The frank vectorcardiogram of the normal 4 month old infant

The Frank Vectorcardiogram of the Normal 4 Month Old Infant

LORIN PHILIP

E. AINGER, R. DIXON,

Memphis,

MD, FACC AA, RT

Tennessee

From St. Jude Children’s Research Hospital and the Department of Pediatrics and Division of Clinical Physiology, University of Tennessee Medical Units, Memphis, Tenn. This study was supported in part by U. S. Public Health Service Grants HE05775 and HE-052&5 from the National Heart and Lung Institute, U. S. Public Health Service, Bethesda, Md., and by ALSAC. Manuscript received March 30, 1971; revised manuscript received July 9, 1971, accepted July 23, 1971. Address for reprints: Lorin E. Ainger, MD, St. Jude Children’s Research Hosp,ital, 332 N. Lauderdale, Memphis, Tenn. 38101.

VOLUME

29,

MAY

1972

Mean values and standard errors of estimate are presented for the magnitudes of several P, QRS and T wave vectors of the Frank lead electrocardiogram for a group of 110 normal 4 month old infants. Angular measurements are also presented for vector quantities. These data were derived from digital computer analysis of data recorded on magnetic tape. From the interindividual variation in magnitude and angular measurements noted in this sample of infants, homogenous both in age and race, it is suggested that uniformity of performance of the Frank lead system in this age group is no greater than that of the standard scalar electrocardiogram.

Several recent studies of Frank orthogonal lead electrocardiographic recordings in adults suggest that normal limits for spatial, planar and scalar magnitudes should be stratified by age in order to provide optimal discrimination between normal and pathologic records. Borun et a1.l demonstrated significant multiple correlations of Frank scalar lead amplitude measurements with age, relative body weight, and chest diameter, most of which were accountable by age alone. In a subsequent study, Borun2 demonstrated a significant decrease in spatial vector magnitudes with advancing age, thus confirming the observations reported by Silverberg and Pipberger et al.’ These investigators also noted significant differences in the location of the means for some QRS and T vectors among groups separated on the basis of age and body build, but the overlap of ranges for normal individuals was so large that Borun2 expressed doubt that age stratification of angular measurements would provide additional diagnostic separation of normal from abnormal records. From extensive knowledge accumulated from the normal standard scalar electrocardiogram of normal infants and children, it is apparent that age stratification of both magnitude and angular measurements is even more imperative than in adults in order to achieve optimal diagnostic discrimination between normal and abnormal corrected orthogonal lead recordings. Very few studies have been published which contain quantitative measurements, and those published did not deal with discrete age groups and contained quantitative measurements of only a few of the QRS vectors. In part, this can be attributed to the large number of corrected orthogonal lead networks used in recording, the limitations imposed by the method of data display (usually planar loop displays), the almost infinite number of planar and spatial vector quantities which can be measured, and the relatively large number of discrete age groupings for which these determinations must be made. It is the purpose of this paper to present the results of a digital computer analysis of Frank lead recordings obtained from

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I

DIXON

Magnitude of Scalar Lead Deflections, 4 Month Old Infants Mean (TV) X lead Left Right

Frank System:

SEM

721 536

xk32.0 A22.6

Inferior

215 764

zklO.1 134.7

Z lead Anterior Posterior

1,015 731

zt34.7 1-28.4

Y lead Superior

110 normal 4 month old infants. The data were recorded on magnetic tape as simultaneous X, Y and Z lead deflections. Study Group and Methods The study group has been defined in previous publication@ and consisted of 110 infants followed up from the day of birth. Each infant had a normal neonatal course observed in the newborn nursery and each had normal growth and development. None had experienced a serious illness. Repeat physical examinations at the time the recordings were obtained revealed no significant abnormalities and normal cardiovascular findings. None of the infants had anemia. Most were of Negro racial extraction and from the lower socioeconomic class served by a large municipal hospital. Details of instrumentation, recording and statistical analysis are the same as reported previously.7 Most of the infants were mildly sedated for the recordings (chloral hydrate, 50 mg/kg rectally or secobarbital sodium, 1 to 2 mg/kg intramuscularlyi. Results

Heart rate and electrocardiographic interval measurements : All infants had a sinus mechanism, and the mean heart rate for the group was 136 t 1.3/min (range 108 to 195 beats/min). The mean P-R interval for the group was 88 -+ 1.8 msec, which is somewhat shorter than values reported from studies of standard lead tracings. This is probably due to the fact that the terminal portion of this interval contains a variable portion of the ventricular activation wave (QRS). When the QRS interval is determined from the 3 simultaneous orthogonal scalar lead deflections, the onset of ventricular activation is recognized with greater accuracy, a fact supported by the relatively longer mean duration of the QRS interval of 69 & 1.5 msec. The S-T interval includes both the S-T segment and the T wave, and the mean value for the group was 238 -+ 3.6 msec. The S-T interval only approximates the time required for ventricular depolarization since regions of the ventricle depolarized early in activation are repolarized before ventricular activation is completed. Scalar X, Y and Z lead QRS deflections: Mean magni,tude and standard errors of estimate for the 694

maximal scalar X, Y and Z lead deflections are presented in Table I. The rather large standard errors indicate the considerable interindividual variation in the magnitude of these deflections among normal 4 month old infants. For the group as a whole, the leftward, anterior and inferior deflections were of greatest magnitude. QRS vectors : Magnitudes and directions of planar and spatial QRS vectors are presented in Table II. Successive 0.01 second planar QRS vectors : The interindividual variation in magnitude of each of the successive planar QRS vector magnitudes, as indicated by the standard errors of estimate, were large. In the frontal plane, the prevalent direction of each vector was determined at a confidence level greater than 99 percent excepting the 0.06 second vector, the direction of which was estimated only at the 95 percent confidence level. Low precision values, indicating wide dispersion of the individual vectors about the angle of prevalent direction, were apparent for the 0.01, 0.02, 0.06 and 0.07 second vectors in this plane. In the horizontal plane, A was determined at a confidence level exceeding 99 percent excepting the 0.01 second vector (<95 percent confidence level) and the 0.04 second vector ( >95 percent confidence level). In the sagittal plane, A was determined for each of the 0.01 second vectors at a confidence level exceeding 99 percent with the exception of the 0.01 second vector which was determined at the 95 percent confidence level. Close clustering of individual vectors about A was apparent for all except the 0.01 and 0.07 second vectors. When the QRS interval of each individual was “time-normalized” by division of the QRS into 6 equal segments, a procedure designed to relate the same degree of depolarization among individuals with QRS intervals of different durations, there was no reduction in interindividual variation in vector magnitudes but there was a much closer clustering of each of the individual vectors about the angle of prevalent direction. In each case, A was estimated at a confidence level in excess of 99 percent. The individual maximal planar vector magnitudes were quite variable, but the individual variation was of a lesser magnitude than that observed for the successive timed QRS vectors. The angle of prevalent direction was estimated with a high degree of statistical confidence ( >99 percent), and the values for “d” indicate that the individual vectors were clustered closely about A in each plane. Successive 0.01 second QRS spatial vectors demonstrated almost as much variation in magnitude as was shown by their planar counterparts and the variation in spatial orientation of these vectors was also of the same order. The mean maximal spatial QRS vector was 1,521 t 37.0 pv, the direction of which was defined The

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VECTORCARDIOGRAM

by an azimuth of 126” and an elevation of +43 t 0.37” from the horizontal. The rightmost maximal spatial vector magnitude of 1,355 k 32.6 pv approximated that of the leftmost maximal spatial vector magnitude of 1,411 + 34.6 pv. The mean planar QRS vectors, expressed in microvolt seconds, showed less individual magnitude variation than the maximal QRS vectors; the clustering of individual vectors about A in each plane was slightly closer than for their maximal planar counterparts, and each A was estimated with a high level of statistical confidence (>99 percent). There was close agreement for A between the maximal and mean QRS vectors in the frontal plane (70 and 72”, respectively) but orientations of A in the horizontal and sagittal planes were discordant. The spatial mean QRS vector had a mean magnitude of 35.6 f 0.82 microvolt seconds with a direction defined by an azimuth of 252” and an elevation from the horizontal of +19 t 0.82”. T vectors: Magnitudes and orientations for T vectors and ventricular gradient vectors are presented in Table III.

OF 4 MONTH

OLD INFANT

Successive ‘/ segment planar T vectors: There was considerable interindividual variation among the group in magnitude of these vectors. In each plane A was estimated at a level of confidence in excess of 99 percent for each vector with the exception of the a+&segment horizontal T vector, which was so widely dispersed that no angle of prevalence was apparent. High precision values, indicating close clustering of individual T vectors about the angle of prevalence, were particularly close for each successive l/b segment T vector in the sagittal plane. Planar maximal and mean T vector magnitudes, expressed in microvolts and microvoltseconds, respectively, displayed considerable interindividual variability. However, such close clustering of individual vectors about A was apparent that A could be estimated with a very impressive degree of statistical confidence (>99.99 percent). In each plane the directions of the maximal and mean T vectors were quite similar. The mean maximal spatial T magnitude was 316 f 13.7 pv, and the spatial direction of the vector

TABLE II Frank Lead QRS Vectors for 110 Normal

‘3s Vectors PlanarO.Olsecond instantaneous Frontalplane O.Olsecond 0.02 second 0.03 second 0.04 second 0.05 second 0.06 second Horizontal plane O.Olsecond 0.02 second 0.03 second 0.04 second 0.05 second 0.06 second Left sagittalplane O.Olsecond 0.02 second 0.03 second 0.04 second 0.05 second 0.06 second SpatialO.O1second instantaneous O.Olsecond 0.02second 0.03 second 0.04 second 0.05second 0.06 second

VOLUME

29, MAY 1972

Magnitude (fiv) zt SEM

4 Month Old Infants Orientation d

A(")

101k

x2

8.2 0.3163 160 29Oxt16.0 0.3259 292 696zk33.3 0.8140 27 869zt37.0 0.7116 96 572+ 28.9 0.7126 161 174* 11.7 0.1816 359

20.1267 21.2400 132.5200 101.3000 101.5800 6.6000

1811 15.0 0.1800 173 785i 44.2 0.7986 90 1167+ 43.2 0.8590 59 831zt43.0 0.1650 336 807+ 30.4 0.8660 238 292zk20.8 0.6212 259

7.0400 127.5000 147.5600 5.5000 157.1200 124.2400

166zk15.9 0.1752 105 760). 43.5 0.8360 88 1152f 38.6 0.8663 110 1017+ 46.0 0.7115 17

6.1400 138.6400 150.1200

772~t 34.1 0.8263 103 259& 19.3 0.5271 271

195 f 17.2 859* 38.1 1160 f 39.3 1038 •!Z29.6 526 =k 30.4 153* 7.3

ioi. 1200 136.5600 55.5800

Azimuth Elevation 41 +5"+ 2.4 98 --6"+ 1.6 127 +24" f 1.6 239 24"~k 1.8 254 -3"f 1.9 328 f5"i 2.4

TABLE II (continued)

QRS

Vectors

Magnitude (,uv)fSEM

Orientation -d

AC')

Successive instantaneous (“normalized time") Frontal plane 1321t 10.1 0.2636 201 l/6 segment 2/6 segment 5041k 28.9 0.7271 3 864~t 39.3 0.7237 58 3/6 segment 416 segment 460f 24.3 0.7084 180 13Ok 6.9 0.7649 40 5/6 segment 55 i: 3.1 0.6036 28 6/6 segment Horizontal plane l/6 segment 218f 20.1 0.4492 120 1045iz37.8 0.9450 72 2/6 segment 716xt40.9 0.0099 33 3/6 segment 709zk31.5 0.9080 213 416 segment 158zk11.7 0.6831 147 5/6 segment 45zt 2.6 0.2457 289 6/6 segment Left sagittalplane 215+ 19.6 0.3195 107 l/6 segment 969& 33.3 0.8970 96 2/6 segment 902+ 42.0 0.7350 180 3/6 segment 587f 35.3 0.8450 270 416 segment 188f 18.8 0.3280 253 5/6 segment 51~t 5.3 0.5662 177 6/6 segment Maximal planar vectors 1092* 35.5 0.7035 70 Frontal plane 1359& 32.7 0.6142 54 Horizontal plane 12641t 34.2 0.6324 124 Left sagittalplane Mean planarvectors 23.01 0.68 0.6660 72 Frontalplane 31.5~k 0.76 0.6620 42 Horizontal plane 31.5 Z'C0.80 0.7911 142 Left sagittal plane

x2

13.9000 105.7200 104.7600 100.3600 117.0200 120.7200 40.3600 178.6000 164.4600 1.8200 12.0800 93.5200 20.4200 161.0000 108.0000 142.8800 21.5000 64.1200

99.0000 75.3600 80.0000 88.2200 79.3200 125.1800

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TABLE

TABLE III S-T, T Vectors and Ventricular Gradient System for Normal 4 Month Old Infants, and SEM) and Orientation

Vectors, Frank Lead Magnitude (Mean

IV

Spatial QRS, T and Ventricular

Gradient

Vectors

Spatial Vectors Magnrtude

bv)

Orientation

-

Orientation Magnitude Vectors Successive l/4 time-normalized l/4 segment T vectors Frontal plane l/4 segment Z/4 segment 3/4 segment 4/4 segment Horizontal plane l/4 segment 2/4 segment 3/4 segment 414 segment

(IN

~~ di

1811!~ 8.1 0.8883 122 f 9.8 0.8116 73+ 4.2 0.7323 53+ 3.4 0.5626 d,, 114 -II 7.7 0.5524 104rt 7.6 0.2657 52t 1.2 0.0800 33 % 2.7

0.5626

Left sagittal plane l/4 segment 2/4 segment 314 segment 414 segment Maximal planar T vectors Frontal plane Horizontal plane Left sagittal plane Mean planar T vectors Frontal plane Horizontal plane Left sagittal plane

32.4 t 1.6 18.6* 1.9 37.1_+ 1.5

Planar ventricular gradient Frontal plane Horizontal plane Left sagittal plane

32.7 + 1.5 0.9643 67.0+ 2.6 0.3466 56.0 k 2.7 .0.9700

d> 173k 8.4 0.8567 131 + 8.9 0.8052 711 4.6 0.7294 43 or 3.4 0.6721 d 272t 8.8 0.9810 209t 8.8 0.8554 192 it 7.9 0.9600 0.9526 0.7966 0.9454

A(“)

X2

1521 i

37.0

54”

spatial Leftward

1355 i

32.6

..

. .

.

...

vector maximal

spatial vector Spatial mean QRS 68 153.8314 76 127.7878 90 104.0422 102 61.4398 151 132 95 102

59.2088 13.6964 1.2416 51.1772

lC6

154.5210 98 125.7986 89 103.4214 57 130.3874

33 182.8256 48 143.3545 117 178.7904 62 184.8044 22 123.1124 102 173.1838 49 253

150.8832 22.3532 54 174.8400

was defined by an azimuth of 48” and an elevation of 39” -+ 0.72”. The mean magnitude of the mean spatial T vector was 32.5 + 1.4 pv seconds, and its spatial orientation was defined by an azimuth of 22” and an elevation of 40 i 0.65O. The mean QRS-T angle in the frontal plane was small (10’). In the horizontal plane it was extremely large (202”), and in the sagittal plane, it was 40”. Ventricular gradient : The planar ventricular gradient mean magnitudes, expressed in microvolt seconds, were 32.7 5 1.5, 67.0 f 2.6 and 56.0 i 2.7 in the frontal, horizontal and sagittal planes, respectively. Close clustering of vectors about A occurred in the frontal and sagittal planes, where A was estimated at a high level of confidence (>99.99 percent). In the horizontal plane the individual vectors were dispersed quite widely about A, but the latter was estimated at a confidence level exceeding 99 percent. The mean magnitude of the spatial ventricular gradient was 63.9 -t 2.1 pv seconds, and its mean direction was defined by an azimuth of 253” and an elevation from the horizontal of +13 t 1.9” (Table IV).

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Maximal QRS vector Rightward maximal

35.6 f

vector Spatial Spatial Spatial

1411 k 34.6

maximal T mean T ventricular

gradient

0.82 (pv set)

43” f

72” Azimuth

.

316 + 13.7 (WV) 32.51 1.4(rvsec)

...

63.9 + 2.1 (pv set)

0.037

19” I- 0.82 Elevation 39” i 0.72” 40” f 0.65” 13” Zt 1.9

253”

Mean P vectors: P waves were generally of low amplitude, as indicated by a mean magnitude, expressed in microvolts, of 61 i 4.0, 42 t 3.2 and 65 -t 4.3 in the frontal, horizontal and sagittal planes, respectively. The angles of prevalent direction were estimated at a level of confidence greater than 99 percent in the frontal and sagittal planes, respectively, and at a level approximating 99 percent in the horizontal plane. It is apparent that the leads did not approximate orthogonal performance in regard to P wave registration. The mean magnitude of the mean spatial P wave was 85 -+ 4.8 pv with a direction defined by an azimuth of 300” and an elevation from the horizontal of -27 -+ 2.4” (Table V). Discussion

One of the virtues claimed for corrected orthogonal electrocardiogrpahic lead recording is uniformity of performance. As a result of their design characteristics, such leads should minimize distortion and variation relating to differences in the location of the cardiac dipole source and those relating to extracardiac factors. Initially it was claimed that this uniformity was gained at no expense since all electrocardiographic information was contained in the 3 scalar X, Y and Z leads, but it was subsequently conceded that 3 lead recording TABLE

V

Mean P Vectors Orientation

Magnitude (NJ)

d

Frontal plane Horizontal plane Sagittal plane

61 i 4.0 42 % 3.2 65 + 4.3

0.6019 0.2447 0.6420

Spatial

85 It 4.8

P

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A(“) 90 120 156 Azimuth 300

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69.5616 11.7404 79.5353 Elevation -27 f 24”

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VECTORCARDIOGRAM

is accompanied by some loss in electrocardiographic information.8 The present study, in a group of normal 4 month old infants with the Frank lead system, and studies in adults” also bring into question the assumption that corrected orthogonal leads perform with greater uniformity than the leads of the standard 12 lead electrocardiogram. In the present study, variation in scalar magnitudes of the X, Y and Z lead deflections was of the same order as that observed in standard scalar electrocardiographic recordings. Individual variation in planar and spatial magnitudes was also large. The sources of this interindividual variation are difficult to identify. Obviously it may be real and, therefore, irreducible. In this instance, the fact must be accepted, albeit with resignation, that limitations are imposed by any remote recording of cardiac electrical events. One recent study” suggested that variations in the positions of the chest electrodes relative to the heart among individuals may be an important factor. Although the Frank lead system is more sensitive to variations in chest electrode placement than the axial system,l”*ll the interindividual variation in the latter system does not seem to be of lesser magnitude than in the former.“,lz In this study each chest electrode was placed meticulously in proper relation to the thoracic surface landmarks, the only clinically practical method by which electrode placement can be accomplished. It is also not unreasonable to assume that some of this variation may be related to the departure of the lead system from ideal design attributes due either to errors in design or to adjustments made for achieving clinical practicality. Each lead system in clinical use departs to a greater or lesser extent from the design attributes of orthogonality, orthonormality, insensitivity to shifts in dipole location and nonresponsiveness to non-dipolar generator content.‘:‘~‘~ Preliminary clinical data from this laboratory suggest that no correlation exists between the degree of variation and the extent of departure of a lead system from one or more of these ideal design attributes. If these corrected orthogonal lead systems do not perform with the desired degree of uniformity, they present electrocardiographic data in a display mode in which electromotive force is displayed as vectors along a time continuum. Although there may be considerable overlap in the direction of these vector orientations between normal and abnormal for any selected discrete time point, some may display close enough clustering to be of value in diagnostic discrimination. For example, for a given vector quantity, the magnitude may overlap with the normal, but it may be classed as abnormal on the basis of its spatial or planar orientation, or the converse may be true.

VOLUME

29, MAY 1972

OF 4 MONTH

OLD INFANT

In infants, 4 months of age, mean QRS vectors: and maximal ventricular activation forces are oriented to the left and inferiorly in the frontal plane but spatially these forces are directed to the right, posteriorly and inferiorly or to the right, anteriorly and inferiorly, respectively. These observations not only serve to emphasize that the mean and maximal vectors are different quantities but also emphasize the differences between planar and spatial vector quantities. The value of 1.521 mv for the magnitude of the maximal spatial QRS vector corresponds closely to the value of 1.63 mv reported by Hugenholtz and Liebman.15 Ventricular gradient : The QRS-T angle and ventricular gradient determinations presented in this study are the first to be reported for the Frank lead system for infants and children. The QRS-T angle was small in the frontal plane (lo”), large in the horizontal plane (202”) and of intermediate size (40”) in the left sagittal plane. The meaning and the underlying physiology of the ventricular gradient vectors are currently subjects for debate. Difficulties in the clinical determination of this vector have limited its exploration, and few studies have been published on the normal ventricular gradient in infants and children. Originally this vector was proposed by Wilson et al.‘” as a measure of the time course differential of ventricular depolariaztion and repolarization. Repolarization abnormalities were said to be “secondary” if preceded by an abnormal course of depolarization. Repolarization abnormalities, not preceded by an abnormal time sequence of depolarization, were classed as “primary” and presumably reflected disturbed myocardial cellular metabolism either due to primary myocardial disease or to altered physiologic homeostasis of the myocardial cell. Christian and ScherlT and Cosma et al.ls have presented evidence strongly suggesting that the ventricular gradient does not represent what it should in theory, and the former authors suggest that the relation of an abnormal ventricular gradient to myocardial disease or altered homeostasis may be only empirical and not causal. Empiricism per se does not invalidate the usefulness of a particular clinical observation, although alternative mechanisms must be sought to explain the relation. P wave deflections in the scalar Atria1 forces: X, Y and Z leads were small in amplitude and short in duration. As a rule the P wave in the vertical lead (Y) was of greatest magnitude and its sense positive. From the angle determinations made from these studies, it seems apparent that the function of the Frank lead system in regard to atria1 activation forces was neither orthogonal nor uniform. Acknowledgment

We gratefully acknowledge the technical assistance of Patrick J. Brignole and Bill R. Campbell.

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References Electrocardio1. Borun ER, Chapman JM, Massey FJ Jr: graphic data recorded with leads in subjects without cardaiac disease and those with left ventricular overload. Amer J Cardiol 18:656-663, 1966 of data recorded with orthogonal 2. Borun ER: Variability leads. Amer Heart J 76:62-69, 1968 study of the Frank vector3. Silverberg SM: A quantitative cardiogram. A comparison of younger and older normal population. Amer J Cardiol 18:672-681, 1966 D, et al: Correla4. Pipberger HV, Goldman MJ, Littman tions of the orthogonal electrocardiogram and vectorcardiogram with constitutional variables in 518 normal men. Circulation 35:536-551, 1967 studies in infants and 5. Ainger LE: Vectorcardiographic children. 1: Comparative ortho,gonal lead studies in the neonatal period. Amer J Cardiol 21:196-206, 1968 analysis of the vectorcar6. Ainger LE: Digital computer diogram of the newborn infant. Quantitative and comparative measurements of three orthogonal lead systems. Circulation 36:906-923, 1967 of the 7. Ainger LE, Dixon PR: The Frank vectorcardiogram newborn infant. Amer J Cardiol 29:686-689, 1972 of three lead cardiographic 8. Pipberger HV: Advantages recordings. Ann NY Acad Sci 126:873-881, 1965 E. Schmitt OH: Relationship be9. Kaneko K. Simonson tween the positi’on of chest electrodes (Frank’ and SVEC-III systems) and the anatomic position of the

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heart. Amer Heart J 74:58-65, 1967 10. Gamboa R, Gersony WM: Applicability of the Frank lead system to infants and children. Pediatrics 38:585-595, 1966 11. Gamboa R: Applicability of the axial lead system to infants and children. Amer J Cardiol 18:690-697, 1966 12. Ainger LE: Unpublished data 13. Brody DA, Arzbaecher RC: A comparative analysis of several- corrected vectorcardimographic leads. Circulation 29:533-545, 1964 RC: Intrinsic properties of un14. Brody DA, Arzbaecher corrected and highly corrected leads. Circulatio’n 34: 638-648, 1966 PG. Liebman J: The orthogonal vectorcar15. Hugenholtz diogram in 100 normal children (Frank system). With some comparative data recorded by the cube system. Circulation 26:891-901, 1962 16. Wilson FN, Macleod AG, Barker PS, et al: The determination and significance of the areas of ventricular deflections of the electrocardi’ogram. Amer Heart J 10:4661, 1934 17. Christian E, Scher AM: The effect ‘of ventricular depolarization on the sequence of ventricular repolarization. Amer Heart J 74:530-535, 1967 18. Cosma J, Levy B, Pipberger HV: The spatial ventricular gradient during alterations in the ventricular activation pathway. Amer Heart J 71:84-91, 1966

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