Computer interpretation of Frank vectorcardiogram in normal newborns: Identification of right ventricular dominance patterns

J. ELECTROCARDIOLOGY, 5 (4) 307-316, 1972

Original Communications Computer Interpretation of Frank Vectorcardiogram in Normal Newborns: Identification of Right Ventricular Dominance Patterns BY BARBARA GULLER, M.D., KAY L. M. BERG, WILLIAM H. WEIDMAN, M.D., PETER C. O'BRIEN, PH.D., JAMES W. DUSHANE, M.D., AND RALPH E. SMITH, M.D.

SUMMARY A m o n g 100 normal newborns, the right ventricular d o m i n a n c e pattern h a d a clockwise horizontal loop in 38, a figureof-8 in 40, and a counterclockwise direction in 22. Normal values of vector angles and magnitudes recorded with a computerized Frank vectoreardiographlc system differed for each type of right ventricular d o m i n a n c e pattern and s h o w e d less spread than usually is reported in the newborn. Thus, the vectorcardiographic criteria for right a n d left ventricular hypertrophy proposed in this study m a y allow recognition of congenital heart disease in the neonate, Normal values for the magnitude and direction of vectorcardiographic p a r a m e t e r s are widely distributed in newborn infants (less than 1 week old), as observed with scalar electrocardiograms 1, with orthogonal vectorcardiograms using the Frank ~, the McFee, or the Schmitt SVEC-III system ~, with the cube vectorcardiographic system 8, and with the surface mapping technique 4 of cardiac potentials. The wide range of normal values evident in different recording systems presumably reflects a variation of right ventricular dominance patterns among individuals of this age group. Because detection of abnormal vectorcardiographic parameters might be facilitated by identification of these patterns, we have identified three vectorcardiographic groups with the Frank system in the normal newborn. In each group the horizontal QRS loop differed by the type of right ventricular dominance pattern. Guidelines for the clinician for the recog-

Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55901. This investigation was supported in part by Research Grant HE-5515 from the National Institutes of Health, Public Health Service. Reprint requests to: Section of Publications, Mayo Clinic, Rochester, Mn. 55901

nition of these abnormalities are emphasized in the discussion. MATERIALS

AND

METHODS

A vectorcardiogram was obtained in 100 fullterm newborn infants (ages 12 to 106 hrs). Infants of mothers with an abnormal gestational history or with an abnormal delivery were excluded from the study.All infantshad birth weights greater than 2.5 kg and were healthy by clinicalexamination. The Mayo ClinicFrank vectorcardiographic lead systems was used for recording,with the chest and back electrodesplaced at the height of the fifthintercostalspace and the H electrode fixed on the neck below the right ear or on the forehead. All vectorcardiograms were obtained with the infants in the supine position.The electrodeswere disposablesilver mesh electrodes as described by Mason and Likare, but modified for use in infants.Each vectorcardiogram was obtained in the newborn nursery, with an acquisitiondevice previously described5, and transmitted via the Bell telephone network to a centrallylocated I B M 1800 data acquisitionand controlsystem w h e r e the digitized data were stored and analyzed on-line. The computer outputv'19 (the usual method of displaying vectorcardiograms at the Mayo Clinic) consisted of plotted Q R S and T loops in the frontal,sagittal,and horizontalplanes and a matrix of vectorcardiographic~parameters of a selectedcycle listingdirectionsofthe mean and maximal Q R S vectors,of selected mean 10-msec vectors in the horizontal and frontalplanes,and ofthe mean initial30-msec and terminal 40-msec R vector. Magnitudes of all these vectorswere given in both planes. The magnitude of the maximal Q R S vector in both planes was defined as the projection of the maximal spatialvector on these planes and not as the maximal planar vector of each plane. The m e a n Q R S magnitude in each plane was determined in each newborn from the m e a n of all vector magnitudes of this plane. Reference frames for the directions

307

308

GULLER

ET AL

Frontol plone

Horizontol plone

Superior

Posterior

+9o

+180

Right + 18o

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Fig. 1. Reference frames in frontal and horizontal planes for vector directions.

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Fig. 2. Typical Frank vectorcardiograms in frontal and horizontal planes in normal newborn. Left, Group 1 (clockwise horizontal loops). Center, Group 2 (figure-of-8 horizontal loops). Right, Group 3 (counterclockwise horizontal loops). were those of the Mayo Clinic vectorcardiographic system and are shown in Fig. 1. In previous descriptions of the Frank vectorcardiogram in the newborn, tracings were not recorded simultaneously in the three planes. 2,s,9 The use of simultaneous recording in this study has minimized errors due to respiratory variations and time-dependent difo

ferences in proximity effect along the X Z axes, resulting from the large heart and thin chest wall of the newborn 1~ The horizontal plane was found to be best suited for differentiation of the right ventricular dominance patterns which were grouped (Fig. 2) as follows: group 1, clockwise r o t a t i o n of h o r i z o n t a l QRS loop; group 2, J. ELECTROCARDIOLOGY, VOL. 5, NO. 4, 1972

VECTORCARDIOGRAM IN NORMAL NEWBORNS

figure-of-8 r o t a t i o n of h o r i z o n t a l QRS 10op; group 3, counterclockwise rotation of t h e horizontal QRS loop. Vectorcardiographic v a r i a b l e s characterizing the t h r e e groups w e r e analyzed statistically. A c o n v e n t i o n a l chi-square test was used to d e t e r m i n e those v a r i a b l e s for which the dist r i b u t i o n of d i r e c t i o n s differed s i g n i f i c a n t l y (P<0.05) according to t h e inscription of rotation. For each variable, a n e s t i m a t e of t h e preva l e n t direction of the vectors, a 95% confidence i n t e r v a l , and a n e s t i m a t e of precision were obtained. T h e confidence i n t e r v a l s for t h e p r e v a l e n t d i r e c t i o n w e r e o b t a i n e d by methods discussed by W a t s o n and W i l l i a m s 11. The m e a s u r e of precision, proposed by Downs a n d L i e b m a n 12, indicated t h e e x t e n t to which

309

i n d i v i d u a l o b s e r v a t i o n s differed from t h e preva l e n t direction, a precision of 1 m e a n i n g no d e v i a t i o n from t h e p r e v a l e n t direction, a n d a precision of 0 m e a n i n g u n i f o r m s c a t t e r i n g on a u n i t circle. ( E q u i v a l e n t l y , 0 precision would indicate t h e n o n e x i s t e n c e of a p r e v a l e n t direction; t h e hypothesis of 0 precision was t e s t e d and rejected in all cases.) R a n g e s of n o r m a l i t y for i n d i v i d u a l a n g l e s also were computed by u s i n g n o n p a r a m e t r i c methods. Differences i n m a g n i t u d e s a m o n g the t h r e e r o t a t i o n a l groups w e r e t e s t e d for each v a r i a b l e a t t h e P = 0.05 l e v e l by u s i n g s t a n d a r d m e t h o d s of a n a l y s i s of variance. M e a n s a n d s t a n d a r d d e v i a t i o n s of the m a g n i t u d e s w e r e c a l c u l a t e d . In a d d i t i o n , r a n g e s of n o r m a l i t y were d e t e r m i n e d by s u i t a b l e t r a n s f o r m a t i o n s

Table 1. - - Prevalent Direction of Vectors Horizontal

Frontal planet Parameter

Group*

MaximalQRS vector

1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3

Maximal T Vector Initial 30-msec vector MeanQRS vector Terminal 40-msec vector 1st 10-msec vector 2nd 10-msec vector 3rd 10-msec vector 3rd last 10-msec vector 2nd last 10-msec vector Last 10-msec vector

Estimate* ] Error (_+)! Precision Estimate* 235 273 267 310 327 342 346 2 333 209} 242w 271w 210} 240} 267w 76 75 62 47 59 70 317w 347w 310} 253 292 287 187w 221w 240} 172 191 183

28 26 24 23 22 32 22 19 20 18 17 12 16 16 11 26 33 31 14 19 16 22 22 14 25 24 17 19 16 21 31 26 48

:0.423 0.447 0.633 0.534 0.529 0.536 0.535 0.585 0.712 0.624 0.656 0.875 0.687 0.680 0.900 0.447 0.334 0.513 0.736 0.593 0.791 0.538 0.534 0.840 0.470 0.479 0.771 0.612 0.676 0.695 0.376 0.448 0.316

311w 354w 155w 118 105 90 15 13 20 315w 328~ 156} 277w 303w 182w 14 6 11 18~ 7w 5~ 13w 16} 43~ 336} 2w 102w 236} 233w 191w 193 199 191

Error(_+ ) Precision 35 42 45 32 28 30 9 3 7 15 18 62 18 27 27 18 22 17 10 5 5 11 6 16 21 24 51 16 24 20 16 13 20

0.314 0.237 0.341 0.371 0.417 0.581 0.867 0.983 0.953 0.713 0.621 0.226 0.629 0.427 0.587 0.622 0.533 0.786 0.844 0.959 0.978 ~}.823 0.936 0.794 0.553 0.482 0.292 0.688 0.485 0.708 0.688 0.757 0.549

*Group 1 = clockwise (cw) horizontal loops; group 2 = figure-of-8 (F8) horizontal loops; group 3 = counterclockwise (ccw) horizontal loops. Numbers of cases in all parameters except maximal T vector: group 1, 38; group 2, 40; group 3, 22. For maximal T vector: group 1, 35; group 2, 38; group 3, 19. ~Loop rotation clockwise in all cases. *Estimated prevalent direction, which, -+ the error, gives a 95% confidence interval for the true prevalent direction. w of angle dependent on rotational group. J. ELECTROCARDIOLOGY, VOL. 5, NO. 4, 1972

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G U L L E R ET A L

of the observed magnitudes to permit the use of p a r a m e t r i c m e t h o d s b a s e d on n o r m a l theory. The results of the statistical analysis outlined above should facilitate the use of these vectorcardiographic parameters in a~omputer for screening of Frank vectorcardiograms in the newborn. RESULTS The QRS lo0p rotation in the frontal plane was clockwise in all 100 newborns. In the horizontal plane it was clockwise in 38 (group 1), figure-of-8 in 40 (group 2), and counterclockwise in 22 (group 3). Although the prevalent directions for all vectors were different depending on the QRS loop rotation in the horizontal plane, this difference was not always statistically significant (Table 1). The degree of clustering around the prevalent direction (as measured by the precision) was high for some parameters, approaching u n i t y in some cases, while for o t h e r parameters it was low. The degree of clustering is shown graphically in Fig. 3, in which the rotational groups have been pooled to

Horizontal

obtain an average level of precision for each parameter. The normal values (Table 2) were determined in such a way that one may expect about 95% of normal subjects to have values within the range of normality. However, it should be emphasized that, because of the small sample sizes, the range of normality could only be estimated approximately. For those parameters in which there were no significant differences among the prevalent direction of the vectors of the three groups, one set of normal values is presented based on the pooled group of 100 newborns. P a r a m e t e r s for which the distribution of m a g n i t u d e s (Table 3) differed according to rotational group in the horizontal plane were: frontal p l a n e - - t e r m i n a l 40-msec vector and second last and last 10-msec R vectors; horizontal plane--mean QRS vector and third 10-msec R vector. Although convention in determining normal ranges for vectorcardiographic magnitudes seems to dictate taking the mean plus or minus two standard deviations, this practice is questionable, at least for present purposes. It is evident from Table 3 that the distribution of the magnitudes is not gaussian: there is

Frontal

plane

Terminal 40 msec Mean QRS 2 nd IO msec 2 nd Last IO msec

Initial 30 msec 2 nd I0 m s e c 3 rd I0 m s e c

Last IO msec Ist IO msec 2 nd Lost IO msec Terminal 40msec Mean Q R S Maximal T 3 rd Lost IO msec Maximal QRS I

1.0

I

plane

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I n i t i a l 30 msec 3 rd Last IO msec Maximal T Maximal ORS I st I 0 m s e c

Lost IO msec

l

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0

Fig. 3. Precision of selected vectorcardiographic prevalent directions in n o r m a l newborns. Length of bars indicates amount of precision (actual values are in Table 1; 1.0 = perfect precision). P a r a m e t e r s at top of list h a v e highest precision. P a r a m e t e r s w i t h h a t c h e d boxes are those for which t h e p r e v a l e n t direction is d e p e n d e n t on rotational group. J. ELECTROCARDIOLOGY,VOL. 5, NO. 4, 1972

VECTORCARDIOGRAM IN NORMAL NEWBORNS

311

Table 2. - - Normal Values of Vector Directions* Horizontal plane

Frontal plane Parameter

Group

Right

Mean

Left

Right

Mean

Left

Maximal QRS vector

1 2 3 1, 2, &3

166 166 166

259 259 259

62 62 62

161 198 8

311 354 155

107 52 224

229

323

124

322

105

253

219 78 108 195 106 66 207

349 209 242 271 210 240 267

85 295 37 320 307 29 315

346 169 169 355 160 164 21

15 315 328 150 277 303 182

63 27 81 307 14 58 355

270 319 319 319 219 190 273 96 129 221 12 18 157

72 57 57 57 317 347 310 253 292 287 187 191 240

234 169 169 169 100 93 111 67 78 76 346 8 82

204 295 330 338 239 274 357 169 187 3 93 76 32

10 18 7 5 13 15 43 336 2 102 235 233 191

169 186 47 31 174 76 170 36 48 215 6 43 223

8

182

359

49

196

259

Maximal T vector Initial 30-msec vector Mean QRS vector Terminal 40 -msec vector 1st 10-msec vector 2nd 10-msec vector 3rd 10-msec vector 3rd last 10-msec vector 2nd last 10-msec vector Last 10-msec vector

1, 2, &3 1 2 3 1 2 3 1, 2, &3 1 2 3 1 2 3 1 2 3 1 2 3 1, 2, &3

*Groups, rotations, and numbers of cases as in Table I. The transit from right to leftover the mean is made in a counterclockwise direction. s k e w i n g of t h e data, with m e a n s n e a r e r t h e m i n i m u m t h a n t h e m a x i m u m . Vector magn i t u d e s were, therefore, t r a n s f o r m e d as outlined in t h e M a t e r i a l s a n d Methods section, a n d t h e n o r m a l v a l u e s (Table 4) should be used for u p p e r a n d lower limits. S u g g e s t e d vectorcardiographic c r i t e r i a for t h e d i a g n o s i s of r i g h t a n d l e f t v e n t r i c u l a r h y p e r t r o p h y from a c o m p u t e r p r o g r a m a r e shown i n T a b l e 5. T h e y are b a s e d on t h e type of loop rotation i n t h e horizontal a n d frontal planes. Fig. 4 shows some of the typical vectorcardiographic f e a t u r e s a c c o m p a n y i n g clockwise, figure-of-8, a n d c o u n t e r c l o c k w i s e h o r i z o n t a l loops i n the n o r m a l n e o n a t e . I n the n e w b o r n s with a clockwise horizontal loop (group 1), the m a x i m a l axis of the frontal loop was directed to t h e right a n d inferiorly, a n d the vertical c o m p o n e n t of t h e loops was more p r o m i n e n t J. ELECTROCARDIOLOGY, VOL. 5, NO. 4, 1972

than the horizontal component in most instances. I n i t i a l forces were to t h e left a n d u p w a r d , a n d t e r m i n a l forces w e r e d i r e c t e d inferiorly and to t h e right. I n t h e horizontal p l a n e , t h e loop occupied p r e d o m i n a n t l y t h e r i g h t a n t e r i o r q u a d r a n t b u t had large t e r m i n a l forces to t h e r i g h t a n d p o s t e r i o r l y . W i t h a figure-of-8 horizontal loop (group 2), t h e frontal p l a n e loops w e r e s i m i l a r to those associated w i t h a clockwise horizontal loop. I n t h e horizontal p l a n e t h e r e was a n i n i t i a l counterclockw i s e loop i n a l l i n s t a n c e s , p r e d o m i n a n t l y

situated in the left anterior quadrant. Terminal horizontal forces formed a posterior clockwise loop swinging over to the right. With a counterclockwise horizontal loop (group 3), the frontal loop resembled those in the other two groups. The horizontal loop pointed to the left a n d posteriorly and its terminal forces were rightward and large.

312

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Table 5. - - Suggested Vectorcardiographic Criteria for Diagnosis of Ventricular Hypertrophy in Newborns Right ventricular hypertrophy

Left ventricular hypertrophy Maximal QRS vector >1.7 mv in the horizontal plane if directed between 0~ and 180 ~ and if loop rotation is counterclockwise or figure-of-8

Clockwise horizontal plane loop with: Maximal QRS vector >1.7 mv in horizontal plane

Counterclockwise horizontal QRS loop with initial horizontal 30-msec vector >0.6 mv and directed between 0r and 45~

or

Angle of initial horizontal 30-msec vector between 60~ and 180~ or

Last or second last 10-msec vector in right anterior quadrant

Figure-of-8 horizontal loop with maximal horizontal QRS vector directed between 40 ~ and 200 ~

F igure-of-8 horizontal loop with: Magnitude of anterior projection of initial 30-msec horizontal vector >0.6 mv

Maximal QRS vector >1.1 mv in frontal plane if directed between 270 r and 360 ~ in frontal plane Counterclockwise frontal QRS loop*

*In newborns, counterclockwise frontal QRS loops occur more frequently with anomalies of conduction system (endocardial cushion defects, tricuspid atresia) than with left ventricular hypertrophy alone.

+ 8O

+ 180

+270 ~

+90

; "'"

+90

+270

~A

/

0

0 + 8O 1

+270

-k90

Fig. 4. Prevalent directions and mean magnitudes of selected horizontal vectors in normal newborn with clockwise horizontal loops, figure-of-8 horizontal loops, or counterclockwise horizontal loops. A = second 10-msec vector; B = third 10-msec vector; C = m a x i m a l p l a n a r QRS vector; D = second last 10-msec vector; E = last 10-msec vector. A through E are in the horizontal plane. Upper Left, Group 1. Upper Right, Group 2. Lower Left, Group 3.

0 J. ELECTROCARDIOLOGY, VOL. 5, NO. 4, 1972

VECTORCARDIOGRAM IN NORMAL NEWBORNS

315

maximal QRS vectors in the horizontal plane were usually directed anteriorly and to the right, and there was an increased magnitude The percentage of full-term newborns with of late forces to the right and posteriorly. This a counterclockwise horizontal loop was higher is an unusual feature of clockwise horizontal than reported previously. N a m i n et al e found loops due to right ventricular pressure overthat 19% of 57 newborns (birth to 30 hrs old) load and helps to differentiate the right venhad counterclockwise horizontal plane loops tricular dominance pattern in the normal newrecorded with the Frank system, but Ainger born from right ventricular hypertrophy due and Campbell 2 did not observe it in 33 neonates (up to 72 hrs old). Within the brief obser- to congential heart disease. In infants with transposition of the great arteries, a type of vation period of this study the p r e s e n c e or absence of a counterclockwise horizontal loop congential heart disease in which right ventricular hypertrophy is always present, there was not age-dependent. In healthy p r e m a t u r e is a clockwise horizontal loop if the left vennewborns, counterclockwise horizontal QRS tricular pressure is not severely increased, 16 loops may even develop a clockwise orientaT h e s e clockwise loops differ from t h e one tion with repeated frequent observations. 13 observed in the normal newborn by exhibiting The rapidity of changes in vectorcardiomore leftward direction of initial forces and graphic patterns renders unlikely that they less magnitude of right posterior forces, which result from a relative change in muscle mass places nearly the entire loop in the r i g h t of the right and left ventricles. It seems likely a n t e r i o r quadrant. The vectorcardiographic that the different vectorcardiographic patfeatures in infants with hypoplastic left heart t e r n s of right v e n t r i c u l a r dominance result syndrome, another important type of congenifrom v a r i a t i o n s of physiologic p a r a m e t e r s tal cardiac defect in the newborn, associated which include relative or absolute decreases in with right ventricular hypertrophy, have not right ventricular pressure and cavity volume been published, but preliminary observations and increases in left ventricular pressure and at this institution suggest that the characteriscavity volume, but the contribution of each tics of the horizontal plane F r a n k vectorcarp a r a m e t e r has not been ascertained in this diogram in hypoplastic left heart syndrome are study. None of the newborns in the study had similar to those in transposition of the great anemia; anemia can result in increased left arteries in which left ventricular pressure is ventricular stroke volume and end-diastolic volume. 14,15 not increased. In 40 of 100 newborns, there was a right In this study a m o n g newborns, w i t h t h e same type of horizontal right ventricular domi- ventricular dominance pattern with an elonnance p a t t e r n t h e r e was less spread of vector- gated figure-of-8 loop in the horizontal plane. The initial portion of these loops was countercardiographic p a r a m e t e r s characterizing the clockwise and s i t u a t e d in t h e left a n t e r i o r QRS loop t h a n has been reported in newborns quadrant; the terminal portion, located in the of the same age but not divided into groups. This is especially true for the wide scatter of right posterior quadrant, was oriented clockwise. Figure-of-8 horizontal QRS loops with i n i t i a l and m a x i m a l v e c t o r s r e p o r t e d by an initial c o u n t e r c l o c k w i s e and t e r m i n a l N a m i n et aL e Fig. 3 shows that, in the normal clockwise rotation constitute a pattern of right newborn, the initial forces in the horizontal ventricular conduction delay frequently seen plane and the terminal forces in the frontal in older infants (3 wks to 12 mos). While in plane have the highest precision; the direction this older age group most of the horizontal of the maximal planar QRS vector in either plane is not well suited for differentiation of figure-of-8 is positioned to the left of the midline, the right v e n t r i c u l a r conduction delay normal from abnormal with the Frank vectorpattern observed in the normal newborn in cardiogram. Prevalent vector directions and this study was characterized by large terminal ranges may be used for computer screening r i g h t w a r d and p o s t e r i o r forces. Thus, t h e of Frank vectorcardiograms of the newborn. figure-of-8 loop in the normal newborn resemThe group 1 right v e n t r i c u l a r dominance bles that reported in atrial septal defect of pattern of this study, seen in 38 of 100 normal newborns, is characterized by a clockwise hori- the secundum type with pulmonary hypertension (pulmonary artery systolic pressure more zontal vector loop with a prominent longitudinal axis extending from the right anterior to than 40 m m Hg) in which the ratio of maximal r i g h t w a r d to l e f t w a r d forces a p p r o a c h e s or the right posterior quadrant. The mean and DISCUSSION

d. ELECTROCARDIOLOGY, VOL. 5, NO. 4, 1972

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graphic potential distributions in newborn infants e x c e e d s 1.0.17 T h e i n i t i a l c o u n t e r c l o c k w i s e from 12 hours to 8 days after birth. Am. Heart r o t a t i o n of h o r i z o n t a l figure-of-8 loops in t h e J. 78: 292, 1969. n o r m a l n e w b o r n a l l o w s o n e to d i f f e r e n t i a t e 5. Smith, R. E., and Hyde, C. M.: A computer system t h i s figure-of-8 p a t t e r n from t h e one d e s c r i b e d for electrocardiographic analysis. Third Annual in t r a n s p o s i t i o n o f t h e g r e a t a r t e r i e s , w i t h Rocky Mountain Bioengineering Symposium, University of Colorado, Boulder, May 2-3, 1966. i n c r e a s e d left v e n t r i c u l a r p r e s s u r e , in w h i c h 6. Mason, R. E., and Likar, I.: A new system of t h e i n i t i a l r o t a t i o n r e m a i n s clockwise, le multip[e-lead exercise electrocardiography. Am. T w e n t y - t w o o f 100 n o r m a l n e w b o r n s h a d a Heart J. 71: 196, 1966. right ventricular dominance pattern with a 7. Smith, R. E., and Hyde, C. M.: Computer analysis c o u n t e r c l o c k w i s e horizontal QRS loop, m o s t of of the electrocardiogram in clinical practice. In t h e forces b e i n g d i r e c t e d to t h e left o f t h e midElectrical Activity of the Heart. G. W. Manning line. T h e o v a l - s h a p e d loops e x t e n d e d p r e d o m i and S. P. Ah~a, eds., Charles C. Thomas, Co., Springfield, Ill., 1969, pp. 305-315. n a n t l y in an a n t e r o p o s t e r i o r d i r e c t i o n a n d h a d 8. Namin, E. P., Arcilla, R. A., D'Cruz, I. A., and m e a n a n d m a x i m a l QRS vectors in t h e left Gasual, B. M.: Evolution of the Frank vectorcarposterior quadrant. These counterclockwise diogram in normal infants. Am. J. Cardiol. 13: h o r i z o n t a l QRS loops in t h e n o r m a l n e w b o r n 757, 1964. resembled the counterclockwise horizontal 9. Rosen, I. L., and Gardberg, M.: The electrocarp a t t e r n s e e n in p a t i e n t s w i t h l e f t - t o - r i g h t diogram and vectorcardiogram of the normal infant. Dis. Chest 32: 493, 1957. shunts, s y s t e m i c p r e s s u r e in t h e r i g h t v e n t r i c l e , a n d p u l m o n a r y - t o - s y s t e m i c b l o o d flow 10. Gamboa, R., and Gersony, W.M.: The applicability of the Frank lead system to infants and chilr a t i o s g r e a t e r t h a n 2.0 b e c a u s e i n i t i a l s e p t a l dren. Pediatrics 38: 585, 1966. forces w e r e l a r g e (the second 10-msec v e c t o r 11. Watson, G. S., and Williams, E. J.: On the conwas larger than that of newborns without struction of significance tests on the circle and c o u n t e r c l o c k w i s e loops). T h i s f e a t u r e is indicathe sphere. Biometrika 43: 344, 1956. t i v e of left ventricular volume overloading. Is 12. Downs, T. D., and Liebman, J.: S t a t i s t i c a l methods for vectorcardiographic directions. Unlike in the normal newborn, however, counIEEE Trans. Biomedic. Eng. 16: 87, 1969. terclockwise horizontal loops with large septal 13. Liebman, J., Romberg, H. C., Downs, T., and forces in patients with left-to-rightshunts are Agusti, R.: The Frank QRS vectorcardiogram in almost invariably accompanied by anterior T the premature infant. In Vectorcardiography. I. loops. Newborns with malformations of the Hoffman and R. C. Taymor, eds. J. B. Lippincott right ventricle m a y show counterclockwise Co., Philadelphia, 1966,. pp. 256-271. horizontal Q R S configurations. While the vec- 14. Yano, K., and Pipberger, H. V.: Correlations torcardiogram in patients with tricuspid between radiologic heart size and orthogonal electrocardiograms in patients with left venatresia is recognized by the absence of signifitricular overload. Am. Heart J. 67: 44, 1964. cant anterior forces and large leftward forces, the counterclockwise horizontal Q R S loop in 15. Rosenthal, A., Restieaux, N. J., and Feig, S. A.: Influence of acute variations in hematocrit on patients with pulmonary atresia with intact the QRS complex of the Frank electrocardioventricular septum and a small right vengram. Circulation 44: 456, 1971. tricular cavity m a y be identical to that of the 16. Mair, D. D., Macartney, F. J., Weidman, W. H., normal newborn. Large P and anteriorly Ritter, D. G., Ongley, P. 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