Clinical electrocardiography / by Sir Thomas Lewis.

  • Thomas Lewis
Date:
1913
Catalogue details

Licence: Public Domain Mark

Credit: Clinical electrocardiography / by Sir Thomas Lewis. Source: Wellcome Collection.

    25/136 (page 13)
    / V 1 L .) ) CHAPTER II. THE PHYSIOLOGICAL ELECTROCARDIOGRAM. The electrocardiogram of a physiological heart beat consists of a series of deflections, some of which are rapid and of short duration while others are slow and of longer duration. They have been named in a purely empirical fashion, P. Q, R, S and T. The electrocardiogram opens with a blunt summit P, which occupies presystole, and is due to contraction of the two auricles (Fig. 7 and 8). Following upon this deflection the string shadow either maintains the zero position or dips somewhat. I speak of these portions of the electrocardiogram as the “ auricular complex ” ; this complex begins with the upstroke of P and terminates at the opening of the “ ventricular complex.” The latter varies in the number of its component deflections ; in its full form it comprises Q, a small downward deflection, R a steep, tall and pointed summit, S a steep depression of variable depth, and T a broad rounded summit. The period occupied by these deflections is approximately that of the ventricular systole to which they are due. The earliest sign of con¬ traction in the ventricle occurs a little after the commence¬ ment of R, and usually during its upstroke. The contraction ends where T passes into the horizontal line of diastole, or within a few hundredths of a second of this point. These relations are indicated in Fig. 8, which is a simultaneous record of the electric changes and the apical heart sounds.