ELECTROCARDIOGRAPHY 



37" 



TABLE 4. Alean Durations and Standard Deviations of 

 the Normal Orthogonal Electrocardiogram* 



* Recorded with the SVEC III system (see fig. 21). 

 [Data from Pipbergcr & Tanenbaum (374) and Pipbcrger 

 (368).] 



t Corrected Q-T duration was calculated by dividing the 

 actual Q-T duration by the square root of the preceding 

 P-R interval. 



direction (angles in fig. 58). The T vector (frontal) 

 shows a completely different form of migration, 

 starting with 0° value (a), and after having reached 

 60° the vector turns back again and ends at the 

 position 0° at the age of 60 years. In the horizontal 

 plane, the vector starts with 120° and turns to the 

 front, reaching 50° at the age of 60 years (497)- 

 With healthy persons between the age of 30 and 50 

 years, the main QRS axis in 97 per cent of cases has 

 been found to be between g° and 90° (a), with an 

 average of 43° (310) or 47° (357). The magnitude of 

 the angles a is distributed on a Gauss probability 

 curve with the mean both for QRS and T angles for 

 all groups of people between the ages of 5 and 50 

 at the same angle of about 45° (538). However, with 

 another method to be described immediately, a shift 

 to a more horizontal position of the vector in the 

 course of age is apparent (498). 



This other method for calculating vector positions 

 in a fairly simple manner involves determining the 

 so-called "null contour" of potential distribution at 

 the surface of the thorax (34, 228). The procedure of 

 such determinations is as follows: one observes a uni- 

 polar EGG at various points on the thorax, and lo- 

 cates certain electrode positions at which the recorded 

 time-voltage area is minimal. One connects these 

 points and thus gets a "transitional zone," on one 

 side of which the polarity of the main deflection of 

 the EGG is reversed as compared to the other. This 

 zone in most cases has an elliptic form. This ellipse 



FIG. 55. Illustration of the null-contour method to determine 

 the direction of a vector in space. The plane is determined 

 which separates the predominantly positi\e from the negative 

 QR.S groups. The \ector stands perpendicular to this plane. 



can be regarded as a plane of zero potential though 

 the thorax to which the vector QRS is perpendicular 

 (fig- 55)- The error in this method is rather high, as 

 observed with a cylindrical model (205). This is not 

 surprising, because in such observations the distortion 

 of the electrical field exerts its greatest effect. Never- 

 theless, the "null-contour method" is not much 

 inferior to determinations of the heart vector with 

 conventional leads, without the lead vector correc- 

 tion. 



The theory of the null contour is closely correlated 

 to the potential distribution at the surface of the 

 thorax. This may be seen in figure 56, in which the 

 intersection of the null contour plane with a hori- 

 zontal cross section of the thorax is shown and the 

 isopotential lines are drawn in a somewhat arbitrary 

 manner. The potential distribution is, of course, the 

 result of the distorted field. In an ideal field, the 

 source and sink of the surface potential distribution 

 would never lie so close together. Such fields lead to 

 gross misinterpretations in the position of a heart 

 vector by assuming it to be derived from parallel 

 homogeneous lead fields. 



The vectors of the QRS areas can be determined, 

 of course, with every corrected lead system. Their 

 spatial values are listed in tables 5 and 6. We should 

 admit however, that the vectorial presentation of the 

 time-voltage areas has only a restricted physiological 

 meaning, insofar as QRS is concerned. The areas 

 integrate the whole spread of excitation to an average 

 direction of momentary vectors and thereby conceal 

 even the limited information given by the vector 

 loop. The very purpose of such time-voltage integra- 

 tions can only be to have a better understanding of 

 how T is generated. The method which best presents 



