1913.] 



Electrical Axis of the Human Heart. 



523 



To compare effects in the sagittal plane, the leads to be taken are :— 



Mouth to precorclium and mouth to back for the upper part of the body ; 

 back to foot and precordium to foot for the lower part. We can calculate 

 the value of an angle « formed by the current-axis and the vertical in 

 the antero-posterior or sagittal plane, by taking the values of the two 

 upper and two lower spikes. And without laying stress upon the precise 

 values obtained for the amde it is satisfactory to find that the arrow 

 representing its position and direction comes out from the calculation 

 conformably with what might be anticipated. 



To complete our picture of the current direction we may compare effects 

 horizontally in transverse section across the body ; this can be done roughly 

 by the leads from precordium. and back to the right and left hands, or 

 better, by takiug the effects from four symmetrical leads encircling the chest 

 on a level with the heart. 



This symmetrical arrangement of electrodes gives a more satisfactory set of 

 values than is afforded by the two hands with the front and back of the 

 chest, which gives values in an oblique and principally frontal plane, as 

 is illustrated by the following group of measurements : — 



B. 0. B. connected to an oscillograph by large (100 x 75 mm.) electrodes on 

 the right and left sides of the chest, and by the right and left hands dipping 

 in saline, gave the following values : — 



At first sight these results appeared rather perplexing, but their obscurity 

 disappears when we reflect that leads from the hands are, as regards the 

 heart, equivalent to leads from the shoulders, and plan the results accordinglv 

 along the lines of a frontal diagram. We then realise that of the four 

 leads, the 3rd, being " axial " as regards the heart, must be the " strongest " 

 lead, and the -1th lead, being " equatorial," must be the " weakest " lead. 



In a transverse section of the thorax, i.e. in the horizontal plane with the 

 body in the erect posture, similar differences obtain between the two sides. 

 Taking leads from the precordium and first the right then the left hand, we 



vol. r.xxxvi. — b. 2 Q 



Eight hand 



