Physiology and biochemistry in modern medicine . e taking of elec-trocardiograms is indeed quite a simple matter, and the extremely im-portant information which they give us concerning the mechanism ofthe heartbeat and the evidence of myocardial disease should make theiremployment a universal practice in all cardiac clinics. Some of theseclinical applications arc described elsewhere (page 266). ELECTROCARDIOGRAMS 261 What particularly interests us here is the contour of the electrocardio-gram in n normal person (Fig. 82). It will be observed thai there arethree waves above the Line of zero pot
Physiology and biochemistry in modern medicine . e taking of elec-trocardiograms is indeed quite a simple matter, and the extremely im-portant information which they give us concerning the mechanism ofthe heartbeat and the evidence of myocardial disease should make theiremployment a universal practice in all cardiac clinics. Some of theseclinical applications arc described elsewhere (page 266). ELECTROCARDIOGRAMS 261 What particularly interests us here is the contour of the electrocardio-gram in n normal person (Fig. 82). It will be observed thai there arethree waves above the Line of zero potential and two waves below have been lettered from before backward, P, <,), R, S, and T, and in all such records when correctly obtained, the waves above theline of zero potential indicate that the base of the heart is negative tothe apex. The exact cause of each wave has been ascertained by takingsimultaneously with the electrocardiogram a record of the mechanicalchanges occurring in the heart during each cardiac eycle. Such records. Fig. 82.—Normal electrocardiogram. Leads 1, 2, 3. Note that the height of the R deflection inlead 3 equals the difference between the height of Rx and R2. have been secured by taking intracardiac pressure curves with the resultsas shown in Fig. 83. The top curve represents auricular and the secondone ventricular pressure, Avhereas the lowest is an will be observed: (1) that the P-wave occurs just antecedent to con-traction of the auricles; (2) that the small positive wave, Q, which is ab-sent in these tracings, must occur just before the beginning of the con-traction of the ventricles; (3) that the negative wave, R, occurs just be-fore and during the early part of ventricular systole—that is, duringthe presphygmic period; and (4) that the long upward wave, T, culmi-nates at the moment the ventricle begins relaxing. 262 THE CIRCULATION OP THE BLOOD Although such comparisons give us considerable insight into the c
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