US 3572321 A
Description (OCR text may contain errors)
'March 23,' 1971 K BLQQMFIELD ETALL' I 3,572,321
ELECTROCARDIOMETER Filed April 1. 1969 3 Sheets-Sheet 1 INVENTOR. DAN/EL KBLOOMFIELD HAZE/50M A. Z/E5KE Ai TOEQ lVlaIiEE "23, 1971 0. K. BLCOVIVIFIELD ET AL 3,572,321
ELECTROCARDIOMETER 3 Sheets-Sheet 8 Filed April 1, 1969 INVENTORS.
we m E 5 F5 N WW W 0 MA T 5 .MN KN.90 Li .5 N mwW March 23, 1971 Filed April 1. l9
D. K. BLOOMFIELD ET AL 3,572,321
ELECTROCARDIOMETER 3 Sheets-Sheet 3 Fig. 4
' DAN/EL K- .BLOOMFIELD HAZE/501V A. Z/ESKE' 4 TTOENEYS.
United States Patent 3,572,321 ELECTROCARDIOMETER Daniel K. Bloomfield, Cleveland, and Harrison A. Zieske, Mentor, Ohio, assignors to Frigitronics Inc. Filed Apr. 1, 1969, Ser. No. 812,167 Int. Cl. A61b /04 U.S. Cl. 1.28-2.06 18 Claims ABSTRACT OF THE DISCLOSURE An electrocardiometer permits a rapid check, in the order of 15 seconds time, of the condition of a persons electrocardiogram by utilizing a single pair of leads connected across the heart to obtain the voltage of the QRS wave and the T wave. The voltages are compared and when the T wave peak amplitude is less than approximately sixteen percent of the QRS wave peak amplitude, an indicating means is provided to indicate this faulty condition.
BACKGROUND OF THE INVENTION The routine electrocardiogram is a through and indispensable means of thoroughly checking a person to see if he has an abnormal heart condition, but is has several disadvantages in that (1) it requires trained personnel, (2) twelve pairs of leads are required to be connected to the person, (3) it takes approximately 15 minutes to complete, and (4) it takes a skilled physician additional time to interpret the results of the various readings on the electrocardiogram. Accordingly it cannot be used as a screening tool, for example, by relatively unskilled personnel or for a quick check in the general practioners oflice, dental oflices, insurance examinations, and corporations giving physical examinations to their employees.
Attempts have been made to simplify the electrocardiogram by using only four or five pairs of leads and also attempts have been made to utilize some form of a computer to analyze the voltages obtained on the various pairs of leads in order to save the time of the skilled physician in interpreting the findings of such electrocardiogram. However, to date to our knowledge there has not been put in practice any form of electrocardiography device which may be used as a screening tool giving a rapid check on a number of persons who may literally pass through a line, touch two electrodes with hands for about or seconds, and obtain an initial check on the condition of such persons electrocardiogram.
Through long experience in interpreting elcctrocardiograms, it has been learned that one distinctive characteristic of abnormal electrocardiograms is the condition of a low or flat T wave in the lead pair between the right arm and left arm, called Lead I, such that the T wave peak amplitude is less than approximately 16 percent of the QRS wave peak amplitude. It has been found that abnormal heart conditions in the great majority of cases show up in various ways but in about 80 percent of the cases do show up at least by this condition of the Lead I T wave amplitude being less than a definite proportion of the QRS wave peak amplitude.
The typical electrocardiographic pattern consists of three major electrical deflections, the P wave representing atrial depolarization, the QRS wave representing de polarization of the ventricles and the T wave which represents repolarization of the ventricles.
Accordingly an object of the invention is to provide a means for simple electrocardiographic interpretation.
Another object of the invention is to provide an electrocardiometer, which compares maximum amplitudes of different waves of the electrical activity of the heart.
3,572,321 Patented Mar. 23, 1971 ice Another object of the invention is to provide an electrocardiometer which compares a given percentage of the QRS wave with the maximum amplitude of the T wave.
Another object of the invention is to provide an electrocardiometer which will indicate an abnormality if either the T wave is too late or is too small in amplitude relative to the QRS wave.
Another object of the invention is to provide a simple electrocardiometer which may be operated by relatively unskilled personnel simply reading a meter or observing flashing lamps to indicate an abnormal or a normal condition.
SUMMARY OF THE INVENTION This invention may be incorporated in an electrocardiometer to obtain electrical deflections of the QRS wave representing ventricle depolarization and the T wave representing ventricle repolarization, comprising in combination, a pair of leads, means to connect said pair of leads effectively across the heart, first means to measure the amplitude of the QRS wave across said pair of leads, second means to measure the amplitude of the T wave across said pair of leads, means to compare said amplitudes, and indicating means to indicate when said T wave amplitude is greater than or less than approximately 12 to 18 percent of said QRS wave amplitude.
Other objects and a fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 taken together show a schematic drawing of the preferred embodiment of electrocardiometer;
FIG. 3 is a modified form of amplifier;
FIG. 4 is a series of graphs of voltages illustrating the operation of the electrocardiometer of FIGS. 1 and 2; and
FIG. 5 is a modification of the read-out circuit of FIG. 2.
. DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 1 and 2 show a preferred embodiment of the electrocardiometer 11, however it will be understood that many different forms of electrical circuits may be used and the following description of the preferred embodiment is only one of many which may be utilized. The electrocardiometer 11 includes several main components; namely, an amplifier 12, a trigger circuit 13, a multivibrator circuit 14, a peak-reader-memory circuit 15, a zero-order hold circuit 16, and a read-out circuit 17.
The typical electrocardiogram shows electrical activity of the heart. The events occurring which generate this activity are the depolarization and repolarization of the myocardium. The typical electrocardiographic pattern is shown at the top of FIG. 4. It consists of three major electrical deflections, the P wave representing atrial depolarization, the QRS wave representing depolarization of the ventricles, and the T wave, which represents repolarization of the ventricles. Repolarization of the atria is usually obscured. A fourth deflection, the U wave, is insignificant in Lead I.
The top of FIG. 1 shows the amplifier 12 which, for example, consists of three differential operational amplifiers 20, 21 and 22 which may be integrated circuit amplifiers with a combined gain of about 10,000, considering the feedback circuit. Coupling resistors 23, coupling capacitors 24, feedback resistors 25 and feedback capacitors 26 are chosen to have resistance-capacitance ratios to obtain a band pass from 0.5 Hz. to 30 Hz. This band pass passes the electrical signals of the heart beat but eliminates much spurious noise and interference and eliminates noise from 60 Hz. power frequency sources. Terminals 27 and 28 are the input terminals from the right arm and left arm respectively, and are identical to Lead I or the first pair of leads of the standard electrocardiogram. These may be taken between the arms or between the shoulders but preferably for simplicity they are taken between the hands of the subject being tested and for convenience one may easily dip his hands into small metal bowls containing a saline solution as a good conductivity electrolyte, with the terminals 27 and 28 connected to these bowls. It has been found that the contact with the arms or hands is not critical.
The input across the terminals 27 and 28 is approximately 0.65 millivolt peak during the R wave. With the combined gain of about 10,000 in the amplifier 12, the output at point A is the typical ECG signal from the first pair of leads with a peak -R wave amplitude of about 6.5 volts, and a typical electrocardiograph wave is shown at the top of FIG. 4. Power of plus and minus to volts is supplied to the operational amplifiers but is not indicated on the drawing. The amplifier could be built entirely with resistors, capacitors and transistors instead of the operational amplifiers 20, 21 and 22, if desired.
At the top right of FIG. 1, the trigger circuit 13 is shown. This incorporates an inverting transistor amplifier 31 with a gain from two to three. The input is the signal at terminal A and the output circuit includes a diode 32, resistor 33 and capacitor 34. The time constant of the RC circuit 33-34 is approximately one second, which is in the order of one period of a human heart beat. The capacitor 34 receives a negative charge as the amplitude of the R wave is increasing, and then discharges toward plus 15 volts, as illustrated. The negative-going portion of this output is designated as an R trigger or RT signal, and is used to trigger the first of four sequential monostable multivibrators in the circuit 14.
The lower portion of FIG. 1 shows the four monostable multivibrators 35, 36, 37 and 38, which are identical except for the different time constants, as indicated on FIG. 4. In each of these monostable vibrators the second of the pair of transistors is normally conducting, and is turned off at the time that the first of the pair of transistors is turned on by an input signal. The length of the time that the first transistor of the pair is on, which is the unstable condition, is dependent upon the R-C time constants of the circuit, in a well-known manner.
The first monostable multivibrator 35 is triggered into its unstable state by the RT signal during the time that the ECG R wave is approaching its peak. There is a three volt drop across the common emitter resistor 39. Accordingly the output B switches from a 12 volts to +15 volts for a period of 100 milliseconds, as shown in FIG. 4.
This 100 millisecond period includes the time during which the R wave is at its greatest amplitude. When the voltage at terminal B returns to 12 volts by conduction of the second of the pair of transistors, the next multivibrator 36 is triggered, and its output C goes from -12 volts to +15 volts for a 300 millisecond period. This period includes all of the T wave of the normal ECG on the first pair of leads. The third multivibrator 37 is triggered as the voltage at terminal C returns to 12 volts. This third multivibrator 37 has a period of milliseconds as shown on FIG. 4 and then the fourth multivibrator 38 is triggered. The 25 millisecond period of +15 volts at terminal D is normally after the T wave is completed and before the P wave has started. The fourth monostable multivibrator 38 produces a 25 millisecond output of +15 volts at terminal E which begins when the voltage at D returns to 12 volts.
, The complete schematic diagram is continued from FIG. 1 onto FIG. 2 and the left side of FIG. 2 shows three identical peak-reader-memory circuits 15 each of which consists of three N-channel junction field effect transistors 42, 43 and 44 with source and drain interchangeable. The first two field effect transistors 42 and 43 in each of the circuits are normally open switches. The first set of PET switches 42 are closed by the +15 signals at terminals B, C and D, and these respectively connect the ECG signal A to the diode-capacitor networks including a diode 45 and capacitor 46. Signal A is thus passed by the respective diode to charge the capacitor 46 which reads and remembers the peak values of the R wave, T wave, and post-T reference levels, respectively. Upon being sensed by voltage follower FET 44, these voltages are available at low impedance points F, G, and H as the outputs of voltage followers, the circuits in which the tran sistors 44 are connected. The second PET switch 43 in each circuit 15 is a normally open switch which closes to discharge the capacitor with which it is associated to -8 volts at the time that +15 volts is present at terminals E, making the peak-reader-memory circuits 15 ready for the next cardiac cycle. The voltage wave forms in these circuits on terminals F, G and H are included in FIG. 4.
The three zero-order hold circuits 16 shown on the right half of FIG. 2 each consist of a normally open switch, shown as an FET switch 49, a charge storing capacitor 50, and a voltage follower shown as a field effect transistor 51. Each transistor 49 and 51 has an interchangeable source and drain and is a junction field effect N-channel transistor. The voltage at terminal D, FIG. 1, is used to enable the FET switches since, at the time when +15 volts is present at terminals D, the peak-reader-memory circuits 15 contain maximum R wave, maximum T wave, and post-T reference voltages at terminals F, G and H, respectively, the inputs to the zero-order hold circuits 16.
Terminals J, K and L are held at voltages corresponding to the peak of the previous R wave (at terminal A), the maximum amplitude of the previous T wave and the current post-T reference level, respectively, for the duration of one cardiac cycle. This is also shown in FIG. 4. At the end of the period of time determined by the cardiac cycle the corresponding voltages of the subsequent cycle are gated into the zero-order hold circuits 16. These three voltages accordingly may make an abrupt change at the end of each such cycle. The read-outcircuit 17, as illustrated at the lower portion of FIG. 2, will supply the answer to questions: (1) Is the maximum amplitude of the T wave at terminal K less than, equal to, or greater than x percent of the maximum amplitude of the R wave at terminal I, both referred to the post-T, reference level at terminal L? (2) The maximum T wave amplitude is equal to what percent of the maximum R wave amplitude? To answer the first question a predetermined ratio is set on the potentiometer 54 which is connected across the I and L terminals, so that a center-zero microammeter 55 is connected between x percent of the maximum R wave voltage and the entire T wave voltage. Thus the meter deflects to the right for greater than answer, to the left for less than and stays at the center for an equal to answer. To answer the second question the potentiometer rotation is calibrated from zero percent to percent as the wiper is moved from L terminal toward I terminal. The setting at which the meter nulls is that percentage of the maximum R wave amplitude to which the T wave maximum amplitude is equal, both referred to the reference level present at terminal L.
The meter switch 57 is shown in the correct position for test cycles to read-out the above information. This is a two-pole, four position switch and when the switch is moved to the next position 59 it connects the meter 55 between ground and the voltage at terminal A through a filter 60. A near zero reading indicates that transients introduced by electrode application have settled down and that the device is ready to be read. The other two switch positions 61 and 62 connect the meter to read the condition of the plus and minus 15 volt power supplies, e.g. batteries.
FIG. 4 shows the voltage wave forms present at the various points throughout the circuits which are designated by letters A through L. The ECG on the first pair of leads is represented for two cardiac cycles on wave form A with a large difference in the R to T ratio for purposes of showing how marked changes in the ECG affect wave forms F-L. The wave form B shows the voltage on termi nal B and shows that it goes from l2 to +15 volts for a 100 millisecond period after being triggered by the RT signal from the trigger circuit 13. The wave form C shown in FIG. 4 starts at the time of termination of the wave on terminal B and lasts for 300 milliseconds which is long enough for the usual T wave of a normal ECG. The wave form D lasts for 25 milliseconds and is initiated upon the termination of the wave form C. This form D gives a post-T level of voltage to establish a reference level from which the R and T waves are measured. The wave form E shown in FIG. 4 occurs upon termination of the D Wave at terminal D and this wave at terminal E is used to trigger the peak-reader-memory circuits 15 to cause conduction of the FET switches 43 and discharge the capacitors 46.
In FIG. 4 the voltage Wave form at terminal F is shown as following the upper portion of the rising QRS wave until the peak voltage is reached whereupon the diode 45 prevents reverse current and hence the voltage of capacitor 46 remains at this peak value and the voltage follower 44 maintains this peak voltage at the terminal F. This is maintained for a total of 100 plus 300 plus 25 or 425 milliseconds until the signal at terminal E appears. The voltage wave form G in FIG. 4 shows that the voltage is initially at 8 volts, then rises to the level of the signal at A, and then rises as the T wave rises, thereafter remaining at the peak amplitude thereof until the end of that wave which is again 425 milliseconds after the trigger signal at terminal RT. The wave form at terminal H is shown in FIG. 4 as rising from 8 volts to a reference level established at the post T time, namely a time after the T wave has passed. During the times that no trace is shown for the voltages on terminals F, G and H, these points are at 8 volts. The signals on the terminals J, K and L, where missing, cannot be represented, since at that time the values depend upon the R wave and the T wave preceding those shown. At the time of the second pulse on terminal D, the meter 55 would swing from a right deflection, for a satisfactory ECG, to a left deflection, for an abnormal ECG, had the potentiometer 54 been set at 25 percent.
Upon a recent review of at least 200 normal and abnormal electrocardiograms it has been determined that there is a relatively sharp cutoff between normality and abnormality when the T wave height is 14 to 16 percent of the R wave. T waves greater than 16 percent usually indicate a normal electrocardiogram and T waves less than 16 percent are usually associated with abnormal electrocardiograms. Depending upon age of the subject and other factors a percentage between 12 and 18 percent may be considered the dividing line between normality and abnormality. Using this criteria, 99 out of 100 randomly selected normal electrocardiograms demonstrated a normal relationship between the R wave and the T wave, and 80 out of 100 abnormal cardiograms showed an abnormal relationship.
This electrocardiographic test which relies only upon the potential difference between the right and left arm is far simpler than the routine 12 pairs of leads electrocardiogram which requires a skilled technician 15 minutes to complete, and then requires a skilled physician to interpret. We have found that screening a single pair of leads with a direct read-out of normality and abnormality will require only 15 to 30 seconds.
Based on the data on hand, this test when applied to a sample population would theoretically select 80 percent of persons with abnormal electrocardiograms while giving false positive tests in only one percent of normals. The practical application of such a test can be appreciated if one assumes the screening of a population of 10,000,
persons, percent of whom have abnormal electrocardiograms. The results from such a ing are shown in the following table:
theoretical screen- The time saved in such a screening as compared to routine electrocardiography can be appreciated when one considers that the screening time of this population would be 83.3 hours or approximately two working Weeks. Routine electrocardiography on this population would require 2,500 hours or 62 working weeks. This screening would be 97.1 percent accurate.
From the above it will be seen that the electrocardiometer 11 provides a means to compare the amplitude of the T wave with the amplitude of the QRS wave and more particularly it compares the peak amplitude of these two waves. Still further the electrocardiometer circuit 11 will detect the abnormality of a T wave which is late, that is, the QT interval is a long time. As will be noticed from the wave form at terminal G on FIG. 4, if the peak of the T wave has not occurred at the end of the 400 millisecond time delay period established by the first and second monostable multivibrators 35 and 36, then this will appear as an abnormally low amplitude of T wave and as a result the meter 55 will indicate this as an abnormality. Further, 1f the T wave is not completed at the end of the 400 millisecond time delay, the waveform at terminal H, FIG. 4, will be elevated. The effect of a more positive post-T reference is the same as that of a less positive T wave, and as a result the meter 55 will indicate this as abnormal. The time period in this preferred embodiment is 400 milliseconds which is approximately one-half the period of the cardiac cycle between successive QRS waves.
FIG. 3 shows an alternative circuit for the amplifier 12 shown at the upper part of FIG. 1. FIG. 3 ShOWs this alternative amplifier circuit 65 which includes four of the operational amplifiers rather than only three as shown in the preferred embodiment. Separate inputs at terminals 27 and 28 lead to separate operational amplifiers before the two signals are combined on the last two operational amplifiers connected in cascade. In other ways this operational amplifier circuit of FIG. 3 will operate in the same manner as that shown in FIG. 1.
FIG. 5 shows a read-out circuit 69 which can be used as an alternative to that shown at 17 at the lower part of FIG. 2. The visual indication, either of two lamps 70 or 71 flashing, answers yes or no to this question: Is the maximum amplitude of the T wave greater than x percent of the maximum R wave amplitude, both referred to the post-T reference level. X is determined by the setting of potentiometer 54. An operational amplifier 72 is connected with one input coming from potentiometer 54 which is connected across terminals J and L, and the other input connected to terminal K as a post-T reference.
The operational amplifier 72 is connected in a bangbang circuit so that its output at 73 is +12 volts when T x% R and is -l2 volts when T x% R This output, when +12 volts, makes an NPN transistor 74 conducting; and the l2 volt output makes a PNP transistor 75 conducting. The N channel field effect transistors 76 and 77 in series with transistors 74 and 75, respectively, are made conducting, for example, for milliseconds initiated by the R wave signal at terminal B. During this 100 milliseconds of each cardiac cycle one of the capacitors 78 or 79 discharges through one of the field effect transistors 76 or 77 and corresponding transistor 74 or 75, as determined by the bang-bang circuit input, and the lamp 70 or 71 associated with transistor 74 or 75, causing in combination,
The RC networks may have a time constant of. about 0.8 second permitting a full volt charge to accumulate on the capacitors 78 and 79 between discharges. The discharge time is limited to a duty cycle of approximately 10 percent. Thus, using 10 volt, ma. lamps, the average current requirement is only plus or minus 2 ma., depending on which lamp is flashing.
The present disclosure includes that contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of the circuit and the combination and arrangement of circuit elements may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.
What is claimed is:
1. An electrocardiometer to obtain electrical deflections of the QRS wave representing ventricle depolarization and the T wave representing ventricle repolarization, comprising in combination,
a pair of leads,
means to connect said pair of leads elfectively across the heart,
first means to measure the amplitude of the QRS wave across said pair of leads,
second means to measure the amplitude of the T wave across said pair of leads,
means to compare said amplitudes,
and indicating means to indicate when said T wave amplitude is less than approximately 12 to 18 percent of said QRS wave amplitude.
2. An electrocardiometer as set forth in claim 1, wherein said first means includes means to measure the peak amplitude of said QRS wave.
3. An electrocardiometer as set forth in claim 2, wherein said second means includes means to measure the peak amplitude of said T wave.
4. An electrocardiometer as set forth in claim 1, wherein said second means includes means to measure the peak amplitude of said T wave during a time interval and means terminating said time interval at a time subsequent to the occurrence of one QRS wave and at a time prior to the occurrence of the next QRS wave.
5. An electrocardiometer as set forth in claim 4, including means terminating said time interval at approximately one-half the period between successive QRS waves.
6. An electrocardiometer as set forth in claim 4, including means initiating said time interval in accordance with the occurrence of a QRS wave.
7. An electrocardiometer as set forth in claim 6, wherein said first means includes means to measure the peak amplitude of said QRS wave.
8. An electrocardiometer as set forth in claim 1, wherein said indicating means indicates when the value of said T wave peak amplitude is less than approximately 16 percent of said QRS wave peak amplitude.
9. An electrocardiometer as set forth in claim 1, wherein indicating means is a meter, and
circuit means energizing said meter to remain at an essentially constant reading on the meter throughout any given cycle between successive QRS waves.
10. An electrocardiometer as set forth in claim 9, wherein said meter indicates the comparison of a certain proportion of said QRS wave peak amplitude with said T wave peak amplitude.
11. An electrocardiometer as set forth in claim 1, wherein said indicating means is lamp means illuminable in accordance with ratio of the amplitude of the QRS wave and T wave.
12. An electrocardiometer as set forth in claim 1, wherein said indicating means includes first and second selectively illuminable each period of the heart beat.
13. An electrocardiometer as set forth in claim 1, including means to initiate the start of a test cycle includ ing means to sense the rising peak of the QRS wave.
14. An electrocardiometer as set forth in claim 13, wherein said cycle initiation means includes an RC time delay means having a period in the order of the period of a human heart beat.
15. An electrocardiometer as set forth in claim 13, wherein said cycle initiation means includes a plurality of monostable multivibrators sequentially triggered, and the triggering of the first of the multivibrators starting the cycle.
16. An electrocardiometer as set forth in claim 1, including a peak-reader-memory circuit means to read the peak amplitude of each of the QRS wave and of the T wave. 1
17. An electrocardiometer as set forth in claim 16, wherein said peak-reader-memory circuit means includes capacitor means charged by the positively increasing voltage, and diode means to prevent discharge of said capacitor means so that the voltage across said capacitor means charges to the peak of the applied voltage and remains at said peak.
18. An electrocardiometer as set forth in claim 17, including zero-order hold circuit means which includes voltage follower means to produce voltages remaining at a 4 constant level dependent upon said capacitor means voltage throughout a complete cycle.
References Cited UNITED STATES PATENTS WILLIAM E. KAMM, Primary Examiner