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Quantitative comparison of six nominally orthogonal vectorcardiographic systems
Quantitative comparison of six nominally orthqonal vectorcardiographic F. W. Beswick, M.B., Ch.B. R. C. Jordan, D.Sc., Ph.D., M.R.C.S., Cardiff, Wales.
I
t has been stated1 that the number of systems of vectorcardiography in daily use is not much smaller than the number of cardiologists who occupy themselves with this branch of electrocardiography. Although this expression is obvious hyperbole, it serves to emphasize the currently unsatisfactory state of development in this field of cardiac electrophysiology. At present it appears unlikely that the ideal of a single theoretically accurate system equally applicable to all subjects in every circumstance can be attained. It is, therefore, the more imperative that the best systems available be thoroughly investigated to determine their interrelationships when applied to the same subject population. Few such direct comparisons have so far been carried out using techniques which can claim satisfactory theoretical foundations. Langner and associates2 studied the interchangeability of the systems of Schmitt and Simonson (SVEC III),3 Frank,4 McFee and Johnston,s and Helm,6 but their method of assessment was such as to accentuate similarities and to minimize differences, since they paired the 3 leads of each orthogonal reference frame individually with a common lead to produce a loop. As a result of a somewhat subjective analysis, they concluded that these four systems were interchangeable, “judged by present clinical standards,” in all normal and the majority of abnormal subjects. From the Physiology Department, University Received for publication Aug. 5. 1963.
657
College
systems
L.R.C.P.
Pipberger and Lilienfield’ compared the so-called “corrected” orthogonal systems of Schmitt and Simonson and of Frank with two that involve conventional bipolar and unipolar leads (Wilson’s tetrahedron and Grishman’s cube). They claimed that “the two corrected systems, different in lead design, showed a very close relationship in their performance in man,” but marked discrepancies occurred between the more conventional techniques. Subsequently, Pipberger* stated that the systems proposed by McFee and Johnston, Schmitt and Simonson (SVEC III), Frank and Helm all gave results in close agreement. In 1959, Simonson, Schmitt and Nakagawa,s in a comparison of eight vectorcardiographic lead systems in 4 subjects, cautioned against the too free interchange of results derived from the currently available nominally orthogonal lead systems. Large discrepancies were noted in the orientation and magnitude of mean and maximum QRS and T vectors and of the loop contour. In addition, vectorial respiratory shifts as recorded by the various techniques were large and mutually inconsistent. A less satisfactory type of analysis has involved the comparison of the mean values obtained from the study of one group of subjects by a given lead system with the corresponding data from a second system applied to a different population. Such a of South
Wales
and
Monmouthshire,
Cardiff,
Wales.
6.58
Beswick
.itn.
and Jordatl
study has been made by Bristow,l” who compared his own results using the Frank system with those of Pipberger, using the SVEC III method, and the data of Jordan and Beswick” obtained with a system based upon the lead-field concept of McFee and Johnston. He demonstrated relatively minor differences between the first two methods, but that the last gave spatial QRS loops which were usually oriented more posteriorly and inferiorly. In contrast, Forkner, Hugenholtz and Levine,‘* commenting on the findings of several authors investigating separate populations, concluded that, whereas good agreement exists between the Frank and SVEC III systems in the frontal plane projections of the spatial vector, sagittal and horizontal plane projections diverge considerably. An interesting experimental approach involving the insertion of an artificial dipole into the human cadaver was described by Burch, Cronvich and Zao,13 who, in spite of considerable technical difficulty, were able to show that the Frank and SVEC III procedures gave results in reasonable agreement. The only attempts which have previously been made quantitatively to relate pairs of vectorcardiographic systems were those
Table I. Mean lead scalar area magnitudes
---__
Multipleelectrode grid technique QRS Mean S.D. Coefficient variation
Large disc modification
of Burger, van Milaall and k’lipla and Burger, van Brummelen and van Herpen.16s16 They sought to derive linear expressions to allow of transformation between the results of several systems, including those of Schmitt and Simonson, McFee and Parungao,” and Frank,4 in order that investigators could continue to use the systems which they prefer, but in order that the resnlts would become generally comparable. When applied to single individuals, the transformations were reasonably successful, but for large populations the average transformation showed a much wider scatter, which they interpreted as indicating that a linear expression is not a satisfactory description of the interrelationship between any two systems. The primary purpose of the present investigation was to compare quantitatively, on the same group of subjects, the results given by the two nominally orthogonal lead systems developed in this laboratory, in order to determine the degree of interchangeability betGeen a technique involving the use of multiple electrode grids for the Z lead and one which differed only in that the grids were replaced by a pair of large metal discs. Secondarily, the results from these two methods were to be com-
( in microvolt-seconds)
Lead I__._---.-
for QRS and T as determined
X
----
Heart J. May, 19tJ.l
/
p-__p---_I
Mc Fee
Frank
Dower and Osborne
10.0 5.1
11.0 5.6
12.0 6.4
13.5 6.4
10.0 7.2
51
51
53
41
72
26.5 12.1
26.0 11.5
33.0 14.8
25.5 11.3
46
44
45
44
S VEC III
8.5 7.7
Lead
Y
_-_--------
Multipleelectrode grid technique
Large disc modification
20.0 9.9
20.5 10.0
91
50
49
24.5 9.7
25.5 20.6
36.5 13.6
36.5 13.9
40
81
37
38
of
(percent)
T Mean SD. Coefficient of variation (per cent) Ratio
means
T/QRS
2.65
2.36
2.75
1.89
2.45
3.00
1.83
1.78
Volume
Number
67
Quantitative
5
comparison
of six nominally
Methods Sixteen clinically normal male medical students were the subjects of this investigation. Each was examined successively by the following six vectorcardiographic techniques: our multiple-electrode grid Z lead method,” our disc 2 lead modification,18 McFee and Parungao’s,” Frank’s,4 Dower and Osborne’s,lg and Schmitt and Simonson’s (SVEC III).3 It may be pointed out that, whereas the same X lead electrode placements are used in the first two of these methods, all the remainder have individually different electrode positions for this lead. Lead Y in all except Frank’s and Dower and Osborne’s systems is fundamentally the same, although an amplifier calibration factor of 0.71 is imposed in SVEC III, whereas the Z lead employed is different in each case. With the subject lying supine the above-mentioned order of
Lead
Y-continued
Lead Z --_-________
Mc Fee
Frank
Dower and Osborne
SVEC III
21.0 10.6
16.0 7.3
8.0 4.1
14.5 1.0
51
46
39.0 16.6
25.5 10.4
43
41
1.86
Results Scalar lead magnitude values. In Table 1 are presented for all six vectorcardio-
techniques applied to 16 normal subjects
---------
1.59
51
3.5 3.7
106
0.44
659
VCG systems
procedure was found to give least disturbance to the individual and minimized the difficulty of changing electrode placements and recalibrating amplifiers. Scalar tracings from the X, Y and Z leads for each system were recorded synchronously on a 4-channel Elema Mingograph 42 direct-writing electrocardiograph at a paper speed of 100 mm. per second. Frontal, horizontal, and right sagittal planar loops were photographed on Kodak R 60 film from the screen of a Sanborn Vectorscope whose lead selector switch had been modified to permit the input of 3 independent bipolar leads. The electron beam was interrupted every 0.0025 second, and the direction of inscription was indicated by the blunt ends of the tear-shaped light spots. The methods used for vectorial analysis of results, and the symbols employed for presentation of the data are as previously described,llJO except that the lead nomenclature has been changed to conform with the conventional labeling of 3-dimensional Cartesian coordinates.*s
pared with those obtained by means of four other currently used techniques of vectorcardiography, and at the same time the opportunity was to be taken of making detailed comparisons between the six methods in all combinations of pairs to establish their levels of correlation and interconversion.
by 6 vectorcardiographic
orthogonal
Multi+ electrode grid technipe
----Large disc modijcation
Mc Fee
Frank
Dower and Osborne
SVEC III
-28.5 15.8
-20.0 11.1
-14.0 7.3
-9.0 5.9
48
55
56
52
66
27.5 10.7
67.5 26.4
54.0 18.2
26.5 16.7
29.5 10.9
34.0 11.1
27.0 12.0
39
39
34
63
37
33
44
1.90
2.37
2.70
1.89
3.28
-7.5 8.6
115
4.53
-7.0 4.7
67
3.86
660
Beswick
a.1tn. Heart 1.
and Jordan
May,
graphic methods the mean scalar area magnitudes (in microvolt-seconds) for QRS and T in each lead as derived by algebraic summation of the areas enclosed by these deflections. For lead X, QRS by Frank’s method gave the largest area value (13.5 mvs., S.D. 6.4) and SVEC III the smallest (8.5 mvs., SD. 7.7) but, in contrast, the former system manifested the closest grouping of individual observations around the mean, as evidenced by the coefficient of variation (47 per cent), whereas the latter method showed the largest scatter, with a coefficient of variation of 91 per cent. For T, McFee’s technique gave the largest magnitude (33.0 mvs., SD. 14.8), the remainder of the methods yielding results approximately 15 per cent smaller, but
Table II. Stutistical
analysis
Lead
again the scatter was largest for the SVEC II1 system (C.V. 81 per cent). In lead Y, the most striking feature was the disparate nature of the results given by the Dower and Osborne method, especially for T, where the mean observed area magnitude was some 12 per cent of those derived by the Frank and SVEC III systems and only about 9 per cent of the remainder. In addition, the individual values for T were excessively widely scattered, with a coefficient of variation of 106 per cent. As might be expected, the mean scalar magnitudes for the Z lead demonstrated the greatest variability between the various methods. The QRS value ranged from 28.5 mvs. for the multiple-electrode grid technique to 7.0 mvs. for SVEC III, and for T
of the diyerences
DiSC electrodeMultiple electrode
19 64
between the lead scalar area magnitude
Disc electrodeMc Fee
DiSC electrodeFrank
Disc electrodeSVEC III
Disc electrodeDower
means
Multiple electrodeMc Fee
Mean difference S.D. Significance
1.0 2.1 -
0.5 4.9 -
2.5 3.3 +
2.5 9.3
1.5 3.5
1.5 4.5
Mean difference SD. Significance
0.5 5.1
7.0 10.0 +
0.5 5.8 -
0.5 14.1 -
1.0 7.0
6.5 11.8 zk
Mean difference S.D. Significance
0.5 1.5 -
0.5 2.1
5.0 3.3 ++
6.0 3.5 ++
12.5 8.1 ++
1.0 1.9 -
Mean difference S.D. Significance
0.5 5.6 -
3.0 10.7
11.5 6.9 ++
9.0 7.7 -t
33.0 10.9 ++
3.0 7.4 -
Mean difference SD. Significance
8.5 6.6 ++
6.0 6.2 +
11.0 8.5 ++
13.0 t-t
12.5 11.6 +
14.5 10.7 ++
Mean difference SD. Significance
13.5 16.3 +
21.5 16.7 -t-+
24.0 15.0 -t-f
26.5 10.4 +-t
20.5 16.8 +
41.0 22.3 ++
x T
QRS
Y T
QRS
8-2
2 T
Levels
of significance:
-
indicates
p > 0.05;
f indicates
p=
0.05
-
0.02;
+
indicates
p < 0.02;
++
indicates
p < < 0.01;
t > 5.0.
Volume Number
67 5
Quantitative
comparison
661
of six nominally orthogonal VCG systems
from 67.5 mvs. for the grid system down to 26.5 mvs. for that of McFee. In order to establish for each lead the statistical significances of the differences between the scalar area magnitudes as determined by the six techniques, the means of the 16 observed individual differences, each estimated to the nearest 0.5 mvs., have been utilized in preference to the differences between the gross means (as presented in Table I). The results of this statistical analysis are set out in Table II, from which it is apparent that for both QRS and T in lead X most systems showed remarkably small differences between scalar areas, the only significant disagreement for QRS being between the mean of Frank’s system, on the one hand, and the comparable values for the large disc elec-
trode, the multiple-electrode grid, and the Dower-Osborne techniques, on the other. In the case of T, however, the discrepant method appeared to be that of McFee, which showed significant differences from the disc and Dower-Osborne values and, also, possibly from those of the multipleelectrode grid and Frank. In contrast, there was little agreement between the means for lead Y among most of the pairs of methods, only the disc, multiple-electrode grid, and McFee techniques yielding statistically the same values for both QRS and T, respectively. Frank’s method and that for SVEC III agreed only in the case of T. Similarly, there was striking absence of agreement between the six systems as far as the Z lead was concerned, only the
for QRS and T in all pairs of vectorcardiographic techniques
Multiple electrodeFrank
Multiple electrodeSVEC III
Multiple electrodeDower
McFeeFrank
McFeeSVEC III
McFeeDower
FrankSVEC III
FrankDower
SVEC IIIDower
3.5 3.3 +
1.5 8.9 -
0.5 4.6
2.0 4.0 -
3.5 8.3 -
2.5 5.1 -
5.0 9.3 -
4.0 4.4 +
2.0 10.6 -
1.0 5.0
1.0 16.0 -
1.5 1.8 -
7.5 12.4 *
1.5 18.9 -
9.0 10.0 +
0.0 15.8 -
1.0 5.9 -
1.0 16.2 -
12.5 8.3 ++
5.5 3.9 ++
6.5 4.2 ++
13.0 8.9 ++
1.5 0.9 ++
8.5 5.4 ++
7.0 5.0 ++
14.0 8.0 ++
11.5 8.8 ++
35.5 13.6 ++
2.0 4.7 -
22.0 8.0 ++
23.5 8.4 -I-+
4.5 :;”
5.5 :;’
11.0 6.4 ++
9.0 t-9;”
32.5 11.5 ++
19.0 4.0 ++
21.0 12.9 ++
21.5 14.5 ++
5.0 6.0 +
7.0 4.5 ++
7.0 9.7 Lk
2.0 3.3 *
1.0 5.7 -
0.5 6.6
38.0 22.3 ++
40.5 19.2 ++
33.0 18.8 -I-+
3.0 10.3 -
0.5 14.0 -
7.5 14.6 -
2.5 8.7
4.0 11.0 -
7.0 11.3 -
662
Beswick
and Jordan
Dower-Osborne method being indistinguishable from Frank and SVEC III for both QRS and T, whereas McFee, Frank, SVEC III, and Dower-Osborne agreed in respect of T only. Whether for any pair of methods the means differ significantly, it is possible for the pairs of individual values to be statistically correlated. Consequently, the correlation coefficients for both QRS and T area magnitudes in each of the 3 leads for all pairs of systems have been calculated, together with their levels of significance, and these data are presented in Table III. The only system which, for QRS, failed to correlate with any of the others in lead X was Schmitt’s SVEC III, although its mean did not differ significantfy from that of any other method. For T, SVEC III correlated better with the remainder, except in the combination with McFee. For QRS in lead Y, all systems were remarkably well correlated, despite the fact that only three pairs of methods gave difTable III. techniques
Significance
of the correlation
ferences between means which were not statistically significant. A generally similar situation existed for T, with the exception of those pairs involving the Dower-Osborne technique. This method was also less well correIated with the remaining five systems in lead Z. Where corresponding leads from pairs of systems were shown to be correlated, the regression equations (y = a + bx) were calculated, the constants of which are set out in Table IV. From the value of a f 2 SD. it is obviously possible to determine whether the regression line passes through the origin, and from b & 2 SD. whether the results are related by a slope of unity. If these two criteria are satisfied bv corresponding leads of any two techniques, they can be regarded as directly interchangeable, as is observed by the coincident results obtained for QRS and T in leads X and Y for the disc electrode and multipleelectrode grid methods, wherein, in fact, the electrode placements for the derivation
coeficients
calculated from
DiSC electrodeMult~$le electrode
DiSC electrodeMc Fee
DiSC electrodeFrank
r
+0.93
+0.68
$0.85
Significance
++
+
++
+0.91
$0.73
f0.87
+
++
+ f0.98
Lead
QRS
DiSC
electrodeSVEC III
+0.03
-
the 16 indiv&&
values
Disc electrode-Dower
Multiple electrode-hfc Fee
+0.84
$0.71
fS
+
X
‘ISignLance QRS Y
T
i-f
+o.
75
$0.73
$0.63
+
+
r Significance
+0.99
+0.98
f0.97
+-l-
-k+
++
-I-+
+
++
r Significance
f0.92
-f-O.86
+0.88
$0.84
+0.53
+0.90
++
++
QRS
++
++ .
r Significance
+0.95
$0.82
+0.61
++
++
+
+
r Significance
$0.79 +
+0.55 I
+0.57 f
+o.s4 ++
+o.
+o.
74
$0.93
++ 75
+0.41
-
+0.81
++
Z T
Levels of significance:
+0.45
t-o.55 +
- indicates p > 0.05; f indicates p = 0.05 - 0.02; + indicates p < 0.02; ++ indicates p < < 0.01; t t 5.0.
Volume Number
67 5
Quantitative
comparison
of these leads are respectively identical. Planar and spatial vectorial values. Since the majority of previous comparative analyses of vectorcardiographic methods have utilized planar rather than scalar data, planar angular values are presented in Table V to correspond with the mean scalar area magnitudes, from the individual leads, shown in Table I. In addition, the mean spatial QRS-T angle [(SP)Aoqs-T] and spatial vectorial magnitudes [(SP)A] for QRS, T, and ventricular gradient (G) have been calculated. A statistical analysis comparable to that given in Table 11, but involving the vectorial data for all fifteen pairs of systems, has been completed and the results are summarized in Table VI. In the frontal plane the Dower-Osborne and Frank techniques gave angular values for QRS (42 and 49 degrees respectively) which were considerably smaller (i.e., the vectors were directed more horizontally) than the corresponding values as given by
of six nominally
orthogonal
663
VCG systems
the other four systems, which were among themselves statistically identical. The same general relationships were manifest for T, except that the Dower-Osborne value (7 degrees) was approximately 40 degrees less than any comparable angle, and, therefore, the frontal plane QRS-T angle derived with these authors’ system is by far the greatest at 35 degrees. It is to be expected that, because of the participation of the controversial Z lead (see Tables I and II), there will be little agreement between the angular values as calculated from the various systems for the horizontal and sagittal planes. The only pair which showed good agreement for QRS and T in both planes was that involving Frank’s and the SVEC III systems. Both modifications of our technique yielded larger spatial QRS-T angles than any other method, except, possibly, Dower and Osborne’s. This is due to the more posterior location of the QRS vector, together with a more anterior position of the T.
for QRS and T lead scalar area magnitudes respectively for all pairs of vectorcardiographic
Multiple electrode-
Frank
Multiple electrodeSVEC III
Multiple ekctrode-
McFeeFrank
i-O.86 ++
+0.08 -
+0.71 +
+0.79 +
$0.32 -
$0.70 f
$0.13 -
+0.7a +
-0.08 -
i-O.82 ++
+0.64 +
+0.73 +
$0.58 +
$0.47 -
+0.68 +
+0.65 +
+0.83 +
+0.59 It
+0.99 ++
+0.99 ++
+0.74 -t
+0.97 ++
+0.97 ++
+0.73 +
+0.99 ++
$0.74 -t
$0.74 +
+o.a9 ++
i-O.89 -t+
$0.47 -
+0.92 ++
+0.87 ++
+0.19 -
+0.90 ++
+0.38 -
$0.60 rk
+0.68 +
+o.so ++
+0.60 *
+0.60 +
+O.SO +
+0.29 -
+0.82 ++
+0.80 +
+0.65 +
to.56 f
$0.75 +
+0.65 -I-
$0.80 ++
+0.57 Ik
+0.54
$0.72 +
+0.53 -
$0.53 -
Dower
McFeeSVEC III
McFeeDower
FrankSVEC III
FrankDower
SVEC
if IDower
664
Beswick
and Jordan
Since the 2 lead value is also involved in the determination of all spatial vector magnitude data, it follows that there will be wide variability among the values for (SP)AoRs and (SP)AT. The largest magnitudes for both QRS and T were manifest by the multiple-electrode grid technique (39 and 83 mvs., respectively), and the smallest by the Dower-Osborne method. Only SVEC III and Dower-Osborne gave spatial vector magnitudes which did not differ statistically. The spatial ventricular gradient, as defined by Ashman and Byer,21 is obtained by vectorial addition of QRS and T, and,
Table IV. Constants leads
(and standard
consequently, is dependent on the direction and magnitude of both components. Although, in general, the differences in ventricular gradient values reflected similar changes in T, it is possible, as shown by the pair multiple-electrode and SVEC III, for there to be no difference between the spatial orientations of G, even though there may be between their magnitudes, or conversely, difference in orientation with constancy of magnitude, e.g., for the multiple-electrode/McFee combination. Typical sets of planar loops from 2 subjects are illustrated in Fig. 1 as recorded at the same levels of amplification. Apart
deviations)
DiSC electrodeMultiple electrode
DiSC electrodeMC Fee
a
+0.88 1.10
+4.09 2.00
b
fl.008 0.109
a
of the regression
Disc electrodeS VEC III
Multiple
electrodeDower
Multiple electrodeMc Fee
electrodeFrank
$0.88 1.68
$3.61 1.26
-t-3.37 1.75
$0.66 1.51
+0..591 0.170
+o.
$0.729 0.124
$0.572 0.150
3-0.691 0.111
+3.14 2.82
+7.39 4.68
+3.22 3.44
+8.04 5.02
f9.42 5.53
+3.98 4.24
b
+0.860 0.106
$0.564 0.143
+o.
+0.420 0.098
+O. 722 0.203
$0.520 0.169
1-0.881 0.166
a
+0.44 0.81
+0.91 1.08
-0.43 1.30
+0.30 1.16
f6.22 4.31
j-1.77 2.02
-0.90 0.95
b
+0.99s 0.040
+0.931 0.051
+1.334 0.082
+1.404 0.080
$1.919 0.533
+o.a7i 0.095
+1.338 0.060
a
+2.75 3.97
$8.58 4.53
+6.81 4.35
+6.87 5.22
+7.40 3.78
+6.52 4.02
b
+0.934 0.109
+O. 716 0.116
+1.176 0.171
+l.oal 0.190
+o.
+1.174 0.158
a
-0.85 1.61
-2.23 3.28
-9.65 3.49
-7.55 2.87
-3.68 4.80
b
+0.668 0.057
+1.253 0.234
+1.142 0.394
+1.770 0.416
+1.760 0.344
Lead
DiSC electrodeFrank
equations y = a + bx relating
DiSC
QRS 745 0.123
X t15.24 2.48
T 888 0.135
QRS Y
T
QRS Z a
+i6.88 7.58
f19.31 6.00
T b
-f-O.548 0.112
+1.273 0.221
737 0.096
-12.20 4.58 $1.819 0.518
Volume Number
67 5
Quantitative
comparison
of six nominally
from confirming the general vectorial analysis described above, they provide a further basis for comparison by studying in detail the form of the inscribed loops to detect moment-to-moment characteristic features of outline. For example, in Subject No. 1 the multiple-electrode grid, disc, McFee, and SVEC III all demonstrate similar anterosuperior terminal depolarization activity. Discussion
The spatial vectorial approach to the investigation of cardiac electrical phenomena offers undoubted advantages, as
orthogonal
665
VCG systems
outlined by Pipberger,8 over conventional 12-lead electrocardiography, but these merits cannot be fully achieved until general agreement has been reached on the fundamental physical bases which govern the distribution of electrical phenomena throughout the body during the varying conditions of the cardiac cycle, and until a system has been devised to measure accurately the corresponding instantaneous surface potentials. In the present state of knowledge and absence of such agreement the benefits of vectorcardiography can probably best be realized by investigating in detail the rela-
the individual values of lead scalar area magnitude for all correlated pairs of vectorcardiographic
Multiple electrodeSVEC III
+16.95 3.07
Multiple electrodeDower
Mc FeeFrank
+4.34 1.72
+0.89 2.26
+4.67 2.18
+5.85 1.91
to.563 0.169
+0.797 0.165
$0.694 0.214
+O. 764 0.178
+5.11 5.96
Mc FeeSVEC III
+13.43 7.32
+0.375 0.121
+o.m3 0.241
+0.758 0.287
-0.15 0.89
+6.01 4.26
-0.82 1.53
+1.404 0.061
+1.912 0.527
Mc FeeDower
+10.25 7.68
FrankSVEC
III
$16.48 2.68
FrankDower
SVEC IIIDower
+3.71 4.46
+0.953 0.311
+0.357 0.110
$0.879 0.181
+0.01 1.45
+5.63 4.66
+0.72 0.48
+.5.57 3.08
+4.87 2.90
+1.394 0.097
$1.463 0.100
j-2.049 0.577
f1.041 0.033
+1.387 0.381
+1.321 0.359
+5.33 4.34
+I.64 4.15
+2.11 5.59
+1.45 3.10
+1.124 0.157
+1.480 0.163
+1.346 0.202
$0.869 0.112
-9.80 3.13
-1.52 2.30
-5.50 1.71
-1.67 1.32
-6.03 0.80
-4.56 1.00
+2.682 0.541
+0.731 0.261
+1.230 0.249
+1.041 0.191
to.467 0.104
+0.367 0.130
+22.94 10.62 +1.643 0.393
t15.1.5 17.19 f1.429 0.505
-10.17 7.31 +I.234 0.246
+12.07 4.57 +0.649 0.1.58
666
Beswick
and Jordan
Table V. .Mean @mar and spat&
vectoriab data derived
from
the 6 vectorcardiographic
techniques
I Multipleelectrode
grid
technique
Planar values FAQRS
63” 13 54”
60 13 55”
& 1.5 58” 8
+Z” 16 58” 8
296” 22 68”
304” 23 65”
F& ^
FAQRB-T
FAG HAQRS
HAT ^ HAQRB-T
SAT
^ SAQRS-T
S&4,0
Spatial
values (SP)~QRfrT
(SPMQRS (SP)AT
(SP)An
Mc Fee and
Parungao
Frank
61” 16 51” +:i”
49” 15 46”
16 54” 12
::a 17 47” 9
312’ 22 41”
327” 26 50”
Dower and Osborne
42” 22 7” 7 +35” 24 20” 9
29 41” 14
36 13” 20
34 27” 12
+% 45 38” 13
140” 23 29”
132” 23 35”
12.5” 20 56”
120” 24 40”
117” 40 6”
117” 23 45”
+1%
+l:b 28 61” 20
104” 28 39 mvs. 13 83 mvs. 27 82 mvs. 31
+:27, 28 60” 13
90” 27 33 mvs. 10 72 mvs. 20 78 mvs. 25
tive performances of the currently available techniques, with the ultimate object of selecting the most nearly ideal method, or, more likely, of achieving a most satisfactory compromise, which, incidentally, will have to take account not only of purely theoretical factors but also of the technical practicability of its application in all circumstances of health and disease, habitus and posture, and possibly during exercise. It was with these considerations in mind that we undertook the present study, first to ascertain to what extent simplification of the method originally developed in this
+Z
+C
+& 31 80” 15
62” 27 30 mvs. 10 61 mvs. 20 79 mvs. 2.5
+~~” 33 64” 12
66O 30 25 mvs. 6 49 mvs. 14 62 mvs. 19
+lll”
III
61” 14 54” 17 +7” 14 56” 1.5
30 39” 25
+&
327” 36 53”
SVEC
322” 31 53” 18 +91” 43 3.5” 16
H&L SAQRS
Large disc modi$cation
+E 43 26” 14
29 6.5” 9
88 43 18 mvs. 6 43 mvs. 12 47 mvs. 16
62” 28 20 mvs. 8 49 mvs. 21 60 mvs. 28
laboratory influenced the recorded surface potentials, and then to compare the results from this simplified technique with those obtained by four other, nominally orthogonal, vectorcardiographic lead systems. The simplification18 achieved by subst itution of a single thin, fenestrated tin disc for each of the multiple-electrode/resistor grids previously used for the 2 lead had the dual advantages of extreme ease of actual manufacture of the discs, and also of facility in their application to the thorax. Since only the Z lead has been modified, it is obvious that all corresponding results involving exclusively leads X and Y, either
Volume Number
67 5
Quantitutive
SUBJECT
FRONTAL
HORIP ONTAL
comparison
of six nominally
orthogonal
VCG systems
SUBJECT
No. I FRONTAL
SAGITTAL
667
Na 2
SAC IllAL
HORIP QNTAL
Multiple electrode
Disc electrode
McFee
(r
Parunqoo
Frank
Dower ..
G
Osborne
SVEC
III
.: . ,
, i: .’
..’
\‘3 ‘.
--.;
Fig. 1. Representative planar loops for two typical subjects by six vectorcardiographic methods. ’ singly or in combination for the multipleelectrode grid technique and its large disc modification, should be identical, and the fact that this is seen to be the case on reference to Tables I-VI proves, inter alia, the validity of the experimental and analytical procedures employed in this investigation. There was no significant difference between
the mean scalar area magnitudes for QRS or T (Tables I and II), a highly significant level of correlation was demonstrated to exist between the two methods for all 16 individual subjects (Table III), and the calculated regression lines all passed through the origin and had slopes which did not differ from unity (Table IV). In
668
Beswick
Am. Hcnvt 1. May, 1964
and Jordan
addition, the analogous frontal planar projected angles for both QRS and T were statistically identical for the two methods (Tables V and VI), although it should be mentioned that, possibly fortuitously, the difference of 4 degrees in the manifest frontal QRS-T angle was apparently significant. In contrast, the mean scalar area magnitudes for both QRS and T as determined by the disc modification were significantly smaller by approximately 25 per cent than those obtained by the multiple-electrode grid technique, but, nonetheless, the corresponding individual values were well correlated by the equations: QRS: (Disc method value) = -0.85 + 0.67 (Multiple electrode method value). T: (Disc method value) = +16.88 j-0. 55 (Multiple electrode method value). As a result of the attenuation of this Z lead activity the mean spatial QRS-T angle according to the disc method was significantly reduced by 14 degrees, as compared with the multiple-electrode grid, because of a less posterior location of QRS and a tendency to a less anterior location of T. In addition, the spatial magnitudes
Table VI.
Sign$cance DiSC electrodeMultiple electrode
of the di$erences between the vector&
DiSC electrodeMc Fee
DiSC electrodeFrank
-
+-l+ -
-
+-t
FAQRB
F& +
FAQRS-T
-
Fill3 ^
of QRS and 7’ were both retluced by 15 per cent, but the ventricular gradient was unchanged in direction and magnitude. The secondary purpose of this investigation, the comparison of the interrelationships between these two methods and the four other currently used orthogonal systems, involved the analysis of all possible (i.e., fifteen) pairs of corresponding sets of data. However, for clarity of discussion it appeared to be advisable to consider the relative performances of the methods in the chronological order of their dates of publication, commencing with Schmitt and Simonson’s SVEC III technique in comparison with all the others, followed by Frank’s, Dower and Osborne’s, McFee and Parungao’s, and the disc modification of our technique. Having demonstrated above the mathematical interchangeability between disc and multiple-electrode grid methods, we thought that inclusion of this last system in any further discussion was unnecessary. The major differences for QRS between the SVEC III and the other systems could be related primarily to smallness of the mean scalar area magnitude given by that
mean vakues for all pairs of vec-
DiSC electrodeSVEC III
Disc electrode-Dower
Multiple electrodeMc Fee
-
++ ++ ++
-
++
++
-
+
+
++
HAT
-
H~~QRFI-T
+ -
+-t ++ ++
Et +
z -
:z -
++ +
+&+
+ -
++ ++
+k+
+‘=
+ -
++ +
++
HAQR~
HAG SAQRB S4T SAQRB-T
-I-
SA,
I /
Multiple electrodeFrank ++ +
-
+++
+++ ++ ++
Et ++ k
+
++
:: ++
+++ -
(SP)WQRWT rSS%= (SP)A:
Levels
of significance:
- indicates
p > 0.05;
f
indicates
p = 0.05
- 0.02;
+ indicates
p < 0.02;
++
indicates
p < < 0.01;
t > 5.0.
Volume Number
67 5
Quantitative
comparison
of six nominally
system for lead X. However, the very high degree of scatter of the individual values was probably the reason that significant differences could not be demonstrated (Table II) nor any correlation be shown to exist between SVEC III and any other system for lead X scalar magnitudes. The high coefficient of variation was also probably responsible for the apparent lack of statistical differences between the T mean values for this lead, but good correlation was observed between SVEC I II, Frank’s, and the disc methods, although they were not directly interchangeable. For QRS there were also important differences in lead Y which characterized the SVEC III method, presumably due to its calibration factor. The mean area magnitude differed significantly from those derived from all other systems, although the corresponding individual observations were well correlated. The T mean area in this lead agreed only with that of Frank’s method, but, again, there was good correlation between the SVEC III individual values and those of the other techniques, except that of Dower and Osborne. In lead Z the SVEC 111 mean values torcardiografihic
Mzrltiple electrodeSVEC III
orthogonal
VCG systems
669
were similarly among the smallest in magnitude but differed significantly only from those of McFee and our disc modification. As before, there was, however, good individual correlation between this method and the others. For T there was good agreement in this lead between SVEC III and all the others except the disc technique. In summary, therefore, it can be shown that Schmitt and Simonson’s system registered, in general, smaller surface potentials, especially for QRS, in all 3 leads and wide variability between observations from different subjects, with lack of complete interchangeability with other methods. This finding would supplement the previous observations of Simonson, Schmitt and Nakagawag that the SVEC III method was not freely interchangeable with several additional systems, and tends to oppose the view of Langner, Okada, Moore and Fies2 that, for practical purposes, SVEC III is interchangeable with Frank’s method, although the present results do suggest that the latter system showed fewer points of difference from SVEC III than any other of the techniques investigated. Consideration of the performance of the
techniaucs
M&ipZe elcctrodeDower
Mc FeeFrank
Mc FeeSVEC III
Mc FeeDower
FrankSVEC
III
FrankDower
SVEC IIIDower
670
Beswick
and Jordan
Frank technique in comparison with those of Dower and Osborne, McFee and Parungao, and our disc electrode shows that it. disagreed in lead Y with all the others for both QRS and T mean scalar area magnitudes, whereas in the remaining leads its comparative treatment of QRS and T in relation to the other methods was less consistent. In lead X, although the T values agreed with all other systems, QRS agreed only with McFee, and in lead Z the observed data for both QRS and T agreed only with Dower’s system. Despite this lack of complete agreement between mean values, the individual values for QRS in all four of these systems could be mathematically interrelated, since satisfactory correlation coefficients could be derived from all paired sets of data. It is apparent, therefore, that, although Dower and Osborne based their method essentially on that of Frank, the practical simplification involving the reduction of electrode positions from 7 to 4 resulted in appreciable modification of lead response. The outstanding characteristic of the Dower and Osborne system was the insensitivity of the Y lead relative to those of the other techniques investigated, particularly in respect to T, so that for this lead the ratio of T to QRS scalar area was reduced to 0.44 compared with approximately 1.8 for the other methods, and the frontal plane projection of T was raised nearly to the horizontal. From the point of view of voltages registered, the McFee and Parungao system approximated most closely those of the disc method, and, consequently, the planar loops obtained by these two lead systems were of generally most similar dimensions, but the outstanding difference lay in the more vertical disposition of the T loop in the McFee records. This is apparently due to the unequal attentuation of QRS and T voltages resulting in a ratio of T to QRS mean scalar areas of 1.9, which is substantially lower than for any other technique. In conclusion, it may be emphasized that, in order ultimately to decide on the most satisfactory compromise lead system to be adopted for universal application in vectorcardiography, account should be taken not only of the quantitative mathematical
comparisons but also of those characteristics which can be included under the term “practicability.” Such features as least quantity, complexity and cost of equipment, its ease of calibration and immunity from extraneous electrical interference, and simplicity of electrode application in adverse circumstances should also be considered. Our subjective impressions are that the most practicable of these techniques is the large disc modification of our original method, and that the sequence McFee and Parungao, Dower and Osborne, Frank, and Schmitt and Simonson’s SVEC III lists the other methods in order of increasing complexity. Summary Each of 16 normal males was examined by two vectorcardiographic techniques previously described by us, and also by the lead systems of Schmitt and Simonson (SVEC III), Frank, Dower and Osborne, and McFee and Parungao. For each subject the scalar area magnitudes in leads X, Y, and Z, and the planar and spatial vectorial values were determined by all six methods of vectorcardiography. The corresponding means and the results of a statistical analysis comparing the performance of every technique with that of the others are presented. We wish to thank Miss S. Braithwaite, Miss V. Holden, Mr. W. Barry, and Mr. R. Boothby for technical and secretarial assistance, and also the Medical Research Council for a grant toward the cost of equipment. REFERENCES 1. Burger, H. C., van Milaan, J. B., and Klip, W.: Comparison of two systems of vectorcardiography with an electrode to the frontal and dorsal sides of the trunk respectively, AM. HEART J. 51:26, 1956. 2. Langner, P. H., Okada, R. H., Moore, S. R., and Fies, H. L.: Comparison of four orthogonal systems of vectorcardiography, Circulation 27 ~46, 1958. 3. Schmitt, 0. H., and Simonson, E.: The present status of vectorcardiography, A.M.A. Arch. Int. Med. 96:574, 1955. 4. Frank, E.: An accurate clinically practical system for spatial vectorcardiography, Circulation 13:737, 1956. .5 McFee, R., and Johnston, F. D.: Electrocardiographic leads. III. Synthesis, Circulation 9:868, 1954. 6. Helm, R. A.: An accurate lead system for spatial vectorcardiography, AM. HEART J. 53:415, 1957.
Vokme Number
67 5
Quantitative
comparison
7. Pipberger, H. V., and Lilienfield, L. S.: Application of corrected electrocardiographic lead systems in man, Am. J. Med. 25:539, 1958. 8. Pipberger, H. V.: Current status and persistent problems of electrode placement and lead systems for vectorcardiography and electrocardiography, Prog. Cardiovas. Dis. 2:248, 1959. 9. Simonson, E., Schmitt, 0. H., and Nakagawa, H.: Quantitative comparison of eight vectorcardiographic lead systems, Circulation Res. 7:296, 1959. 10. Bristow, J. D.: A study of the normal Frank vectorcardiogram, AM. HEART J. 61:242, 1961. 11. Jordan, R. C., and Beswick, F. W.: Lead field scalar and loop spatial electrocardiography: a preliminary survey on normal adult males and comparison with other methods, Circulation 18:256, 1958. 12. Forkner, C. E., Hugenholtz, P. G., and Levine, H. D.: The vectorcardiogram in normal young adults: Frank lead system, Aaa. HEART J. 62:237, 1961. 13. Burch, G. E., Cronvich, J. A., and Zao, Z. Z.: Vectorcardiographic deflections obtained with various reference systems in cadavers, AM. HEART J. 61:667, 1961. 14. Burger, H. C., van Milaan, J. B., and Klip, W.:
of six nominally
orthogonal VCG systems
671
Comparison of three different systems of vectorcardiography, AM. HEART J. 57:723, 1959. 15. Burger, H. C., van Brummelen, A. G. W., and van Herpen, G.: Compromise in vectorcardiography. Displacement of electrodes as a means of adapting one lead system to another, AM.
HEART
J. 62:398,
1961.
16. Burger, H. C., van Brummelen, A. G. W., and van Herpen, G.: Compromise in vectorcardiography. II. Alteration of coefficients as a means of adapting one lead system to another, AM. HEART
J. 64:666,
1962.
17. McFee, R., and Parungao, A.: An orthogonal lead system for clinical electrocardiography, AM. HEART J. 62:93, 1961. 18. Beswick, F. W., and Jordan, R. C.: A simple chest electrode for orthogonal vectorcardiography, AM. HEART J. 67:232,1964. 19. Dower, G. E., and Osborne, J. A.: A clinical comparison of three VCG lead systems using resistance-combining networks, AM. HEART J. 55:523, 1958. 20. Beswick, F. W., and Jordan, R. C.: Cardiological observations at the Sixth British Empire and Commonwealth Games, Brit. Heart J. 23:113, 1961. 21. Ashman, R., and Byer, E.: The normal human ventricular gradient, AM. HEART J. 25:16, 1943.
I
t has been stated1 that the number of systems of vectorcardiography in daily use is not much smaller than the number of cardiologists who occupy themselves with this branch of electrocardiography. Although this expression is obvious hyperbole, it serves to emphasize the currently unsatisfactory state of development in this field of cardiac electrophysiology. At present it appears unlikely that the ideal of a single theoretically accurate system equally applicable to all subjects in every circumstance can be attained. It is, therefore, the more imperative that the best systems available be thoroughly investigated to determine their interrelationships when applied to the same subject population. Few such direct comparisons have so far been carried out using techniques which can claim satisfactory theoretical foundations. Langner and associates2 studied the interchangeability of the systems of Schmitt and Simonson (SVEC III),3 Frank,4 McFee and Johnston,s and Helm,6 but their method of assessment was such as to accentuate similarities and to minimize differences, since they paired the 3 leads of each orthogonal reference frame individually with a common lead to produce a loop. As a result of a somewhat subjective analysis, they concluded that these four systems were interchangeable, “judged by present clinical standards,” in all normal and the majority of abnormal subjects. From the Physiology Department, University Received for publication Aug. 5. 1963.
657
College
systems
L.R.C.P.
Pipberger and Lilienfield’ compared the so-called “corrected” orthogonal systems of Schmitt and Simonson and of Frank with two that involve conventional bipolar and unipolar leads (Wilson’s tetrahedron and Grishman’s cube). They claimed that “the two corrected systems, different in lead design, showed a very close relationship in their performance in man,” but marked discrepancies occurred between the more conventional techniques. Subsequently, Pipberger* stated that the systems proposed by McFee and Johnston, Schmitt and Simonson (SVEC III), Frank and Helm all gave results in close agreement. In 1959, Simonson, Schmitt and Nakagawa,s in a comparison of eight vectorcardiographic lead systems in 4 subjects, cautioned against the too free interchange of results derived from the currently available nominally orthogonal lead systems. Large discrepancies were noted in the orientation and magnitude of mean and maximum QRS and T vectors and of the loop contour. In addition, vectorial respiratory shifts as recorded by the various techniques were large and mutually inconsistent. A less satisfactory type of analysis has involved the comparison of the mean values obtained from the study of one group of subjects by a given lead system with the corresponding data from a second system applied to a different population. Such a of South
Wales
and
Monmouthshire,
Cardiff,
Wales.
6.58
Beswick
.itn.
and Jordatl
study has been made by Bristow,l” who compared his own results using the Frank system with those of Pipberger, using the SVEC III method, and the data of Jordan and Beswick” obtained with a system based upon the lead-field concept of McFee and Johnston. He demonstrated relatively minor differences between the first two methods, but that the last gave spatial QRS loops which were usually oriented more posteriorly and inferiorly. In contrast, Forkner, Hugenholtz and Levine,‘* commenting on the findings of several authors investigating separate populations, concluded that, whereas good agreement exists between the Frank and SVEC III systems in the frontal plane projections of the spatial vector, sagittal and horizontal plane projections diverge considerably. An interesting experimental approach involving the insertion of an artificial dipole into the human cadaver was described by Burch, Cronvich and Zao,13 who, in spite of considerable technical difficulty, were able to show that the Frank and SVEC III procedures gave results in reasonable agreement. The only attempts which have previously been made quantitatively to relate pairs of vectorcardiographic systems were those
Table I. Mean lead scalar area magnitudes
---__
Multipleelectrode grid technique QRS Mean S.D. Coefficient variation
Large disc modification
of Burger, van Milaall and k’lipla and Burger, van Brummelen and van Herpen.16s16 They sought to derive linear expressions to allow of transformation between the results of several systems, including those of Schmitt and Simonson, McFee and Parungao,” and Frank,4 in order that investigators could continue to use the systems which they prefer, but in order that the resnlts would become generally comparable. When applied to single individuals, the transformations were reasonably successful, but for large populations the average transformation showed a much wider scatter, which they interpreted as indicating that a linear expression is not a satisfactory description of the interrelationship between any two systems. The primary purpose of the present investigation was to compare quantitatively, on the same group of subjects, the results given by the two nominally orthogonal lead systems developed in this laboratory, in order to determine the degree of interchangeability betGeen a technique involving the use of multiple electrode grids for the Z lead and one which differed only in that the grids were replaced by a pair of large metal discs. Secondarily, the results from these two methods were to be com-
( in microvolt-seconds)
Lead I__._---.-
for QRS and T as determined
X
----
Heart J. May, 19tJ.l
/
p-__p---_I
Mc Fee
Frank
Dower and Osborne
10.0 5.1
11.0 5.6
12.0 6.4
13.5 6.4
10.0 7.2
51
51
53
41
72
26.5 12.1
26.0 11.5
33.0 14.8
25.5 11.3
46
44
45
44
S VEC III
8.5 7.7
Lead
Y
_-_--------
Multipleelectrode grid technique
Large disc modification
20.0 9.9
20.5 10.0
91
50
49
24.5 9.7
25.5 20.6
36.5 13.6
36.5 13.9
40
81
37
38
of
(percent)
T Mean SD. Coefficient of variation (per cent) Ratio
means
T/QRS
2.65
2.36
2.75
1.89
2.45
3.00
1.83
1.78
Volume
Number
67
Quantitative
5
comparison
of six nominally
Methods Sixteen clinically normal male medical students were the subjects of this investigation. Each was examined successively by the following six vectorcardiographic techniques: our multiple-electrode grid Z lead method,” our disc 2 lead modification,18 McFee and Parungao’s,” Frank’s,4 Dower and Osborne’s,lg and Schmitt and Simonson’s (SVEC III).3 It may be pointed out that, whereas the same X lead electrode placements are used in the first two of these methods, all the remainder have individually different electrode positions for this lead. Lead Y in all except Frank’s and Dower and Osborne’s systems is fundamentally the same, although an amplifier calibration factor of 0.71 is imposed in SVEC III, whereas the Z lead employed is different in each case. With the subject lying supine the above-mentioned order of
Lead
Y-continued
Lead Z --_-________
Mc Fee
Frank
Dower and Osborne
SVEC III
21.0 10.6
16.0 7.3
8.0 4.1
14.5 1.0
51
46
39.0 16.6
25.5 10.4
43
41
1.86
Results Scalar lead magnitude values. In Table 1 are presented for all six vectorcardio-
techniques applied to 16 normal subjects
---------
1.59
51
3.5 3.7
106
0.44
659
VCG systems
procedure was found to give least disturbance to the individual and minimized the difficulty of changing electrode placements and recalibrating amplifiers. Scalar tracings from the X, Y and Z leads for each system were recorded synchronously on a 4-channel Elema Mingograph 42 direct-writing electrocardiograph at a paper speed of 100 mm. per second. Frontal, horizontal, and right sagittal planar loops were photographed on Kodak R 60 film from the screen of a Sanborn Vectorscope whose lead selector switch had been modified to permit the input of 3 independent bipolar leads. The electron beam was interrupted every 0.0025 second, and the direction of inscription was indicated by the blunt ends of the tear-shaped light spots. The methods used for vectorial analysis of results, and the symbols employed for presentation of the data are as previously described,llJO except that the lead nomenclature has been changed to conform with the conventional labeling of 3-dimensional Cartesian coordinates.*s
pared with those obtained by means of four other currently used techniques of vectorcardiography, and at the same time the opportunity was to be taken of making detailed comparisons between the six methods in all combinations of pairs to establish their levels of correlation and interconversion.
by 6 vectorcardiographic
orthogonal
Multi+ electrode grid technipe
----Large disc modijcation
Mc Fee
Frank
Dower and Osborne
SVEC III
-28.5 15.8
-20.0 11.1
-14.0 7.3
-9.0 5.9
48
55
56
52
66
27.5 10.7
67.5 26.4
54.0 18.2
26.5 16.7
29.5 10.9
34.0 11.1
27.0 12.0
39
39
34
63
37
33
44
1.90
2.37
2.70
1.89
3.28
-7.5 8.6
115
4.53
-7.0 4.7
67
3.86
660
Beswick
a.1tn. Heart 1.
and Jordan
May,
graphic methods the mean scalar area magnitudes (in microvolt-seconds) for QRS and T in each lead as derived by algebraic summation of the areas enclosed by these deflections. For lead X, QRS by Frank’s method gave the largest area value (13.5 mvs., S.D. 6.4) and SVEC III the smallest (8.5 mvs., SD. 7.7) but, in contrast, the former system manifested the closest grouping of individual observations around the mean, as evidenced by the coefficient of variation (47 per cent), whereas the latter method showed the largest scatter, with a coefficient of variation of 91 per cent. For T, McFee’s technique gave the largest magnitude (33.0 mvs., SD. 14.8), the remainder of the methods yielding results approximately 15 per cent smaller, but
Table II. Stutistical
analysis
Lead
again the scatter was largest for the SVEC II1 system (C.V. 81 per cent). In lead Y, the most striking feature was the disparate nature of the results given by the Dower and Osborne method, especially for T, where the mean observed area magnitude was some 12 per cent of those derived by the Frank and SVEC III systems and only about 9 per cent of the remainder. In addition, the individual values for T were excessively widely scattered, with a coefficient of variation of 106 per cent. As might be expected, the mean scalar magnitudes for the Z lead demonstrated the greatest variability between the various methods. The QRS value ranged from 28.5 mvs. for the multiple-electrode grid technique to 7.0 mvs. for SVEC III, and for T
of the diyerences
DiSC electrodeMultiple electrode
19 64
between the lead scalar area magnitude
Disc electrodeMc Fee
DiSC electrodeFrank
Disc electrodeSVEC III
Disc electrodeDower
means
Multiple electrodeMc Fee
Mean difference S.D. Significance
1.0 2.1 -
0.5 4.9 -
2.5 3.3 +
2.5 9.3
1.5 3.5
1.5 4.5
Mean difference SD. Significance
0.5 5.1
7.0 10.0 +
0.5 5.8 -
0.5 14.1 -
1.0 7.0
6.5 11.8 zk
Mean difference S.D. Significance
0.5 1.5 -
0.5 2.1
5.0 3.3 ++
6.0 3.5 ++
12.5 8.1 ++
1.0 1.9 -
Mean difference S.D. Significance
0.5 5.6 -
3.0 10.7
11.5 6.9 ++
9.0 7.7 -t
33.0 10.9 ++
3.0 7.4 -
Mean difference SD. Significance
8.5 6.6 ++
6.0 6.2 +
11.0 8.5 ++
13.0 t-t
12.5 11.6 +
14.5 10.7 ++
Mean difference SD. Significance
13.5 16.3 +
21.5 16.7 -t-+
24.0 15.0 -t-f
26.5 10.4 +-t
20.5 16.8 +
41.0 22.3 ++
x T
QRS
Y T
QRS
8-2
2 T
Levels
of significance:
-
indicates
p > 0.05;
f indicates
p=
0.05
-
0.02;
+
indicates
p < 0.02;
++
indicates
p < < 0.01;
t > 5.0.
Volume Number
67 5
Quantitative
comparison
661
of six nominally orthogonal VCG systems
from 67.5 mvs. for the grid system down to 26.5 mvs. for that of McFee. In order to establish for each lead the statistical significances of the differences between the scalar area magnitudes as determined by the six techniques, the means of the 16 observed individual differences, each estimated to the nearest 0.5 mvs., have been utilized in preference to the differences between the gross means (as presented in Table I). The results of this statistical analysis are set out in Table II, from which it is apparent that for both QRS and T in lead X most systems showed remarkably small differences between scalar areas, the only significant disagreement for QRS being between the mean of Frank’s system, on the one hand, and the comparable values for the large disc elec-
trode, the multiple-electrode grid, and the Dower-Osborne techniques, on the other. In the case of T, however, the discrepant method appeared to be that of McFee, which showed significant differences from the disc and Dower-Osborne values and, also, possibly from those of the multipleelectrode grid and Frank. In contrast, there was little agreement between the means for lead Y among most of the pairs of methods, only the disc, multiple-electrode grid, and McFee techniques yielding statistically the same values for both QRS and T, respectively. Frank’s method and that for SVEC III agreed only in the case of T. Similarly, there was striking absence of agreement between the six systems as far as the Z lead was concerned, only the
for QRS and T in all pairs of vectorcardiographic techniques
Multiple electrodeFrank
Multiple electrodeSVEC III
Multiple electrodeDower
McFeeFrank
McFeeSVEC III
McFeeDower
FrankSVEC III
FrankDower
SVEC IIIDower
3.5 3.3 +
1.5 8.9 -
0.5 4.6
2.0 4.0 -
3.5 8.3 -
2.5 5.1 -
5.0 9.3 -
4.0 4.4 +
2.0 10.6 -
1.0 5.0
1.0 16.0 -
1.5 1.8 -
7.5 12.4 *
1.5 18.9 -
9.0 10.0 +
0.0 15.8 -
1.0 5.9 -
1.0 16.2 -
12.5 8.3 ++
5.5 3.9 ++
6.5 4.2 ++
13.0 8.9 ++
1.5 0.9 ++
8.5 5.4 ++
7.0 5.0 ++
14.0 8.0 ++
11.5 8.8 ++
35.5 13.6 ++
2.0 4.7 -
22.0 8.0 ++
23.5 8.4 -I-+
4.5 :;”
5.5 :;’
11.0 6.4 ++
9.0 t-9;”
32.5 11.5 ++
19.0 4.0 ++
21.0 12.9 ++
21.5 14.5 ++
5.0 6.0 +
7.0 4.5 ++
7.0 9.7 Lk
2.0 3.3 *
1.0 5.7 -
0.5 6.6
38.0 22.3 ++
40.5 19.2 ++
33.0 18.8 -I-+
3.0 10.3 -
0.5 14.0 -
7.5 14.6 -
2.5 8.7
4.0 11.0 -
7.0 11.3 -
662
Beswick
and Jordan
Dower-Osborne method being indistinguishable from Frank and SVEC III for both QRS and T, whereas McFee, Frank, SVEC III, and Dower-Osborne agreed in respect of T only. Whether for any pair of methods the means differ significantly, it is possible for the pairs of individual values to be statistically correlated. Consequently, the correlation coefficients for both QRS and T area magnitudes in each of the 3 leads for all pairs of systems have been calculated, together with their levels of significance, and these data are presented in Table III. The only system which, for QRS, failed to correlate with any of the others in lead X was Schmitt’s SVEC III, although its mean did not differ significantfy from that of any other method. For T, SVEC III correlated better with the remainder, except in the combination with McFee. For QRS in lead Y, all systems were remarkably well correlated, despite the fact that only three pairs of methods gave difTable III. techniques
Significance
of the correlation
ferences between means which were not statistically significant. A generally similar situation existed for T, with the exception of those pairs involving the Dower-Osborne technique. This method was also less well correIated with the remaining five systems in lead Z. Where corresponding leads from pairs of systems were shown to be correlated, the regression equations (y = a + bx) were calculated, the constants of which are set out in Table IV. From the value of a f 2 SD. it is obviously possible to determine whether the regression line passes through the origin, and from b & 2 SD. whether the results are related by a slope of unity. If these two criteria are satisfied bv corresponding leads of any two techniques, they can be regarded as directly interchangeable, as is observed by the coincident results obtained for QRS and T in leads X and Y for the disc electrode and multipleelectrode grid methods, wherein, in fact, the electrode placements for the derivation
coeficients
calculated from
DiSC electrodeMult~$le electrode
DiSC electrodeMc Fee
DiSC electrodeFrank
r
+0.93
+0.68
$0.85
Significance
++
+
++
+0.91
$0.73
f0.87
+
++
+ f0.98
Lead
QRS
DiSC
electrodeSVEC III
+0.03
-
the 16 indiv&&
values
Disc electrode-Dower
Multiple electrode-hfc Fee
+0.84
$0.71
fS
+
X
‘ISignLance QRS Y
T
i-f
+o.
75
$0.73
$0.63
+
+
r Significance
+0.99
+0.98
f0.97
+-l-
-k+
++
-I-+
+
++
r Significance
f0.92
-f-O.86
+0.88
$0.84
+0.53
+0.90
++
++
QRS
++
++ .
r Significance
+0.95
$0.82
+0.61
++
++
+
+
r Significance
$0.79 +
+0.55 I
+0.57 f
+o.s4 ++
+o.
+o.
74
$0.93
++ 75
+0.41
-
+0.81
++
Z T
Levels of significance:
+0.45
t-o.55 +
- indicates p > 0.05; f indicates p = 0.05 - 0.02; + indicates p < 0.02; ++ indicates p < < 0.01; t t 5.0.
Volume Number
67 5
Quantitative
comparison
of these leads are respectively identical. Planar and spatial vectorial values. Since the majority of previous comparative analyses of vectorcardiographic methods have utilized planar rather than scalar data, planar angular values are presented in Table V to correspond with the mean scalar area magnitudes, from the individual leads, shown in Table I. In addition, the mean spatial QRS-T angle [(SP)Aoqs-T] and spatial vectorial magnitudes [(SP)A] for QRS, T, and ventricular gradient (G) have been calculated. A statistical analysis comparable to that given in Table 11, but involving the vectorial data for all fifteen pairs of systems, has been completed and the results are summarized in Table VI. In the frontal plane the Dower-Osborne and Frank techniques gave angular values for QRS (42 and 49 degrees respectively) which were considerably smaller (i.e., the vectors were directed more horizontally) than the corresponding values as given by
of six nominally
orthogonal
663
VCG systems
the other four systems, which were among themselves statistically identical. The same general relationships were manifest for T, except that the Dower-Osborne value (7 degrees) was approximately 40 degrees less than any comparable angle, and, therefore, the frontal plane QRS-T angle derived with these authors’ system is by far the greatest at 35 degrees. It is to be expected that, because of the participation of the controversial Z lead (see Tables I and II), there will be little agreement between the angular values as calculated from the various systems for the horizontal and sagittal planes. The only pair which showed good agreement for QRS and T in both planes was that involving Frank’s and the SVEC III systems. Both modifications of our technique yielded larger spatial QRS-T angles than any other method, except, possibly, Dower and Osborne’s. This is due to the more posterior location of the QRS vector, together with a more anterior position of the T.
for QRS and T lead scalar area magnitudes respectively for all pairs of vectorcardiographic
Multiple electrode-
Frank
Multiple electrodeSVEC III
Multiple ekctrode-
McFeeFrank
i-O.86 ++
+0.08 -
+0.71 +
+0.79 +
$0.32 -
$0.70 f
$0.13 -
+0.7a +
-0.08 -
i-O.82 ++
+0.64 +
+0.73 +
$0.58 +
$0.47 -
+0.68 +
+0.65 +
+0.83 +
+0.59 It
+0.99 ++
+0.99 ++
+0.74 -t
+0.97 ++
+0.97 ++
+0.73 +
+0.99 ++
$0.74 -t
$0.74 +
+o.a9 ++
i-O.89 -t+
$0.47 -
+0.92 ++
+0.87 ++
+0.19 -
+0.90 ++
+0.38 -
$0.60 rk
+0.68 +
+o.so ++
+0.60 *
+0.60 +
+O.SO +
+0.29 -
+0.82 ++
+0.80 +
+0.65 +
to.56 f
$0.75 +
+0.65 -I-
$0.80 ++
+0.57 Ik
+0.54
$0.72 +
+0.53 -
$0.53 -
Dower
McFeeSVEC III
McFeeDower
FrankSVEC III
FrankDower
SVEC
if IDower
664
Beswick
and Jordan
Since the 2 lead value is also involved in the determination of all spatial vector magnitude data, it follows that there will be wide variability among the values for (SP)AoRs and (SP)AT. The largest magnitudes for both QRS and T were manifest by the multiple-electrode grid technique (39 and 83 mvs., respectively), and the smallest by the Dower-Osborne method. Only SVEC III and Dower-Osborne gave spatial vector magnitudes which did not differ statistically. The spatial ventricular gradient, as defined by Ashman and Byer,21 is obtained by vectorial addition of QRS and T, and,
Table IV. Constants leads
(and standard
consequently, is dependent on the direction and magnitude of both components. Although, in general, the differences in ventricular gradient values reflected similar changes in T, it is possible, as shown by the pair multiple-electrode and SVEC III, for there to be no difference between the spatial orientations of G, even though there may be between their magnitudes, or conversely, difference in orientation with constancy of magnitude, e.g., for the multiple-electrode/McFee combination. Typical sets of planar loops from 2 subjects are illustrated in Fig. 1 as recorded at the same levels of amplification. Apart
deviations)
DiSC electrodeMultiple electrode
DiSC electrodeMC Fee
a
+0.88 1.10
+4.09 2.00
b
fl.008 0.109
a
of the regression
Disc electrodeS VEC III
Multiple
electrodeDower
Multiple electrodeMc Fee
electrodeFrank
$0.88 1.68
$3.61 1.26
-t-3.37 1.75
$0.66 1.51
+0..591 0.170
+o.
$0.729 0.124
$0.572 0.150
3-0.691 0.111
+3.14 2.82
+7.39 4.68
+3.22 3.44
+8.04 5.02
f9.42 5.53
+3.98 4.24
b
+0.860 0.106
$0.564 0.143
+o.
+0.420 0.098
+O. 722 0.203
$0.520 0.169
1-0.881 0.166
a
+0.44 0.81
+0.91 1.08
-0.43 1.30
+0.30 1.16
f6.22 4.31
j-1.77 2.02
-0.90 0.95
b
+0.99s 0.040
+0.931 0.051
+1.334 0.082
+1.404 0.080
$1.919 0.533
+o.a7i 0.095
+1.338 0.060
a
+2.75 3.97
$8.58 4.53
+6.81 4.35
+6.87 5.22
+7.40 3.78
+6.52 4.02
b
+0.934 0.109
+O. 716 0.116
+1.176 0.171
+l.oal 0.190
+o.
+1.174 0.158
a
-0.85 1.61
-2.23 3.28
-9.65 3.49
-7.55 2.87
-3.68 4.80
b
+0.668 0.057
+1.253 0.234
+1.142 0.394
+1.770 0.416
+1.760 0.344
Lead
DiSC electrodeFrank
equations y = a + bx relating
DiSC
QRS 745 0.123
X t15.24 2.48
T 888 0.135
QRS Y
T
QRS Z a
+i6.88 7.58
f19.31 6.00
T b
-f-O.548 0.112
+1.273 0.221
737 0.096
-12.20 4.58 $1.819 0.518
Volume Number
67 5
Quantitative
comparison
of six nominally
from confirming the general vectorial analysis described above, they provide a further basis for comparison by studying in detail the form of the inscribed loops to detect moment-to-moment characteristic features of outline. For example, in Subject No. 1 the multiple-electrode grid, disc, McFee, and SVEC III all demonstrate similar anterosuperior terminal depolarization activity. Discussion
The spatial vectorial approach to the investigation of cardiac electrical phenomena offers undoubted advantages, as
orthogonal
665
VCG systems
outlined by Pipberger,8 over conventional 12-lead electrocardiography, but these merits cannot be fully achieved until general agreement has been reached on the fundamental physical bases which govern the distribution of electrical phenomena throughout the body during the varying conditions of the cardiac cycle, and until a system has been devised to measure accurately the corresponding instantaneous surface potentials. In the present state of knowledge and absence of such agreement the benefits of vectorcardiography can probably best be realized by investigating in detail the rela-
the individual values of lead scalar area magnitude for all correlated pairs of vectorcardiographic
Multiple electrodeSVEC III
+16.95 3.07
Multiple electrodeDower
Mc FeeFrank
+4.34 1.72
+0.89 2.26
+4.67 2.18
+5.85 1.91
to.563 0.169
+0.797 0.165
$0.694 0.214
+O. 764 0.178
+5.11 5.96
Mc FeeSVEC III
+13.43 7.32
+0.375 0.121
+o.m3 0.241
+0.758 0.287
-0.15 0.89
+6.01 4.26
-0.82 1.53
+1.404 0.061
+1.912 0.527
Mc FeeDower
+10.25 7.68
FrankSVEC
III
$16.48 2.68
FrankDower
SVEC IIIDower
+3.71 4.46
+0.953 0.311
+0.357 0.110
$0.879 0.181
+0.01 1.45
+5.63 4.66
+0.72 0.48
+.5.57 3.08
+4.87 2.90
+1.394 0.097
$1.463 0.100
j-2.049 0.577
f1.041 0.033
+1.387 0.381
+1.321 0.359
+5.33 4.34
+I.64 4.15
+2.11 5.59
+1.45 3.10
+1.124 0.157
+1.480 0.163
+1.346 0.202
$0.869 0.112
-9.80 3.13
-1.52 2.30
-5.50 1.71
-1.67 1.32
-6.03 0.80
-4.56 1.00
+2.682 0.541
+0.731 0.261
+1.230 0.249
+1.041 0.191
to.467 0.104
+0.367 0.130
+22.94 10.62 +1.643 0.393
t15.1.5 17.19 f1.429 0.505
-10.17 7.31 +I.234 0.246
+12.07 4.57 +0.649 0.1.58
666
Beswick
and Jordan
Table V. .Mean @mar and spat&
vectoriab data derived
from
the 6 vectorcardiographic
techniques
I Multipleelectrode
grid
technique
Planar values FAQRS
63” 13 54”
60 13 55”
& 1.5 58” 8
+Z” 16 58” 8
296” 22 68”
304” 23 65”
F& ^
FAQRB-T
FAG HAQRS
HAT ^ HAQRB-T
SAT
^ SAQRS-T
S&4,0
Spatial
values (SP)~QRfrT
(SPMQRS (SP)AT
(SP)An
Mc Fee and
Parungao
Frank
61” 16 51” +:i”
49” 15 46”
16 54” 12
::a 17 47” 9
312’ 22 41”
327” 26 50”
Dower and Osborne
42” 22 7” 7 +35” 24 20” 9
29 41” 14
36 13” 20
34 27” 12
+% 45 38” 13
140” 23 29”
132” 23 35”
12.5” 20 56”
120” 24 40”
117” 40 6”
117” 23 45”
+1%
+l:b 28 61” 20
104” 28 39 mvs. 13 83 mvs. 27 82 mvs. 31
+:27, 28 60” 13
90” 27 33 mvs. 10 72 mvs. 20 78 mvs. 25
tive performances of the currently available techniques, with the ultimate object of selecting the most nearly ideal method, or, more likely, of achieving a most satisfactory compromise, which, incidentally, will have to take account not only of purely theoretical factors but also of the technical practicability of its application in all circumstances of health and disease, habitus and posture, and possibly during exercise. It was with these considerations in mind that we undertook the present study, first to ascertain to what extent simplification of the method originally developed in this
+Z
+C
+& 31 80” 15
62” 27 30 mvs. 10 61 mvs. 20 79 mvs. 2.5
+~~” 33 64” 12
66O 30 25 mvs. 6 49 mvs. 14 62 mvs. 19
+lll”
III
61” 14 54” 17 +7” 14 56” 1.5
30 39” 25
+&
327” 36 53”
SVEC
322” 31 53” 18 +91” 43 3.5” 16
H&L SAQRS
Large disc modi$cation
+E 43 26” 14
29 6.5” 9
88 43 18 mvs. 6 43 mvs. 12 47 mvs. 16
62” 28 20 mvs. 8 49 mvs. 21 60 mvs. 28
laboratory influenced the recorded surface potentials, and then to compare the results from this simplified technique with those obtained by four other, nominally orthogonal, vectorcardiographic lead systems. The simplification18 achieved by subst itution of a single thin, fenestrated tin disc for each of the multiple-electrode/resistor grids previously used for the 2 lead had the dual advantages of extreme ease of actual manufacture of the discs, and also of facility in their application to the thorax. Since only the Z lead has been modified, it is obvious that all corresponding results involving exclusively leads X and Y, either
Volume Number
67 5
Quantitutive
SUBJECT
FRONTAL
HORIP ONTAL
comparison
of six nominally
orthogonal
VCG systems
SUBJECT
No. I FRONTAL
SAGITTAL
667
Na 2
SAC IllAL
HORIP QNTAL
Multiple electrode
Disc electrode
McFee
(r
Parunqoo
Frank
Dower ..
G
Osborne
SVEC
III
.: . ,
, i: .’
..’
\‘3 ‘.
--.;
Fig. 1. Representative planar loops for two typical subjects by six vectorcardiographic methods. ’ singly or in combination for the multipleelectrode grid technique and its large disc modification, should be identical, and the fact that this is seen to be the case on reference to Tables I-VI proves, inter alia, the validity of the experimental and analytical procedures employed in this investigation. There was no significant difference between
the mean scalar area magnitudes for QRS or T (Tables I and II), a highly significant level of correlation was demonstrated to exist between the two methods for all 16 individual subjects (Table III), and the calculated regression lines all passed through the origin and had slopes which did not differ from unity (Table IV). In
668
Beswick
Am. Hcnvt 1. May, 1964
and Jordan
addition, the analogous frontal planar projected angles for both QRS and T were statistically identical for the two methods (Tables V and VI), although it should be mentioned that, possibly fortuitously, the difference of 4 degrees in the manifest frontal QRS-T angle was apparently significant. In contrast, the mean scalar area magnitudes for both QRS and T as determined by the disc modification were significantly smaller by approximately 25 per cent than those obtained by the multiple-electrode grid technique, but, nonetheless, the corresponding individual values were well correlated by the equations: QRS: (Disc method value) = -0.85 + 0.67 (Multiple electrode method value). T: (Disc method value) = +16.88 j-0. 55 (Multiple electrode method value). As a result of the attenuation of this Z lead activity the mean spatial QRS-T angle according to the disc method was significantly reduced by 14 degrees, as compared with the multiple-electrode grid, because of a less posterior location of QRS and a tendency to a less anterior location of T. In addition, the spatial magnitudes
Table VI.
Sign$cance DiSC electrodeMultiple electrode
of the di$erences between the vector&
DiSC electrodeMc Fee
DiSC electrodeFrank
-
+-l+ -
-
+-t
FAQRB
F& +
FAQRS-T
-
Fill3 ^
of QRS and 7’ were both retluced by 15 per cent, but the ventricular gradient was unchanged in direction and magnitude. The secondary purpose of this investigation, the comparison of the interrelationships between these two methods and the four other currently used orthogonal systems, involved the analysis of all possible (i.e., fifteen) pairs of corresponding sets of data. However, for clarity of discussion it appeared to be advisable to consider the relative performances of the methods in the chronological order of their dates of publication, commencing with Schmitt and Simonson’s SVEC III technique in comparison with all the others, followed by Frank’s, Dower and Osborne’s, McFee and Parungao’s, and the disc modification of our technique. Having demonstrated above the mathematical interchangeability between disc and multiple-electrode grid methods, we thought that inclusion of this last system in any further discussion was unnecessary. The major differences for QRS between the SVEC III and the other systems could be related primarily to smallness of the mean scalar area magnitude given by that
mean vakues for all pairs of vec-
DiSC electrodeSVEC III
Disc electrode-Dower
Multiple electrodeMc Fee
-
++ ++ ++
-
++
++
-
+
+
++
HAT
-
H~~QRFI-T
+ -
+-t ++ ++
Et +
z -
:z -
++ +
+&+
+ -
++ ++
+k+
+‘=
+ -
++ +
++
HAQR~
HAG SAQRB S4T SAQRB-T
-I-
SA,
I /
Multiple electrodeFrank ++ +
-
+++
+++ ++ ++
Et ++ k
+
++
:: ++
+++ -
(SP)WQRWT rSS%= (SP)A:
Levels
of significance:
- indicates
p > 0.05;
f
indicates
p = 0.05
- 0.02;
+ indicates
p < 0.02;
++
indicates
p < < 0.01;
t > 5.0.
Volume Number
67 5
Quantitative
comparison
of six nominally
system for lead X. However, the very high degree of scatter of the individual values was probably the reason that significant differences could not be demonstrated (Table II) nor any correlation be shown to exist between SVEC III and any other system for lead X scalar magnitudes. The high coefficient of variation was also probably responsible for the apparent lack of statistical differences between the T mean values for this lead, but good correlation was observed between SVEC I II, Frank’s, and the disc methods, although they were not directly interchangeable. For QRS there were also important differences in lead Y which characterized the SVEC III method, presumably due to its calibration factor. The mean area magnitude differed significantly from those derived from all other systems, although the corresponding individual observations were well correlated. The T mean area in this lead agreed only with that of Frank’s method, but, again, there was good correlation between the SVEC III individual values and those of the other techniques, except that of Dower and Osborne. In lead Z the SVEC 111 mean values torcardiografihic
Mzrltiple electrodeSVEC III
orthogonal
VCG systems
669
were similarly among the smallest in magnitude but differed significantly only from those of McFee and our disc modification. As before, there was, however, good individual correlation between this method and the others. For T there was good agreement in this lead between SVEC III and all the others except the disc technique. In summary, therefore, it can be shown that Schmitt and Simonson’s system registered, in general, smaller surface potentials, especially for QRS, in all 3 leads and wide variability between observations from different subjects, with lack of complete interchangeability with other methods. This finding would supplement the previous observations of Simonson, Schmitt and Nakagawag that the SVEC III method was not freely interchangeable with several additional systems, and tends to oppose the view of Langner, Okada, Moore and Fies2 that, for practical purposes, SVEC III is interchangeable with Frank’s method, although the present results do suggest that the latter system showed fewer points of difference from SVEC III than any other of the techniques investigated. Consideration of the performance of the
techniaucs
M&ipZe elcctrodeDower
Mc FeeFrank
Mc FeeSVEC III
Mc FeeDower
FrankSVEC
III
FrankDower
SVEC IIIDower
670
Beswick
and Jordan
Frank technique in comparison with those of Dower and Osborne, McFee and Parungao, and our disc electrode shows that it. disagreed in lead Y with all the others for both QRS and T mean scalar area magnitudes, whereas in the remaining leads its comparative treatment of QRS and T in relation to the other methods was less consistent. In lead X, although the T values agreed with all other systems, QRS agreed only with McFee, and in lead Z the observed data for both QRS and T agreed only with Dower’s system. Despite this lack of complete agreement between mean values, the individual values for QRS in all four of these systems could be mathematically interrelated, since satisfactory correlation coefficients could be derived from all paired sets of data. It is apparent, therefore, that, although Dower and Osborne based their method essentially on that of Frank, the practical simplification involving the reduction of electrode positions from 7 to 4 resulted in appreciable modification of lead response. The outstanding characteristic of the Dower and Osborne system was the insensitivity of the Y lead relative to those of the other techniques investigated, particularly in respect to T, so that for this lead the ratio of T to QRS scalar area was reduced to 0.44 compared with approximately 1.8 for the other methods, and the frontal plane projection of T was raised nearly to the horizontal. From the point of view of voltages registered, the McFee and Parungao system approximated most closely those of the disc method, and, consequently, the planar loops obtained by these two lead systems were of generally most similar dimensions, but the outstanding difference lay in the more vertical disposition of the T loop in the McFee records. This is apparently due to the unequal attentuation of QRS and T voltages resulting in a ratio of T to QRS mean scalar areas of 1.9, which is substantially lower than for any other technique. In conclusion, it may be emphasized that, in order ultimately to decide on the most satisfactory compromise lead system to be adopted for universal application in vectorcardiography, account should be taken not only of the quantitative mathematical
comparisons but also of those characteristics which can be included under the term “practicability.” Such features as least quantity, complexity and cost of equipment, its ease of calibration and immunity from extraneous electrical interference, and simplicity of electrode application in adverse circumstances should also be considered. Our subjective impressions are that the most practicable of these techniques is the large disc modification of our original method, and that the sequence McFee and Parungao, Dower and Osborne, Frank, and Schmitt and Simonson’s SVEC III lists the other methods in order of increasing complexity. Summary Each of 16 normal males was examined by two vectorcardiographic techniques previously described by us, and also by the lead systems of Schmitt and Simonson (SVEC III), Frank, Dower and Osborne, and McFee and Parungao. For each subject the scalar area magnitudes in leads X, Y, and Z, and the planar and spatial vectorial values were determined by all six methods of vectorcardiography. The corresponding means and the results of a statistical analysis comparing the performance of every technique with that of the others are presented. We wish to thank Miss S. Braithwaite, Miss V. Holden, Mr. W. Barry, and Mr. R. Boothby for technical and secretarial assistance, and also the Medical Research Council for a grant toward the cost of equipment. REFERENCES 1. Burger, H. C., van Milaan, J. B., and Klip, W.: Comparison of two systems of vectorcardiography with an electrode to the frontal and dorsal sides of the trunk respectively, AM. HEART J. 51:26, 1956. 2. Langner, P. H., Okada, R. H., Moore, S. R., and Fies, H. L.: Comparison of four orthogonal systems of vectorcardiography, Circulation 27 ~46, 1958. 3. Schmitt, 0. H., and Simonson, E.: The present status of vectorcardiography, A.M.A. Arch. Int. Med. 96:574, 1955. 4. Frank, E.: An accurate clinically practical system for spatial vectorcardiography, Circulation 13:737, 1956. .5 McFee, R., and Johnston, F. D.: Electrocardiographic leads. III. Synthesis, Circulation 9:868, 1954. 6. Helm, R. A.: An accurate lead system for spatial vectorcardiography, AM. HEART J. 53:415, 1957.
Vokme Number
67 5
Quantitative
comparison
7. Pipberger, H. V., and Lilienfield, L. S.: Application of corrected electrocardiographic lead systems in man, Am. J. Med. 25:539, 1958. 8. Pipberger, H. V.: Current status and persistent problems of electrode placement and lead systems for vectorcardiography and electrocardiography, Prog. Cardiovas. Dis. 2:248, 1959. 9. Simonson, E., Schmitt, 0. H., and Nakagawa, H.: Quantitative comparison of eight vectorcardiographic lead systems, Circulation Res. 7:296, 1959. 10. Bristow, J. D.: A study of the normal Frank vectorcardiogram, AM. HEART J. 61:242, 1961. 11. Jordan, R. C., and Beswick, F. W.: Lead field scalar and loop spatial electrocardiography: a preliminary survey on normal adult males and comparison with other methods, Circulation 18:256, 1958. 12. Forkner, C. E., Hugenholtz, P. G., and Levine, H. D.: The vectorcardiogram in normal young adults: Frank lead system, Aaa. HEART J. 62:237, 1961. 13. Burch, G. E., Cronvich, J. A., and Zao, Z. Z.: Vectorcardiographic deflections obtained with various reference systems in cadavers, AM. HEART J. 61:667, 1961. 14. Burger, H. C., van Milaan, J. B., and Klip, W.:
of six nominally
orthogonal VCG systems
671
Comparison of three different systems of vectorcardiography, AM. HEART J. 57:723, 1959. 15. Burger, H. C., van Brummelen, A. G. W., and van Herpen, G.: Compromise in vectorcardiography. Displacement of electrodes as a means of adapting one lead system to another, AM.
HEART
J. 62:398,
1961.
16. Burger, H. C., van Brummelen, A. G. W., and van Herpen, G.: Compromise in vectorcardiography. II. Alteration of coefficients as a means of adapting one lead system to another, AM. HEART
J. 64:666,
1962.
17. McFee, R., and Parungao, A.: An orthogonal lead system for clinical electrocardiography, AM. HEART J. 62:93, 1961. 18. Beswick, F. W., and Jordan, R. C.: A simple chest electrode for orthogonal vectorcardiography, AM. HEART J. 67:232,1964. 19. Dower, G. E., and Osborne, J. A.: A clinical comparison of three VCG lead systems using resistance-combining networks, AM. HEART J. 55:523, 1958. 20. Beswick, F. W., and Jordan, R. C.: Cardiological observations at the Sixth British Empire and Commonwealth Games, Brit. Heart J. 23:113, 1961. 21. Ashman, R., and Byer, E.: The normal human ventricular gradient, AM. HEART J. 25:16, 1943.