288 



THE MECHANICS OF THE HEART 



as the "auricular complex of the electrocardiogram."^ The ''ven- 

 tricular complex" of the curve is much more complex. When fully 

 developed, it consists of a deflection below the abscissa, called the Q- 

 wave, a very conspicuous upward deviation or i^-wave, a second 

 depression or S-wave, and ^ b road rounded elevation or T-wave. 

 The largest variation at R dlhyies 0.02 to 0.04 sec. and the one at 

 T, 0.1 sec. The total time of thft complex corresponds approximately 

 to the duration of the ventricular contraction, which has been proved 



ll ll ll l li ii 



ojSee. 



Fig. 146. — Electrocardiogram Obtained by Photographing the Movements of the 

 Thread of a String-galvanometer. 

 The upper figure shows the photographed curve while the lower one is a diagram 

 constructed from the photograph to show the electrical changes occurring during a single 

 cardiac cycle. To obtain this record the electrodes were connected with the right and 

 left hands. Waves with the apex upward indicate that the base of the heart (or the 

 right ventricle) is negative to the apex (or left ventricle) . Waves with the apex down- 

 ward have the opposite significance. Wave P is due to the contraction of the auricle. 

 Waves Q, R, S, and T occur during the systole of the ventricle. The curve seems to 

 show that the contraction in the ventricles begins first toward the apex (or in the left 

 ventricle), since the negativity first appears toward that side (waveQ). (Einthoven.) 



to begin very shortly after the onset of the deflection at R and to con- 

 tinue to about the end of the T-wave. 



A detailed discussion of the individual variations in the electro- 

 cardiogram ^ cannot prove of much value, because many matters 

 pertaining to it must first be thoroughly investigated. Its complexity, 

 however, clearly betrays the segmental arrangement of the cardiac 

 musculature as well as the wave-like character of its contraction. It 

 appears that the excitation wave, on being distributed to the different 

 areas of the heart, gives rise to a muscular activity which is not at all 



^ Lewis, Clinic. Electrocardiography, London, 1913. 



2 Einthoven, Pfliiger's Archiv, cxlix, 1913, 65; Meek and Eyster, Am. Jour, of 

 Physiol., XXX, 1912, 271; James and Williams, Am. Jour, of the Medical Sciences, 

 1910, and Kraus and Nicolai, "Das Electrocardiogram," Leipzig, 1910. 



