Arrhythmia rejection circuit for gated cardiac image display systems

Signals associated with heart beats occurring at the normal rhythm of the heart and also with extrasystoles or PVCs are fed to a one-shot multivibrator which is enabled to produce clock signals corresponding with incoming heart activity indicating signals such as R-wave signals provided the R-wave signals are spaced in time to correspond with normal heart rhythm. An analog signal corresponding with average heart rate is fed to an integrator. The ramp output of the integrator is fed to one input of a comparator and a reference signal representative of a percentage of time between normal rhythm R-waves is fed to the other input of the comparator. Until the two input signals cross over, the output signal of the comparator is such as to inhibit output of a clock signal from the multivibrator so R-wave signals associated with extrasystoles occurring during the integration or lockout period are not gated through the multivibrator. The clock signals corresponding with predictable rhythmically occurring heart activity signals are used for gating image forming devices and image data devices on and off at identical times in a sequence of heart cycles to produce a stop-motion effect.

This invention is applicable to systems such as conventional and 
computerized tomography x-ray systems, nuclear radiation systems and 
ultrasonic radiation camera systems which display images of quiescent 
organs and moving organs such as the heart. 
The invention will be demonstrated and described in reference to a nuclear 
camera system as used for evaluating cardiac function by taking a nuclear 
radiation image or exposure of the heart at exactly the same time during 
successive heart cycles so that an image or sequence of images of 
sufficient intensity for diagnosis can be integrated. Basically, the 
invention enables motion of an organ to be stopped. The invention is for 
permitting data for an image to be gated to the display device only in 
synchronism with heart beats that occur at the regular or ostensibly 
normal heart rate and for prohibiting gating upon occurrence of 
extrasystoles or premature ventricular contractions. If gating of data for 
each view or image is not initiated at the same time in each heart cycle 
in relation to some stable reference, such as R-waves occurring at normal 
sinus rhythm, the stop motion effect will not be obtained and the image or 
sequence of images will be blurred. 
A well-known nuclear camera, hereafter called a gamma camera system, with 
which the invention may be used is described in U.S. Pat. No. 3,011,057 to 
Anger. This camera has a large scintillation crystal that is disposed over 
an organ such as a heart which has been infused with blood containing a 
radioisotope. The crystal responds to absorption of gamma ray photons 
emitted from the heart by producing visible light scintillations. A 
closely packed array of phototubes is located behind the scintillator 
crystal and their output signals, corresponding with scintillation events, 
are processed in an analog computer to determine the x and y coordinates 
of the scintillations and the energies of the gamma photons. The electric 
pulses which result from the scintillations are fed first to a pulse 
height analyzer. Pulses falling outside of a narrow energy range, called a 
window, are rejected and pulses within the window are considered valid. 
For every pair of valid x and y coordinate signals, a coincident z signal 
is produced with known electronic circuitry. 
The x and y coordinate signals are used to drive the beam deflection 
control circuits of a cathode ray tube on which the cumulative image of a 
large number of scintillation events is displayed. The cathode ray tube is 
unblanked only by z signals so that only valid scintillations are 
displayed. Typical methods of developing suitable x, y and z signals are 
described in U.S. Pat. Nos. 3,697,753 and 3,919,556. 
Images displayed on the cathode ray tube (CRT) screen are usually recorded 
with a photographic camera. There are known systems for displaying the 
images in different formats on the CRT screen and for recording the images 
correspondingly on photographic film. For instance, a CRT may be 
controlled so that the image occupies the whole area on the screen, in 
which case the whole area of the film will be covered in one exposure or 
the same or another CRT may be controlled with a formatter to display a 
sequence of smaller images for being recorded on adjacent film areas. A 
formatter is described in U.S. Pat. No. 4,075,485 which is owned by the 
assignee of the present invention and is incorporated herein by reference. 
In evaluating cardiac function with an ultrasonic camera system or a gamma 
camera system, it is necessary to make repeated exposures of the heart 
while the heart is in the same state during each cycle. Most commonly, the 
QRS complex or R-wave of the electrocardiogram (ECG) waveform is used as a 
reference point for initiating each exposure because the R-wave is a 
strong signal. It is conceivble that one of the lower amplitude portions 
of the ECG waveform such as the P-wave or T-wave could be used as the 
reference under proper circumstances. Moreover, oscillatory signals such 
as are obtained with ultrasonographics equipment corresponding with 
regularly occurring physiological events such as heart beats could be used 
as a reference. There are known systems for gating the gamma camera output 
or for turning on the CRT display only during short window intervals in 
each cardiac cycle. This is achieved with a delay control which varies the 
time between the R-wave occurrence and the window opening time when 
recording of a particular exposure is initiated. The CRT recorder is, in 
effect, turned on and off for one or more brief window intervals during 
each heart cycle and only radiation integrated during those intervals 
contributes to forming the image or sequence of images. Information lying 
outside of any exposure interval is rejected. This produces the 
stop-motion effect. 
A typical gamma camera diagnostic procedure is to determine the left 
ventricular ejection fraction (LVEF) of the heart which is a measure of 
the ability of the left ventricle (LV) to eject blood. It is calculated 
from the following formula: 
EQU LVEF=EDV-ESV/EDV 
EDV is the left ventricular end-diastolic volume and ESV is the left 
ventricular end-systolic volume of the heart. The normal value for LVEF is 
59%.+-.6%. At EDV, the heart is filled with blood and has maximum volume. 
At ESV, the left ventricle has contracted, much of its blood has been 
expelled and its volume is minimum. If the heart is infused with blood 
containing a radioisotope, usually technetium99m (Tc99m), it will emit 
radiation or gamma rays in a pattern which defines the entire range of 
heart sizes and shapes between diastole and systole. Hence, to get its 
shape or the blood volume it contains at the end of systole or the end of 
diastole it is necessary to stop motion and make exposures at these times. 
There is not enough radiation to make a readable image during one exposure 
interval so exposures at the same time in successive heart cycles have to 
be made. As implied above, the present state of the art permits making 
short systole and diastole exposures after fixed delays following 
occurrence of an R-wave. However, patients undergoing examinations of this 
type usually have some cardiac malfunction. As a result, the heart does 
not beat as rhythmically as it would in a normal healthy person but there 
are premature ventricular contractions which upset the rhythm. These PVCs 
cause false triggering of the gamma camera and all of the exposures are 
not made at a corresponding time within each heart cycle. 
SUMMARY OF THE INVENTION 
In order to facilitate non-invasive, cardionuclear imaging such as 
equilibrium, gated blood pool and ejection fraction studies, the gamma 
camera system must have a device that is capable of processing 
physiological signals for controlling a variety of camera system 
functions. 
In accordance with the invention a synchronizer, also called an 
extrasystole rejector, is provided for rejecting the arrhythmic heart 
beats in order to prevent erroneous data from being added to the gated 
images during a study which typically encompasses hundreds of cardiac 
cycles. Of the many types of arrhythmias produced by the heart, the new 
synchronizer rejects the most common types which are single, or infrequent 
beat, extrasystoles. Extrasystoles are simply premature contractions of 
the heart which may be either ventricular, atrial or nodal in origin. The 
new synchronizer receives patient electrocardiogram signals and gates 
gamma camera data tallying, data presentation and data recording at 
preselected periods within the cardiac cycle. The gating intervals, or 
windows, occur after operator selected delays from the R-wave or other 
reference point in the ECG or other physiological waveforms and reoccur at 
the same points in time for each cardiac cycle. 
The new arrhythmia rejection circuit (1) rejects the PVC itself; (2) 
rejects the beat immediately following the PVC, if the heart does not 
pause to compensate for the PVC and reestablish rhythm, but if a 
compensatory pause occurs, the following beat is accepted as normal; and 
(3) disables all gating window circuit functions when the PVC occurs and 
they remain disabled until a beat in normal rhythm is recognized. 
In general terms, the illustrative embodiment of the new synchronizer and 
arrhythmia rejection circuit employs an electrocardiogram to obtain the 
usual ECG waveform. Means are provided to produce a flag pulse for every 
QRS complex or R-wave in the ECG waveform. In one circuit, these R-wave or 
QRS flag pulses of constant duration and amplitude are integrated to 
produce an analog voltage signal which is proportional to flag pulse rate 
and, hence, to heart rate. An essentially conventional rate meter circuit 
may be used. 
The QRS flag pulses are also supplied to the arrhythmia rejection circuit. 
It has an integrator which is turned on and produces an output ramp 
voltage that is supplied to a comparator which compares this voltage with 
a reference voltage. The reference voltage is set to correspond with a 
certain percentage of the time between QRS flags that correspond with 
normal heart rate or rhythm. When the ramp voltage equals the reference 
voltage the comparator trips or changes state. Any premature QRS flags 
occurring during integration are locked out. This is done by controlling a 
gating device such as a one-shot multivibrator to which all QRS flag 
pulses are supplied and which supplies output pulses only if it is enabled 
and not locked out as a result of the comparator not having changed its 
state. Thus, the one-shot multivibrator produces output pulses only if the 
QRS flag pulses are sufficiently spaced to approximate the spacing between 
QRS flags or R-waves occurring at the normal heart rate. The pulses from 
the one-shot multivibrator are used to initiate image integration at the 
proper times as mentioned previously. 
In the illustrative embodiment, R-waves which are detected in the ECG 
waveform and which are determined to be in synchronism with normal or 
regular sinus rhythm are used as reference points for gating image forming 
data to the display or recording devices but it will be understood that 
other parts of the ECG waveform such as the P-wave or T-wave could also be 
used. Moreover, the reference signals do not necessarily have to be based 
on the examination subject's ECG. Any signal indicative of physiological 
activity such as signals of heart activity obtained with cardiosonographic 
apparatus may be employed and the new rejector will distinguish 
physiological events which occur at a substantially regular rate from 
those events that do not. 
The basic object of this invention is to provide means for eliminating or 
rejecting arrhythmic physiological signals in real time so an image 
recording device will be enabled or gated only in response to heart beats 
occurring in normal heart rhythm. An adjunct to this object is to reject 
any signals derived from heart activity immediately following a PVC if the 
heart does not pause to compensate for the PVC and reestablish normal 
rhythm. 
How the foregoing and other more specific objects are achieved will be 
evident in the more detailed description of a preferred embodiment of the 
invention which will now be set forth in reference to the drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to FIG. 1, a heart patient is represented by the pictograph 
marked 10. For the purposes of discussion, it may be assumed that the 
beating heart of this patient and the blood which it pumps are infused 
with a radioisotope which emits gamma radiation. One of the medical 
procedures which may be accomplished is to determine the blood volume in 
the left ventricle of the heart at the end of diastole when it contains 
maximum blood volume and also at the end of systole when it contains 
minimum blood volume. The object might be to determine the left ventricle 
ejection fraction (LVEF) for evaluating the pumping efficiency of the 
heart as mentioned earlier. 
To perform this procedure, a conventional gamma camera 11 such as an Anger 
type camera, is disposed over the body 10. Although the details are not 
shown, it will be understood that gamma camera 11 has a crystalline disk 
which produces scintillations in response to absorption of gamma ray 
photons radiated from the isotope in the infused heart. An array of 
photomultiplier tubes in the camera, intercepts the scintillations and 
produces output signals which are fed to camera electronics module 12. 
This module, in which the signals are processed, cooperates with an analog 
computer 13 that computes the x and y coordinates of the scintillations. 
Signals representative of the energies of the scintillations are supplied 
to a pulse height selector, in the camera electronics, not shown, and 
signals falling within the window of the selector are caused to produce z 
signals which are outputted on cable 14. Valid x and y coordinate 
representative signals are also outputted on cable 14. The z signals are 
effective to unblank a cathode ray tube (CRT) 17 in correspondence with 
the electron beam of the tube being deflected to the point defined by the 
x and y coordinate signals which are processed in the camera electronics 
and are delivered to the horizontal and vertical deflection coils 18 of 
the CRT 17. When the CRT is unblanked, a light spot, corresponding 
positionally with a scintillation, appears on its display screen 21. The x 
coordinate signals are supplied to deflection coils 18 through a suitable 
control 19 which processes the signals to effectuate proper deflection of 
the CRT beam in the x direction. Circuitry for controlling deflection in 
the y direction is symbolized by the block 20. Circuitry for controlling z 
signals which unblank the cathode ray tube beam to produce a light spot on 
the screen 21 of CRT 17 for every pair of x and y coordinate signals 
simultaneously produced is represented by the block marked 22. The z 
signals are supplied to a control logic and switching circuit which gates 
them at appropriate times to the control grid 23 of the CRT 17 as will be 
discussed in more detail later. Z signals would normally be supplied 
directly to the control grid 23 in the absence of the new synchronizer. 
Thus, in a conventional manner, light spots corresponding with 
scintillations corresponding with particular points in the patient's heart 
are repeatedly developed on screen 21 of CRT 17. If the process is 
permitted to persist long enough, scintillations from all points on the 
heart will be gathered and the shape of the heart and its chambers will be 
defined. Of course, if a continuous exposure is made while the heart is 
expanding and contracting as it fills with blood and discharges blood, the 
image will be blurred since the points from which gamma photons are 
emitted would be continuously in motion or spread out over the area of the 
heart. The new synchronizer enables exposures to be made during the same 
short gate intervals in a succession of heart cycles to obtain the 
equivalent of stopping motion. A unique feature of the new synchronizer is 
that it inhibits gating of signals for recording if they are related to 
certain irregular physiological events such as to an R-wave that 
corresponds with an extrasystole or PVC. 
In FIG. 1, the light spots which appear on the screen 21 of CRT 17 are 
integrated on a film in a camera 24 which is in a light-tight enclosure 
25. The film integrates the light spots during each exposure and forms the 
image of the heart and its blood-filled chambers. 
Another CRT 27 is provided to enable displaying a formatted sequence of 
images on its screen 28. The images are integrated on a film 30 by 
projecting them with a lens in a light-tight enclosure 32. These 
successive images would be the result of making a sequence of exposures at 
differently phased short intervals in successive heart cycles. An image 
formatter system is provided and is symbolized by the block 26 in FIG. 1. 
A suitable formatter is described in U.S. Pat. No. 4,075,485 which is 
owned by the assignee of this application and is incorporated herein by 
reference. The formatter, in effect, applies a fixed bias to the x and y 
deflection coils 29 of CRT 27 so that the image or images are formed on 
screen 28 at a determinable location and within bound areas. The x, y and 
z signals are supplied to the CRT by way of respective lines collectively 
designated by reference numeral 33. 
A typical format is shown in FIG. 2 where there could be as many as 42 
small images formed by recording light-dot after light-dot on screen 28. 
The light dots are projected to the film in cassette 30 where they are 
integrated successively. The images on the screen are indicated as small 
circles. In this particular example, there are six-by-seven images giving 
a total of 42. It should be understood, however, that if the normal heart 
rate is fast, there may be time for fewer than 42 individual images to be 
formed on one sheet of film in cassette 30. For instance, in a practical 
embodiment the format control is such that five milliseconds must elapse 
between consecutive views or exposures and adding that time to the time 
required for each exposure sets the limit for the number of exposures that 
can be obtained between normally and regularly spaced R-waves. 
The formatter 26 permits integrating light spots for a sequence of views at 
different sequential points of the heart cycle between substantially 
equally timed physiological reference signals such as R-waves occurring at 
the regular normal heart rhythm. The end result is an orderly sequence of 
views of the heart at different stages from 
diastole-to-systole-to-diastole, etc. A regularly occurring R-wave starts 
the first view, then after five milliseconds the formatter shifts the 
image on the display screen 28 and the second view is made. This is 
repeated for five or ten minutes, usually, to form good images of the 
ventricle or blood volume shape at many different times in the heart 
cycle. 
As indicated, the exposure time itself is variable. The patient's heart 
rate determines how many of the 42 separate views obtainable in this case 
will be filled up. If, let us say, only 17 views, as indicated by the 
solid line circles in FIG. 2, could be taken before another regular or 
normal rate R-wave occurred, the formatter would reset so it would go back 
to No. 1 view again to start building it up. To assure getting as many as 
42 separate views between regular heart beats, the operator may shorten 
the exposure time for each view so more steps may occur before the next 
valid R-wave, and not an extrasystole, caused a reset. 
If PVCs occur at any time during the sequence of heart cycles, they could 
trigger the gamma camera and formatter to gate images which are out of 
phase with others in the sequence on the display screen which would cause 
those images following a PVC to be blurred. The new synchronizer uses only 
substantially fixed rate physiological signals such as R-waves that occur 
in substantially the normal rhythm of the heart for all system timing and 
rejects false-triggering R-waves resulting from PVCs. 
As in FIG. 1, another component usually found in gamma camera systems for 
making heart studies is a scaler timer which is symbolized by the block 
marked 56. The scaler timer is gated by the z signals produced by the new 
synchronizer or rejector 39 to count scintillation events at predetermined 
times. Control logic and switching circuit 55 determines when scaler timer 
56 is to start counting for a short interval or during a window interval. 
The windows are determined by action of the systole delay 41, systole 
window control 42, diastole delay 44 and diastole window control 45 as 
will be discussed further. One example might be counting for selected 
short intervals at diastole when the left ventricle is filled and at 
systole when the left ventricle blood volume is at a minimum. The number 
of scintillation counts at diastole and systole are, therefore, indicative 
of left ventricle volume if that is the nature of the study being made. To 
find LVEF, for example, the equation given earlier can be used where the 
number of counts at the end of diastole would be substituted for EDV and 
the number of counts at the end of systole would be substituted for ESV. 
Of course, counting by the scaler timer must be initiated only by valid 
physiological signals such as R-waves or QRS flags which fall within the 
natural rhythm of the heart and not by signals that correspond with PVCs. 
Known gamma camera systems for heart studies also usually include a 
minicomputer which is symbolized by the block 57. The minicomputer is 
programmed for using scintillation events to produce a number of 
indications of heart function. It can also be used for calculating LVEF, 
for example. It must be provided with information as to when valid R-waves 
or other regularly occurring reference signals have occurred, that is, 
R-waves which fall within the natural rhythm of the heart and are not 
extrasystoles. Hence, the new synchronizer can provide the minicomputer, 
for example, with valid R-wave flag signals which are indicative of 
certain events being of significance in a long chain of continuous 
scintillation data so the minicomputer can make all of its calculations 
with the use of valid physiological reference points which are the 
R-waves, in this example, that are associated with normal heart beating 
rate with the exclusion of PVCs. 
In FIG. 1, all timing is based on detection of valid normal rhythm QRS 
complexes or R-waves occurring in the ECG. Detection is accomplished with 
an ECG isolation and R-wave detection circuit which is symbolized by the 
block 35 in FIG. 1 and is basically known. It couples to the same patient 
10 that is in view of the gamma camera at the time. Its output on line 36 
is a series of square wave pulses, called flag pulses, which coincide in 
time with R-waves or QRS complexes that are incidental to normal rhythmic 
heart beats and also to premature ventricular contractions or 
extrasystoles. 
Pulses that correspond with R-wave flag pulses which occur at a rate 
corresponding with the normal and substantially regular heart rate are 
called clock pulses herein. The clock pulses are used for initiating 
counting or recording scintillations which represent various stages of 
heart activity. 
One use of these QRS flag pulse signals is in a heart rate calculator which 
is symbolized by the block 37 in FIG. 1. The heart rate calculator 
integrates the incoming pulses, which are mostly normal rhythm pulses, and 
produces an analog voltage signal whose magnitude corresponds with the 
repetition rate of QRS complexes or, in effect, the heart rate. This 
signal is supplied by way of a line 38 to the new arrhythmia rejection 
device or circuit which is represented by the block 39 in FIG. 1. The QRS 
flag pulses from R-wave detector 35 are also supplied to arrhythmia 
rejection circuit 39 by way of a line 40. The manner in which the analog 
voltage signal indicative of heart rate and the R-wave flag signals are 
utilized in the arrhythmia rejection circuit 39 will be explained in 
greater detail when the latter is described in reference to FIG. 5. 
FIG. 3, consisting of parts A-F, illustrates an electrocardiogram waveform 
in part A which will serve as a basis for discussion. This ECG has a 
series of QRS complexes and their peaks, known as the R-wave peaks, are 
marked R1-R8. A ventricular contraction usually occurs coincident with an 
R-wave. The spacing between R1 and R2, between R3 and R4 and between R6, 
R7 and R8 in this example are equal and correspond with the normal heart 
rate which, even in a reasonably healthy heart may vary by about .+-.10% 
from one R-to-R interval to the next. A normal heart rate with a subject 
at rest might be about 72 beats per minute or about 833 milliseconds 
between beats. An unhealthy heart might beat much faster or much slower. 
Most patients having a need for heart evaluation will also exhibit 
premature ventricular contractions or extrasystoles that result from QRS 
complexes or R-waves falling out of the natural rhythm such as those 
marked R3 and R5 in FIG. 3 which are indicated by QRS complexes comprised 
of dashed lines in FIG. 3, part A. The new arrhythmia rejection circuit 
39, shown in detail in FIG. 5, would negate or reject PVCs R3 and R5 since 
they follow valid or normal R-waves R2 and R4 too closely. If R3 were much 
closer to R4, it might be considered a valid R-wave and not a PVC as will 
be shown later when the arrhythmia rejection circuit 39 is described in 
detail. 
In FIG. 3, PVC R3 is followed by a long pause before R4 occurs. If the 
pause is long enough, the new arrhythmia rejection circuit interprets this 
as restoration of natural rhythm and it follows the mode in which it 
permits signals for forming an image to be gated to the CRT 17 display to 
the scaler timer 56 and to the minicomputer 57 at the proper times as 
dictated by switching circuit 55 as governed by delay and window controls 
41, 42, 44 and 45. By way of example, any R-wave that occurs, let us say 
arbitrarily, within 75% of the interval between successive normal heart 
rate R-waves might be considered a PVC in which case any occurring within 
25% of the time interval preceding the second in a pair of successive 
R-waves might be considered a valid R-wave and, in accordance with the 
invention, a clock pulse or timing reference pulse corresponding with a 
valid R-wave would be produced. 
In FIG. 3, part B, under the ECG, there is a time axis line. Some short 
intervals along this line are marked ED. The duration of these intervals 
can be set. The ED intervals occur at a time that coincides with the end 
of diastole when the left ventricle has maximum volume of blood in it. At 
this point in the heart cycle the diagnostician wants to stop motion and 
form an image of the ventricle. As will be explained, the short intervals 
can be adjusted in time relative to accepted or valid R-waves and the 
length of the intervals can be adjusted using known techniques. It is 
during these intervals or time windows that the image data is gated to the 
various image forming and data gathering devices. Also appearing along the 
time axis is the typical location of short intervals marked ES which 
coincide with the end of systole or when the left ventricle contains 
minimum blood volume. Generally, the end of systole occurs at about 40% of 
the time interval between R-waves such as between R1 and R2 in FIG. 3. 
Thus, the lengths of both intervals ED and ES must be settable relative to 
successive R-waves and the lengths of the intervals must be variable. This 
is accomplished in FIG. 1 with some conventional circuits which are 
symbolized by blocks 41 and 42 for the systole delay and systole window 
intervals. The circuitry in the systole delay block 41 sets the location 
of ES interval relative to the preceding R-waves such as R1 in FIG. 3. The 
systole delay may be anything from 0 to 1500 ms. The circuitry in the 
systole window duration controller 42 is adjustable to set the duration of 
the interval ES. The ES intervals in an actual embodiment are adjustable 
between 0 and 300 ms. The systole delay and window circuits, 41 and 42, 
are clocked only in correspondence with valid R-wave flag pulses occurring 
at what is considered the normal rhythm of the heart and which come out of 
arrhythmia rejection circuit 39 on line 43. 
In FIG. 1 there is also a block 44 representative of the circuitry for the 
diastole delay which locates the interval ED in FIG. 3 relative to 
successive clock pulses corresponding with valid R-waves. There is also a 
block 45 containing the circuitry for controlling the duration of the ED 
or end diastole window of FIG. 3. The outputs from the systole and 
diastole delay devices and the systole and diastole window duration 
setting devices are sent, by means of lines 46 and 47, in FIG. 1 to 
various devices that require gated signals. Signals representing the 
systole and diastole delay and open gate or open window durations are also 
sent to the control logic and switching circuit 55 which outputs the 
gating signals at appropriate times for turning the scaler timer 56 and 
CRT 17 on and off as required. Clock pulses corresponding with valid 
R-waves coming out of arrhythmia rejection circuit 39 on line 43 are also 
fed to a block bearing the legend R-wave synchronized oscillator 54 which 
is used for multiple gating such as is accomplished with formatter 26. 
Block 54 responds to clock pulses corresponding with valid R-waves by 
providing signals which are sent over line 58 to the formatter circuit 26 
that controls stepping of the images along the display screen 28 of the 
CRT 27 to enable obtaining as many views of the heart in variously 
blood-filled states as are desired. The formatter also receives the clock 
pulses outputted on line 43 from arrhythmia rejection circuit 39 so the 
formatter will only start each image in a sequence of images displayed on 
CRT screen 28 if there is synchronism with or reference to a clock pulse. 
Referring further to FIG. 1, the physiological waveform on which 
synchronism of the system with regularly occurring physiological events is 
based is displayed on a cathode ray tube monitor 60. The particular 
physiological event used and displayed in this example is the ECG 
waveform. The ECG waveform signals from ECG detector 35 are fed through a 
filter-buffer device, symbolized by the block 61, which provides the y 
axis deflection signal to monitor 60. The synchronizer has associated with 
it an R-wave triggered horizontal sweep generator which is symbolized by 
the block 62. The sweep generator responds to detected R-waves by 
initiating x-direction deflection of the waveform on the monitor screen. 
The monitor brightness or intensity and blanking control is represented by 
the block 63. The CRT is of the persistence or slow decay type. Successive 
ECG waveforms appear on it and persist until replaced by ensuing waves. 
The intensity and blanking control 63 responds to the signals coming from 
delay signal output lines 46 and 47 and indicative of the delays and 
windows associated with the gating intervals such as ED and ES in FIG. 3 
by modulating the ECG waveforms to high brightness during these intervals. 
This is exemplified in FIG. 4 where the bright ED and ES gating intervals 
are correspondingly marked as they appear superimposed on the ECG 
waveform. 
The specified example of the new arrhythmia rejection circuit, which is 
shown at block 39 in FIG. 1, will now be described in reference to the 
FIG. 5 circuit diagram. 
In FIG. 5 there are two inputs for the continuous sequence of R-wave or QRS 
signals that are delivered from the ECG isolation and R-wave detection 
block 35 and are outputted on line 36 in FIG. 1. This line 36 is 
correspondingly marked in FIG. 5 as line 36 to heart rate calculator 37 
and as line 36 constituting the QRS flag signals to the depicted 
arrhythmia rejection circuit. There is a QRS flag pulse input for every 
ECG QRS complex which occurs whether it is one at the natural heart rhythm 
rate or a PVC. The QRS flag pulses are shown to be in coincidence with 
R-waves R1-R8 in part C of FIG. 3 where exemplary flag pulses are marked 
103-106. 
The output line for clock pulses which correspond with valid R-wave or QRS 
flag pulses that occur at the normal heart rate and are usable for 
synchronous clocking of the minicomputer 32, formatter 26, the systole and 
diastole delay and window controls 41, 42 and 44, 45 and the multiple 
gating oscillator 54 are outputted from the FIG. 5 circuit on line 43. 
These clock pulses corresponding with R-wave pulses occurring at a regular 
rate are outputted from pin 3 of a one-shot multivibrator (MV) 70 through 
an inverter 71. MV70 serves as a clock pulse gate which is enabled and 
disabled in accordance with whether the physiological events being 
detected are in or out of rhythm. By way of example and not limitation in 
an actual embodiment, an NE555 timer was used for the one-shot MV70. Also 
by way of example, the output clock pulses from pin 3 can typically have 
one millisecond durations and be at TTL voltage levels. MV70 serves as an 
R-wave clock for the utilization circuits which were described above. In 
this design, MV70 acts like a switch which gates incoming QRS flag pulses 
to its output pin 3 when properly timed R-waves in a sequence of R-waves 
have been detected, that is, only R-waves which are in synchronism with 
the normal rhythm or R-wave rate of the heart. 
The positive going QRS flag pulses are fed in from line 36 through an 
inverter 71, a line 72, a differentiator capacitor 73 and resistor 77 and 
to trigger signal input pin 2 of one-shot MV70. The one-shot MV has the 
usual RC timing circuit consisting of resistor 74 and capacitor 75, and a 
noise filtering capacitor 76. 
In the lower right area of FIG. 5 there is an operational amplifier 
(op-amp) 78 connected as an integrator and having a fixed input resistor 
79 and an integrating capacitor 80. One side of capacitor 80 and resistor 
79 connect to a common point 81 which also connects to the inverting input 
pin 2 of op-amp 78. The input to pin 2 is the variable analog voltage 
signal corresponding with the integrated or substantially average of 
regular or normal heart rate provided by the heart rate calculator 37 over 
line 38. The DC voltage level at point 81 and pin 2, therefore, is 
proportional to the patient's heart rate in beats per minute. There are 
two analog switch elements 82 and 83 connected in the input circuit of 
op-amp 78. Analog switch 82 has a field effect transistor 84 with a line 
85 being connected to its gate terminal. When analog switch 82 is made 
conductive by an appropriate signal being applied to the gate of 
transistor 84, integrating capacitor 80 is short-circuited and therefore 
discharged through a resistor 86 and transistor 84 so amplifier 78 cannot 
integrate. The output pin of op-amp 78 is pin 6. 
Analog switch control line 85 is the output line from the Q output pin 8 of 
flip-flop (FF) 87. The clock pulses from the output pin of one-shot MV70 
are fed by way of line 88 to the clock input pin 11 of FF87. The rising 
edge of each clock pulse causes pin 8 or the Q pin of FF87 to go high 
which turns off the channel inside of analog switch 82. This removes the 
short circuit across integrating capacitor 80 which is then allowed to 
charge and integrate through resistor 86. This results in a positive-going 
ramp output from pin 6 of op-amp integrator 78. The ramp signal is coupled 
by way of line 89 and an input resistor 90 to the non-inverting input pin 
3 of an operational amplifier 91 which is connected as a comparator. The 
non-inverting input pin 2 of comparator 91 is connected through a resistor 
92 to a potentiometer 93. The potentiometer is connected in a series 
circuit with resistors 94 and 95 and the series circuit is connected 
between DC supply and ground. Potentiometer 93 is characterized as the 
extrasystole inhibit potentiometer. The reference voltage level at which 
potentiometer 93 is set determines the time range within which QRS 
complexes in the ECG waveform are to be considered PVCs or extrasystoles. 
Thus, the positive-going ramp from integrator op-amp 78 is repeatedly 
compared by comparator 91 with the extrasystole inhibit or reference 
signal derived from potentiometer 93. When the voltage ramp on 
non-inverting input pin 3 of comparator 91 reaches the reference voltage 
level on the inverting input pin 2, the comparator 91 trips and its output 
pin 6 goes high. The high going signal is coupled through a resistor 96, a 
line 97 and an inverter 98 to the reset pin 10 of FF87. This changes the 
state of pin 8 of FF87 which thereby operates analog switch 82 so it 
resets the integrator by discharging capacitor 80. The conditions at pin 
10 and 12 of FF87 are now such that integration will begin when the next 
clock pulse from one-shot MV70 comes along. Note that the output Q pin 9 
of FF87 goes low during integration and output Q pin 8 goes high to start 
integration. 
The ramp output of integrator op-amp 78 is reset to ground when either of 
the channels in analog switches 82 or 83 become conductive. Analog switch 
83, it will be noted, is connected in parallel with analog switch 82 so 
both have the ability to discharge integrator capacitor 80. The channel in 
analog switch 82 is closed each time a normal QRS complex and 
corresponding clock pulse occurs, because for every such event pin 8 of 
FF87 is clocked to go high by a clock pulse from one-shot MV70. Thus, pin 
8 of FF87 goes high to start integration and stays high until a comparison 
is made and a reset signal is received on pin 10 of FF87 through inverter 
98 from output pin 6 of comparator 91. On the other hand, the other analog 
switch 83 closes its channel in response to QRS flag signals whether they 
correspond with normal or premature heart beats. This is so because 
control gate pin 7 of analog switch 83 connects by way of line 100, in 
which there is a coupling capacitor 101, to line 72 which feeds in both 
normal and premature QRS flag pulses. 
All QRS flag pulses corresponding with heart beats, whether premature or 
not, are inputted to trigger pin 2 of one-shot MV70 for triggering it. If 
they are at the normal heart rate, a one millisecond output pulse appears 
on pin 3 of multivibrator 70 as mentioned earlier. If they are PVCs, 
output pin 3 is inhibited and no system clock or valid rhythmic R-wave 
indicating clock pulse is delivered to the various utilizing devices over 
line 43. 
An example of the manner in which the arrhythmia rejection circuit of FIG. 
5 functions will now be given and reference will also be made to the 
timing diagrams in FIG. 3. Assume that the first R-wave or QRS complex 
detected is in the normal rhythm and is the one marked R1 in FIG. 3. In 
such case, a one millisecond pulse, such as 107 in part D of FIG. 3, from 
pin 3 of one-shot MV70 is fed to the clock input pin 11 of FF87. The 
flip-flop 87 will change the state on its Q pin 8 which goes high to start 
integration by capacitor 80. The high state turns off short-circuiting 
transistor 84 in analog switch 82 to start integration. During 
integration, the ramp output of op-amp 78 is compared to the extrasystole 
inhibit reference voltage level from potentiometer 93. When the comparator 
91 trips and its output pin 6 goes high, the signal is coupled to the 
reset input pin 10 of FF87, causing its Q output pin 8 to go low again. 
The trip level of comparator 91 is indicated in part E of FIG. 3 which 
shows successive ramp signals. Pin 8 of FF87 going low constitutes a reset 
command to analog switch 82 which means that the switch is 
short-circuiting capacitor 80 again and preventing integration. 
The Q output or pin 9 of FF87 is low while integration is taking place and 
high while the reset condition exists. This output pin 9 controls the 
clear or reset input pin 4 of the one-shot clock MV70. When the clear pin 
4 is low, the one-shot MV cannot output a one millisecond pulse on line 43 
which means that the utilization devices are not clocked while the 
one-shot multivibrator 70 is inhibited or in a clear state. It will be 
apparent then that if the reference voltage level set by the extrasystole 
inhibit potentiometer 93 resulted in a pulse width on the clear pin 4 of 
one-shot MV70 that was a percentage of the total time between normal heart 
beats, then a lockout period between R-waves is established. During this 
period, any premature beat that occurs is ignored. A typical normal 
lockout or inhibit interval is designated in part F of FIG. 3. 
FIG. 3 shows two successive QRS flag pulses 103 and 103 which are 
coincident with normally spaced QRS complexes R1 and R2. For each of these 
there is a one millisecond clock pulse 107 and 108 produced by one-shot 
multivibrator 70 and supplied to the utilization devices over line 43. The 
ramp voltage from op-amp 78 for these two normal QRS complexes is marked 
109. The lockout period during which one-shot multivibrator is inhibited 
or disabled from producing any one millisecond clock pulses is marked 110 
and is coextensive in time with ramp 109. The lockout period is 
represented by the state or voltage on pin 9 of FF87. The lockout period 
is governed by the extrasystole inhibit reference voltage setting and is 
typically set for 75% of the normal rhythm R-wave-to-R-wave interval. 
The example of a PVC occurring corresponding with the QRS complex R3, shown 
in dashed lines, between normal rhythm beats R2 and R4 is also depicted in 
part A of FIG. 3. It will have a corresponding QRS flag pulse 104 but 
since the output of one-shot MV70 is still inhibited because the ramp 109' 
in part E has not reached trip level, it will not produce a one 
millisecond clock pulse at the time where such pulse might have otherwise 
occurred as is depicted in dashed lines and marked 111 in FIG. 6. However, 
the QRS flag pulse due to the PVC marked R3 will trigger the gate of 
analog switch 83 and make it conductive momentarily to discharge capacitor 
80 and thereby restart the integration period as indicated by the second 
ramp 112 in FIG. 6. The lockout period, that is, the period during which 
pin 10 of FF87 will not get a reset signal from comparator 91, will be 
extended as indicated by its waveform 113 in part F of FIG. 3. Analog 
switch 83, it should be noted, is made conductive by QRS flag pulses 
associated with normal rate and PVC R-waves. The flag pulses are fed from 
input line 72 through a differentiator capacitor 101 and resistor 102. An 
incoming QRS flag pulse pulls the gate pin 7 of analog switch 83 down to 
make the switch conduct. 
FIG. 3 shows how a QRS complex R6 is also rejected if, in the example, it 
is in close proximity in time to a PVC marked R5. As indicated, any PVC 
causes a reset signal to be sent to analog switch 83 to make it conductive 
for discharging and resetting integrating capacitor 84. It is evident in 
part E of FIG. 3 that integration is in progress at the time of the PVC 
marked R5 but the trip point of the comparator 91 has not been reached at 
this time as indicated by the shorter than normal ramp 114. Because of the 
QRS flag pulse triggering the capacitor discharging analog switch 83 to 
conduct, integration restarts and a new ramp starts at point 115. The new 
ramp extends the lockout period. The momentary reset was not ordered by 
the control flip-flop 87 because it cannot change state until the 
comparator 91 trip point is reached. The next QRS complex R6 will also 
extend the lockout period unless it occurs so long after the PVC at R5 as 
to correspond with normal heart rhythm. For example, assume that a normal 
QRS complex R6 occurred as indicated while the one-shot MV70 is inhibited 
or locked out so that the R-wave clock pulse 117', in dashed lines in part 
D of FIG. 3, did not occur. Of course, the QRS flag 105 would have 
occurred and would have reset the integrator by reason of the QRS flag 
pulse being applied to analog switch 83. Then, in FIG. 3, a new ramp 118 
would be started and if sufficient time elapsed for the comparator 91 to 
reach the trip point, the lockout period 119 would be extended until the 
trip point was reached in which case FF87 would change the states of its 
outputs and one-shot MV70 would become inhibited. Then, since the next 
ensuing QRS complex R7 would lie outside of the lockout period 119, its 
occurrence would result in a one millisecond synchronizing clock pulse 
being emitted by one-shot MV70 to output line 43 in FIG. 5. Clock pulses 
in correspondence with normal rhythm would then be restored. Thus, if the 
heart does not pause naturally long enough to compensate for the PVC 
marked R5 and reestablish rhythm at R6, the R6 QRS complex and heart beat 
following the PVC marked R5 is rejected, that is, no clock pulse is 
produced. If the heart does pause, the ramp voltage will have time to 
reach a point where it will cause the comparator 91 to trip and this 
corresponds with substantially normal rhythm having been attained as is 
the case where R7 occurs. 
It will be evident that all gating window circuit functions are disabled 
when a PVC occurs and that they will remain disabled until a beat in 
normal rhythm is recognized. 
Another kind of rejection is obtainable with the circuitry in FIG. 5 and 
involves a D type flip-flop marked 126. All normally spaced and premature 
detected QRS complexes or QRS flag pulses are allowed to clock this 
flip-flop on its clock pin 11. The integrate and reset command pulses from 
FF87 are fed into pin 12 of flip-flop 126. When a PVC occurs during a 
lockout period and pin 12 of flip-flop 126 is high as is pin 8 of FF87, 
the output on the Q pin 8 of flip-flop 126 will change state or go low. It 
will stay low until the next normal rate QRS complex and heart beat occurs 
and then go high. If another PVC occurred, it would not go high because 
the lockout period is still in effect. The pin 8 output of flip-flop 126 
is tied to the clear lines 65, 67 and 68 in FIG. 1, which are the clear 
lines for one-shot multivibrators, not shown, in the systole, diastole and 
multiple gating circuits 42, 45 and 54. Upon occurrence of a PVC, these 
clear lines are pulled low to disable these circuits. They remain disabled 
until a normal beat has been recognized. 
In summary, the invention may be broadly characterized as a device for 
detecting in a sequence of physiological signals, which are mostly 
occurring at a substantially uniform rate or in a regular rhythm, those 
signals which occur arrhythmically. The device produces synchronizing 
clock pulses coincident with signals that are determined to be rhythmic. 
The clock pulses may be used for synchronizing a variety of medical 
electronic devices.