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The normal adolescent electrocardiogram
Fundamentals of clinical cardiology
The normal
adolescent
electrocardiogram
William B. Strong, M.D.” Thomas D. Downs, Ph.D.** Jerome Liebman, M.D. Robert Liebowitz, M.D. Cleveland, Ohio
T
he electrocardiogram (ECG) of the normal adolescent has never been published independently. It has always been grouped with either the preadolescent1,7,9,14,15,17&3,21-25 or with young adult2,3s8vle electrocardiographic studies. The present study was undertaken to establish standard biologic criteria (i.e., fifth, fiftieth, and ninety-fifth percentiles) for the various electrocardiographic measurements using direct-writer equipment. Materials
and methods
One hundred and fourteen adolescents judged to have a normal heart by history and physical examination ‘comprised the study group. There were 67 male and 47 female subjects. Table I presents the age and sex characteristics. Each sex was arbitrarily divided into two age categories, 11 to 15 years and 16 to 19 years. The II- to IS-year-old group was further subdivided into 11 to 13 years, and 14 to 15 years to determine any differences or trends within the groups. Equipment. The ECG’s were all recorded on a single-channel Cambridge Mark II Versa Scribe Electrocardiograph, No.
24050, at 25 mm. per second, 1 mv. being equal to a stylus deflection of 1 cm. This instrument was advertised to have a frequency response of 100 Hz. However, testing with Dower’s Totemite equipment? revealed a frequency response of only 50 Hz. The ECG measurements analyzed were transcribed onto special mimeographic forms (Fig. I), keypunched onto IBM cards from these forms, and verified. The analyses were performed on an IBM 1620 digital computer and the figures were drawn with a Calcomp plotter operation from the IBM 1620. Methodology. Ninety-five measurements were performed on each ECG. Fig. 1 shows the computer sheet onto which they were tallied. All correlations and analyses made are presented in tabular or graphic form (see Results). Attempts were made to determine the r and s components of the P wave and also the initial forces of the QRS complex. However, after analyzing the data, it was apparent that the P-wave analyses and initial forces in the frontal plane require, at minimum, double standardization and a paper speed of 50 mm. per second (double speed) for accurate
From
the Case Western Reserve University School of Medicine, Departments of Pediatrics and Biometry, University Hospitals, Cleveland. Ohio. Supported in part by National Institutes of Health Grants HE 08286 and HE 05803 and National Institute of General Medical Sciences Research Grant GM 12302. Reprint requests to: Jerome Liebman, M.D., University Hospitals of Cleveland, University Circle, Cleveland, Ohio 44106. *Present address: Medical College of Georgia, Department of Pediatric Cardiology. Augusta, Ga. 30902. **Present address: School of Public Health, University of Texas at Houston.
Vol. 83, No. 1, pp. 115-128
January,1972
American Heart Journal
115
116
Am. Heart I. January, 1972
Strong et al.
Awl ---mm 2
il”R R
Am
III
III
III
III
"6
"6
"6
"6 6
II em.---..-
AW s -..-s--
P Q R ___------------.__--.----
_..--
*vR R’
bYR
,*-‘-III
"6 Ti
T2 III
AVL 2
AVL -_,_
III
"6
Id
AVL
III
Iit
AYL
s--.22-..
AVP
AVF
kVF
I\YP
AVF
*Pais
_TI..-Q-,--R---S----*-‘--.-T-“-.-f III
AVP "5
III
V6
III
III
III
III
III
III
III
___-___
- __----
-- ----
Boys (no.1
Age (YY.1
11-13 14-15 16-19 Total
I 11-15
14 15 38 67
29
Girls (no.)
I 16 10 21
26
47
interpretation. Neither was performed in the present study. The mean, standard deviation, and fifth, fiftieth, and ninety-fifth percentiles were obtained for the amplitude measurements. The purpose for using this mode of presentation was to eliminate the errors inherent in minimum and maximum numbers and to avoid the use of two standard deviations. Because of the skewed nature of ECG data, two standard deviations from the mean could provide numbers less than the minimum and/or more than the maximum. The use of tenth and ninetieth percentiles has not been shown to have any biologic significance and in our opinion should not be used. The sum of the SVi and RVs or RVr, has frequently been used as a criterion of left ventricular hypertrophy.18n1g In the present study we have chosen to sum the voltages
I.F.
III
III.
- --_----___
Fig. 1. A sample data collection sheet used in the present study. F = frontal; H = horizontal; forces; Tr = first deflection of the T wave; TZ = second deflection of the T wave; P, = duration component of the P wave; P. = duration of the negative component of the P wave: Ld, = lead prominent U wave; H+ LJ = height of the most prominent U wave; Lp F = course of the loop plane; and Lp H = course of the loop in the horizontal plane.
Table I. Age and sex of adolescentsubjects
I.F.
L-._P-_-~-~
LP LP
-J-2-.-H_..-
T Ii -v-_u--L-J--
*axis _.._
I. F. = initial of the positive with the most in the frontal
of SV2 and RVs since they are almost perpendicular. (According to Lamb12 Lead Vz is at $90 degrees and Vs is at +S degrees.) Furthermore, these leads best approximate the axes (2 and X) that comprise the horizontal plane. The methods used to analyze the QRS complexes in Leads aVR, V~R, Vi, and Vz are depicted in Figs. 2 and 3 and described in the respective legends. The interpretation of Lead Vds is applicable to Leads Vi and VZ. Unless one understands the vector loop and its projections, mistakes can be made in pooling the data. Clearly, for example, in Lead aVr the QS, the Q of Qr, and the S of rSr’ represent the same projection. The only difference in the vector is that the initial force of the rsr’ is more to the right than that of the Qr. Data has been reported in which the Q’s and S’s have been treated separately though they should have been pooled. We have elected, therefore, to use the term “first negative deflection” for the Q and S described above and to use the terms initial or terminal positive deflection for the R wave, (e.g., the r of rSr’ would be the initial positive deflection, the r’ would be the terminal positive deflection, and the r of a qr would be the terminal positive deflection). Table II shows the pooling schema for Lead aVr. Angular data, such as electrocardio-
Volume Number
83 1
The normal adolescent electrocardiogram
Fig. 2. A hypothetical diagram of the vector loop in the frontal plane to illustrate the minor alterations which can produce four different QRS patterns in Lead aVn. The initial deflection in examples 1 and 3 is more to the right than in 2 and 4. The Q or the S in all four examples represent the same deflection. The r’ in example 1 is the same vector force as the r (Qr) in number 2.
Table II. Pooling schemaof the QRS cOm#lex
:R QRS QRSR R
in
Lead
1 -
avR
ii S S
R R R R'
graphic mean vectors, should not be analyzed in the same manner as linear data. The arithmetic mean as a measure of the direction in which angular observations on a plane tend to cluster is not appropriate.4 Downs and associates5have developed an angular analysis based on the concept of the center of gravity. The prevalent direction (a) is taken as the direction from the origin to the center of gravity of a disk when all individual data points are placed on the rim of the disk according to their planar coordinates for the instant of time under study. The closenessof clustering of the data is measured by the length of the radius of the line from the center of the disk toward the circumference of the unit circle at the prevalent direction. This distance is a measure of the precision (d) of
VW
117
A
Fig. 3. Hypothetical diagram of the vector loop in the horizontal plane to illustrate the correlate of the rSr’ complex as seen in Lead Vta. R = right; L = left; A = anterior. If the terminal force to the right is relatively anterior (heavy dashed line), it crosses the perpendicular to Lead V~R and a prominent r’ will be seen. If the terminal rightward vector is just as far to the right but is well posterior, it will not cross the perpendicular to Lead V~R and there will be no r’. (The S in VS should be the same in each case, but the S in Vs will be larger when the terminal vector is more anterior.) Published with the permission of J. Liebman and the Williams and Wilkins Publishing Co.
the observations. To test the significance of the clustering a chi-square test is done; chi square = nd2, where n is the sample size and d2is the precision squared. A chi square greater than 5.99 indicates a 5 per cent level of significance while a chi square greater than 9.21 indicates a 1 per cent level of significance. The final analysis compares the present data with that obtained from a composite of studies in younger and older population.s3s13 Results
The ECG findings in the 114 normal adolescents are presented in Tables II through XI. The tables are divided only by sex since there were no important significant differences between age groups. The measurements which attain statistical significance (p < 0.01) are marked by an asterisk. Durations. The only pertinent significant difference which was noted within the age groups was the duration of the P waves, the duration being greater (p < 0.01) in
118
Am. Heart
Strong et al.
January,
Table III. Analysis of the QRS complex in Leads V412, VI, and V2 showed the following patterns 1
Parameter
lirR
(y.
of total)
1
,
F’,
(% of total)
~
Tuble IV. Heart rate and dzrrations
1’2
(%,
of
total)
JI F B
69 ;;
11 12 12
52 57 55
70 ;;
M B
0.09 0.09 0.09
0.02 0.02 0.02
0.06 0.06 0.06
0.08 0.09 0.09
0.12 0.11
M F B
0.1.5
(0
0.15 0.15
0.03 0.02 0.02
0.10 0.12 0.11
0.15 0.15 0.15
0.20 0.19 0.20
0)
iv1 F B
0.08 0.08 0.08
0.01 0.01 0.01
0.06 0.05 0.06
0.08 0.08 0.08
0.10 0.09 0.10
03
M F B
0.38 0.37 0.37
0.04 0.03 0.04
0.32 0.32 0.32
0.38 0.38 0.38
0.42 0.42 0.43
(F)
M F B
0.21 0.19 0.20
0.06 0.04 0.05
0.16 0.15 0.15
0.20 0.18 0.20
0.35 0.28 0.31
(A) 4 1 1 0 0 1 88 3 4
0 1 1 0 1 0 92 5 0
I. 1972
0 0 0 0 0 0 96 4 0
03)
F
Abbreviations: interval; duration.
A = heart rate; D = QRS duration;
90 92 90 0.11
B = P ~me duration; C = PR E = Q-T interval; F = T wave
Amplitudes.
Fig. 4. Diagrammatic representation of a vector “figure S” loop in the horizontal plane illustrating the major portion of the loop to be counterclockwise and only the terminal portion to be clockwise.
the 16- to 19-year-old boys (0.09 sec.) than in the ll- to 15year-old boys (0.08 sec.). However, for practical purposes, this seems of little clinical significance. QRS-complex rotations. In the frontal plane, the loop inscribed was clockwise in 62 per cent of the subjects, counterclockwise in 33 per cent, and figure-of-eight in the remainder. Almost all QRS loops in the horizontal plane were counterclockwise (97 per cent). There were no clockwise rotations and 3 per cent were figure-of-eight. However, in the latter the major portion of the loop was counterclockwise with a lesser degree of clockwise rotation terminally (e.g., Fig. 4).
P WAVE. The ninety-fifth percentile for the P wave in Lead II was 2.0 mm., which suggests that the criterion for right atria1 enlargement (2.5 mm.) is rather generous, as also suggested by Reynolds.19 Q WAVE. The Q wave was measured in Leads III, aVF, Vg, and VS, and the ninetyfifth percentile never exceeded 3.0 mm. in these leads. R AND s WAVES. The amplitudes of the R wave and S wave are shown in Tables VI, C, and VI, D. Table VII summarizes SV2 and RVS and demonstrates that this number is significantly different (p < 0.01) between sexes (males greater than females) and that the sum decreases with age. However, the ninety-fifth percentile, even for girls 16 to 19 years, is 41.4 mm. which is greater than the standard of 35 mm. suggested for adults. Significant differences (p < 0.01) of clinical implication between male and female subjects and between age groups were apparent only in the precordial QRS and T-wave amplitudes. The major difference
Volume Number
83 1
The normal adolescent electrocardiogram
119
Table V. Rotation of the QRS complex
Sex
Clockwise ____--_I-~________-~
No.
No.
(A)
(B)
: B
;
Abbreviations:
Figure
eight
Counterclockwise ---
I
%
NO.
I
%
No.
%
I
67 47 114
42 29 71
62.6 61.7 62.2
2 3 5
2.9 6.3 4.3
23 38
34.3 31.9 33.3
67 47 114
0 0 0
0 0 0
1 2 3
1.4 4.2 2.6
66 4.5 111
98.5 95.7 97.3
A = Frontal
plane;
B = horizontal
1.5
plane.
Table VI. Amplitudes A.
B.
I’ wave
(Lead
II)
I
St. Dev.
/
5%
/
50%
/
95%
Sex
Mean
M F B
1.4 1.4 1.4
0.6 0.5 0.6
0.0 1.0 1.0
2.0 1.0 1.5
2.0 2.0 2.0
0.8 0.7 0.8
1.0 0.9 0.9
0.0 0.0 0.0
1.0 1.0
3.0 3.0 3.0
0.7 0.6 0.7
0.8 0.7 0.8
0.0 0.0 0.0
1.0 1.0
2.6 2.0 2.0
1.0 0.5 0.8
0.8 0.6 0.7
0.0 0.0 0.0
1.0 1.0 1.0
3.0 2.0 2.2
1.2 0.7 1.0
0.7 0.6 0.7
0.0 0.0 0.0
1.0 1.0 1.0
2.6 2.0 2.0
Q wave 1. Lead
III
M F B 2. Lead
aVF
M F B 3. Lead
M F B
1.0
V5*
M F B 4. Lead
1.0
Vs*
was that the voltage of the Q, R, S, and T waves was uniformly greater in the males than in the females. This was primarily a reflection of the 16- to 19-year-old boys
being
greater than Table VI, of the T wave for all T wave in Leads III, T WAVE.
the same-aged girl. E, shows the height leads, and divides the aVL, V~R, VI, Vz, and
120
Am. Heart I. January, 1972
Strong-et al.
Table VI. Amplitudes-cont’d C.
R wave
I B
6.2 6.4 6.3
2.6 2.7 2.6
2.4 3.0 3.0
6.0 6.0 6.0
11.0 11.6 11.0
II
M F B
13.6 12.3 13.1
4.6 2.8 4.0
7.0 7.0 7.0
13.0 12.0 13.0
21.6 17.0 20.0
III
M F B
9.4 7.3 8.5
5.1 3.9 4.7
1.4 1.0 1.0
9.0 7.0 8.0
19.0 14.6 17.2
f
See text
ah
and Table
III
and Fig.
2
aVL
M F B
2.2 2.5 2.3
2.0 2.1 2.1
0.0 0.4 0.0
2.0 2.0 2.0
6.0 7.6 6.2
ah
M F B
11.2 9.3 10.4
4.5 3.4 4.2
4.4 3.4 4.0
11.0 10.0 10.0
19.8 15.0 18.0
VbR*
M F B
2.2 1.4 1.9
1.0 0.9 1.0
1.0 0.0 1.0
2.0 1.0 2.0
4.6 3.0 4.0
v1*
M F B
4.2 2.9 3.6
2.2 1.7 2.1
1.0 0.4 1.0
4.0 3.0 3.0
8.6 6.0 8.0
v2*
M F B
8.5 6.2 7.6
3.8 3.0 3.6
3.0 2.4 3.0
8.0 6.0 7.0
17.0 12.0 15.2
\I‘*
M F B
18.8 13.3 16.5
7.6 5.0 7.1
6.4 5.4 6.0
19.0 13.0 15.0
33.2 24.6 30.2
V6*
M F B
19.4 14.5 17.4
6.0 4.2 5.8
10.0 8.0 9.0
19.0 14.0 17.0
26.6 23.2 26.0
V6’
M F B
13.8 11.4 12.8
3.8 3.1 3.7
9.0 7.0 7.0
13.0 11.0 12.0
21.2 18.0 20.0
V4 into the first and second components. This deflection appeared to be one of the most variable measurements we made. J POINT. Together with the observations of the sums of SV2 and RVb the finding of J-point displacement in approximately 30 per cent of adolescents is striking. In adult studies, this is not a frequent finding. In the present subjects, an elevated J point
was found in Leads aVF, Vh, and Va with equal frequency while a depressed J point was seen in VS in only 1 subject and in Leads aVF and V5 in 5 and 6 subjects, respectively. In no individual was the S-T slope, as measured by the method of Lester and associates,13negative. The S-T slope was frequently positively sloped or “U” shaped. The significance of J-point changes
Volt4me Number
83 1
121
The normal adolescent electrocardiogram
Table VI. Am#itudes--cont’d D.
S wave Lead
!
Sex
(
Mean
1
St. Da.
(
5%
(
50%
1
95%
I
M F B
1.6 0.9 1.3
1.4 1.0 1.3
0.0 0.0 0.0
2.0 1.0 1.0
4.6 3.2 4.0
II
M F B
1.6 0.9 1.3
1.7 1.1 1.5
0.0 0.0 0.0
2.0 0.0 1.0
4.6 3.0 4.0
III
M F B
1.4 1.1 1.3
2.0 1.8 1.9
0.0 0.0 0.0
1.0 0.0 0.5
4.0 6.6 4.5
M F B
3.8 2.4 3.2
2.8 2.4 2.1
0.0 0.0 0.0
3.0 2.0 2.5
9.0 6.6 9.0
F” B
1.2 1.0 1.1
::: 1.5
0.0 0.0 0.0
1.0 0.0 0.5
4.0 4.0 4.0
V4R
M F B
5.4 4.8 5.1
2.7 2.3 2.5
0.4 0.0 0.0
5.0 5.0 5.0
10.0 9.6 10.0
VI
M F B
12.2 11.9 12.1
4.6 4.5 4.5
4.4 3.8 4.7
12.0 12.0 12.0
20.6 20.2 20.2
v2*
M F B
19.3 15.6 17.8
7.3 5.8 7.0
6.4 6.4 6.7
19.0 15.0 17.0
31.2 26.8 30.0
VI*
M F B
9.4 5.4 7.7
4.9 3.6 4.8
0.8 0.0 0.0
9.0 5.0 7.0
20.0 14.6 16.5
VK
M F B
3.1 2.2 2.7
2.4 2.4 2.4
0.0 0.0 0.0
3.0 1.0 2.0
7.6 1.0 7.0
VS*
M F B
1.2 0.5 1.0
1.1 1.0 1.1
0.0 0.0 0.0
1.0 0.0 1.0
3.6 2.6 3.0
aVR aVL
aVF
See text,
in children is not understood but could be related to atria1 repolarization rather than to ventricular electrophysiology. LEAD avg. Ninety-seven per cent of the QRS complexes were included in four patterns: QS, 19 per cent; Qr, 33 per cent; rS, 23 per cent; and rSr’, 22 per cent. Fig. 2 demonstrates that these four patterns are projections of the same basic vector loop.
Table
III
and Fig.
2
ANGULAR DATA. Fig. 5 illustrates the distribution of the mean P, QRS, and T vectors for the entire series in both the frontal and horizontal. planes. Table X lists the prevalent direction for the QRS and T angles. There were no significant differences between the boys and girls. (See legend for explanation of the data.) Table IX, A, and B give the angular deviation data of
122
Am. Heart I. Jawuary, 1972
Strong et al.
Table VI. Amplitudes-cont’d E.
T wave Lead M 1; B
2.9 2.5 2.8
0.9 0.8 0.9
1.4 1.4 1.7
3.0 3.0 3.0
5.0 4.5 4.0
M F B
3.8 3.2 3.6
1.5 0.9 1.3
1.0 2.0 1.7
4.0 3.0 4.0
6.0 5.0 6.0
M F B
1.1 0.8 1.0
1.6 1.1 1.4
-1.6 -1.0 -1.0
2.0 1.0 1.0
3.0 2.0 3.0
M F B
0 0 0
0.3 0.3 0.3
-1.0 0.0 -0.2
0.0 0.0 0.0
1.0 1.0 1.0
M F B
-2.9 -2.8 -2.9
1.8 1.2 1.6
-5.0 -5.0 -5.0
-3.0 -3.0 -3.0
2.2 -1.4 -0.5
M F B
1.0 1.1 1.0
1.1 0.6 0.9
-1.0 0.0 -1.0
1.0 1.0 1.0
3.0 2.0 3.0
M F B
-0.1 0.0 -0.1
0.3 0.4 0.3
- 1 0 -1.0 -1.0
0. 0 0 0 0.0
0 0 0.6 0.0
M F B
2.7 2.3 2.5
1.2 0.7 1.1
1 0 1 0 1.0
3.0 2 0 3.0
5.0 3.6 4.0
M F B
-1.1 -1.2 -1.2
1.2 0.9 1.1
-3.0 -2.0 -3.0
-1.0 -1.0 -1.0
1.0 0.6 1.0
M F* B
-0.7 -1.7 -1.1
2.1 1.4 1.9
-3.6 -4.0 -4.0
-1.0 -2.0 -2.0
3 .0 1.0 3.0
M F B
0.0 0.0 0.0
O.-l 0.3 0.4
-1.0 0.0 -1.0
0. 0 0.0 0.0
M F* B
4.9 3.0 4.1
3.2 2.1 2.9
-0.6 -1.6 -1.0
5.0 3.0 4.0
the T from the QRS. A method has been developedz6127 for summarizing aspects of the QRS-T angles. The planar T angle can be measured as a clockwise or counterclockwise deviation from the corresponding planar QRS angle. These angular deviations are then considered as angles A rang-
1.0 1.0 1 .o 10.6 6.0 10.0
ing from 0 to 360 degrees and can be handled the same way as simple planar angles. Whatever the QRS angle is, it must be transposed to 0 degrees to calculate the QRS-T angular deviation. For example, suppose that the directions of the frontal plane maximum QRS and T vectors are
Volume Number
83
The normal adolescent electrocardiogram
1
123
Table VI. Amplitudes-cont’d E.
T wave-cont’d Lead
Mean
St. Deu.
M F B
-0.1 0.0 0.0
0.4 0.6 0.5
M F B
6.1 4.8 5.6
3.6 2.0 3.1
T**
M F B
0.0 0.0 0.0
0.3 0.3 0.3
VS
M F B
5.4 4.6 5.1
2.3 1.5 2.0
F
4.1 3.4 3.8
I
v4 Tl’
V6
Sex
I
B
F.
5%
I
-1.0 -1.0 -1.0
50%
I
95%
0.0 0.0 0.0
1.0 1.6 1.0
7.0 5.0 6.0
12.2 7.6 11.0
0.0 0.0 0.0
0.9 0.0 0.0
2.0 2.0 2.0
6.0 5.0 5.0
10.0 7.6 9.0
1.4 1.0 1.3
2.0 2.0 2.0
4.0 3.0 4.0
7.0 5.0 7.0
St. Dev.
5%
0.4 1.4 1.0 -1.0 -1.0 -1.0
T point Lead
I
Sex
I
Mean
I
50%
I
95 %
aVE
M F B
0.4 0.2 0.3
0.8 0.5 0.7
0.0 -1.0 -0.3
0.0 0.0 0.0
+2.0 +1.0 -cl.3
VS
M F B
0.3 0.1 0.25
0.7 0.6 0.6
0.0 -1.0 -1.0
0.0 0.0 0.0
$2.0 +1.0 +2.0
V6
M F B
0.3 0.3 0.3
0.6 0.5 0.6
0.0 0.0 0.0
0.0 0.0 0.0
f2.0 $1.0 +2.0
340 and 20 degrees, respectively. Then we take the angular deviation, A, to be 40 degrees since T is 40 degrees clockwise of QRS. If the directions had been 20 degrees for QRS and 340 degrees for T, we would have taken the angular deviation, A, of T from QRS to be 320 degrees since T is now 40 degrees counterclockwise of QRS. In Table IX, A, for boys the prevalent direction Gt is 337 degrees so that the average T is 23 degrees counterclockwise of QRS. (Since we know that for boys Gf for QRS is 7.5 degrees, the 8r for T “averages” 52 degrees.) In determining the accepted normal deviation of T from QRS note the
fifth and ninety-fifth percentiles, which range between 285 and 40 degrees. Thus the accepted normal ranges between 75 degrees counterclockwise and 40 degrees clockwise of the QRS. For the above patient with Gf 7.5 degrees, the accepted normal T is from 0 to 115 degrees. Comparisons. Table XI compares the present study with the reviews of Liebman14 and Burch and DePasquale3 for younger and older study populations. Though numbers were not uniformly analyzed (Burch and DePasquale3 used minimum and maximum, and tenth and ninetieth percentiles), the comparisons do offer some
124
Am. Heart J. January, 1972
Strong et al.
270
180
0
B
90 G
QRSF
BtG
Fig. 5. Exact representation of the mean vectors for P, QRS, and T in the frontal (F) and horizontal (H) planes as the data came off the IBM 1620 into the Calcomp plotter. The circles on the left are the boys (B); the middle circles are the girls (G) ; and the final group indicates both boys and girls (B + G). Each circle is divided into 12 quadrants of 30 degrees. (For the QRS the plotter was askew so that the quadrants are 15 degrees counterclockwise of normal. For most others the plotter was only slightly askew.) The data are presented in this manner to demonstrate the use of the prevalent direction (A) and the precision (d). The prevalent direction can be considered the “average angle.” For the horizontal plane the notation is &, and for the frontal plane is &. Each circle has an extra line which is the prevalent direction. For the B + G group the QRS in the horizontal plane has an &, of +345 degrees (or - 15 degrees). If every observation had been +345 degrees, the line would have reached the outer circumference of the circle. For a unit circle, which is standard, the precision then would be 1. The higher the precision, the more reliable is the prevalent direction. If there were a very wide scatter of the observations, the precision would be low. For QRSn, B + G there is little scatter and thus high precision. The significance of this precision can now be tested by doing a simple chi-square test: i.e., chi square = n d* with n the number of observations and d the precision. Values greater than 5.99 are significant at the 5 per cent level; values larger than 9.21 are significant at the 1 per cent level. A significant value is evidence of a prevalent direction. All the chi-square values were very much higher than 9.21.
means of demonstrating one age group should be applied universally adults.
that data from not and cannot to children and
Discussion The data presented illustrate that the adolescent possesses certain ECG characteristics different from those of the adult
v0he a3 Number
The normal adolescent electrocardiogram
1
Table VII. Sex M M F F
Summation Age (YY.1
11-15 16-19 11-15 16-19 11-19 11-19
125
of SVZ and RVS Mean 40.1 37.9 32.8 26.8 38.8 30.1
S.D.
5%
11.5 11.0 8.7 5.8 11.2 8.0
23.5 17.9 18.0 19.1 18.8 19.4
and the younger child. First, the voltages recorded from the precordium in both males and females is greater than that observed in the adult. The ninety-fifth percentile data of the R wave for boys in the following leads were : Vi, 8.6 mm.; VZ, 17.0 mm.; Vq, 33.2 mm.; Vg, 26.6 mm.; and Va, 21.2 mm. For the S wave it was, respectively, 20.6 mm., 31.2 mm., 20.0 mm., 7.6 mm., and 3.6 mm. The same percentile data for girls for the R wave were: Vi, 6.0 mm.; VZ, 12.0 mm.; Vq, 24.6 mm.; Vg, 23.3 mm.; and V6, 18.0 mm. There are also significant differences in these voltages between males and females and between females of different ages. The QRS and T amplitudes change very little in the male 11 through 19 years of age, whereas in the female there is a progressive decline in voltage. Also, the voltages in the male are uniformly greater than those of the female. These findings are consistent with those reported by Walker and Rose,24 and since their report there has been no further elucidation of the reason. In addition to the individual voltages of the QRS and T waves, the summation of SV2 and RVs is much greater than the measurements accepted by adult electrocardiographers for left ventricular hypertrophy in adults. The ninety-fifth percentile for this value in boys 11 to 1.5 years old is 68 mm. and in boys 16 to 19 years old it is 62 mm. Although the respective values for girls are not as high (50 mm. and 41 mm.), they are still greater than the presently excepted value of 35 mm. The second major difference between the adolescent ECG and the adult is the high incidence of J-point elevation (approximately one quarter of the subjects had positive J points in Leads aVr, Vg, and VG). One child had a negative J point in
Table VIII.
I
50%
I
37.0 37.5 31.5 26.0 37.0 29.0
J-point
68.0 62.4 49.6 41.4 58.0 48.6
polarity
Positiwe
Negatiwe -___
Lead
aVF VS VS
95%
No.
%
No.
%
30 27 31
26 24 27
5 6 1
4 5 1
Va, while 5 and 6 children, respectively, had negative J-point displacement in Leads aVr and Vg. None were depressed greater than 1.0 mm. Experience with exercise electrocardiography in adolescents suggests that the etiology of the frequent J+;+t;e;le;atjon may be secondary to an epmephrme effect. However, the possibility of its being due to atria1 repolarization rather than to a ventricular phenomenon has been suggested by Irisawa and associates.1° The third difference between the adolescent and the adult was the finding of a clockwise inscription of the frontal plane loop in 62 per cent of adolescents in contrast to an almost uniformly counterclockwise loop in the adult.
Summary Criteria for the interpretation of the electrocardiogram of the adolescent are presented in tabular form. Three major areas of difference were noted between the electrocardiograms of adolescents and other individuals. These were: (1) The summation of the amplitudes of SV2 and RVb was markedly greater in the adolescent than in adult studies; (2) J-point elevation (Leads aVF, VS, and Ve) was a frequent finding
126
Am. Heart J. January, 1972
Strong et al.
Table IX, A. Frontal angular deviation of T from QRS
Sex
D
Age
Chi sq.
Prevalent direction (ai)
Percentiles -------__-5
50
95
B B z
11-15 16-19 16-19 11-1s
0.90 0.94 0.93 0.97
46.9 66.6 36.0 48.8
337 345 346 340
285 30.5 316 302
335 345 340
40 17 420
B G B&G
11-19 11-19
0.92 0.95 0.93
113.0 84.5 197.5
342 343 342
299 309 305
340 340 340
34 15 18
Table IX, B. Horizontal
angular deviation of T from QRS
D
Age
Chi sq.
Prevalent direction (&J
Percentiles
5
I
50
I
95
B
11-1s
0.85
41.8
45
330
35
98
: G B G B&G
11-1s 16-19 16-19 11-19 11-19
0.83 0.95 0.92 0.84 0.93 0.87
52.8 46.4 35.2 94.3 81.7 174.3
52 39 39 49 39 45
3344 330 339 4 356
45 35 35 45 35 40
108 80 75 103 78 93
Table X. Prevalent direction
of the QRS and T in the frontal Prevalent direction (3
Sex
Age
D
Chi sq,
B B G”
11-1s 16-19 11-1s 16-19
.94 .92 .97 .93
51.2 63.9 48.5 36.0
65 63 62 56
E BSG
11-19 11-19
.95 .93 .93
115.0 84.2 198.9
59 64 62
B B
11-1s 16-19 11-1s 16-19 11-19 11-19 11-19
.94 .92 .96 .95 .93 .96 .94
51.6 64.4 48.0 38.2 116.0 86.2 202.1
330 333 334 332 332 333 332
(A)
(B)
: B G B+G
and horizontal
5%
planes
507”
95%
10 9 38 11
70 70 60 65
90 91 87 80
15 10 14
60 70 65
80 90 90
33s 340 340 340 340 340 340
8 8 354 0 5 0 0
292 289 290 300 292 292 293
Volume Number
83 1
The normal adolescent electrocardiogram
127
Table X. cont’d Sex
Chi sq.
Age I
B B (Q
11-15 16-19 11-15 16-19 11-19 11-19 11-19
: B G B+G
D
.96 .94 .98 .96 .95 .97 .96
Prevalent direction (3
570
5070
95 70
42 48 42 42 45 42 44
1.5 5 17 3 7 17 10
45 5.5 45 45 4.5 4.5 4.5
60 71 60 74 70 60 63
53.8 67.7 49.6 39.0 121.2 88.6 209.6
Prevalent direction (:h)
B B CD) :
11-15 16-19 11-15 16-19
$90 -88 .96 .97
47.5 58.3 48.4 39.2
15 24 12 12
310 338 33.5 310
1.5 1.5 15 15
60 74 38 25
: B+G
11-19 11-19
.89 .97 .92
105.1 87.6 191.4
20 12 17
334 335 335
1.5 15 1.5
60 33 60
Abbreviations:
A = QRS
(frontal
plane);
B = QRS
(horizontal
Table XI. Comparative mean values for (postadolescent) populations
plane):
plane);
adolescents and younger
R wave Lead
C = T (frontal
Platte).
(preadolescent)
S wave
and older
T wave
I-
I II III aVn aVL
aVF V411 VI VZ V4 VS V6
D = T (horizontal
-I
6.0 11.6 6.5 1.3 2.7 10.0 2.5 5.3 9.7 18.4 22.0 15.7
6.3 13.1 8.5 2.3 10.4 1.9 3.6 7.6 16.5 17.4 12.8
5.9 13.1 8.6 3.7 6.9 16.6 17.0 12.8
1.4 2.3 2.6 -
1.3 1.3 1.3 -
5.8 12.6 19.5 10.7 4.0 1.4
2.2 2.8 3.2 -
;l 12.1 17.8 7.7 2.7 1.0
-2.4 0.5 4.7 5.0 3.6
-1.1 4.1 5.6 5.1 3.8
-
-
-
-
(25 per cent) in adolescents; (3) the rotation of the QRS loop in the frontal plane was clockwise in the majority (62 per cent) of adolescents.
-
11.8 17.5 5.7 2.8 1.7
REFERENCES 1. Alimurung, M. M., et al.: The unipolar electrocardiograph children, Circulation
Lester, G. J., Nadas, A. S., precordial and extremity in normal infants and 4:420, 1951.
128
2. 3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Strong
Am. Heart 1. January, 1972
et al.
Battro, A., and Mendy, J. C.: Precordial leads in children, Arch. Intern. Med. 78:31-41, 1946. Burch, G. E., and DePasquale, N. P.: Electrocardiography in the diagnosis of congenital heart disease, Philadelphia, 1967, Lea & Febiger, pp. 732-737. Downs, T. D., and Liebman, J.: Statistical methods for vectorcardiographic directions, I.E.E.E. Transactions on Biomedical Engineering 1:87, 1969. Downs, T. D., Liebman, J., Agusti, R., et al.: The statistical treatment of angular data in vectorcardiography, in Hoffman, I., editor: Vectorcardiography, 1965, Amsterdam, 1966, North Holland Publishing Co., pp. 272-278. Dower, G. E., Ziegler, W. G., Berry, F. G., et al.: A simple test of speed of response of electrocardiographs, AMER. HEART J. 67524, 1964. -. _-. Goodwin, J. F.: The electrocardiogram in normal children and in children with right ventricular hypertrophy, Brit. Heart J.- 14:173, 1952. Hiss, R. G., and Lamb, L. E.: Electrocardiocraohic findines in 122.043 individuals. CirculaiioI; 25:947, 1562. ' Hafkesbring, E. M., Drawe, C. E., and Ashman, R.: Children’s electrocardiograms. I. Measurements for 100 normal children, Amer. J. Dis. Child. 53:1457, 1937. Irisawa, H., Ninomiya, I., and Sayama, I.: Repolarization phase- at various sites of the right atrium. Circ. Res. 19:96. 1966. Kyause, D. A.: The vectorcardiogram in cystic fibrosis: A four year follow-up, submitted in partial fulfillment of the requirement for the decree of Docotor of Medicine. Case Western R&erve University School of Medicine, June 5, 1969, pp. 12-14. Also presented by Liebman, J., Krause, D. A., Downs, T. D., et al., at annual meeting of the American College of Chest Physicians, Oct. 31, 1969, Chicago, Ill. Lamb, E.: Electrocardiography and vectorcardiography, Philadelphia, 1965, W. B. Saunders co., pp. 95-145. Lester, F. M., Sheffield, L. T., and Reeves, T. J.: Electrocardiographic changes in clinically normal older men following near maximal and maximal exercise, Circulation 36:5-14, 1967. Liebman, J.: Electrocardiography, Chapter 9 pp. 183-231, in Moss, A. J., and Adams, F. H., editors: Heart disease in infants, children and adolescents, Baltimore, 1968, Williams and Wilkins. Lincoln, E. M., and Nicolson, H. B.: The hearts of normal children. III. Electrocardiographic records, Amer. J. Dis. Child. 35:1001, 1928.
16.
17.
18.
19.
20.
21.
22.
Massie, E., and Walsh, F. J.: Clinical vectorcardiography and electrocardiography, pp. 64-69. Year Book Publishers. Inc.. 1960. Chicago, Ill. Masters, A. M., Dack, S., and Jaffe, H. L.: The precordial lead of the electrocardiogram of normal children, Amer. J. Dis. Child. 53:1000, 1937. Namin, E. P., and Miller, R. A.: The normal electrocardiogram and vectorcardiogram in children, in Cassels, D. E., and Ziegler, R. F., editors: Electrocardiography in infants and children, New York, 1966, Grune & Stratton, Inc., pp. 99-108. Reynolds, J.: The normal magnitude of the P wave in Lead II. Presented at the 100th Anniversary, Boston Children’s Hospital, 1969. Scott, R. C., Sewert, V. J., Simon, D. L., et al.: Left ventricular hypertrophy: A study of the accuracy of current electrocardiographic criteria when compared with autopsy findings in one hundred cases, Circulation 11:89, 1965. Sokolow, M., and Lyon, T. P.: The ventricular complex in left ventricular hypertrophy as obtained by unipolar precordial and limb leads, AMER. HEART J. 37:161, 1949. Switzer, J. L., and Besoain, M.: Electrocardiograms of-normal children with special reference to aV limb leads and chest leads. Amer. T. Dis. Child. 79:449, 1950. Veasy, L. G., and Adams, F. H.: Unipolar lead electrocardiography in children with special reference to its value in congenital heart disease, Pediatrics 9:395, 1952. Walker, C. H. M., and Rose, R. L.: Importance of age, sex and body habitus in the diagnosis of left ventricular hypertrophy from the precordial electrocardiogram in childhood and adolescence, Pediatrics 28:705, 1961. Zeigler, R. F.: Electrocardiographic studies in normal infants and children, Springfield, Ill., 1951, Charles C Thomas, Publisher. Downs, T. D., Liebman, J., and Mackay, W.: Statistical methods for vectorcardiogram orientations. Presented at the IX International Vectorcardiography Symposium, May, 1970. To be published in Symposium Proceedings, Vectorcardiography, 1970, Hoffman, I., editor. Liebman, J., and Downs, T. D.: The Frank and McFee vectorcardiogram in normal children. A detailed quantitative analysis of 105 children between the ages of two and nineteen years. Presented at the IX International Vectorcardiography Symposium, May, 1970. To be published in Symposium Proceedings, Vectorcardiography, 1970, Hoffman, I., editor. ”
23.
24.
25.
26.
27.
The normal
adolescent
electrocardiogram
William B. Strong, M.D.” Thomas D. Downs, Ph.D.** Jerome Liebman, M.D. Robert Liebowitz, M.D. Cleveland, Ohio
T
he electrocardiogram (ECG) of the normal adolescent has never been published independently. It has always been grouped with either the preadolescent1,7,9,14,15,17&3,21-25 or with young adult2,3s8vle electrocardiographic studies. The present study was undertaken to establish standard biologic criteria (i.e., fifth, fiftieth, and ninety-fifth percentiles) for the various electrocardiographic measurements using direct-writer equipment. Materials
and methods
One hundred and fourteen adolescents judged to have a normal heart by history and physical examination ‘comprised the study group. There were 67 male and 47 female subjects. Table I presents the age and sex characteristics. Each sex was arbitrarily divided into two age categories, 11 to 15 years and 16 to 19 years. The II- to IS-year-old group was further subdivided into 11 to 13 years, and 14 to 15 years to determine any differences or trends within the groups. Equipment. The ECG’s were all recorded on a single-channel Cambridge Mark II Versa Scribe Electrocardiograph, No.
24050, at 25 mm. per second, 1 mv. being equal to a stylus deflection of 1 cm. This instrument was advertised to have a frequency response of 100 Hz. However, testing with Dower’s Totemite equipment? revealed a frequency response of only 50 Hz. The ECG measurements analyzed were transcribed onto special mimeographic forms (Fig. I), keypunched onto IBM cards from these forms, and verified. The analyses were performed on an IBM 1620 digital computer and the figures were drawn with a Calcomp plotter operation from the IBM 1620. Methodology. Ninety-five measurements were performed on each ECG. Fig. 1 shows the computer sheet onto which they were tallied. All correlations and analyses made are presented in tabular or graphic form (see Results). Attempts were made to determine the r and s components of the P wave and also the initial forces of the QRS complex. However, after analyzing the data, it was apparent that the P-wave analyses and initial forces in the frontal plane require, at minimum, double standardization and a paper speed of 50 mm. per second (double speed) for accurate
From
the Case Western Reserve University School of Medicine, Departments of Pediatrics and Biometry, University Hospitals, Cleveland. Ohio. Supported in part by National Institutes of Health Grants HE 08286 and HE 05803 and National Institute of General Medical Sciences Research Grant GM 12302. Reprint requests to: Jerome Liebman, M.D., University Hospitals of Cleveland, University Circle, Cleveland, Ohio 44106. *Present address: Medical College of Georgia, Department of Pediatric Cardiology. Augusta, Ga. 30902. **Present address: School of Public Health, University of Texas at Houston.
Vol. 83, No. 1, pp. 115-128
January,1972
American Heart Journal
115
116
Am. Heart I. January, 1972
Strong et al.
Awl ---mm 2
il”R R
Am
III
III
III
III
"6
"6
"6
"6 6
II em.---..-
AW s -..-s--
P Q R ___------------.__--.----
_..--
*vR R’
bYR
,*-‘-III
"6 Ti
T2 III
AVL 2
AVL -_,_
III
"6
Id
AVL
III
Iit
AYL
s--.22-..
AVP
AVF
kVF
I\YP
AVF
*Pais
_TI..-Q-,--R---S----*-‘--.-T-“-.-f III
AVP "5
III
V6
III
III
III
III
III
III
III
___-___
- __----
-- ----
Boys (no.1
Age (YY.1
11-13 14-15 16-19 Total
I 11-15
14 15 38 67
29
Girls (no.)
I 16 10 21
26
47
interpretation. Neither was performed in the present study. The mean, standard deviation, and fifth, fiftieth, and ninety-fifth percentiles were obtained for the amplitude measurements. The purpose for using this mode of presentation was to eliminate the errors inherent in minimum and maximum numbers and to avoid the use of two standard deviations. Because of the skewed nature of ECG data, two standard deviations from the mean could provide numbers less than the minimum and/or more than the maximum. The use of tenth and ninetieth percentiles has not been shown to have any biologic significance and in our opinion should not be used. The sum of the SVi and RVs or RVr, has frequently been used as a criterion of left ventricular hypertrophy.18n1g In the present study we have chosen to sum the voltages
I.F.
III
III.
- --_----___
Fig. 1. A sample data collection sheet used in the present study. F = frontal; H = horizontal; forces; Tr = first deflection of the T wave; TZ = second deflection of the T wave; P, = duration component of the P wave; P. = duration of the negative component of the P wave: Ld, = lead prominent U wave; H+ LJ = height of the most prominent U wave; Lp F = course of the loop plane; and Lp H = course of the loop in the horizontal plane.
Table I. Age and sex of adolescentsubjects
I.F.
L-._P-_-~-~
LP LP
-J-2-.-H_..-
T Ii -v-_u--L-J--
*axis _.._
I. F. = initial of the positive with the most in the frontal
of SV2 and RVs since they are almost perpendicular. (According to Lamb12 Lead Vz is at $90 degrees and Vs is at +S degrees.) Furthermore, these leads best approximate the axes (2 and X) that comprise the horizontal plane. The methods used to analyze the QRS complexes in Leads aVR, V~R, Vi, and Vz are depicted in Figs. 2 and 3 and described in the respective legends. The interpretation of Lead Vds is applicable to Leads Vi and VZ. Unless one understands the vector loop and its projections, mistakes can be made in pooling the data. Clearly, for example, in Lead aVr the QS, the Q of Qr, and the S of rSr’ represent the same projection. The only difference in the vector is that the initial force of the rsr’ is more to the right than that of the Qr. Data has been reported in which the Q’s and S’s have been treated separately though they should have been pooled. We have elected, therefore, to use the term “first negative deflection” for the Q and S described above and to use the terms initial or terminal positive deflection for the R wave, (e.g., the r of rSr’ would be the initial positive deflection, the r’ would be the terminal positive deflection, and the r of a qr would be the terminal positive deflection). Table II shows the pooling schema for Lead aVr. Angular data, such as electrocardio-
Volume Number
83 1
The normal adolescent electrocardiogram
Fig. 2. A hypothetical diagram of the vector loop in the frontal plane to illustrate the minor alterations which can produce four different QRS patterns in Lead aVn. The initial deflection in examples 1 and 3 is more to the right than in 2 and 4. The Q or the S in all four examples represent the same deflection. The r’ in example 1 is the same vector force as the r (Qr) in number 2.
Table II. Pooling schemaof the QRS cOm#lex
:R QRS QRSR R
in
Lead
1 -
avR
ii S S
R R R R'
graphic mean vectors, should not be analyzed in the same manner as linear data. The arithmetic mean as a measure of the direction in which angular observations on a plane tend to cluster is not appropriate.4 Downs and associates5have developed an angular analysis based on the concept of the center of gravity. The prevalent direction (a) is taken as the direction from the origin to the center of gravity of a disk when all individual data points are placed on the rim of the disk according to their planar coordinates for the instant of time under study. The closenessof clustering of the data is measured by the length of the radius of the line from the center of the disk toward the circumference of the unit circle at the prevalent direction. This distance is a measure of the precision (d) of
VW
117
A
Fig. 3. Hypothetical diagram of the vector loop in the horizontal plane to illustrate the correlate of the rSr’ complex as seen in Lead Vta. R = right; L = left; A = anterior. If the terminal force to the right is relatively anterior (heavy dashed line), it crosses the perpendicular to Lead V~R and a prominent r’ will be seen. If the terminal rightward vector is just as far to the right but is well posterior, it will not cross the perpendicular to Lead V~R and there will be no r’. (The S in VS should be the same in each case, but the S in Vs will be larger when the terminal vector is more anterior.) Published with the permission of J. Liebman and the Williams and Wilkins Publishing Co.
the observations. To test the significance of the clustering a chi-square test is done; chi square = nd2, where n is the sample size and d2is the precision squared. A chi square greater than 5.99 indicates a 5 per cent level of significance while a chi square greater than 9.21 indicates a 1 per cent level of significance. The final analysis compares the present data with that obtained from a composite of studies in younger and older population.s3s13 Results
The ECG findings in the 114 normal adolescents are presented in Tables II through XI. The tables are divided only by sex since there were no important significant differences between age groups. The measurements which attain statistical significance (p < 0.01) are marked by an asterisk. Durations. The only pertinent significant difference which was noted within the age groups was the duration of the P waves, the duration being greater (p < 0.01) in
118
Am. Heart
Strong et al.
January,
Table III. Analysis of the QRS complex in Leads V412, VI, and V2 showed the following patterns 1
Parameter
lirR
(y.
of total)
1
,
F’,
(% of total)
~
Tuble IV. Heart rate and dzrrations
1’2
(%,
of
total)
JI F B
69 ;;
11 12 12
52 57 55
70 ;;
M B
0.09 0.09 0.09
0.02 0.02 0.02
0.06 0.06 0.06
0.08 0.09 0.09
0.12 0.11
M F B
0.1.5
(0
0.15 0.15
0.03 0.02 0.02
0.10 0.12 0.11
0.15 0.15 0.15
0.20 0.19 0.20
0)
iv1 F B
0.08 0.08 0.08
0.01 0.01 0.01
0.06 0.05 0.06
0.08 0.08 0.08
0.10 0.09 0.10
03
M F B
0.38 0.37 0.37
0.04 0.03 0.04
0.32 0.32 0.32
0.38 0.38 0.38
0.42 0.42 0.43
(F)
M F B
0.21 0.19 0.20
0.06 0.04 0.05
0.16 0.15 0.15
0.20 0.18 0.20
0.35 0.28 0.31
(A) 4 1 1 0 0 1 88 3 4
0 1 1 0 1 0 92 5 0
I. 1972
0 0 0 0 0 0 96 4 0
03)
F
Abbreviations: interval; duration.
A = heart rate; D = QRS duration;
90 92 90 0.11
B = P ~me duration; C = PR E = Q-T interval; F = T wave
Amplitudes.
Fig. 4. Diagrammatic representation of a vector “figure S” loop in the horizontal plane illustrating the major portion of the loop to be counterclockwise and only the terminal portion to be clockwise.
the 16- to 19-year-old boys (0.09 sec.) than in the ll- to 15year-old boys (0.08 sec.). However, for practical purposes, this seems of little clinical significance. QRS-complex rotations. In the frontal plane, the loop inscribed was clockwise in 62 per cent of the subjects, counterclockwise in 33 per cent, and figure-of-eight in the remainder. Almost all QRS loops in the horizontal plane were counterclockwise (97 per cent). There were no clockwise rotations and 3 per cent were figure-of-eight. However, in the latter the major portion of the loop was counterclockwise with a lesser degree of clockwise rotation terminally (e.g., Fig. 4).
P WAVE. The ninety-fifth percentile for the P wave in Lead II was 2.0 mm., which suggests that the criterion for right atria1 enlargement (2.5 mm.) is rather generous, as also suggested by Reynolds.19 Q WAVE. The Q wave was measured in Leads III, aVF, Vg, and VS, and the ninetyfifth percentile never exceeded 3.0 mm. in these leads. R AND s WAVES. The amplitudes of the R wave and S wave are shown in Tables VI, C, and VI, D. Table VII summarizes SV2 and RVS and demonstrates that this number is significantly different (p < 0.01) between sexes (males greater than females) and that the sum decreases with age. However, the ninety-fifth percentile, even for girls 16 to 19 years, is 41.4 mm. which is greater than the standard of 35 mm. suggested for adults. Significant differences (p < 0.01) of clinical implication between male and female subjects and between age groups were apparent only in the precordial QRS and T-wave amplitudes. The major difference
Volume Number
83 1
The normal adolescent electrocardiogram
119
Table V. Rotation of the QRS complex
Sex
Clockwise ____--_I-~________-~
No.
No.
(A)
(B)
: B
;
Abbreviations:
Figure
eight
Counterclockwise ---
I
%
NO.
I
%
No.
%
I
67 47 114
42 29 71
62.6 61.7 62.2
2 3 5
2.9 6.3 4.3
23 38
34.3 31.9 33.3
67 47 114
0 0 0
0 0 0
1 2 3
1.4 4.2 2.6
66 4.5 111
98.5 95.7 97.3
A = Frontal
plane;
B = horizontal
1.5
plane.
Table VI. Amplitudes A.
B.
I’ wave
(Lead
II)
I
St. Dev.
/
5%
/
50%
/
95%
Sex
Mean
M F B
1.4 1.4 1.4
0.6 0.5 0.6
0.0 1.0 1.0
2.0 1.0 1.5
2.0 2.0 2.0
0.8 0.7 0.8
1.0 0.9 0.9
0.0 0.0 0.0
1.0 1.0
3.0 3.0 3.0
0.7 0.6 0.7
0.8 0.7 0.8
0.0 0.0 0.0
1.0 1.0
2.6 2.0 2.0
1.0 0.5 0.8
0.8 0.6 0.7
0.0 0.0 0.0
1.0 1.0 1.0
3.0 2.0 2.2
1.2 0.7 1.0
0.7 0.6 0.7
0.0 0.0 0.0
1.0 1.0 1.0
2.6 2.0 2.0
Q wave 1. Lead
III
M F B 2. Lead
aVF
M F B 3. Lead
M F B
1.0
V5*
M F B 4. Lead
1.0
Vs*
was that the voltage of the Q, R, S, and T waves was uniformly greater in the males than in the females. This was primarily a reflection of the 16- to 19-year-old boys
being
greater than Table VI, of the T wave for all T wave in Leads III, T WAVE.
the same-aged girl. E, shows the height leads, and divides the aVL, V~R, VI, Vz, and
120
Am. Heart I. January, 1972
Strong-et al.
Table VI. Amplitudes-cont’d C.
R wave
I B
6.2 6.4 6.3
2.6 2.7 2.6
2.4 3.0 3.0
6.0 6.0 6.0
11.0 11.6 11.0
II
M F B
13.6 12.3 13.1
4.6 2.8 4.0
7.0 7.0 7.0
13.0 12.0 13.0
21.6 17.0 20.0
III
M F B
9.4 7.3 8.5
5.1 3.9 4.7
1.4 1.0 1.0
9.0 7.0 8.0
19.0 14.6 17.2
f
See text
ah
and Table
III
and Fig.
2
aVL
M F B
2.2 2.5 2.3
2.0 2.1 2.1
0.0 0.4 0.0
2.0 2.0 2.0
6.0 7.6 6.2
ah
M F B
11.2 9.3 10.4
4.5 3.4 4.2
4.4 3.4 4.0
11.0 10.0 10.0
19.8 15.0 18.0
VbR*
M F B
2.2 1.4 1.9
1.0 0.9 1.0
1.0 0.0 1.0
2.0 1.0 2.0
4.6 3.0 4.0
v1*
M F B
4.2 2.9 3.6
2.2 1.7 2.1
1.0 0.4 1.0
4.0 3.0 3.0
8.6 6.0 8.0
v2*
M F B
8.5 6.2 7.6
3.8 3.0 3.6
3.0 2.4 3.0
8.0 6.0 7.0
17.0 12.0 15.2
\I‘*
M F B
18.8 13.3 16.5
7.6 5.0 7.1
6.4 5.4 6.0
19.0 13.0 15.0
33.2 24.6 30.2
V6*
M F B
19.4 14.5 17.4
6.0 4.2 5.8
10.0 8.0 9.0
19.0 14.0 17.0
26.6 23.2 26.0
V6’
M F B
13.8 11.4 12.8
3.8 3.1 3.7
9.0 7.0 7.0
13.0 11.0 12.0
21.2 18.0 20.0
V4 into the first and second components. This deflection appeared to be one of the most variable measurements we made. J POINT. Together with the observations of the sums of SV2 and RVb the finding of J-point displacement in approximately 30 per cent of adolescents is striking. In adult studies, this is not a frequent finding. In the present subjects, an elevated J point
was found in Leads aVF, Vh, and Va with equal frequency while a depressed J point was seen in VS in only 1 subject and in Leads aVF and V5 in 5 and 6 subjects, respectively. In no individual was the S-T slope, as measured by the method of Lester and associates,13negative. The S-T slope was frequently positively sloped or “U” shaped. The significance of J-point changes
Volt4me Number
83 1
121
The normal adolescent electrocardiogram
Table VI. Am#itudes--cont’d D.
S wave Lead
!
Sex
(
Mean
1
St. Da.
(
5%
(
50%
1
95%
I
M F B
1.6 0.9 1.3
1.4 1.0 1.3
0.0 0.0 0.0
2.0 1.0 1.0
4.6 3.2 4.0
II
M F B
1.6 0.9 1.3
1.7 1.1 1.5
0.0 0.0 0.0
2.0 0.0 1.0
4.6 3.0 4.0
III
M F B
1.4 1.1 1.3
2.0 1.8 1.9
0.0 0.0 0.0
1.0 0.0 0.5
4.0 6.6 4.5
M F B
3.8 2.4 3.2
2.8 2.4 2.1
0.0 0.0 0.0
3.0 2.0 2.5
9.0 6.6 9.0
F” B
1.2 1.0 1.1
::: 1.5
0.0 0.0 0.0
1.0 0.0 0.5
4.0 4.0 4.0
V4R
M F B
5.4 4.8 5.1
2.7 2.3 2.5
0.4 0.0 0.0
5.0 5.0 5.0
10.0 9.6 10.0
VI
M F B
12.2 11.9 12.1
4.6 4.5 4.5
4.4 3.8 4.7
12.0 12.0 12.0
20.6 20.2 20.2
v2*
M F B
19.3 15.6 17.8
7.3 5.8 7.0
6.4 6.4 6.7
19.0 15.0 17.0
31.2 26.8 30.0
VI*
M F B
9.4 5.4 7.7
4.9 3.6 4.8
0.8 0.0 0.0
9.0 5.0 7.0
20.0 14.6 16.5
VK
M F B
3.1 2.2 2.7
2.4 2.4 2.4
0.0 0.0 0.0
3.0 1.0 2.0
7.6 1.0 7.0
VS*
M F B
1.2 0.5 1.0
1.1 1.0 1.1
0.0 0.0 0.0
1.0 0.0 1.0
3.6 2.6 3.0
aVR aVL
aVF
See text,
in children is not understood but could be related to atria1 repolarization rather than to ventricular electrophysiology. LEAD avg. Ninety-seven per cent of the QRS complexes were included in four patterns: QS, 19 per cent; Qr, 33 per cent; rS, 23 per cent; and rSr’, 22 per cent. Fig. 2 demonstrates that these four patterns are projections of the same basic vector loop.
Table
III
and Fig.
2
ANGULAR DATA. Fig. 5 illustrates the distribution of the mean P, QRS, and T vectors for the entire series in both the frontal and horizontal. planes. Table X lists the prevalent direction for the QRS and T angles. There were no significant differences between the boys and girls. (See legend for explanation of the data.) Table IX, A, and B give the angular deviation data of
122
Am. Heart I. Jawuary, 1972
Strong et al.
Table VI. Amplitudes-cont’d E.
T wave Lead M 1; B
2.9 2.5 2.8
0.9 0.8 0.9
1.4 1.4 1.7
3.0 3.0 3.0
5.0 4.5 4.0
M F B
3.8 3.2 3.6
1.5 0.9 1.3
1.0 2.0 1.7
4.0 3.0 4.0
6.0 5.0 6.0
M F B
1.1 0.8 1.0
1.6 1.1 1.4
-1.6 -1.0 -1.0
2.0 1.0 1.0
3.0 2.0 3.0
M F B
0 0 0
0.3 0.3 0.3
-1.0 0.0 -0.2
0.0 0.0 0.0
1.0 1.0 1.0
M F B
-2.9 -2.8 -2.9
1.8 1.2 1.6
-5.0 -5.0 -5.0
-3.0 -3.0 -3.0
2.2 -1.4 -0.5
M F B
1.0 1.1 1.0
1.1 0.6 0.9
-1.0 0.0 -1.0
1.0 1.0 1.0
3.0 2.0 3.0
M F B
-0.1 0.0 -0.1
0.3 0.4 0.3
- 1 0 -1.0 -1.0
0. 0 0 0 0.0
0 0 0.6 0.0
M F B
2.7 2.3 2.5
1.2 0.7 1.1
1 0 1 0 1.0
3.0 2 0 3.0
5.0 3.6 4.0
M F B
-1.1 -1.2 -1.2
1.2 0.9 1.1
-3.0 -2.0 -3.0
-1.0 -1.0 -1.0
1.0 0.6 1.0
M F* B
-0.7 -1.7 -1.1
2.1 1.4 1.9
-3.6 -4.0 -4.0
-1.0 -2.0 -2.0
3 .0 1.0 3.0
M F B
0.0 0.0 0.0
O.-l 0.3 0.4
-1.0 0.0 -1.0
0. 0 0.0 0.0
M F* B
4.9 3.0 4.1
3.2 2.1 2.9
-0.6 -1.6 -1.0
5.0 3.0 4.0
the T from the QRS. A method has been developedz6127 for summarizing aspects of the QRS-T angles. The planar T angle can be measured as a clockwise or counterclockwise deviation from the corresponding planar QRS angle. These angular deviations are then considered as angles A rang-
1.0 1.0 1 .o 10.6 6.0 10.0
ing from 0 to 360 degrees and can be handled the same way as simple planar angles. Whatever the QRS angle is, it must be transposed to 0 degrees to calculate the QRS-T angular deviation. For example, suppose that the directions of the frontal plane maximum QRS and T vectors are
Volume Number
83
The normal adolescent electrocardiogram
1
123
Table VI. Amplitudes-cont’d E.
T wave-cont’d Lead
Mean
St. Deu.
M F B
-0.1 0.0 0.0
0.4 0.6 0.5
M F B
6.1 4.8 5.6
3.6 2.0 3.1
T**
M F B
0.0 0.0 0.0
0.3 0.3 0.3
VS
M F B
5.4 4.6 5.1
2.3 1.5 2.0
F
4.1 3.4 3.8
I
v4 Tl’
V6
Sex
I
B
F.
5%
I
-1.0 -1.0 -1.0
50%
I
95%
0.0 0.0 0.0
1.0 1.6 1.0
7.0 5.0 6.0
12.2 7.6 11.0
0.0 0.0 0.0
0.9 0.0 0.0
2.0 2.0 2.0
6.0 5.0 5.0
10.0 7.6 9.0
1.4 1.0 1.3
2.0 2.0 2.0
4.0 3.0 4.0
7.0 5.0 7.0
St. Dev.
5%
0.4 1.4 1.0 -1.0 -1.0 -1.0
T point Lead
I
Sex
I
Mean
I
50%
I
95 %
aVE
M F B
0.4 0.2 0.3
0.8 0.5 0.7
0.0 -1.0 -0.3
0.0 0.0 0.0
+2.0 +1.0 -cl.3
VS
M F B
0.3 0.1 0.25
0.7 0.6 0.6
0.0 -1.0 -1.0
0.0 0.0 0.0
$2.0 +1.0 +2.0
V6
M F B
0.3 0.3 0.3
0.6 0.5 0.6
0.0 0.0 0.0
0.0 0.0 0.0
f2.0 $1.0 +2.0
340 and 20 degrees, respectively. Then we take the angular deviation, A, to be 40 degrees since T is 40 degrees clockwise of QRS. If the directions had been 20 degrees for QRS and 340 degrees for T, we would have taken the angular deviation, A, of T from QRS to be 320 degrees since T is now 40 degrees counterclockwise of QRS. In Table IX, A, for boys the prevalent direction Gt is 337 degrees so that the average T is 23 degrees counterclockwise of QRS. (Since we know that for boys Gf for QRS is 7.5 degrees, the 8r for T “averages” 52 degrees.) In determining the accepted normal deviation of T from QRS note the
fifth and ninety-fifth percentiles, which range between 285 and 40 degrees. Thus the accepted normal ranges between 75 degrees counterclockwise and 40 degrees clockwise of the QRS. For the above patient with Gf 7.5 degrees, the accepted normal T is from 0 to 115 degrees. Comparisons. Table XI compares the present study with the reviews of Liebman14 and Burch and DePasquale3 for younger and older study populations. Though numbers were not uniformly analyzed (Burch and DePasquale3 used minimum and maximum, and tenth and ninetieth percentiles), the comparisons do offer some
124
Am. Heart J. January, 1972
Strong et al.
270
180
0
B
90 G
QRSF
BtG
Fig. 5. Exact representation of the mean vectors for P, QRS, and T in the frontal (F) and horizontal (H) planes as the data came off the IBM 1620 into the Calcomp plotter. The circles on the left are the boys (B); the middle circles are the girls (G) ; and the final group indicates both boys and girls (B + G). Each circle is divided into 12 quadrants of 30 degrees. (For the QRS the plotter was askew so that the quadrants are 15 degrees counterclockwise of normal. For most others the plotter was only slightly askew.) The data are presented in this manner to demonstrate the use of the prevalent direction (A) and the precision (d). The prevalent direction can be considered the “average angle.” For the horizontal plane the notation is &, and for the frontal plane is &. Each circle has an extra line which is the prevalent direction. For the B + G group the QRS in the horizontal plane has an &, of +345 degrees (or - 15 degrees). If every observation had been +345 degrees, the line would have reached the outer circumference of the circle. For a unit circle, which is standard, the precision then would be 1. The higher the precision, the more reliable is the prevalent direction. If there were a very wide scatter of the observations, the precision would be low. For QRSn, B + G there is little scatter and thus high precision. The significance of this precision can now be tested by doing a simple chi-square test: i.e., chi square = n d* with n the number of observations and d the precision. Values greater than 5.99 are significant at the 5 per cent level; values larger than 9.21 are significant at the 1 per cent level. A significant value is evidence of a prevalent direction. All the chi-square values were very much higher than 9.21.
means of demonstrating one age group should be applied universally adults.
that data from not and cannot to children and
Discussion The data presented illustrate that the adolescent possesses certain ECG characteristics different from those of the adult
v0he a3 Number
The normal adolescent electrocardiogram
1
Table VII. Sex M M F F
Summation Age (YY.1
11-15 16-19 11-15 16-19 11-19 11-19
125
of SVZ and RVS Mean 40.1 37.9 32.8 26.8 38.8 30.1
S.D.
5%
11.5 11.0 8.7 5.8 11.2 8.0
23.5 17.9 18.0 19.1 18.8 19.4
and the younger child. First, the voltages recorded from the precordium in both males and females is greater than that observed in the adult. The ninety-fifth percentile data of the R wave for boys in the following leads were : Vi, 8.6 mm.; VZ, 17.0 mm.; Vq, 33.2 mm.; Vg, 26.6 mm.; and Va, 21.2 mm. For the S wave it was, respectively, 20.6 mm., 31.2 mm., 20.0 mm., 7.6 mm., and 3.6 mm. The same percentile data for girls for the R wave were: Vi, 6.0 mm.; VZ, 12.0 mm.; Vq, 24.6 mm.; Vg, 23.3 mm.; and V6, 18.0 mm. There are also significant differences in these voltages between males and females and between females of different ages. The QRS and T amplitudes change very little in the male 11 through 19 years of age, whereas in the female there is a progressive decline in voltage. Also, the voltages in the male are uniformly greater than those of the female. These findings are consistent with those reported by Walker and Rose,24 and since their report there has been no further elucidation of the reason. In addition to the individual voltages of the QRS and T waves, the summation of SV2 and RVs is much greater than the measurements accepted by adult electrocardiographers for left ventricular hypertrophy in adults. The ninety-fifth percentile for this value in boys 11 to 1.5 years old is 68 mm. and in boys 16 to 19 years old it is 62 mm. Although the respective values for girls are not as high (50 mm. and 41 mm.), they are still greater than the presently excepted value of 35 mm. The second major difference between the adolescent ECG and the adult is the high incidence of J-point elevation (approximately one quarter of the subjects had positive J points in Leads aVr, Vg, and VG). One child had a negative J point in
Table VIII.
I
50%
I
37.0 37.5 31.5 26.0 37.0 29.0
J-point
68.0 62.4 49.6 41.4 58.0 48.6
polarity
Positiwe
Negatiwe -___
Lead
aVF VS VS
95%
No.
%
No.
%
30 27 31
26 24 27
5 6 1
4 5 1
Va, while 5 and 6 children, respectively, had negative J-point displacement in Leads aVr and Vg. None were depressed greater than 1.0 mm. Experience with exercise electrocardiography in adolescents suggests that the etiology of the frequent J+;+t;e;le;atjon may be secondary to an epmephrme effect. However, the possibility of its being due to atria1 repolarization rather than to a ventricular phenomenon has been suggested by Irisawa and associates.1° The third difference between the adolescent and the adult was the finding of a clockwise inscription of the frontal plane loop in 62 per cent of adolescents in contrast to an almost uniformly counterclockwise loop in the adult.
Summary Criteria for the interpretation of the electrocardiogram of the adolescent are presented in tabular form. Three major areas of difference were noted between the electrocardiograms of adolescents and other individuals. These were: (1) The summation of the amplitudes of SV2 and RVb was markedly greater in the adolescent than in adult studies; (2) J-point elevation (Leads aVF, VS, and Ve) was a frequent finding
126
Am. Heart J. January, 1972
Strong et al.
Table IX, A. Frontal angular deviation of T from QRS
Sex
D
Age
Chi sq.
Prevalent direction (ai)
Percentiles -------__-5
50
95
B B z
11-15 16-19 16-19 11-1s
0.90 0.94 0.93 0.97
46.9 66.6 36.0 48.8
337 345 346 340
285 30.5 316 302
335 345 340
40 17 420
B G B&G
11-19 11-19
0.92 0.95 0.93
113.0 84.5 197.5
342 343 342
299 309 305
340 340 340
34 15 18
Table IX, B. Horizontal
angular deviation of T from QRS
D
Age
Chi sq.
Prevalent direction (&J
Percentiles
5
I
50
I
95
B
11-1s
0.85
41.8
45
330
35
98
: G B G B&G
11-1s 16-19 16-19 11-19 11-19
0.83 0.95 0.92 0.84 0.93 0.87
52.8 46.4 35.2 94.3 81.7 174.3
52 39 39 49 39 45
3344 330 339 4 356
45 35 35 45 35 40
108 80 75 103 78 93
Table X. Prevalent direction
of the QRS and T in the frontal Prevalent direction (3
Sex
Age
D
Chi sq,
B B G”
11-1s 16-19 11-1s 16-19
.94 .92 .97 .93
51.2 63.9 48.5 36.0
65 63 62 56
E BSG
11-19 11-19
.95 .93 .93
115.0 84.2 198.9
59 64 62
B B
11-1s 16-19 11-1s 16-19 11-19 11-19 11-19
.94 .92 .96 .95 .93 .96 .94
51.6 64.4 48.0 38.2 116.0 86.2 202.1
330 333 334 332 332 333 332
(A)
(B)
: B G B+G
and horizontal
5%
planes
507”
95%
10 9 38 11
70 70 60 65
90 91 87 80
15 10 14
60 70 65
80 90 90
33s 340 340 340 340 340 340
8 8 354 0 5 0 0
292 289 290 300 292 292 293
Volume Number
83 1
The normal adolescent electrocardiogram
127
Table X. cont’d Sex
Chi sq.
Age I
B B (Q
11-15 16-19 11-15 16-19 11-19 11-19 11-19
: B G B+G
D
.96 .94 .98 .96 .95 .97 .96
Prevalent direction (3
570
5070
95 70
42 48 42 42 45 42 44
1.5 5 17 3 7 17 10
45 5.5 45 45 4.5 4.5 4.5
60 71 60 74 70 60 63
53.8 67.7 49.6 39.0 121.2 88.6 209.6
Prevalent direction (:h)
B B CD) :
11-15 16-19 11-15 16-19
$90 -88 .96 .97
47.5 58.3 48.4 39.2
15 24 12 12
310 338 33.5 310
1.5 1.5 15 15
60 74 38 25
: B+G
11-19 11-19
.89 .97 .92
105.1 87.6 191.4
20 12 17
334 335 335
1.5 15 1.5
60 33 60
Abbreviations:
A = QRS
(frontal
plane);
B = QRS
(horizontal
Table XI. Comparative mean values for (postadolescent) populations
plane):
plane);
adolescents and younger
R wave Lead
C = T (frontal
Platte).
(preadolescent)
S wave
and older
T wave
I-
I II III aVn aVL
aVF V411 VI VZ V4 VS V6
D = T (horizontal
-I
6.0 11.6 6.5 1.3 2.7 10.0 2.5 5.3 9.7 18.4 22.0 15.7
6.3 13.1 8.5 2.3 10.4 1.9 3.6 7.6 16.5 17.4 12.8
5.9 13.1 8.6 3.7 6.9 16.6 17.0 12.8
1.4 2.3 2.6 -
1.3 1.3 1.3 -
5.8 12.6 19.5 10.7 4.0 1.4
2.2 2.8 3.2 -
;l 12.1 17.8 7.7 2.7 1.0
-2.4 0.5 4.7 5.0 3.6
-1.1 4.1 5.6 5.1 3.8
-
-
-
-
(25 per cent) in adolescents; (3) the rotation of the QRS loop in the frontal plane was clockwise in the majority (62 per cent) of adolescents.
-
11.8 17.5 5.7 2.8 1.7
REFERENCES 1. Alimurung, M. M., et al.: The unipolar electrocardiograph children, Circulation
Lester, G. J., Nadas, A. S., precordial and extremity in normal infants and 4:420, 1951.
128
2. 3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Strong
Am. Heart 1. January, 1972
et al.
Battro, A., and Mendy, J. C.: Precordial leads in children, Arch. Intern. Med. 78:31-41, 1946. Burch, G. E., and DePasquale, N. P.: Electrocardiography in the diagnosis of congenital heart disease, Philadelphia, 1967, Lea & Febiger, pp. 732-737. Downs, T. D., and Liebman, J.: Statistical methods for vectorcardiographic directions, I.E.E.E. Transactions on Biomedical Engineering 1:87, 1969. Downs, T. D., Liebman, J., Agusti, R., et al.: The statistical treatment of angular data in vectorcardiography, in Hoffman, I., editor: Vectorcardiography, 1965, Amsterdam, 1966, North Holland Publishing Co., pp. 272-278. Dower, G. E., Ziegler, W. G., Berry, F. G., et al.: A simple test of speed of response of electrocardiographs, AMER. HEART J. 67524, 1964. -. _-. Goodwin, J. F.: The electrocardiogram in normal children and in children with right ventricular hypertrophy, Brit. Heart J.- 14:173, 1952. Hiss, R. G., and Lamb, L. E.: Electrocardiocraohic findines in 122.043 individuals. CirculaiioI; 25:947, 1562. ' Hafkesbring, E. M., Drawe, C. E., and Ashman, R.: Children’s electrocardiograms. I. Measurements for 100 normal children, Amer. J. Dis. Child. 53:1457, 1937. Irisawa, H., Ninomiya, I., and Sayama, I.: Repolarization phase- at various sites of the right atrium. Circ. Res. 19:96. 1966. Kyause, D. A.: The vectorcardiogram in cystic fibrosis: A four year follow-up, submitted in partial fulfillment of the requirement for the decree of Docotor of Medicine. Case Western R&erve University School of Medicine, June 5, 1969, pp. 12-14. Also presented by Liebman, J., Krause, D. A., Downs, T. D., et al., at annual meeting of the American College of Chest Physicians, Oct. 31, 1969, Chicago, Ill. Lamb, E.: Electrocardiography and vectorcardiography, Philadelphia, 1965, W. B. Saunders co., pp. 95-145. Lester, F. M., Sheffield, L. T., and Reeves, T. J.: Electrocardiographic changes in clinically normal older men following near maximal and maximal exercise, Circulation 36:5-14, 1967. Liebman, J.: Electrocardiography, Chapter 9 pp. 183-231, in Moss, A. J., and Adams, F. H., editors: Heart disease in infants, children and adolescents, Baltimore, 1968, Williams and Wilkins. Lincoln, E. M., and Nicolson, H. B.: The hearts of normal children. III. Electrocardiographic records, Amer. J. Dis. Child. 35:1001, 1928.
16.
17.
18.
19.
20.
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