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AREA DISPLAYS OF THE ELECTRICAL ACTIVITY
OF THE HEART
STANFORD GOLDMAN
W. F. SANTELMANN, JR.
CONGER WILLIAMS, M. D.
FRED ALEXANDER, M. D.
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TECHNICAL REPORT NO. 121
NOVEMBER 15, 1950
RESEARCH LABORATORY OF ELECTRONICS
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MASSACHUSETTS INSTITUTE OF TECHNOLOGY
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The research reported in this document was made possible
through support extended the Massachusetts Institute of Technology, Research Laboratory of Electronics, jointly by the Army
Signal Corps, the Navy Department (Office of Naval Research)
and the Air Force (Air Materiel Command), under Signal Corps
Contract No. W36-039-sc-32037, Project No. 102B; Department
of the Army Project No. 3-99-10-022.
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JMASSACHUSETTS
INSTITUTE
OF TECHNOLOGY
RESEARCH LABORATORY OF ELECTRONICS
Technical Report No. 121
Nov. 15, 1950
AREA DISPLAYS OF THE ELECTRICAL ACTIVITY OF THE HEART*
Stanford Goldman
W. F. Santelmann, Jr.
Conger Williams
Fred Alexander
Abstract
Routine methods of studying electrical activity of the heart by means of curves
recorded from various points on the precordium and extremities have contributed much
to our knowledge of electrocardiography.
Nevertheless, it has been very difficult to
visualize movements of electrical activity across the surface of the heart by using the
curves obtained in routine fashion.
A new method of visualizing these phenomena has
been developed and is presented in this paper.
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*
This work was completed June 30,
1949.
** Massachusetts General Hospital, Boston, Mass.
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AREA DISPLAYS OF THE ELECTRICAL ACTIVITY OF THE HEART
I.
Area Display
The present paper describes a new method, called electronic mapping or area display, for obtaining information about the electrical activity of the heart. This method
gives motion pictures of the movement of electric potentials in the heart, as projected
on the surface of the chest.
These pictures make available a great deal of apparently
new information about the electrical activity of the heart, which when properly interpreted should be of value in studying the physiology of the heart and in the diagnosis
of heart disease.
In the method of area display of chest potentials, a picture of the electrical potential
distribution on the surface of the chest is shown on the screen of a cathode ray tube.
A diagram of the method is shown in Fig. 1. A number of electrodes are placed in an
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1 Locations of electrodes on the chest and corresponding locations of areas
on the cathode ray tube screen.
ordered array on the chest.
Corresponding to each electrode is a small square on the
screen of the cathode ray tube, each square being identified in Fig. 1 by the same
number as its corresponding electrode.
With the aid of electronic means described
elsewhere (1) the light intensity of each square on the screen is made proportional to
the instantaneous voltage of the corresponding electrode on the chest.
As the potential
at an electrode rises and falls, the brightness of the corresponding square rises and
falls in exact synchronism with it.
If all of the chest were electrically neutral (isoelectric),
cathode ray tube would be of a dull medium intensity.
all the squares on the
If positive potentials appeared
at any electrodes, the corresponding squares would be bright* and the relative brightness
* The frame prints in Figs. 5 and 7 are photographic negatives, and show the roles of
brightness and darkness reversed from the present description.
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would be proportional to the corresponding positive potential.
If negative potentials
appeared at any electrodes, the corresponding squares would be dark and the relative
degree of darkness would be proportional to the magnitude of the corresponding negative
potential.
In this way, if a wave of positivity crosses the chest, a wave of brightness
crosses the cathode ray tube screen.
of darkness crosses the screen.
If a wave of negativity crosses the chest, a wave
More generally, if a wave of electrical activity crosses
the chest, a wave of activity can be seen to cross the screen, picturing the path of the
electrical activity.
It is obvious that the potentials used in the method of area display are the same as
those studied in conventional electrocardiography.- One might therefore be tempted to
ask what information is given by the method of area display that is not given by more
orthodox electrocardiography. One who has not seen the moving pictures of area display might conclude erroneously that this technique shows nothing not already known.
The value of the area display depends particularly upon two characteristics of
visual perception (2). In the first place, the human visual perception mechanism has
a remarkable ability for recognizing and analyzing area patterns. Thus, for example,
family resemblances can be recognized between parents and children in cases where
the details of the geometry of the face which are the basis for the recognition often cannot be analyzed or even described.
experience in such situations.
It is also well to point out the importance of
For example, to a European who does not know any
Chinese people well, all Chinese tend to look alike.
Similarly, to a Chinese who does
not know any Europeans well, all Europeans look quite alike.
Nevertheless, both
Europeans and Chinese easily recognize minute differences between people of their
own race and especially between people of their own acquaintance.
The second charac-
teristic of the human visual perception mechanism which is useful in dealing with area
displays is the ability to detect motion.
The perception mechanism is able to ignore
even a complicated stationary pattern and to discern within it that portion which is
moving.
The foregoing two characteristics make it possible for an experienced operator to
recognize in area display, patterns and motion which could be derived with difficulty,
if at all, from orthodox tracings.
There are four possible conventions which could be used in the visual and electrical
polarities of area displays. The system described above shows brightness on the screen
for positive potentials and darkness for negative potentials.
screen outside the array is dark.
The background area of the
Negative prints of this system will, of course, show
brightness and darkness reversed. The foregoing possibilities give rise to convention
I and II in Table 1. If the electrical polarities required for brightness and darkness
on the cathode ray tube screen are reversed, we will then have conventions III and IV.
It is not entirely a matter of indifference which convention is used in practice. The
acuity of the human visual perception system in dealing with various types of activity
will depend on the convention used.
The final choice to be made for general use will
-2-
depend upon what electrical and visual conventions turn out to be best.
It is too early
to recommend a choice at this time.
Table I
Possible Conventions Regarding Visual and Electrical
Polarities in Area Displays
Convention
Electrical polarity
Color of
Type of photo-
specification
for whiteness on
background
graphic print
number
film
I
Positive
Black
Positive
II
Negative
White
Negative
III
Negative
Black
Positive
IV
Positive
White
Negative
It is found that the electrical activity on the surface of the chest gives an informative
picture of the conduction of electrical impulses within the heart itself. This was to be
expected in the light of experience with conventional precordial electrocardiography.
In most cases, however, the activity takes place so rapidly that the best results are
obtained by taking moving pictures of the cathode ray tube screen and showing the
pictures in slow motion.
These pictures show the location and sequences or paths of
activity of the P, QRS and T waves in normal individuals and in those having heart
disease.
By way of illustration, diagrams of the paths of activity observed in a few
typical cases are shown in Fig. 2.
The arrows in the figure indicate the direction of
a
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Fig. 2 Location and sequences or paths of activity of the QRS and T waves in
typical cases: a) normal; b) right bundle-branch block; c) left ventricular
hypertrophy.
It is interesting to note that it is often difficult and sometimes
impossible to synthesize the movements of the potentials across the chest from a
study of sets of consecutive frames such as shown in Figs. 5 and 7, even though the
motion of the activity.
eye sees these movements readily in the moving pictures.
Motion pictures of area displays are suitable for the purposes of obtaining permanent
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records and for detailed study in slow motion.
Direct observation of the oscilloscope
is more suitable for studying transient changes in the heart in response to stimuli
and changes during bodily activity, as well as effects of differences in posture.
II.
Electrical Connections to the Patient
The pick-up electrodes now used in this work are small circular discs about 3/16
inch in diameter.
An electrode is formed by dipping a wire into molten solder, and
flattening the drop thus collected as it cools.
A small amount of electrode paste should
be inserted between the electrode and the skin in order to obtain good electrical contact.
The electrode is then secured to the skin with a small strip of adhesive.
Figure 3 is
a photograph of a subject with the electrodes attached.
Fig. 3 Photograph of a patient connected for area display
investigation.
The grounded cage shown in Fig. 3 is used to eliminate electrical interference.
The subject lies or sits on the cot inside the enclosure.
In studies of the heart, it has
not been found necessary to use the covering screen which completes the box.
PICK-UP
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The cover is usually necessary, however, in mapping skull potentials when studying
the brain.
The sides of the shielding screen box are fastened together with wing nuts
a
and are readily removable.
The electrode wires are marked or color coded at both ends with the position they
are to assume in the array.
This avoids the necessity of tracing the wires each time
and allows them to be laced into a bundle.
Each lead wire has a banana plug at the end
which leads to the amplifiers so that it can be plugged into a pickup box.
The pickup
box is located in an opening in one of the sides of the shielding enclosure.
Between the
pickup box and the amplifiers, the lead wires are surrounded with a grounded shield.
Each of the array terminals in the pickup box is connected through a resistance to
a common reference terminal (see Fig. 4).
With the circuits used, the potential of
this reference terminal is approximately the average of the potentials appearing on the
16 array electrodes at that instant.
The actual voltage which is sent through the ampli-
fiers from any array terminal is the difference in potential between this terminal and
the reference terminal.
We also usually ground the subject's left arm to the shielding
enclosure, which in turn is tied to the electrical ground of the amplifiers. This last
procedure tends to reduce artifacts, and with suitable values for R and R 1 it should
have very little effect on the physiological potentials sent to the amplifiers.
We are
studying the desireability of replacing the above reference terminal with a Wilson central
te rm inal.
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Fig. 6 Standard cardiogram of same subject as that of Fig. 5 ·
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III.
Discussion of Two Records
Figure 5 represents consecutive frame prints of the film taken on a normal young
student. A standard electrocardiogram of the same subject is shown in Fig. 6. For
purposes of comparison, it may be noted that frames numbered 3 through 5 represent
the approximate duration of the P wave.
mate duration of QRS.
Frames 10 through 16 represent the approxi-
T activity appears to start around frame 16 and continues to
somewhere in the vicinity of frame 34.
The next P activity then occurs in the approxi-
mate range between 57 and 60 with QRS starting at 66. A detailed analysis of these
frame prints will not be attempted at this time. It may be pointed out, however, that
brightness on the frame prints represents electrical negativity while darkness represents
electrical positivity. When the motion picture is viewed, rapid motion is observed
during the QRS activity.
The direction of the motion is shown in Fig. 2 a.
During the
T interval, a slower motion of less intense activity may be observed in the direction
indicated for T in the same figure. It should be emphasized that the directions of the
arrows shown in Fig. 2 represent the direction of movement of activity as seen on the
motion picture screen. They do not represent the directions of vectors of electrical
force.
Figure 7 represents the prints of consecutive frames of a motion picture reel
showing the area display of a subject having left ventricular hypertrophy. Figure 8
is a six lead electrocardiogram on this subject. Figure 7 includes a premature beat.
In Fig. 7, frames 18 through 25 represent the approximate duration of the QRS of a
normal beat. T activity of this beat ranges approximately from frame 24 through 38.
QRS activity of the next beat is approximately from frame 64 through 71, and the corresponding T activity runs from frame 70 to about 84.
In frames 100 to 106, the QRS
activity of a premature beat is seen which is followed by T activity that appears to have
an initial phase from frame 108 through 120 and a final phase from frame 121 through
135.
Frames 155 through 161 show the QRS activity of the next regular beat and the
corresponding T activity is seen in frame 161 through 176. In the case of this subject
also, no detailed analysis of the frames will be attempted.
The directions of motion
observed in the moving picture for the regular beats of this subject are shown in Fig. 2c.
IV.
Plans for the Future
The use of area displays in physiological studies is in its infancy.
Many things
which can and should be done in area display investigations are fairly obvious. For
reasons of cost and size, we have so far used only equipment with sixteen pickup
electrodes.
It seems likely, however, that the electrical information on the surface
of the chest has sufficient resolution to justify the use of at least as many as 200
electrodes. The technical obstacles which must first be overcome before the use of
such a large number of electrodes is feasible are not fundamental, so that the use of
larger numbers of electrodes may soon be expected.
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Another obvious improvement is the use of larger slow-down ratios in the motion
pictures. This is particularly important in studies of the QRS activity. Cameras
have recently appeared on the market which make a ratio of as much as 200 to 1 possible.
This is more than adequate for present studies.
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Fig. 8 Standard cardiogram of same subject as that of Fig. 7.
Early in this work, the necessity for synchronized registration of a standard tracing
along with the area display became apparent. Apparatus which accomplishes this is
now nearly completed.
As pointed out in the beginning of this paper, the motion pictures so far obtained give
information only about the movement of electrical potentials in the heart as projected on
It would, of course, be desirable to have more direct information about actual movement of electrical activity in the heart itself. We are planning
to improve our interpretation in this respect in two ways as soon as possible. In the
the surface of the chest.
first place, we shall attempt to coordinate our motion pictures with vector cardiography
in the same patients. In the second place, we intend to study area pictures taken with
electrodes located directly on the hearts of experimental animals.
It is hoped that the application of this method will prove helpful in arriving at a
better understanding of the T wave.
It is also possible that abnormal patterns of area
display will be recorded in patients with heart disease who show normal electrocardiograms by routine methods.
We are already accumulating the beginning of a library of motion picture reels of
the area displays of normal and abnormal hearts. These will, of course, become obsolete as soon as equivalent reels taken with newer equipment are available.
We hope that other investigators will also start to use area displays. After more
general experience has been gained, it will be desirable to standardize electrode locations and also to standardize terminology for the description of pictures.
Area displays will undoubtedly be used in other fields of physiology and diagnosis.
-10-
I
They have already begun to be used in studies of the brain (3) and attempts will be made
to use them in studies of the bladder, in childbirth, and in studies of spastic and paralyzed muscles.
References
1.
S. Goldman, W. E. Vivian, C. K. Chien, H. N. Bowes: Science
2.
S. Goldman:
3.
S. Goldman, W. E. Vivian, W. F. Santelmann, Jr., D. Goldman:
108, 720 (1948).
Proc. I.R.E. 36, 584 (1948).
Science 109,
524 (1949).
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