interval 118. For pur¬ poses of illustration, the electrocardiographic signals depicted during each successive 7.5 second time interval 120

20 of the continuous one minute time interval 118 show only the signals associated with two heart beats rather than those for the approximately seven heart beats which would normally occur during each 7.5 second time interval 120. During each successive 7.5 second time interval 120 of the one minute

25 time interval 118, the multiplexer 82 couples one of the signals transmitted by electrodes 11 through 18 from one of its switched signal input 83 to its switched signal output 85. Because an ambulatory individual's normal muscle move¬ ment generates electrical noise which may mask the

3_Q electrocardiographic signal, a sequence for selecting the signals from the electrodes 11 through 18 is chosen in which, on the average, successive selected signals are transmitted from electrodes at widely separated locations. Thus during the first 7.5 second time interval 120, the

35 signal transmitted by electrode 11 is coupled to the multi¬ plexer output signal line 86. During the second 7.5 second time interval 120, the signal -transmitted by electrode 17 is coupled to the multiplexer output signal line 86. This /// -21 -

process of coupling a signal transmitted by one of the electrodes 11 through 18 to the multiplexer output signal line 86 continues in accordance with the electrode numbers shown in Fig. 4 for eight periods of the 7.5 second time interval 120 until all eight electrode signals have been coupled from the inputs switched signal input 83 to the multiplexer output signal line 86 during the one minute time interval 118. Thus the multiplexer 82 generates a composite electrode signal as shown in Fig. 4 which is transmitted from the switched signal output 85 via the multiplexer output signal line 86 to the non-inverting input 87 of the buffer amplifier 88 with which the multiplexer 82 is as- sociated. To reduce the possibility that an ambulatory individual's normal muscle movement will generate electrical noise which is simultaneously recorded on both channels of the electrocardiocorder 80, the signal from the electrodes 19 through 26 selected by the other multiplexer 82 is chosen to be from an electrode which, on the average, is widely separated location from that being simultaneously selected from electrodes 11 through 16. Thus the sequence of paired electrode signals selected simultaneously by the multi¬ plexers 82 is that depicted adjacent to the multi-pin con- nectors 72 of Fig. 3,i.e. 11 and 22, 17 and 24, 15 and 26, 13 and 20, 18 and 23, 12 and 21, 14 and 19, and 16 and 25.

Referring again to Fig. 3, each buffer amplifier 88, which may be selected from various commercial types of integrated circuit amplifiers such as the type LF442 dual low power operational amplifier marketed by National Semi¬ conductor of Santa Clara, California, has an output 122 which is coupled back to its inverting input 124. Thus each buffer amplifier 88 operates at unity gain and presents a high impedance to the switched signal output 85 of its associated multiplexer 82. Further, the output 122 of one of the buffer amplifiers 88 is coupled via a first composite electrode signal wire 126 of the multi-conductor cable 78 to one signal recording input of the electrocardiocorder 80

-22-

while the output 122 of the other buffer amplifier 88 is coupled via a second composite electrode signal wire 128 of 5 the multi-conductor cable 78 to the other signal recording input of the multi-conductor cable 78. Because the high impedance which each non-inverting 'input 87 of the buffer amplifiers 88 presents to the switched signal output 85 of its associated multiplexer 82 is coupled through the ulti-

10 plexer 82 to the electrodes 11 through 26, the buffer amplifiers 88 isolate the signals transmitted by the electrodes 11 through 26 from the relatively low impedance of the signal recording inputs of the electrocardiocorder 80. A ground shield 132 of the multi-conductor cable 78

15 couples the circuit ground of the electronic switching circuit 76 to the circuit ground of the electrocardiocorder 80.

At the electrocardiocorder 80, the signal of the nega¬ tive reference electrode 30 is applied to both negative

20 reference inputs respectively associated with the signal recording inputs to which the first composite electrode signal wire 126 and second composite electrode signal wire 128 are coupled. Thus, as the electrocardiocorder 80 operates in its usual manner as a two channel electrocardio-

25 corder, it records on one of its channels the composite signal present at the switched signal output 85 of one multiplexer 82 while its other channel records the signal present at the switched signal output 85 of the other multi¬ plexer 82. By the various techniques described above, the

30 ambulatory recorder system 10 of the present invention achieves an eight fold compression of the electrocar¬ diographic data without significantly increasing the pos¬ sibility of failing to detect an episode of myocardial ischemia.

35 /// /// /// ///

OMPI y V- IPO Industrial Applicability

Once the signals from the sixteen electrodes 11 through 26 of the precordial map have been recorded by the electro¬ cardiocorder 80, the record thus preserved may be most conveniently analyzed using a digital computer by techniques well known in the art. In particular, because of the dis¬ tinctly different shapes of the signal associated with each of the electrodes 11 through 18 and electrodes 19 through 26, the computer program which analyzes the recorded signals may determine the beginning and end of each 7.5 second interval during which the signal from successive electrode were recorded. Further, the differences among these signals also allows a computer program to recognize the particular electrode which transmitted each 7.5 second long signal. Since each successive 7.5 second interval contains, on the average, the electrocardiographic signal 32 for 7 heart beats, the computer program analyzing the recorded signal may employ signal averaging to improve the signal to noise ratio of the recorded data without significantly increasing the possibility of failing to detect an episode of myocar¬ dial ischemia.

Regarding the structure of the ambulatory recorder system 10, it is readily apparent that the electronic switching circuit 76 enclosed within the housing 74 may alternatively be enclosed within the electrocardiocorder 80 together with the one-half of the multi-pin connectors 72 mounted thereon thereby eliminating all need for the housing 74. If the electronic switching circuit 76 were thus in¬ tegrated into the electrocardiocorder 80 the multi-conductor cable 78 could then be totally enclosed within the electro¬ cardiocorder 80. Further, if so integrated, the electrical power to operate the electronic switching circuit 76 could be obtained from the batteries of the electrocardiocorder 80 and the 9 volt batteries 116 could be eliminated. /// ///

/

-24-

hile the ambulatory recorder system 10 of the present invention uniquely adapted for preserving a representation of a precordial map in accordance with the teachings of The '78 Fox Article, it may be easily adapted to record alterna¬ tive types of precordial maps or alternative electrode matrices. For example, using the ambulatory recorder system 10 for recording different types of precordial maps or electrode matrices could be achieved by further adding a multi-position mode switch to the electronic switching circuit 76. In a first position of such a mode switch, the ambulatory recorder system 10 would operate in the manner described above. In a second position, only one of the multiplexers 82 would select signals from successive electrodes for recording while the other multiplexer 82 would continuously transmit the signal from a single electrode for recording. Thus, this second position of the mode switch would adapt the ambulatory recorder system 10 to successively record signals from eight electrodes while simultaneously recording a signal from a ninth electrode continuously. In a third position of the mode switch, both of the multiplexers 82 would continuously transmit signals from individual electrodes and thus the ambulatory recorder system 10 could be operated identically to the current Holter type electrocardiocorders. It is readily apparent that the ambulatory recorder system 10 of the present inven¬ tion could be easily adapted for recording all various types of precordial maps or alternative electrode matrices by adaptations analogous to the mode switch described above.

While the ambulatory recorder system 10 of the present invention is particularly adapted for continuous ambulatory electrocardiographic monitoring, it is also suitable for non-ambulatory use perhaps during monitoring performed in a hospital immediately following a myocardial ischemia. Depending upon the particular electrode locations chosen for the precordial map, it may be possible to employ a single cable assembly for the electrode signal wires 54 rather th

-25-

the dual cable assemblies 58 and 64 without adversely af¬ fecting the accurate recording of the S-T segment 44 even during continuous ambulatory electrocardiographic monitor¬ ing. Particularly if the ambulatory recorder system 10 of the present invention is used in a hospital environment the strict control of lead placement afforded by the dual cable assemblies 58 and 64 may prove unnecessary. While the best mode ambulatory recorder system 10 of the present invention has been described as employing a conventional, dual channel, continuous electrocardiocorder 80, the cable assemblies 58 and 64 and the electronic switching circuit 76 may, in general, be used with any type of electrocardiocorder. Thus, the cable assemblies 58 and 64 and the electronic switching circuit 76 may be used with real-time analysis electrocardiocorders and with intermit¬ tent electrocardiocorders.

Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is purely illustrative and is not to be interpreted as limiting. Consequently, without departing from the spirit and scope of the invention, various alterations, modifications, and/or alternative applications of the invention will, no doubt, be suggested to those skilled in the art after having read the preceding disclosure. Accordingly, it is intended that the following claims be interpreted as encompassing all alterations, modifications, or alternative applications as fall within the true spirit and scope of the invention. /// /// /// /// /// /// /// /// ///

Claims

THE CLAIMS

What is claimed is:

1. An ambulatory recorder system as may be used for preserving a record of an electrocardiogram in which a plurality of electrical signals as may be transmitted from an equal plurality of electrodes attached to an ambulatory individual are sequentially and repetitively recorded, said ambulatory recorder system comprising:

A cable assembly for coupling a plurality of distinct electrical signals as may be transmitted from an equal plurality of electrodes attached to an individual between such electrodes and an electrode signal switching recorder means, said cable assembly including:

A plurality of electrode signal wires equal in number to the plurality of electrodes, said cable assembly having a trunk into which the electrode signal wires are gathered and along the length of which the electrode signal wires are guided, the trunk having a first terminal end from which extend individual seg¬ ments of the electrode signal wires'^" length, each such extending electrode signal wire length having a connec- tor especially adapted for attachment to an electrode secured to its terminal end projecting furthest outward from the first terminal end of said trunk, the trunk of said cable assembly also having a second terminal end which is adapted for coupling to an electrode signal switching recorder means by a multi-pin connector in which individual electrode signal wires are respec¬ tively attached to individual pins of the multi-pin connector; and

Cable support means as may be secured to an in- dividual, said cable support means being attached to the trunk of said cable assembly about the first ter¬ minal end thereof whereby the weight of said cable assembly may be mechanically supported and whereby the /// f OMPI spatial relationship between electrodes as may be attached to an individual and the first terminal end of 5 the cable assembly's trunk may be maintained; and

Electrode signal switching recorder means as may be used .for preserving a representation of an electrocar¬ diogram, said electrode signal switching recorder means including: o Switching means as may be coupled to the second terminal end of said cable assembly for receiving a plurality of distinct input electrical signals trans¬ mitted thereto via said cable assembly from an equal plurality of electrodes attached to an individual and for switching among those input electrical signals whereby particular ones of the input electrical signals may be successively selected as an output signal, said switching means including output means for transmitting the output signal thus selected by said switching means; and

Recording means as may be electrically coupled to the output means of said switching means for receiving the selected output signal therefrom and for preserving a representation of the selected output signal received by said recording means.

2. The ambulatory recorder system of claim number 1 wherein the cable support means includes a pad made from a foamed material attached to the trunk of said cable as- sembly, said pad having an adhesive surface formed thereon for adhering to the skin of an individual.

3. The ambulatory recorder system of claim number 1 wherein the cable support means includes a pair of pads having an adhesive surface formed thereon for adhering to the skin of an individual, said pads being attached to and longitudinally separated along the length of said cable assembly's trunk about the first terminal end thereof. ///

OMPI 4. The ambulatory recorder system of claim number 1 further comprising a plurality of electrodes as may be respectively mated with and attached to the connectors secured to the terminal ends of lengths of the electrode signal wires projecting furthest outward from the first terminal end of said trunk.

5. The ambulatory recorder system of claim number 1 wherein the recording means records continuously to preserve a total representation of the selected output signals which it receives.

6. The ambulatory recorder system of claim number 1 wherein the recording means records intermittently to preserve a representation of sequentially segmented time intervals of the selected output signals which it receives.

7. The ambulatory recorder system of claim number 1 wherein the electrode signal switching recorder means in¬ cludes dual switching means, each individual switching means being adapted to receive a separate plurality of distinct input electrical signals as may be transmitted thereto from distinct pluralities of electrodes attached to an in¬ dividual, the electrode signal switching recorder means further including dual output means which respectively transmit the selected output signals from particular switch¬ ing means, and wherein the recording means of the electrode signal switching recorder means is a dual channel recorder each channel of the dual channel recorder respectively recording the selected output signal transmitted from one particular output means.

8. The ambulatory recorder system of claim number 1 further comprising means for removing the direct current offset voltage as may be present in signals transmitted by the electrodes before those signals are coupled to said

recording means.

9. The ambulatory recorder system of claim number 1 wherein the switching means and the recording means of said electrode signal switching recorder means are physically enclosed within a single mechanical housing.

10. A cable assembly as may be used in making an ambulatory electrocardiogram, said cable assembly coupling a plurality of electrical signals between an equal plurality of electrodes attached to an individual for transmitting the signals and a recording means for preserving a repre- sentation thereof, said cable assembly comprising:

A plurality of electrode signal wires for coupling an equal plurality of distinct electrical signals as may be transmitted from an equal plurality of electrodes attached to an individual between such electrodes and a recording means, said cable assembly having a trunk into which the electrode signal wires are gathered and along the length of which the electrode signal wires are guided, the trunk having a first terminal end from which extend individual segments of the electrode signal wires' length, each such extending electrode signal wire length having a connector especially adapted for attachment to an electrode secured to its terminal end projecting furthest outward from the first terminal end of said trunk, the trunk of said cable assembly also having a second terminal end adapted for coupling the cable assembly to a recording means; and

Cable support means as may be secured to an individual, said cable support means being attached to the trunk of said cable assembly about the first terminal end thereof whereby the weight of said cable assembly may be mechanically sup- ported and whereby the spatial relationship between electrodes as may be attached to an individual and the first terminal end of the cable assembly's trunk may be main¬ tained. -so¬

il. The cable assembly of claim number 10 wherein the cable support means includes a pad made from a foamed

5 material attached to the trunk of said cable assembly, said pad having an adhesive surface formed thereon for adhering to the skin of an individual.

12. The cable assembly of claim number 10 wherein the o cable support means includes a pair of pads having an ad¬ hesive surface formed thereon for adhering to the skin of an individual, said pads being attached to and longitudinally separated along the length of said cable assembly's trunk about the first terminal end thereof. 5

13. The cable assembly of claim number 10 further comprising a plurality of electrodes as may be respectively mated with and attached to the connectors secured to the terminal ends of lengths of the electrode signal wires ₀ projecting furthest outward from the first terminal end of said trunk.

14. An electrode signal switching recorder as may be used for preserving a record of an ambulatory electrocar- 5 diogram in which a plurality of electrical signals as may be transmitted from an equal plurality of electrodes attached to an ambulatory individual are sequentially and repeti¬ tively recorded, said electrode signal switching recorder comprising: 0 Switching means as may receive a plurality of distinct input electrical signals transmitted thereto from a plurality of electrodes attached to an individual and for switching among those input electrical signals whereby particular ones of the input electrical signals may be 5 successively selected as an output signal, said switching means including output means for transmitting the output signal thus selected from said switching means; and ///

///

OMPI -31 -

Recording means as may be coupled to the output of said switching means for receiving the selected output signal 5 therefrom and for preserving a representation of the selected output signal received by said recording means.

15. The electrode signal switching recorder of claim number 14 wherein the recording means records continuously o to preserve a total representation of the selected output signals which it receives.

16. The electrode signal switching recorder of claim number 14 wherein the recording means records intermittently 5 to preserve a representation of sequentially segmented time intervals of the selected output signals which it receives.

17. The electrode signal switching recorder of claim number 14 wherein the electrode signal switching recorder 0 includes dual switching means, each individual switching means being adapted to receive a separate plurality of distinct input electrical signals as may be transmitted thereto from distinct pluralities of electrodes attached to an individual, the electrode signal switching recorder 5 further including dual output means which respectively transmit the selected output signals from particular switch¬ ing means, and wherein the recording means of the electrode signal switching recorder is a dual channel recorder each channel of the dual channel recorder respectively recording 0 the selected output signal transmitted from one particular output means.

18. The electrode signal switching recorder of claim number 14 further comprising means for removing the direct 5 current offset voltage as may be present in signals trans¬ mitted by the electrodes before those signals are coupled to said recording means. ///

-32-

19. The electrode signal switching recorder of claim number 14 wherein the switching means and the recording

5 means of said electrode signal switching recorder are physi¬ cally enclosed within a single mechanical housing.

20. An ambulatory recorder electrode switch for use in preserving a record of an ambulatory electrocardiogram in

10 which a plurality of electrical signals as may be trans¬ mitted from a plurality of electrodes attached to an am¬ bulatory individual are sequentially and repetitively re¬ corded with a recording means, said ambulatory recorder electrode switch comprising:

15 Switching means for receiving a plurality of distinct input electrical signals as may be transmitted thereto from a plurality of electrodes attached to an individual and for switching among those input electrical signals whereby particular ones of the input electrical signals may be

20 successively selected as an output signal; and

Output means for transmitting the output signal thus selected from said switching means to a recording means.

21. The ambulatory recorder electrode switch of claim 25 number 20 wherein the ambulatory recorder electrode switch is adapted for use with a dual channel recorder by including dual switching means, each individual switching means being adapted to receive a separate plurality of distinct input electrical signals as may be transmitted thereto from dis- 30 tinct pluralities of electrodes attached to an individual, the ambulatory recorder electrode switch further including dual output means which respectively transmit the selected output signals from particular switching means.

35 22. The ambulatory recorder electrode switch of claim number 20 further comprising means for removing the direct current offset voltage as may be present in signals trans¬ mitted by the electrodes before those signals are coupled

from the ambulatory recorder electrode switch to the record¬ ing means.

5

23. A method of recording an ambulatory electrocar- diogram comprising the steps of:

Receiving at a plurality of inputs to a switching means an equal plurality of input electrical signals as may be o transmitted from a plurality of electrodes attached to an ambulatory individual;

Automatically and repetitively switching among those input electrical signals with said switching means whereby particular ones of the input electrical signals may be 5 successively selected as an output signal thereof; and

Transmitting the output signal thus selected from said switching means to a recording means for preserving a repre¬ sentation of the selected output signal received by said recording means.

24. The method of claim number 23 wherein the input electrical signals received at the switching means' plurality of inputs are periodic in time, and wherein the time interval during which successive input electrical signals are selected as the output signal of said switching means is no less than several times the duration of the input electrical signals period.

25. The method of claim number 23 further comprising the step of removing the direct current offset voltage as may be present in signals received from the electrodes before the selected output signal is coupled to the record¬ ing means.

26. The method of claim number 23 further comprising the step of continuously recording the selected output signal transmitted from said switching means to preserve a total representation of the selected output signals.

27. The method of claim number 23 further comprising the step of intermittently recording the selected output signal transmitted from said switching means to preserve a representation of sequentially segmented time intervals of the selected output signals.

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