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The corrected orthogonal electrocardiogram in normal children
The corrected orthogonal in normal children &Fee
and
Parungao
lead
electrocardiogram
system
Ruul Gumboa, M.D.* Nancy White, M.D.** Dallas, Texas
T
he wide scatter of normal ranges for electrocardiographic parameters in children represents a major obstacle to correct interpretation of ECG’s for the pediatric patient. The intra- and interindividual variability of the lead fields of the conventional 12-lead ECG1w3 probably contributes significantly to the broad distribution of normal values. The development of corrected orthogonal lead systems which exhibit more constant lead fields, regardless of variations in body build, facilitates a better quantitative approach to electrocardiographic interpretation. Several studies done in adults seem to demonstrate that much of the clinical information contained in the standard 12-lead ECG may be furnished by the corrected orthogonal 3-lead systems. 4-e These studies suggest that application of the corrected lead systems to pediatric electrocardiography might reduce the wide range of normal findings, and consequently, lead to a better separation of normal from abnormal readings. Of the orthogonal lead systems which have been proposed, it would appear that those based on multiple electrode networks
present certain theoretical advantages377 Among these systems, the one proposed by McFee and Parungao* “represents a careful compromise between the simultaneous needs to maximize accuracy and to minimize complexity.” Recently, Brody and Arzbaecherg have shown that, in the homogeneous model, the “axial” lead system of &Fee and Parungao is superior to the lead systems of FranklO and of Schmitt and Simonson.r In addition, Duchosal and Paschen have recently emphasized the greater reliability of the “axial” lead system for routine clinical use. The present study was undertaken in order to define the normal characteristics of the child’s orthogonal ECG, as obtained by means of McFee and Parungao’s lead system. Material
and
methods
Orthogonal ECG’s (X, Y, and Z leads) were taken from 100 “normal” children, aged 1 to 1.5 years, who were considered free from any cardiovascular abnormality on the basis of history and physical examination, and, in some cases, standard electrocardiography and chest x-ray. Fifty per
From the University of Texas Southwestern Medical School Department of Pediatrics. Supported in part by the Texas Heart Association and the Dallas Heart Association. Received for publication April Z?7- 196i’. *This work was done during the tenure of an Advanced Research Fellowship from the American **Fellow in Pediatric Cardiology, Texas State Department of Health, Crippled Children Division, the Children’s Bureau.
449
Heart Association. in cooperation with
4.50
Gamboa and White
4G
fVumber of Subjecfs
l----l
~~
,MALE
FEMALE
0 l-4
Fig. 2. Reference QRS vectors.
5-10
frames
for
spatial
orientation
of
Age Groups Fig. 1. Age in years normal children.
and
sex
distribution
of
100
cent were children from a public school in Dallas, and the rest were from an orthopedic service of the Children’s Medical Center, Dallas, Texas. The age and sex distribution are shown in Fig. 1. McFee and Parungao’s lead system was used, with electrodes placed as recommended by the authors.8 The three orthogonal leads were recorded simultaneously on frequencymodelated magnetic tape (Sanborn 3907) at 30 i.p.s., and played back on a recording system (Poly-beam, Sanborn 4568, and 350-1600 carrier amplifiers) at slow tape speeds (3% i.p.s.) utilizing fast paper speed (200 mm. per second). This resulted in an elongation of the time base to 16 mm. for each 0.01 second, allowing measurements to the nearest 0.0025 second. The amplitude of each deflection was measured to the nearest 1 mm. An IBM 1620 digital computer was used for the following calculations: 1. Spatial magnitude 2. Azimuth 3. Elevation
= dXz + Y’ i- Z2. 57 = +tan-r$ of each vector. =
+tan-r
&&2 (the reference frames for spatial orientations are shown in Fig. 2). 4. Spatial velocity = d(Xa - Xb)z + (Ya - Yb)2 + (Za - Zb)2, where a and b represent the consecutive vectors, and the magnitude of the spatial displacement between the termini of these vectors, plotted against time, represents the spatial velocity.
Only the QRS complex was studied. %leasurements from scalar Leads X, Y, and Z included amplitudes and durations of Q, R, and S waves, as well as the amplitude ratios for Q/R and R/S. Each parameter was correlated with age, body weight, body surface area, and chest circumference. Considering the inter-individual variability of the QRS duration, the QRS complex was also normalized in time by dividing it into eight equal parts.r2 Results Table I presents the QRS duration for the total group of cases, as well as for each of three subgroups: 1 to 4, 5 to 10: and 11 to 1.5 years of age. A partial relationship between the QRS interval and age is observed~ However, considerable overlapping is noted between the subgroups! with no statistically significant differences between consecutive groups (p > O.OS), but significant variance at p < 0.05 level between the youngest and oldest groups of children. Results for the total group of cases are shown in TabIes II to IV. Table II shows the quantitative analysis of the QRS complex of scalar Leads X, Y? and Z. Correlation of the parameters illustrated in this table with age, body weight, torso surface or chest circumference indicated, in general, no significant relationship. Multiple regression equations did not improve the correlation However, low, but statistically significant correlations were found between both the Q wave and Q/R ratio in the Z lead; and body surface area, body weight, and age. The best correlations were obtained against age (r = -0.33, p < 0.01 with the Q wave, and r = -0.39, p < 0.01
Corrected orthogonal ECG in nounal childrem
451
Table I. QRS interval and age Age
groups
cY=l Total
group
~-~-----
---------1-4
QRS
interual
(sec.)
Mean * Range*
SD.
0.070 * 0.006 0.055+0.085
5-10
0.065 * 0.005 0.0.55-+0.080
0.070 k 0.006 0.06.5+0.085
1 L.+ p> o.os?.J 1-p p < 0.05 Limits
of 96.percentile
11-15
0.075 * 0.007 0.065+0,085
> o.o&--1
range.
Table II. Measwements
of QRS in scalar leads 27, Y, and Z
.z
Y
Q magnitude
(mv.)
Mean * SD. Range* Q duration (sec.) Mean + SD. Range* R mug&de (mu.) Mean * SD. Range* R duration (sec.) Mean =t S.D. Range* S magv&uh (fm.) Mean * S.D. Range* S dumtion (sec.) Mean * S.D. Range* Q/R magnitude (ratio) Mean * S.D. Range* R/S map&& (ratio) Mean * S.D. Range*
*Limits
1
of a. 96.percentile
0.21 0.04
+ 4
O.Oll* o.oos-+
0.07 0.52
0.17 0.04
0.008 0.045
* +
0.09 0.40
0.98 0.13
* 0.41 41.87
0.015 zt O.OOS+
0.010 0.023
0.039 * 0.012 0.015-+0.040
1.60 0.63
* 4
0.42 2.S2
1.61 0.63
* +
0.46 2.70
1.43 0.60
* 0.37 -2.36
0.047 0.017+
=k
0.020 0.075
0.033 0.0254
*
0.006 0.050
0.043 0.022
* 0.052 -0.050
0.50 0.12
* 4
0.30 1.81
0.33 0.08
* -+
0.20 0.70
0.015 0.0074
*
0.011 0.035
0.012 0.005~
*
0.011 0.035
0.11 0.03
* 4
0.06 0.25
0.05 0.02
+ 4
0.05 0.17
0.72 0.09
* 0.33 bl.70
4.82 0.77
* 3.47 +1.5..50
6.78 1.66
zt 5.10 -+22.47
range.
with the Q/‘R ratio). Fig. 3 shows the plotting of the Q/R ratio of the 2 lead against age. It may be seen that ratios greater than 1 are observed only below 5 years of age. Fig. 4 shows the scalar X, Y, and 2 leads, constructed from the mean values of Q, R, and S, and the amplitude ratios, arranged according to age groups. Table III presents the quantitative anal-
ysis of early and late QRS vectors of X, Y, and 2 leads taken at 0.01 second intervals; their spatial magnitudes, and their spatial orientations in terms of azimuth and elevation. Table IV shows the normalized data of the QRS complex, including scalar amplitude, spatial magnitude and orientation, spatial velocity, and the maximum spatial
$52
Gamboa
and White
ps.01
Fig. 3. The Q/R ratio of the Z lead plotted against age.
tion. The final vectors are directed toward the right, posteriorly and superiorly, and present smaller values for the spatial magnitude and velocity: 0.03 and 0.01 mv. per millisecond, respectively. The possible influences of such variables as age, body weight, body surface area, and chest circumference on the maximum spatial magnitude of the QRS complex were analyzed statistically (Table V). The mean maximum spatial magnitude is similar for all the groups. Comparisons of all individual values by analysis of variance for a complete randomized design model13 demonstrated no significant differences among them. Discussion
7-4
yrs
5-toyrs
II-f!5
yrs
Fig. 4. Scalar X, Y, and Z leads constructed from the mean values oc Q, R, and S deflections. The leads and corresponding amplitude ratios are ar1anged according to age groups. magnitude (1EM). Fig. 5 shows the mean values of the curves of spatial magnitude, orientation, and velocity, and the 96percentile ranges. As disclosed in Table IV and Fig. 5, initial QRS vectors are oriented anteriorly and slightly superiorly with spatial magnitude and velocity at the level of 0.58 and 0.8 mv. per millisecond, respectively. The maximum mean spatial magnitude, 2.05 mv., is reached between the 3/8 and 4/8 interval of the QRS. At this time, the spatial velocity approaches maximal value of 0.22 mv. per millisecond, and the curves of spatial orientation show posterior (320’) and inferior (35’) orienta-
QRS duration. Although the present study does not demonstrate a highly significant relationship between age and QRS duration, it is possible to observe a partial association indicating a longer QRS duration in the older children. Furthermore, noticeable differences are observed when comparing our data, particularly for the first two age groups (0.065 sec. mean for 1 to 4P and 0.070 sec. mean for 5 to 10 years of age) with the values reported by Draper and associates14 for adults (0.093 sec. mean). It is conceivable that the differences between children and adults might be related to the growth of the heart. It has been shown by Linzbach15 that, during physiologic growth, the myocardial fibers enlarge. If the ventricular mass is increased, the QRS must increase in duration, because the activation wave will take longer to course through the ventricles. It is noteworthy that, although there is a fifteenfold increase in heart weight from birth to adulthood,16 the QRS duration increases steadily, but never exceeds twice its value at birth. This can be explained, as suggested by Lepeschkin,lT by simultaneous increase in conduction rate due to the growth in diameter of the conduction fibers. Hechtlg has shown that the differences in conduction velocity in normal cardiac tissues depend largely upon the fiber diameter. Although no comparable data on the duration of the QRS waves of the orthogonal electrocardiogram in infants and children have been published, it is interest-
Cowected
Tuble III.
QuurAtutive
~~ndysis
Scalar Time (sec.) A-
QRS
~LLC
in normal &ildren
ECG
Spatial Spatial magnitude (ma.)
~-
Y
!
Z
I
453
vectors
amplitude
Cmv.) ~I
11jter QRS mzs~t Mean * S.D. Range* 0.02 ajter QRS onset Mean * S.D. Range* 0.03 after QRS onset Mean * S.D. Range* 0.0-F ufter QRS onset Mean * S.D. Range* 0.01 before end oj QRS Mean * S.D. Range* 0.02 before end of QRS Mean + S.D. Range* 0.03 bejore end of QRS Mean * S.D. Range* 0.04 before end of QRS Mean * S.D. Range*
md
OJ curly
orthogonal
orientation (degrees)
Azimutk
Elevation
0.01
*Limits
of a 96-percentile
-0.06 -0.60
* 0.12 + OS8
-0.04 -0.30
0.48 -0.07
* 0.30 + 1.2.5
0.30 * -0.18 + 1.15 * 0.10 +
1.20 * 0.14 +
0.50 2.50
32 0.12 + 0.20
-0.45 * 0.00 4
0.20 1.20
0.50 * 0.15 4
0.37 1.34
-0.80 -1.75
90 * 20 18 -P 140
+5 -40
* 1.5 ++55
0.50 1.15
1.18 zt 0.39 0.45 4 2.39
50 * 87 4
29 150
+20 -40
* ++30
15
0.39 2.40
0.17 * 0.68 -0.85 + 1.75
2.00 * 0.50 1.10 +3.00
330 * 300 -+
25 3.5
+40 +10
+ *+30
12
30 10
+2.5 =k +29---10
20
12
* +
0.24 1.40
0.50 -0.78
* 0.70 + 2.00
0.68 -0.80
* 0.60 -+ 2.00
1.10 * 0.50 0.00 -+ 2.00
1.70 =t 0.45 0.75 42.50
280 + 260 4
0.01 -0.07
* 0.03 4 0.04
-0.02 -0.07
zt 0.02 - 0.00
0.02 * 0.05 0.00 4 0.09
0.02 * 0.00 +
220 z+z 70 200 + 260
-15
-0.07 -0.38
* 0.05 -+ 0.08
-0.04 -0.35
* 0.07 + 0.10
0.04 * 0.08 0.00 + 0.40
0.06 0.00
zt 0.10 + 0.58
240 * 170 +
30 340
-12 -25
-0.09 -1.10
Tk 0.15 + 0.18
-0.06 -0.60
* +
0.12 0.10
0.28 + 0.2s 0.00 4 1.25
0.35 =k 0.30 0.00 + 1.45
250 * 210 +
15 300
+s* +30 +
-0.21 z!z 0.28 - 1.25 + 0.40
-0.05 -0.15
* 0.30 + 1.00
0.80 * 0.29 0.10 4 1.70
1.00 + 0.39 0.20 + 2.00
240 ziz 13 225 + 300
0.05 0.30
+5 -30
* 0 h-25
zt 18 ++30 20 -25
* 15 ++30
EXI&?Z
ing to compare these measurements with those obtained from adult subjects. As shown in Table II, all the values are lower than those observed in adults, except the duration of the Q wave in Lead Z, which shows a mean of 0.039 sec. as compared with 0.033 sec. reported by Draper and associates.i4 QRS magnitude and orientation. Corn. parison of our data with measurements in adults reported by Tannenbaum and coworkers,ig who used McFee and Parungao’s lead system, demonstrates higher values for every deflection of the QRS complex in children. The significance of these differences remains to be evaluated. The study of the amplitudes of the three waves of the QRS complex reveals that the Q wave of Lead Z is the only deflection which is related to age, body surface, and body weight. Similarly, the Q/R ratio in the Z lead is the only amplitude ratio signifi-
cantly associated with these Iparameters. The variation of the Q/R ratia in Lead Z probably reflects the progressive changes in the anatomic relationship between the right and left ventricles that are associated with growth. z” The importance of quantitatively defining this evolutionary pattern lies in its application to the diagnosis of ventricular hypertrophy in infants and children. It has been shown by Yano and Pipberger ~2that the analysis of instantaneous spatial vectors, in terms of magnitude and orientation, contains most of the diagnostic electrocardiographic information. However, these investigators have pointed out that comparative analysis of instantaneous vectors at fixed time intervals is not appropriate if the QRS duration differs from subject to subject. The 0.03 sec. vector of an infant with a QRS interval of 0.06 sec. will necessarily correspond to a different
454
Am. Heart 3. A@il, 1968
Gamboa and White
Table IV. Quantitative analysis of eight instantaneous
QKY vectors 8patial
Spatial
Zpat{al
0Tientation
(degTeee)
magnitude
velocity
118 Mean 5 S,D. Ranget
z/8 Mean k S.D. Ranget 3/z Mean & S.D. Ranget 8 d/Mean k S.D. Range?
-0.51 k 0.25 O.OO+ 1.27
0.58 T- 0.26 0.19+ 1.50
96? 24 IT-+159
+7 5 -51++55
20
0.08 * 0.03 0.03+0.20
-0.81 -1.804
zk 0.60 1.20
1.22 J! 0.46 0.47+2.44
52 k 35 97-+ 180
+25 + A6++35
17
0.14 + 0.06 0,01-+0.39
1.20 k 0.46 0.10+2.50
0.18 AZ 0.71 -0.90+1.81
2.05 k 0.52 1.11+3,02
354 I!Z 28 3004 40
+48 & lO+
15 40
0.21 k 0.10 0.05jO.52
0.59 * 0.81 -0.81+2.08
0.79 IL 0.73 -0.90+2.20
I.10 L!Z 0.56 0.00+2.04
1.85 IL 0.51 0,7?a-+2.98
299 zk 35 270-+ 1
+28 & +34-+14
23
O.l$ & 0.06 0.05+0,39
-0.21 k 0.32 -1.25+0.50
-0.06 * 0.38 -O.E+l.lO
Cl.91 k 0.39 0.12*1.75
1.04 zk 0.44 0.22+2.06
259 k 18 240-330
+7 & AO++36
18
0.13 & 0.07 0.03-+0.34
-0.09 zk 0.20 -1.16+0.18
-0.0s * 0.15 -0.63-+0,10
0.31 5 0.26 O.OO+ 1.40
0.38 jz 0.31 O.OO+ 1.50
260 & 20 210+ 314
0 2~ +40+-30
24
0.06 5 0.03 0.02-s 0.13
-0.09 -0.41+
!L 0.06 0.09
-0.04 I!I 0.09 -0.50~0.10
0.05 31 0.10 0.00+ 0.50
0.08 T!Z 0.14 O.OO+ 0.67
250 k 36 180+360
-10 k -30++30
21
0.04 + 0.02 0.02-+ 0.13
0.01 * 0.03 -0.08+0.03
-0.02 * 0.02 -0.08-+0.00
0.02 * 0.06 o.@+ 0.10
0.03 k 0.06 0.00+ 0.33
227 !c 89 215+ 270
-18
k o+-30
10
0.01 + 0.01 -+ 0.03
2.45 + 0.41 1.43+3.25
320 k 2604
+40
k
15 70
-0.07 & 0.22 -0.81+0.63
-0.05 -0.35+
31 0.15 0.27
0.53 -O.K+
* 0.34 1.33
0.37 2 0.40 -0.20+ 1.36
1.40 Yk 0.57 0.18+2.62
5/t Mean * S.D. Ranget
d/8 Mean Z!Z S.D. Ranget 718 Mean * S.D. Ranget
,3/g Mean * S.D. Range? Afaximum QRii Mean k S.D. Range?
vector
*Measurements obtained tLimits of .3 96percentile
32 27
o+
each eight of the total QRS duration. range.
state of the ventricular “depolarization” than the 0.03 sec. vector of a child with a QRS interval of 0.08 sec. A better approach consists of obtaining time measurements from both ends of the QRS; however, this technique might produce either an overlap or a gap in the middle of the QRS These shortcomings are avoided by normalization of the QRS into time intervals which permit inter-individual comparisons, disregarding differences in QRS durations.r4 The qualitative and quantitative analyses of the curves of spatial magnitude and orientation have demonstrated value in recognizing electrocardiographic abnormalities in adults.rz The usefulness of this type of spatial data display remains to be tested in children. The spatial velocity of the QRS, The interruption of vectorcardiographic loops at
a given unit of time is considered of value for the diagnosis of intraventricular conduction defects. However, descriptions such “terminal delay” or “slowing of the ;Rs,, are only subjective evaluations. The introduction of curves of spatial velocity21 permits an accurate quantitation of the directional changes of the electrocardiogram. The present study demonstrates that higher velocities are reached at the time the curve of spatial magnitude reaches its higher values. This finding calls our attention to the dependence of the calculated spatial velocity on the magnitude of the vectors.= For this reason, values obtained from normal hearts with normal QRS amplitudes are not comparable to those obtained from hypertrophied hearts with increased QRS magnitudes. It must
Corrected orthogonal ECG in normal children
-go-
imuth
1
45.5
Elevation
-248-270’-300°-33d+360*+0’+30°+60’+ 90°+12$+150*-/ r 0
1 ‘A 8
# 2,8
Fig, 5. Mean curves of spatial the 96-percentile limits.
Table V. J.!faxiwzum circumference
Groups
I 3%
, 4~8
, 5~8
, 6~8
magnitude,
, T/8
spatial
s$atial magnitude
, 8~~
velocity,
(MSM)
azimuth,
and
elevation.
The
shaded
area indicates
and age, body weight, body surface, and ch.est
No. of cases
Mean
MSM =t S.D.
34 38 28
2.50 2.45 2.41
0.10 0.09 0.10
p < 0.90%
74 24 2
2.42 2.S6 2.43
0.06 0.12 0.41
p < 0.7s*
38 SO 12
2.51 2.40 2.50
0.09 0.08 0.17
p < 0.70*
40 32 28
2.51 2.46 2.37
0.09 0.10 0.11
p < o,s.s*
A@ CY=) l-4 S-10 11-15 Body weight (lbs.) 30-75 75-120 120-150 Body szuf. (sq. M.) 0.40-0.70 0.80-1.10 1.12-1.16 Chest circu+nf.(inches) 18-25 2.5-28 28-32
Am Heart .T. &d, 1968
be kept in mind that the spatial velocity is not a measure of the speed of ventricular activation.21-23 Instead, it reflects the rate of change in the location of the dom&0zt “sinks” and “sources” of the heart currents, as studied from the body surface. It has been demonstrated that the curves of spatial velocity are sensitive indicators of the presence of ventricular conduction defects,n and also allow an accurate quantitation of progressive degrees of right bundle branch block.22 The rn(lximaLrn s$atid mugnitude und the dipole moment of the he&. The influence of age, body weight, body surface area, and chest circumference upon the MS34 of the QRS in infants and children seems to have escaped general attention. Our findings demonstrate (Table V) that in “normal” children the MSM is not significantly affected by these variables. This is not in conflict with the results obtained in torso models, where an inverse relationship between torso size and body surface potentials was foundz4; in concurrence with Burger and Van Milaan’s2 studies demonstrating that the magnitude of the lead vectors is inversely proportional to the dimensions of the body* What the present study tends to show, rather, is that in the living subject the effective electric moment of the heart increases with body growth, thus compensating for the increments in body size. On the other hand, in the torso model studies a fixed-current dipole was used; thus, the magnitude of the potentials at the body surface was affected by the volume of the model.24 Recent considerations have emphasized that the absolute magnitude of the body surface potentials can be affected by many factors acting upon the heart’s dipole moment and upon the lead fields.1-3f25s2G Among the factors that will enhance the dipole moment of the heart during body an increased growth, ‘those producing amount of longitudinal current generated in each heart muscle fiber, and a decreased amount of internal cancellation must be taken into account. There is no evidence that the number of fibers increases during physiologic growth ; however, it is known that the cross-sectional area of the muscle fiber does increase.15 This would probably decrease the intracellular resistance and
increase the rate of polarization reversal, with consequent increased amount of longitudinal current generated in each fiber. A decreased amount of internal cancellation between the ventricles probably plays a role during early infancy when the “physiologic” right ventricular hypertrophy disappears. This might explain in part the steady increase in AISnI reported by Liebman and co-worker?r in infants from birth to six months of age. Besides the factors directly influencing the current dipole moment, those which affect the heart-lead relationship-such as the finite boundary effect, torso resistivity, and end-diastolic volume-must be taken into consideration in order to explain the absolute magnitude of body surface potentials. It has been demonstrated by Canfield,z8 and Wilson and colleagues*g~30 that the boundary between the body tissues and the surrounding air augments the magnitude of body surface potentials. The influence of the finite boundary in comparisons of surface potentials between children and adults remains to be tested. Certain differences might be expected because of the changes in angle of curvature of the thoracic walls during body growth. It might be anticipated that the augmentative effect of the boundary would bear an inverse relationship with torso volume. Bayley and Berry r25demonstrated that increasing the specific resistivity of body tissue exterior to the heart produces an increase in the absolute magnitude of the body surface potentials. The demonstrated differences in torso resistivity between children and adults, and the positive linear relationship of this resistivity with body size,31 suggest that it must play a part in increasing the body surface potentials. The effect of the intracavitary blood volume upon body surface potentials has been theoretically analyzed by Brody.26 This investigator stated that the presence of the intracavitary blood mass augments the effective strength of normal components of myocardial doublets, and reduces the effective strength of tangential components, Since under normal circumstances most of the ventricular “depolarization” expands in a radial direction, Brody’s observations are of the utmost importance. In previous studies done in this laboratory32 regarding
Covected orthogonal ECG in normal children
the effect of ventricular and end-diastolic volume upon the MSM in dogs, it was found that increasing the end-diastolic volume by one-third of the original control value increased the MSM an average of 18 per cent. It is conceivable that the significant differences in end-diastolic volumes between infants and adults (13 cc. for a child of 0.40 sq. M. body surface area, and 12.5 C.C. for an adult of 1.80 sq. M. body surface area33s34-about a lo-fold increase above the child’s end-diastolic volume) must contribute significantly to the augmentation of the electric output of the myocardial fibers. Because of the number of variables that might affect the absolute magnitude of the potentials on the body surface, it seems impossible to calculate the “true electric moment” of the heart from body surface potentials only. Knowledge of the dimensions of the thorax and integration of potentials over the body surface,35 as well as over every interface within the nonhomogeneous human torso must be required in order to approach the actual dipole moment of the heart.26g3o Since this tremendous task is certainly too complicated to be accomplished by routine clinical procedures, the cardiologist7 at least for the present, must rely on a practical electrocardiographic lead system that will permit accurate quantitation of the absolute magnitude of body surface potentials. Theoretical and clinical studiesz’gJ1 have demonstrated that the lead system proposed by McFee and F’arungaos meets the requirements of accuracy and simplicity which are desired for routine clinical use. Summary
Corrected orthogonal electrocardiograms, obtained by means of NIcFee and Parungao’s lead system, were recorded from 100 normal children, ranging in age from 1 to 15 years. Data from the QRS complex were analyzed by means of a digital computer. The amplitudes and duration of the QRS deflections, as well as the curves of spatial magnitude, orientation, and velocity are presented. Correlations of the QRS amplitudes and MSM against age, weight, body surface area, and chest circumference demonstrate, in general, no significant relationship. A low, but statistically significant
4.57
correlation was found between both the Q wave and the Q/R ratio in the Z lead; and body surface area, body weight, and age. The authors Elizabeth Carey of the manuscript.
express their for her assistance
gratitude in the
to Mrs. preparation
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16.
17.
Schmitt, 0. H., and Simonson, E.: The present status of vectorcardiography, Arch. Int. Med. 96:574, 195.5. Burger, H. C., and Van Milaan, J. B.: Heart vector and leads. I, II, and III, Brit. Heart J. 8:157, 1946; 9:154,1947; 10:229,1948. McFee, R., and Johnston, F. D.: Electrocardiographic leads. I, Introduction. II, Analysis. III, Synthesis, Circulation 8:554, 1953; 9:22S, 1954; 9:868, 1954. Abildskov, J. A., Street, W. W., Solomon, N., and Toomajian, A. H.: Clinical observations with the Frank precordial lead system, Circulation 17:1069, 19.58. Pipberger, H. V., Bialek, S. M., Perloff, J. K., and Schnaper, H. W.: Correlation of clinical information in the standard 12-lead ECG and in a corrected orthogona1 3-lead ECG, A&c. HEART J. 61:34, 1961. Abildskov, J. A., and Wilkinson, R. S.: The relation of precordial and orthogonal leads, Circulation 27:58, 1963. Brody, D. A.: A method for applying approximately ideal lead connections to homogeneous volume conductors of irregular shape, AX HEART J. 53:174, 19.57. McFee, R., and Parungao, A.: An orthogonal lead system for clinical electrocardiography, AM. HEART J. 62:93, 1961. Brady, D. A., and Arzbaecher, R. C.: A comparative analysis of several corrected vectorcardiographic leads, Circulation 29:533, 1964. Frank, E.: An accurate clinically practical system for spatial vectorcardiography, Circulation 13:737, 1956. Duchosal, P. W., and Pasche, R.: Practical remarks on the McFee and Parungao VCG lead system, Ant. HEART J. 72:287, 1966. Yano, K., and Pipberger, H. V. : Spatial magnitude, orientation, and velocity of the normal and abnormal QRS complex, Circulation 29:107, 1964. Ostle, B.: Statistics in research, Des Moines, 1963, The Iowa State University Press, p. 278, Draper, H. W., Peffer, C. J., Stallmann, F., Littman, D., and Pipberger, H. V.: The corrected orthogonal electrocardiogram and vectorcardiogram in 510 normal men (Frank lead system), Circulation 30:853, 1964. Linzbach, A. J.: Heart failure from .the point of view of quantitative anatomy, Am. J, Cardiol. 5:370, 1960. Altman, P. L., and Dittmer, D. S.: Growth, Washington, D. C., 1962, Federation of American Socyeties for Experimental Biology, p. 347. Lepeschkinr E, ; Modern electrocardiography,
4.58
18.
19.
20.
21.
22.
23.
24.
Gumboa and White
Baltimore, 1951, The Williams & Wilkins Company, p. 337. Hecht, H. H.: Some observations and theories concerning the electrical behavior of heart muscle, Am. J. Med. 30:720, 1961. Tannenbaum, O.# Vesell, H., and Schack, J. A. : Comparison of a good orthogonal lead system and one additional chest lead with the conventional 12-lead electrocardiogram, Circulation 35:146, 1967. Recavarren, S., and Arias-Stella, J.: Growth and development of the ventricular myocardium from birth to adult life, Brit. Heart J. 26:187, 1964. Hellerstein, H. K., and Hamlin, R.: QRS component of the spatial vectorcardiogram and the spatial magnitude and velocity electrocardiograms of the normal dog, Am. J. Cardiol. 6:1049, 1960. Gamboa, R., Gupta, D., and White, N.: Right bundle branch block and the velocity of the electrocardiogram, Arch. Int. Med. 120:286, 1967. Boineau, J. P., Spach, M. S., and Ayers, C. R.: Time-normalized correlation of ventricular activation and the vectorcardiogram, AM. HEART J. 73:64,1967. Gamboa, R.: Applicability of the axial lead system to infants and children, Am. J. Cardiol.
27.
28.
29.
30.
31.
32.
33.
18:690, 1966. 2.5.
26.
Bayley, R. H., and Berry, P. M.: Body surface potentials produced by the eccentric dipole in the heart wall of the nonhomogeneous volume conductor, AX. HEART J. 65:200, 1963. Brodv. D. A.: A theoretical analvsis of intracavitary blood mass influence on the heart lead relationship, Circulation Res. 4:731, 1956.
34.
35.
Liebman, J., Romberg, H. C., Downs, T., and Agusti, R.: The Frank QRS vectorcardiogram in the premature infant, Proc. Long Island Jewish Hospital Symposium Vectorcardiography, Amsterdam, 1966, North-Holland Publishing Company, p. 256. Canfield, R.: On the electrical field surrounding doublets and its significance from the standpoint of Einthoven’s equations, Heart 14:102, 1927. A. G., and Barker, Wilson, F. N., Macleod, P. S.: The distribution of currents of action and injury displayed by heart muscle and other excitable tissue, Ann Arbor, 1933, University of Michigan Science Series, 10. Wilson, F. N.. Iohnston, F. D., Rosenbaum, F. F.? and Bark&, P. S.; On Einthoven’s trii angle, the theory of unipolar electrocardiographic leads, and the interpretation of the precordial electrocardiogram, AX HEART J. 32:227, 1946. Gamboa, R., and Adair, B.: Thorax resistivity in children and adults, J. Appl. Physiol. 23:109, 1967. Gamboa$ R., and Gupta, D.: Influence of end-diastolic volume on the magnitude of the QRS complex in dogs. In preparation. Miller, G. A. H., and Swan, H. C. J.: Effect of chronic pressure and volume overload on left heart volumes in subjects with congenital heart disease, Circulation 30:205, 1964. Kennedy, Jo W., Baxley, W. A., Figley, M. M.> Dodge, -H.-T., and Blackman, J. R.: Quantitative angiocardiogranhv. I. The normal left ventricle in ma;, ~Circulation 34:272, 1966. Nelson, C. V.: Design of accurate vector lead systems, J. Maine M. At 58:Sz 1967.
and
Parungao
lead
electrocardiogram
system
Ruul Gumboa, M.D.* Nancy White, M.D.** Dallas, Texas
T
he wide scatter of normal ranges for electrocardiographic parameters in children represents a major obstacle to correct interpretation of ECG’s for the pediatric patient. The intra- and interindividual variability of the lead fields of the conventional 12-lead ECG1w3 probably contributes significantly to the broad distribution of normal values. The development of corrected orthogonal lead systems which exhibit more constant lead fields, regardless of variations in body build, facilitates a better quantitative approach to electrocardiographic interpretation. Several studies done in adults seem to demonstrate that much of the clinical information contained in the standard 12-lead ECG may be furnished by the corrected orthogonal 3-lead systems. 4-e These studies suggest that application of the corrected lead systems to pediatric electrocardiography might reduce the wide range of normal findings, and consequently, lead to a better separation of normal from abnormal readings. Of the orthogonal lead systems which have been proposed, it would appear that those based on multiple electrode networks
present certain theoretical advantages377 Among these systems, the one proposed by McFee and Parungao* “represents a careful compromise between the simultaneous needs to maximize accuracy and to minimize complexity.” Recently, Brody and Arzbaecherg have shown that, in the homogeneous model, the “axial” lead system of &Fee and Parungao is superior to the lead systems of FranklO and of Schmitt and Simonson.r In addition, Duchosal and Paschen have recently emphasized the greater reliability of the “axial” lead system for routine clinical use. The present study was undertaken in order to define the normal characteristics of the child’s orthogonal ECG, as obtained by means of McFee and Parungao’s lead system. Material
and
methods
Orthogonal ECG’s (X, Y, and Z leads) were taken from 100 “normal” children, aged 1 to 1.5 years, who were considered free from any cardiovascular abnormality on the basis of history and physical examination, and, in some cases, standard electrocardiography and chest x-ray. Fifty per
From the University of Texas Southwestern Medical School Department of Pediatrics. Supported in part by the Texas Heart Association and the Dallas Heart Association. Received for publication April Z?7- 196i’. *This work was done during the tenure of an Advanced Research Fellowship from the American **Fellow in Pediatric Cardiology, Texas State Department of Health, Crippled Children Division, the Children’s Bureau.
449
Heart Association. in cooperation with
4.50
Gamboa and White
4G
fVumber of Subjecfs
l----l
~~
,MALE
FEMALE
0 l-4
Fig. 2. Reference QRS vectors.
5-10
frames
for
spatial
orientation
of
Age Groups Fig. 1. Age in years normal children.
and
sex
distribution
of
100
cent were children from a public school in Dallas, and the rest were from an orthopedic service of the Children’s Medical Center, Dallas, Texas. The age and sex distribution are shown in Fig. 1. McFee and Parungao’s lead system was used, with electrodes placed as recommended by the authors.8 The three orthogonal leads were recorded simultaneously on frequencymodelated magnetic tape (Sanborn 3907) at 30 i.p.s., and played back on a recording system (Poly-beam, Sanborn 4568, and 350-1600 carrier amplifiers) at slow tape speeds (3% i.p.s.) utilizing fast paper speed (200 mm. per second). This resulted in an elongation of the time base to 16 mm. for each 0.01 second, allowing measurements to the nearest 0.0025 second. The amplitude of each deflection was measured to the nearest 1 mm. An IBM 1620 digital computer was used for the following calculations: 1. Spatial magnitude 2. Azimuth 3. Elevation
= dXz + Y’ i- Z2. 57 = +tan-r$ of each vector. =
+tan-r
&&2 (the reference frames for spatial orientations are shown in Fig. 2). 4. Spatial velocity = d(Xa - Xb)z + (Ya - Yb)2 + (Za - Zb)2, where a and b represent the consecutive vectors, and the magnitude of the spatial displacement between the termini of these vectors, plotted against time, represents the spatial velocity.
Only the QRS complex was studied. %leasurements from scalar Leads X, Y, and Z included amplitudes and durations of Q, R, and S waves, as well as the amplitude ratios for Q/R and R/S. Each parameter was correlated with age, body weight, body surface area, and chest circumference. Considering the inter-individual variability of the QRS duration, the QRS complex was also normalized in time by dividing it into eight equal parts.r2 Results Table I presents the QRS duration for the total group of cases, as well as for each of three subgroups: 1 to 4, 5 to 10: and 11 to 1.5 years of age. A partial relationship between the QRS interval and age is observed~ However, considerable overlapping is noted between the subgroups! with no statistically significant differences between consecutive groups (p > O.OS), but significant variance at p < 0.05 level between the youngest and oldest groups of children. Results for the total group of cases are shown in TabIes II to IV. Table II shows the quantitative analysis of the QRS complex of scalar Leads X, Y? and Z. Correlation of the parameters illustrated in this table with age, body weight, torso surface or chest circumference indicated, in general, no significant relationship. Multiple regression equations did not improve the correlation However, low, but statistically significant correlations were found between both the Q wave and Q/R ratio in the Z lead; and body surface area, body weight, and age. The best correlations were obtained against age (r = -0.33, p < 0.01 with the Q wave, and r = -0.39, p < 0.01
Corrected orthogonal ECG in nounal childrem
451
Table I. QRS interval and age Age
groups
cY=l Total
group
~-~-----
---------1-4
QRS
interual
(sec.)
Mean * Range*
SD.
0.070 * 0.006 0.055+0.085
5-10
0.065 * 0.005 0.0.55-+0.080
0.070 k 0.006 0.06.5+0.085
1 L.+ p> o.os?.J 1-p p < 0.05 Limits
of 96.percentile
11-15
0.075 * 0.007 0.065+0,085
> o.o&--1
range.
Table II. Measwements
of QRS in scalar leads 27, Y, and Z
.z
Y
Q magnitude
(mv.)
Mean * SD. Range* Q duration (sec.) Mean + SD. Range* R mug&de (mu.) Mean * SD. Range* R duration (sec.) Mean =t S.D. Range* S magv&uh (fm.) Mean * S.D. Range* S dumtion (sec.) Mean * S.D. Range* Q/R magnitude (ratio) Mean * S.D. Range* R/S map&& (ratio) Mean * S.D. Range*
*Limits
1
of a. 96.percentile
0.21 0.04
+ 4
O.Oll* o.oos-+
0.07 0.52
0.17 0.04
0.008 0.045
* +
0.09 0.40
0.98 0.13
* 0.41 41.87
0.015 zt O.OOS+
0.010 0.023
0.039 * 0.012 0.015-+0.040
1.60 0.63
* 4
0.42 2.S2
1.61 0.63
* +
0.46 2.70
1.43 0.60
* 0.37 -2.36
0.047 0.017+
=k
0.020 0.075
0.033 0.0254
*
0.006 0.050
0.043 0.022
* 0.052 -0.050
0.50 0.12
* 4
0.30 1.81
0.33 0.08
* -+
0.20 0.70
0.015 0.0074
*
0.011 0.035
0.012 0.005~
*
0.011 0.035
0.11 0.03
* 4
0.06 0.25
0.05 0.02
+ 4
0.05 0.17
0.72 0.09
* 0.33 bl.70
4.82 0.77
* 3.47 +1.5..50
6.78 1.66
zt 5.10 -+22.47
range.
with the Q/‘R ratio). Fig. 3 shows the plotting of the Q/R ratio of the 2 lead against age. It may be seen that ratios greater than 1 are observed only below 5 years of age. Fig. 4 shows the scalar X, Y, and 2 leads, constructed from the mean values of Q, R, and S, and the amplitude ratios, arranged according to age groups. Table III presents the quantitative anal-
ysis of early and late QRS vectors of X, Y, and 2 leads taken at 0.01 second intervals; their spatial magnitudes, and their spatial orientations in terms of azimuth and elevation. Table IV shows the normalized data of the QRS complex, including scalar amplitude, spatial magnitude and orientation, spatial velocity, and the maximum spatial
$52
Gamboa
and White
ps.01
Fig. 3. The Q/R ratio of the Z lead plotted against age.
tion. The final vectors are directed toward the right, posteriorly and superiorly, and present smaller values for the spatial magnitude and velocity: 0.03 and 0.01 mv. per millisecond, respectively. The possible influences of such variables as age, body weight, body surface area, and chest circumference on the maximum spatial magnitude of the QRS complex were analyzed statistically (Table V). The mean maximum spatial magnitude is similar for all the groups. Comparisons of all individual values by analysis of variance for a complete randomized design model13 demonstrated no significant differences among them. Discussion
7-4
yrs
5-toyrs
II-f!5
yrs
Fig. 4. Scalar X, Y, and Z leads constructed from the mean values oc Q, R, and S deflections. The leads and corresponding amplitude ratios are ar1anged according to age groups. magnitude (1EM). Fig. 5 shows the mean values of the curves of spatial magnitude, orientation, and velocity, and the 96percentile ranges. As disclosed in Table IV and Fig. 5, initial QRS vectors are oriented anteriorly and slightly superiorly with spatial magnitude and velocity at the level of 0.58 and 0.8 mv. per millisecond, respectively. The maximum mean spatial magnitude, 2.05 mv., is reached between the 3/8 and 4/8 interval of the QRS. At this time, the spatial velocity approaches maximal value of 0.22 mv. per millisecond, and the curves of spatial orientation show posterior (320’) and inferior (35’) orienta-
QRS duration. Although the present study does not demonstrate a highly significant relationship between age and QRS duration, it is possible to observe a partial association indicating a longer QRS duration in the older children. Furthermore, noticeable differences are observed when comparing our data, particularly for the first two age groups (0.065 sec. mean for 1 to 4P and 0.070 sec. mean for 5 to 10 years of age) with the values reported by Draper and associates14 for adults (0.093 sec. mean). It is conceivable that the differences between children and adults might be related to the growth of the heart. It has been shown by Linzbach15 that, during physiologic growth, the myocardial fibers enlarge. If the ventricular mass is increased, the QRS must increase in duration, because the activation wave will take longer to course through the ventricles. It is noteworthy that, although there is a fifteenfold increase in heart weight from birth to adulthood,16 the QRS duration increases steadily, but never exceeds twice its value at birth. This can be explained, as suggested by Lepeschkin,lT by simultaneous increase in conduction rate due to the growth in diameter of the conduction fibers. Hechtlg has shown that the differences in conduction velocity in normal cardiac tissues depend largely upon the fiber diameter. Although no comparable data on the duration of the QRS waves of the orthogonal electrocardiogram in infants and children have been published, it is interest-
Cowected
Tuble III.
QuurAtutive
~~ndysis
Scalar Time (sec.) A-
QRS
~LLC
in normal &ildren
ECG
Spatial Spatial magnitude (ma.)
~-
Y
!
Z
I
453
vectors
amplitude
Cmv.) ~I
11jter QRS mzs~t Mean * S.D. Range* 0.02 ajter QRS onset Mean * S.D. Range* 0.03 after QRS onset Mean * S.D. Range* 0.0-F ufter QRS onset Mean * S.D. Range* 0.01 before end oj QRS Mean * S.D. Range* 0.02 before end of QRS Mean + S.D. Range* 0.03 bejore end of QRS Mean * S.D. Range* 0.04 before end of QRS Mean * S.D. Range*
md
OJ curly
orthogonal
orientation (degrees)
Azimutk
Elevation
0.01
*Limits
of a 96-percentile
-0.06 -0.60
* 0.12 + OS8
-0.04 -0.30
0.48 -0.07
* 0.30 + 1.2.5
0.30 * -0.18 + 1.15 * 0.10 +
1.20 * 0.14 +
0.50 2.50
32 0.12 + 0.20
-0.45 * 0.00 4
0.20 1.20
0.50 * 0.15 4
0.37 1.34
-0.80 -1.75
90 * 20 18 -P 140
+5 -40
* 1.5 ++55
0.50 1.15
1.18 zt 0.39 0.45 4 2.39
50 * 87 4
29 150
+20 -40
* ++30
15
0.39 2.40
0.17 * 0.68 -0.85 + 1.75
2.00 * 0.50 1.10 +3.00
330 * 300 -+
25 3.5
+40 +10
+ *+30
12
30 10
+2.5 =k +29---10
20
12
* +
0.24 1.40
0.50 -0.78
* 0.70 + 2.00
0.68 -0.80
* 0.60 -+ 2.00
1.10 * 0.50 0.00 -+ 2.00
1.70 =t 0.45 0.75 42.50
280 + 260 4
0.01 -0.07
* 0.03 4 0.04
-0.02 -0.07
zt 0.02 - 0.00
0.02 * 0.05 0.00 4 0.09
0.02 * 0.00 +
220 z+z 70 200 + 260
-15
-0.07 -0.38
* 0.05 -+ 0.08
-0.04 -0.35
* 0.07 + 0.10
0.04 * 0.08 0.00 + 0.40
0.06 0.00
zt 0.10 + 0.58
240 * 170 +
30 340
-12 -25
-0.09 -1.10
Tk 0.15 + 0.18
-0.06 -0.60
* +
0.12 0.10
0.28 + 0.2s 0.00 4 1.25
0.35 =k 0.30 0.00 + 1.45
250 * 210 +
15 300
+s* +30 +
-0.21 z!z 0.28 - 1.25 + 0.40
-0.05 -0.15
* 0.30 + 1.00
0.80 * 0.29 0.10 4 1.70
1.00 + 0.39 0.20 + 2.00
240 ziz 13 225 + 300
0.05 0.30
+5 -30
* 0 h-25
zt 18 ++30 20 -25
* 15 ++30
EXI&?Z
ing to compare these measurements with those obtained from adult subjects. As shown in Table II, all the values are lower than those observed in adults, except the duration of the Q wave in Lead Z, which shows a mean of 0.039 sec. as compared with 0.033 sec. reported by Draper and associates.i4 QRS magnitude and orientation. Corn. parison of our data with measurements in adults reported by Tannenbaum and coworkers,ig who used McFee and Parungao’s lead system, demonstrates higher values for every deflection of the QRS complex in children. The significance of these differences remains to be evaluated. The study of the amplitudes of the three waves of the QRS complex reveals that the Q wave of Lead Z is the only deflection which is related to age, body surface, and body weight. Similarly, the Q/R ratio in the Z lead is the only amplitude ratio signifi-
cantly associated with these Iparameters. The variation of the Q/R ratia in Lead Z probably reflects the progressive changes in the anatomic relationship between the right and left ventricles that are associated with growth. z” The importance of quantitatively defining this evolutionary pattern lies in its application to the diagnosis of ventricular hypertrophy in infants and children. It has been shown by Yano and Pipberger ~2that the analysis of instantaneous spatial vectors, in terms of magnitude and orientation, contains most of the diagnostic electrocardiographic information. However, these investigators have pointed out that comparative analysis of instantaneous vectors at fixed time intervals is not appropriate if the QRS duration differs from subject to subject. The 0.03 sec. vector of an infant with a QRS interval of 0.06 sec. will necessarily correspond to a different
454
Am. Heart 3. A@il, 1968
Gamboa and White
Table IV. Quantitative analysis of eight instantaneous
QKY vectors 8patial
Spatial
Zpat{al
0Tientation
(degTeee)
magnitude
velocity
118 Mean 5 S,D. Ranget
z/8 Mean k S.D. Ranget 3/z Mean & S.D. Ranget 8 d/Mean k S.D. Range?
-0.51 k 0.25 O.OO+ 1.27
0.58 T- 0.26 0.19+ 1.50
96? 24 IT-+159
+7 5 -51++55
20
0.08 * 0.03 0.03+0.20
-0.81 -1.804
zk 0.60 1.20
1.22 J! 0.46 0.47+2.44
52 k 35 97-+ 180
+25 + A6++35
17
0.14 + 0.06 0,01-+0.39
1.20 k 0.46 0.10+2.50
0.18 AZ 0.71 -0.90+1.81
2.05 k 0.52 1.11+3,02
354 I!Z 28 3004 40
+48 & lO+
15 40
0.21 k 0.10 0.05jO.52
0.59 * 0.81 -0.81+2.08
0.79 IL 0.73 -0.90+2.20
I.10 L!Z 0.56 0.00+2.04
1.85 IL 0.51 0,7?a-+2.98
299 zk 35 270-+ 1
+28 & +34-+14
23
O.l$ & 0.06 0.05+0,39
-0.21 k 0.32 -1.25+0.50
-0.06 * 0.38 -O.E+l.lO
Cl.91 k 0.39 0.12*1.75
1.04 zk 0.44 0.22+2.06
259 k 18 240-330
+7 & AO++36
18
0.13 & 0.07 0.03-+0.34
-0.09 zk 0.20 -1.16+0.18
-0.0s * 0.15 -0.63-+0,10
0.31 5 0.26 O.OO+ 1.40
0.38 jz 0.31 O.OO+ 1.50
260 & 20 210+ 314
0 2~ +40+-30
24
0.06 5 0.03 0.02-s 0.13
-0.09 -0.41+
!L 0.06 0.09
-0.04 I!I 0.09 -0.50~0.10
0.05 31 0.10 0.00+ 0.50
0.08 T!Z 0.14 O.OO+ 0.67
250 k 36 180+360
-10 k -30++30
21
0.04 + 0.02 0.02-+ 0.13
0.01 * 0.03 -0.08+0.03
-0.02 * 0.02 -0.08-+0.00
0.02 * 0.06 o.@+ 0.10
0.03 k 0.06 0.00+ 0.33
227 !c 89 215+ 270
-18
k o+-30
10
0.01 + 0.01 -+ 0.03
2.45 + 0.41 1.43+3.25
320 k 2604
+40
k
15 70
-0.07 & 0.22 -0.81+0.63
-0.05 -0.35+
31 0.15 0.27
0.53 -O.K+
* 0.34 1.33
0.37 2 0.40 -0.20+ 1.36
1.40 Yk 0.57 0.18+2.62
5/t Mean * S.D. Ranget
d/8 Mean Z!Z S.D. Ranget 718 Mean * S.D. Ranget
,3/g Mean * S.D. Range? Afaximum QRii Mean k S.D. Range?
vector
*Measurements obtained tLimits of .3 96percentile
32 27
o+
each eight of the total QRS duration. range.
state of the ventricular “depolarization” than the 0.03 sec. vector of a child with a QRS interval of 0.08 sec. A better approach consists of obtaining time measurements from both ends of the QRS; however, this technique might produce either an overlap or a gap in the middle of the QRS These shortcomings are avoided by normalization of the QRS into time intervals which permit inter-individual comparisons, disregarding differences in QRS durations.r4 The qualitative and quantitative analyses of the curves of spatial magnitude and orientation have demonstrated value in recognizing electrocardiographic abnormalities in adults.rz The usefulness of this type of spatial data display remains to be tested in children. The spatial velocity of the QRS, The interruption of vectorcardiographic loops at
a given unit of time is considered of value for the diagnosis of intraventricular conduction defects. However, descriptions such “terminal delay” or “slowing of the ;Rs,, are only subjective evaluations. The introduction of curves of spatial velocity21 permits an accurate quantitation of the directional changes of the electrocardiogram. The present study demonstrates that higher velocities are reached at the time the curve of spatial magnitude reaches its higher values. This finding calls our attention to the dependence of the calculated spatial velocity on the magnitude of the vectors.= For this reason, values obtained from normal hearts with normal QRS amplitudes are not comparable to those obtained from hypertrophied hearts with increased QRS magnitudes. It must
Corrected orthogonal ECG in normal children
-go-
imuth
1
45.5
Elevation
-248-270’-300°-33d+360*+0’+30°+60’+ 90°+12$+150*-/ r 0
1 ‘A 8
# 2,8
Fig, 5. Mean curves of spatial the 96-percentile limits.
Table V. J.!faxiwzum circumference
Groups
I 3%
, 4~8
, 5~8
, 6~8
magnitude,
, T/8
spatial
s$atial magnitude
, 8~~
velocity,
(MSM)
azimuth,
and
elevation.
The
shaded
area indicates
and age, body weight, body surface, and ch.est
No. of cases
Mean
MSM =t S.D.
34 38 28
2.50 2.45 2.41
0.10 0.09 0.10
p < 0.90%
74 24 2
2.42 2.S6 2.43
0.06 0.12 0.41
p < 0.7s*
38 SO 12
2.51 2.40 2.50
0.09 0.08 0.17
p < 0.70*
40 32 28
2.51 2.46 2.37
0.09 0.10 0.11
p < o,s.s*
A@ CY=) l-4 S-10 11-15 Body weight (lbs.) 30-75 75-120 120-150 Body szuf. (sq. M.) 0.40-0.70 0.80-1.10 1.12-1.16 Chest circu+nf.(inches) 18-25 2.5-28 28-32
Am Heart .T. &d, 1968
be kept in mind that the spatial velocity is not a measure of the speed of ventricular activation.21-23 Instead, it reflects the rate of change in the location of the dom&0zt “sinks” and “sources” of the heart currents, as studied from the body surface. It has been demonstrated that the curves of spatial velocity are sensitive indicators of the presence of ventricular conduction defects,n and also allow an accurate quantitation of progressive degrees of right bundle branch block.22 The rn(lximaLrn s$atid mugnitude und the dipole moment of the he&. The influence of age, body weight, body surface area, and chest circumference upon the MS34 of the QRS in infants and children seems to have escaped general attention. Our findings demonstrate (Table V) that in “normal” children the MSM is not significantly affected by these variables. This is not in conflict with the results obtained in torso models, where an inverse relationship between torso size and body surface potentials was foundz4; in concurrence with Burger and Van Milaan’s2 studies demonstrating that the magnitude of the lead vectors is inversely proportional to the dimensions of the body* What the present study tends to show, rather, is that in the living subject the effective electric moment of the heart increases with body growth, thus compensating for the increments in body size. On the other hand, in the torso model studies a fixed-current dipole was used; thus, the magnitude of the potentials at the body surface was affected by the volume of the model.24 Recent considerations have emphasized that the absolute magnitude of the body surface potentials can be affected by many factors acting upon the heart’s dipole moment and upon the lead fields.1-3f25s2G Among the factors that will enhance the dipole moment of the heart during body an increased growth, ‘those producing amount of longitudinal current generated in each heart muscle fiber, and a decreased amount of internal cancellation must be taken into account. There is no evidence that the number of fibers increases during physiologic growth ; however, it is known that the cross-sectional area of the muscle fiber does increase.15 This would probably decrease the intracellular resistance and
increase the rate of polarization reversal, with consequent increased amount of longitudinal current generated in each fiber. A decreased amount of internal cancellation between the ventricles probably plays a role during early infancy when the “physiologic” right ventricular hypertrophy disappears. This might explain in part the steady increase in AISnI reported by Liebman and co-worker?r in infants from birth to six months of age. Besides the factors directly influencing the current dipole moment, those which affect the heart-lead relationship-such as the finite boundary effect, torso resistivity, and end-diastolic volume-must be taken into consideration in order to explain the absolute magnitude of body surface potentials. It has been demonstrated by Canfield,z8 and Wilson and colleagues*g~30 that the boundary between the body tissues and the surrounding air augments the magnitude of body surface potentials. The influence of the finite boundary in comparisons of surface potentials between children and adults remains to be tested. Certain differences might be expected because of the changes in angle of curvature of the thoracic walls during body growth. It might be anticipated that the augmentative effect of the boundary would bear an inverse relationship with torso volume. Bayley and Berry r25demonstrated that increasing the specific resistivity of body tissue exterior to the heart produces an increase in the absolute magnitude of the body surface potentials. The demonstrated differences in torso resistivity between children and adults, and the positive linear relationship of this resistivity with body size,31 suggest that it must play a part in increasing the body surface potentials. The effect of the intracavitary blood volume upon body surface potentials has been theoretically analyzed by Brody.26 This investigator stated that the presence of the intracavitary blood mass augments the effective strength of normal components of myocardial doublets, and reduces the effective strength of tangential components, Since under normal circumstances most of the ventricular “depolarization” expands in a radial direction, Brody’s observations are of the utmost importance. In previous studies done in this laboratory32 regarding
Covected orthogonal ECG in normal children
the effect of ventricular and end-diastolic volume upon the MSM in dogs, it was found that increasing the end-diastolic volume by one-third of the original control value increased the MSM an average of 18 per cent. It is conceivable that the significant differences in end-diastolic volumes between infants and adults (13 cc. for a child of 0.40 sq. M. body surface area, and 12.5 C.C. for an adult of 1.80 sq. M. body surface area33s34-about a lo-fold increase above the child’s end-diastolic volume) must contribute significantly to the augmentation of the electric output of the myocardial fibers. Because of the number of variables that might affect the absolute magnitude of the potentials on the body surface, it seems impossible to calculate the “true electric moment” of the heart from body surface potentials only. Knowledge of the dimensions of the thorax and integration of potentials over the body surface,35 as well as over every interface within the nonhomogeneous human torso must be required in order to approach the actual dipole moment of the heart.26g3o Since this tremendous task is certainly too complicated to be accomplished by routine clinical procedures, the cardiologist7 at least for the present, must rely on a practical electrocardiographic lead system that will permit accurate quantitation of the absolute magnitude of body surface potentials. Theoretical and clinical studiesz’gJ1 have demonstrated that the lead system proposed by McFee and F’arungaos meets the requirements of accuracy and simplicity which are desired for routine clinical use. Summary
Corrected orthogonal electrocardiograms, obtained by means of NIcFee and Parungao’s lead system, were recorded from 100 normal children, ranging in age from 1 to 15 years. Data from the QRS complex were analyzed by means of a digital computer. The amplitudes and duration of the QRS deflections, as well as the curves of spatial magnitude, orientation, and velocity are presented. Correlations of the QRS amplitudes and MSM against age, weight, body surface area, and chest circumference demonstrate, in general, no significant relationship. A low, but statistically significant
4.57
correlation was found between both the Q wave and the Q/R ratio in the Z lead; and body surface area, body weight, and age. The authors Elizabeth Carey of the manuscript.
express their for her assistance
gratitude in the
to Mrs. preparation
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