A quantitative study of the Frank vectorcardiogram

A Ouantitative

Studv of the Frank

Vectorcardiogram A Comparison

of Younger

and Older Normal Populations*

STANLEY M. SILVERBERG, LVashington,

T

AND

METHODS

Two hundred and twenty-eight young subjects were selected from the house staff and student nurses of the Washington Hospital Center. All had had standard chest roentgenograms and physical examinations and were presumed free of cardiovascular disease. These were labeled group A. A group of 50 adults over 40 years old was selected from the house staff, office *From the Department of Medicine, was supported in part by Grant H-06542 from the Washington Heart Association.

F.A.C.C.

D. C.

These were personnel and patient population. Patients in this group were inlabeled group B. dividually examined by the author and found free of cardiac, pulmonary, central nervous system, metabolic and deficiency diseases known to alter the electrical forces of the heart. Table I describes both series by age and sex. The presence of a majority of female subjects in group A is significantly different from most studies of this type. Comparison of these results with those from young male groups may be useful. The Frank lead system was used, with the patient in a supine position and the electrodes placed at the level of the junction of the fourth intercostal space with the sternum. Recordings were made with a multichannel recorder (Electronics for Medicine, oscilloscopic DR-8) modified to utilize a panoramic resolver. Frontal, horizontal, left sagittal and “open resolved” views were photographed. The comet-shaped markers were interrupted every 0.0025 second, with their The resolved open loop was leading edges sharp. found by the method of Milnor et al.lnJ1 with a The resultant open QRS Schmitt type resolver.‘2 loop was adjusted so that it always rotated in a clockwise direction, in accordance with Milnor’s practice.” Simultaneous X, Y and Z scalar tracings were taken at 100 mm/set. paper speed for use in verifying the direction of the initial movement of the loop. The initial or E point of the loop was amplified to facilitate counting the time markers to obtain instantaneous vector directions. This procedure also served to provide a magnified T loop for analysis. Figure 1 shows the detail available with amplified T loops. Only the QRS and T loop analyses are presented. The P loops will be the subject of a future study. The following measurements were recorded : QRS loop rotation, QRS loop area, maximal QRS vector direction and magnitude, maximal T vector direction and magnitude, half-area QRS vector direction and magnitude, instantaneous vector direction for the

purpose of this study was to collect data on a large group of young people presumably free of heart disease to serve as a basis of comparison for future studies of myocardial disease. Because of the known changes in the heart with aging, a smaller series of adults over 40 years old was studied. These two groups were compared for differences and similarities. Extensive quantitative measurements were underA recent taken to provide objective criteria. computer study of large population samples by Draper et al.’ has greatly added to the data available from previous studiesz-6 However, there is still a paucity of information on the effect of aging on the Frank vectorcardiogram. It is hoped that this study will shed some light on this problem. Additional information regarding the normal spatial repolarization process should enhance the value of the vectorcardiogram in detecting early myocardial abnormalities. Customarily only magnitude and direction of the maximal T vectors have been studied. Lately, increasing attention has been drawn to changes in the rate and direction of inscription and configuration of In this the T loops associated with disease.7-g study, extensive T loop analysis was made in order to establish more comprehensive normal values for most T loop measurements. HE

MATERIAL

M.D.,

The Washington Hospital Center, Washington, D. C. This investigation from the National Heart Institute, U. S. Public Health Service, and grants

672

THE

AMERICAN

JOURNAL

OF CARDIOLOGY

Quantitati\re

Arc

.md Sex* of Subjects

<;roup .\ ( 1s30 1(1-l’) 2(l-29 30-39 hlean: 24.4 Total

Study

of Frank

Vectorcardiogram

in the Two Normal Groups

y”. 1 1 47 47

68 59 6

69 106 53

95

133

228

16 4 3 1 0

31 12 5 1 1

24

50

(;roup l3 140-86 yr.‘) 40- 49 15 so--50 8 ho---69 2 TO-79 0 80.-89 1 Mran: 52 Total 26 * Note the heavy preponderance the younger age group.

‘\.

\

CPWPRIFIJGAL LIRPk’~,

of female subjects in

-

0.

FIG. 2. Frontal plane vector directions. Each arc represents the mean value and two standard deviations on either side. The younger group, under 40 years of age, is depicted with solid or heavy lines. The thin lines or open boxes depict the older group. Note the wide distribution of instantaneous 0.01 and 0.02 second vectors resulting from the anterior direction of the initial limb of the QRS loop. Very slight variations in lateral or vertical direction will project these vectors in any quadrant. VOLUME

18,

NOVEMBER

1966

*.

‘\

‘\

Silverberg

674

GROUP A

w

GROUP

-OR-

8

OR

I

/

0.

I

FIG. 3. Horizontal #lane vector directions. Each arc represents the mean value and two standard deviations on either side, Here, as in Figures 1, 4 and 5, the overlap between the two groups is so marked that no practical separation is available except at some of the extremes of the distribution. first four 0.01 second vectors, T loop rotation, T loop length-to-width ratio, maximal QRS-maximal T vector angle, half-area QRS-maximal T vector angle and polar vector position. 13 The polar vector represents an axis perpendicular to the broadside projection, or plane, of the resolved spatial loop; its direction is defined by elevation and azimuth measurements.r4 The reference system used was that proposed by Helm.15 Areas of the loops were determined planimetrically. The loop areas of different patients were compared by using a standard 1 millivolt square unit. This was done by dividing the area of the QRS loop in each projection by the area of a square, the length of whose side represented a 1 millivolt deflection. Half-area QRS vectors were determined by the method of Pipberger.16 With little practice this vector can be estimated to within 5’ of the measured position, The ratio of length to width was determined by dividing the maximal T loop vector by the maximal width of the loop. Data lvere plotted to ascertain distribution. This was found to be symmetric in all but a few instances.

Therefore, ranges comprising 3~2 standard deviations were considered adequate. Variance was used as a test of population differences. The statistical significance of the F number, which is the ratio of variance, is determined by standard tables.” This ratio was evaluated for significance at both a one and five per cent level. RESULTS The normal maximal and half-area QRS, maximal T loop and instantaneous vectors and their ranges for both older and younger groups are shown graphically in Figures 2-5. Figures 6-9 compare the magnitudes of the maximal QRS and T vectors, half-area QRS vectors and QRS loop areas of the two groups. Quantitative data are shown in Tables II and III. Maximal QRS Vector and Half-area QRS Vector: The group differences in the directions of maximal QRS vectors are significant at the 1 per cent level, primarily because of the large variTHE

AMERICAN

JOURNAL

OF CARDIOLOGY

Quantitative

Study

of Frank

675

Vectorcardiogram

270’

GROUP

A

GROUP n

,*o.

--

-OR-

OR

0

-

__

0.

AREA

oq* FIG. 4. Left sagittal plane vectors directions. Each arc represents the mean value and two standard deviations on either side. Here again, it is only at the extremes of these distributions where any separation between group A and B can be effected. The superior extension of group B instantaneous 0.03 second vectors beyond 180” is a statistical misrepresentation The actual limit of distribution, which is below 180”, is due to asymmetric distribution. exceeded by the computed range.

ante of group A. This difference is reflected in the open and sagittal views but not in the horizontal. Responsibility for this lies in the frequent occurrence of a large, superiorly oriented terminal limb of the QRS loop, which has no projection in the horizontal plane. The maximal vector magnitudes are significantly different only in the open loop. Here the range of group In all but the A far exceeds that of group B. frontal plane, where the range of the group B maximal vectors is exceedingly narrow, the range of the half-area QRS vector direction is less than that of the maximal QRS vector. There is no significant difference in the range of these half-area directions except in the frontal plane, where a slight counterclockwise shift That this represents a leftoccurs in group B. ward and upward shift of the QRS loop is confirmed by the corresponding shift in the measurement of resolved loop elevation. VOLUME

18.

NOVEMBER

1966

QRS Loop: Consistency of QRS rotation in sagittal, horizontal and open planes, as docucontrasts with extreme mented previously, variance in the frontal plane. Since the frontal loop is viewed nearly edge-on, slight shifts in position will cause a change in the apparent rotation. QRS loop areas differ significantly in the frontal plane only through a large group A In genvariance, their means being identical. eral, the areas are larger in group A, but in the horizontal plane the leftward and upward shift of the group B loops increases their projected area. Instantaneous Vectors: The previously observed anterior direction of the 0.01 and 0.02 second vectors, as well as the inferior direction of the 0.03 second vector, are confirmed by this The shift of the QRS loop in the frontal study. plane in the older group (B) is accompanied by a

Silverberg

076

270.

GROUPA

I

GROUP

-ORB

-OR-

FIG. 5. Directions of resolved “opened” plane (broadsideprojection) vectors. Each arc represents the mean value and two standard deviations on either side.

similar shift in the mean values for the 0.03 and 0.04 second vectors. Otherwise, the instantaneous vectors in both groups are similar. T Looj: In all planes the T loops tend to be elongated. The mean of the length-to-width

ratio could not be statistically evaluated, due to the numerous extremely high values in the most linear loops. Minimal values in group A approximate a 2: 1 ratio. Group 6 values are similar 0111~ in the open and frontal planes.

TABLE II QRS and T Loop Measurements Frontnl Group

hfaximal QRS magnitude Maximal QRS direction QRS loop area magnitude I,,2 area vector dir&ion Instantaneous 0.01 sec. l”sta”taneous 0.02 sec. lnstantnneous 0.03 sec. I”sra”ta”eous 0.04 .sec. hlaximal T magnitude hlaximal T dir&ion Maximal ORS-T an& ‘1%area QRS-T angle QRS loop rotation

1 1areavector

T loop rot.+rinn

A

1.34 i 0.30 (228) 35.69 f 27.6 (228) 0.31 (0.0-0.8) (176) 1.30 f 0.28 (164) 54.05 f 14.23 (141) 208 f 81.6 (228) 111 f 114.3 (228) 39.58 * 12.4 (228) 45.39 f 15.3 (228) 0.38 f 0.14 (224) 42.12 i 9.73 (228) 9.99 (O-40) (224) 12.75 (O-60) (140) 129 cw., 27 ECW., 68 fig. of 8 (224) 145 cw., 31 ccw., 5 fig. of 8, 35 lin. (216) Minimum = 3

Plane

(Frontal,

~-~ Group B

1.31 i 0.33 (50) 36.5 f 14.2 (50) 0.31 (0.0-0.7) 1.12 f 0.30 (42) 39.7 i 19.6 196 zt 85.5 (50) 118.8 f 114.0 (50) 29.2 i 13.4 (50) 38.4 f 17.3 (50) 0.29 zt 0.12 (50) 43.8 zt 14.3 (50) 13 3 (O-40) (49) 17.6 (O-60j (42j 34 cw., 6 ccw., 8 fig. of 8 (48) 24 cw., 10 ccw., 16 fig. of 8 (50) Minimum = 3

Horizontal

and Sagittal Planes) -

F

: .t

: t

~- ---Horij Group A

1.28 f 0.26 (228) 332.6 + 39.7 (228) 0.52 f 0.24 (194) 0.98 & 0.20 (164) 338.6 f 20.3 (193) 102.56 zt 27.1 (2281 69.0 f 29.8 (228) 17.0 zk 20.5 (228) 339.9 + 21.2 (228) 0.32 f 0.12 (224) 24.88 +z 16.17 (2’281 47 65 f- 10 9 (224) 49.2 f 25.2 (191) 222 ccw., 6 fig. of 8 1228 8 cw., 200 ccw., 2 fig. of 8, 14 lin. (224) Minimum = 1 ,9

1

1 .oo * 0.26 339.6 zt 36.4 (50) 0.64 zt 0.33 (48) C~.94~024(50) 342.0 zt 20.8 (50) 109.8 (70-160) (SO) -0.1 * 31.2 (501 I7 7 * 33 7 1501 149 2 * 22 1 (SO1 II.27 * 0 13 (501 35.0 = 17.5 (5oj !O-140) (50) 52 6 i+Ionr (501 42 CC,‘. 142

50.0

I

:. t *

* * 4

(, CM.. 39 (_cw.. 5 liq. of 8 (soi Minimu!” = 1 0

* Significant at SCr, level; t significant at 1% level. Mean values and standard deviations are shown. The number of subjects are in parenthews. Statistical signilicance in disrnbution (F) is indiDirections are in ang-rdar denrwr. .\mplitudes nr cated by asterisks. Skewed distributions are described by 95 prrcentile limits in parenthcsi*. in millivolts or fin the case of loop area) millivolts squared.

THE

AMERICAN

JOURNAL

OF

CARDIOLOGY

Quantitative

MAX

MAX

T

)’

Study of Frank

;

’

,

Vectorcardiogram GROUP

A

-

GROUP

6

-

* 4

I

QRS

I 0.50 T 0 so

0 0

677

1 1.00 I I .oo

Y.50 1 I 50

hV2)

I 2.50

2.00

(mb’)

FIG. 6. Frontal plane uector and area magnitudes. Heavy bars represent the young group, while the thinner lines represent the older group. QRS loop area in millivolts squared is depicted on the top scale. Loop areas are not symmetrically distributed; thus their “low” end is cut off at zero. Clinically only the “high” limit of the loop area is being considered in the diagnosis of hypertrophy.

MAX

l/2

9RS

QRS

AREA

LOOP

GROUP

A

-

GROUP

B

-

I

QRS

I

1

AREA

1

!

0

0.50

0

0.50

1.00 ! 1.00

I 1.50 1.50

hv2) 2.00

I 2.50

hV)

7. Horizontal plane vector and area magnitudes. Here, as in Figures 6, 8 and 9, differences in the mean values are readily apparent, but overlapping. This would appear to nullify any practical separation of these groups, except at the extremes of their distribution. FIG.

‘J?ABLE

11

(continued)

Plane Group

--------------Sagitral Group A

I .43 * 0.28 (228) (13.0 * 53.4 (228) 11.50 i 0.24 (194) I .OO f 0.34 (162) 06 * 21.70 (192) 199 + 32 .O (228) 168 zt 27.0 (228) Ill 44 f 29 2 (228) 74.70 f 19.5 (228) 030 i 0.10 (224) 117.17 + 18.40 (2281 43.9 (11-110) (224, il. 31 (O&100) (190) 226 ccw., 2 fir. ” of 8 (12X) 7 cw., 198 ccw., 1 fig. of 8 (206) Minimum = 1.

8

VOLVME

18,

NOVEMBER

-\ B

0.93 i 0.32 58.3 * 33.0 0.47 (0-l 0) 0.79 f 0.35 64.7 i 23.8 191.4 f 35.1 168.6 YJZ26.4 119.1 i 33.0 75.8 f 28.3 0.24 f 0.10 125.1 f 23.3 65.6 (o-140) 57.9 (O-140) 43 ccw. (43)

F

(50) (50) (49) (49) (50) (50) (50) (50) (50) (50) (50) (j0) (50)

’

2 cw., 43 ccw., 5 fig. of 8 (50) Minimum = 1.2

1966

t

+ *

T loop magnitudes are greater in group A, while their directions are largely the same in both groups. T loop rotations, where determined, follow those of the QRS loops, except in a few cases. These latter cases have the typical long, thin loops with high ratios of length to width. Round, short T loops rotating counter to their parent QRS loops are not found in any of our normal vectorcardiograms. One qualitative observation, not tabulated in this study but of unusual interest, is the spacing of the time markers, clearly seen in the enlarged T loops. Normally, these markers or “blips” are closely spaced during the inscription of the early part of the centrifugal limb and the apex of the loop. In the centripetal or terminal limb, however, the spacing widens. This corresponds to the slow, gentle slope of the ascending T wave limb and the sharp, rapid descent of its terminal limb in the scalar electrocardiogram. This spacing pattern is consistently observed in both

Silverberg

678

MAX

I/Z

ORS

1

MAX

QRS

AREA

QRS

, i’

GROUPA

-

GROUP B

-

,

I

I

’

,

LOOP AREA

4 4 1

1’;

0

I 1.00 , 1.00

0.50 I 0.50

0

, I.50 I.50

(&I 2.00

t 2.50

w

FIG. 8. Left sagittal plane vector and area magnitudes. Separation between the two groups appears to be best evaluated by the sagittal maximal QRS vector magnitude. Mean magnitude and distribution at high and low values could separate group A and B, while values between approximately 0.9 to 1.2 millivolts would be of little value.

groups, being seen best in the horizontal and open view or both. Evenly spaced markers in both limbs are not observed in these subjects. Maximal and Half-area QRS-T Angles: These angles appear narrowest in the frontal projection, particularly in group A. The sagittal and horizontal planes display a wide range of values for maximal QRS-T angles, not noticeably narrowed by use of the half-area QRS vector. Resolved loop measurements resemble those in the frontal plane, though somewhat wider.

DISCUSSION In an effort to obtain a truly normal young population free of heart disease, hospital patients were excluded from group A. Instead, a large TABLE

III

QRS and T Loop Measurements

(Open Resolved Plane)

Group A

Azimuth Elevation Maximal QRS magnitude Maximal QRS direction QRS loop area ‘/2 area vector magnitude l/2 area vector direction Maximal T magnitude Maximal T direction Maximal ORS-T

angle _

169.7 ;t 32.7 (51) 53.2 f 14.1 (51) 1.71 f 0.54 (51)

t

98.68 +

91.1 f

31.0 (51)

t

1.26 f 1.53 f

0.59 0.56

* *

1.87 f 1.52 f 95 f

60.3 (95) 0.79 (95) 0.42 (95)

27.0 (95)

0.68 k 0.15 63.2 f

(164)

22.4 (95)

31.2 (O-60)

(172)

36.89 i

QRS loop rotation T loop rotation

228 cw. (228) 3 EW.. 103 ccw.. lin. (124) Minimum = 2.2

T loop L/W

ratio

* Significant at 5%

F

160.85 i 37.6 (163) 42.36 & 11.8 (158) 1.75 f 0.36 (95)

‘/? area QRS-T

angle

Group B

level;

99.7 f

31.1 (51)

0.41 f

0.19

60.5 +

20.8

23.4

11.3 (95)

(O-80)

39.2 (o-100)

18

(51) (51)

(51) (51) (51) (51)

50 cw. (50) 45 cw., 2 ccw., 4 of 8 (51) Minimum = 1.7

fig.

t significant at 1 y. level

t

t t

group of young student nurses was included. They are examined upon entering training, and as a group are less likely to have occult coronary heart disease than men of the same age. The decision to limit this group to those under age 40 was based on the relatively greater prevalence of coronary artery disease and hypertension in subjects over that age. A similar age limit has been used in previous studies.r8 The difficulty of finding normal individuals over 40 years of age in this institution limited group B to SO subjects. Comparison with prior studies’+ reveals Of special interstriking agreement in results. est is the similarity of the present study, analyzed conventionally, to the computer-analyzed study It is reassuring to know that by Draper et al.’ standard vectorcardiographic analysis may be correlated with more elaborate computer procedures. Effect of Aging: A consistently observed tendency in our results is a more leftward and superior position of the QRS loop in the older group. This is seen from the frontal view as a countcrclockwise shift of approximately 10” in the halfarea QRS vector. There is a corresponding shift in the instantaneous 0.03 and 0.04 second vectors in this plane. This would be expected, since these vectors, especially the 0.04 second, normally occur near the half-area vector. That this is a change in position of the entire loop, rather than a change in its configuration, is suggested by a corresponding downward shift of the polar vector, i.e., the position of the viewer in space observing the open resolved loop. Although configurational differences apparently do not play a part in the position shift in group B described above, they do appear fre THE

AMERICAN

JOURNAL

OF CARDIOLOGY

Quantitative

MAX

f

k+___&_&

0.50 I 0.50

0

of Frank

I

1.00 1 1.00

1.50 I 1.50

quently in group A and contribute to its wide range of maximal QRS vector directions. No attempt was made to divide the loops according to configuration, as was done by Abildskov’s and Burch et al.,lg but our finding that the range of maximal QRS vectors narrows with aging suggests fewer configurational differences in this This contrasts with Abildskov’s work,18 group. where a greater number of type 2 loops apIn part, this may be peared in older subjects. due to his use of the equilateral tetrahedral system. It is of interest that there is a statistically significant difference in the horizontal plane areas of the two groups, the older group having the This would not be expected from larger area. the observation of larger maximal and half-area QRS vectors in group A, but can be easily explained by the leftward and upward shift of the spatial loop in the older group. The latter group’s QRS loop presents a more broadside projection in the horizontal plane. A vector bisecting the area of QRS loop represents the median electromotive force during the QRS cycle and should approximate the average potential. PipbergeG found the difference between the half-area vectors and the The true mean spatial vectors to be negligible. half-area vector would be expected to change less than the maximal QRS vector in response to variations in loop configuration. This was found to be true (Fig. 2-5), except for the very narrow range of the group B maximal QRS vectors in the resolved and frontal planes. Although there are statistically significant differences in the maximal QRS-T angle and the half-area QRS-T angle between groups A and B, the overlap is so large as to nullify their value in The differentiating one group from the other. 18,

NOVEMBER

1966

GROUP

A

-

GROUP

B

-

I

I

!

2.00

2.50

3.00

3.50

!mv2)

2.00

2.50

3.00

3.50

(mV)

Resolved “open” plane (broadside projection) vecfor and area magnitudes. the two groups, but again the great overlap must be stressed,

FIG. 9.

VOLlJME

070

Vectorcardiogram

’

I

0

Study

I

There are distributional differences between

narrow range for these parameters in the frontal and resolved planes would nevertheless appear to have practical, although nonspecific, value in separating normal from abnormal populations. Since the range of the half-area QRS vector was generally narrower than that of the maximal QRS vector, it was anticipated that the range of the half-area QRS-T angle would be smaller than that of the maximal QRS-T angle. Xot only did the relation vary considerably, but the half-area QRS-T angle exceeded the maximal QRS-T angle in the resolved and frontal planes. Statistical significance in variation is found in many of the magnitudes, as shown in Tables II and III and Figures 6-9. Here again, overlapping ranges prevent their practical use in separating these two groups. On the basis of previous reports,‘“J1,“” it was hoped that the range of normal would be smaller in the resolved plane. This was not the case. In fact, many measurements exhibited less variation in the frontal plane, especially the maximal and the half-area QRS-T angles. Polar vectors of the resolved plane were extensively studied by Pipberger and CarterI and found to be valuable indicators of abnormalities. They plotted their azimuth and elevation on In our daily clinical use, spherical coordinates. the direction of the polar vector is not an improvment over the diagnostic information readily Considerobtainable from the standard views. ing the time and labor involved in plotting, and the marked overlap observed in our own attempts, we could not recommend this method as a clinically valuable one. Magn$ied T Loop: Of considerable interest to us has been the detail observed in the magnified T loop. Karnig was the first to emphasize its diminution in size and change in shape as a

Silverberg \Vajszczuk and result of my.ocardial lesions. Burch5 studied normal subjects with the tetrahedron system. They analyzed the rotation of the loop but failed to utilize the horizontal plane. Chou et al.’ stressed the length-to-width ratio in their study of the significance of a widened T loop, and reaffirmed Karni’s findings. Analysis of our own series confirms not only the normal findings previously published but also the narrow, ellipsoid shape of the loop, its consistent pattern of rotation, and the rate of change in its inscription, as estimated from the spacing of the time markers. Changes in contour of the scalar electrocardiographic S-T segment without deviation from the baseline cannot be easily seen in vectorcardiograms. However, these S-T changes alter the scalar T wave, making it more symmetric. This symmetry appears in the vectorcardiographic T loop as relatively equal This spacing of time markers in the two limbs. type of change has been of interest in our clinical interpretation, and pathologic material is currently being studied. SUMMARY A quantitative analysis of the Frank system vectorcardiograms, including electronically amplified T loops, of 228 young normal adults and 50 normal adults over 40 years of age, demonstrated remarkable similarities between the two In both, the T loops maintained groups. counterclockwise rotation in the horizontal and sagittal planes, very narrow ranges of magnitude and direction in all planes, and asymmetry of inscription (slow efferent and rapid afferent limbs). The principal T loop change with aging was a decrease in the length-to-width ratio in the horizontal and sagittal planes; the minimal ratio for the older group was 1, compared to 2 for the younger group. The normal QRS loop in adults over the age of 40 differed from that of younger adults in the following respects: (1) It was shifted leftward and superiorly, presenting a greater area broadside to the horizontal plane. (2) The variation in the direction of its maximal vector was decreased, along with the reduction in configurational differences. (3) The magnitude of its maximal vector was significantly less than that of the younger group in the sagittal and horizontal planes. This suggests that different vectorcardiographic voltage criteria for left ventricular enlargement will be required for each group. Analysis of the resolved open plane added

little to nothing to the information readily. available from standard views. In light of the cost and complexity of the equipment and the time reqrrired for its use, a spatial aspect changer is not considered clinically valuable at this time. ACKNOWLEDGMENT The completion of this work has been dependent on the fine technicians and volunteer helpers. Notable among these were Mrs. Barbara Boyle, Mr. Martin Levin, Mrs. Ruthann Bowers and Miss Sarah Hacker, whose suggestions, art work and criticisms greatly exprdited the completion of this paper. I would also like to express my appreciation for the cooperation of the School of Nursing and the many student nurses and house officers.

REFERENCES 1. DRAPER, H. W., PEFFER, C. J., STALLMAN,F. \V., LITTMANN, D. and PIPBERGER, H. V. The corrected orthogonal electrocardiogram and vectorcardiogram in 510 normal men (Frank lead system). Circulation, 30: 853, 1964. 2. LIBRETTI, A. and ZANCHETTI,A. Spatial patterns of ventricular repolarization in arterial hypertension. Am. Heart J., 59: 374, 1960. 3. BRISTOW, J. D. A study of the normal Frank vectorcardiogram. Am. Hea7.t J., 61: 242, 1961. 4. FORKNER, C. E., HUGENHOLTZ, P. G. and LEVINE, H. D. The vectorcardiogram in normal young adults-Frank lead system. Am. Heart J., 62 : 237, 1961. 5. MCCALL, B. W., WALLACE, A. G. and ESTES, E. H. Characteristics of the normal vectorcardiogram recorded with the Frank lead system. Am. J. Curdtof., 10: 514, 1962. 6. GUNTHER, L. and GRAF, W. S. The normal adult spatial vectorcardiogram. Am. J. Cardiol., 15: 656, 1965. 7. CHOW, T., f*ELM, R. A; and LACH, R. The significance of a wide TsE loop. Circulation, 30: 400, 1964. 8. WAJSZCZUK, W. J. and BURCH, G. E. Analysis of the Tsfi loop in normal subjects of different ages. Am. J. Cardiol., 10: 507, 1962. The T& loop in myocardial lesions. 9. KARNI, H. Am. Heart J., 52: 867, 1956. 10. MILNOR, W. R., TALBOT, S. A. and NEWMAN, E. V. A study of the relationship between unipolar leads and spatial vectorcardiograms using the panoramic vectorcardiograph. Circulation, 7: 545, 1953. and Il. MILNOR, W. R. The normal vectorcardiogram a system for the classification of vectorcardiographic abnormalities. Circulation, 16: 95, 1957. 12. SCHMITT, 0. H. Cathode ray presentation of three dimensional data. J. Appl. Physics, 18: 819, 1947. 13. BURGER, H. C. and VAANE, J. P. A criterion characterizing the orientation of a vectorcardiogram in space. Am. Heart J., 56: 29, 1958. 14. PIPBERGER, H. V. and CARTER, T. N. Analysis of the normal and abnormal vectorcardiogram in its own reference frame. Circulation, 25 : 827, 1962. THE AMERICANJOURNAL OF CARDIOLOGY

Quantitative

Study of Frank

15. I 11,L.M. K. \. L’(,cto~c~rl.dioq~;~phic notation. CirIulrrlfo?!. 13: 581. 1956. 10. I'IPRICRGISR. 13.\-. 11\~aluation of quantitative methods for obtaining mean spatial QRS vectors I .\bstr. I. Cmulation,16: 926, 1957. 17. Scic-ntilic I’ables. pp. 40 -41. .Irdsley, N. I’., 1902. (k&y Pti;t~m~~cctltic;ils. 18. \kfI.DSKOV. .1..\. \ study of the spatial vector-

VOLUME

18.NOVEMBER

1966

\,.ectorcardiog-am

hX 1

cardiog-ram in normal subjrcts OXYI tilt, air o! forty years. C~rrulntion, 12: 286, l’J5.~. 19. BURGH, G. E., .\BILDSKOV, .I. .\. ~llld(:R