Appropriate leads in electrocardiography.

Before it is possible to assess the significance of any variation in the electrocardiographic tracing, it is necessary to know the appearances of the tracing in healthy subjects. Current practice is to record three standard limb leads, three augmented unipolar limb leads, and upwards of seven chest leads. In this way, minor variations from the normal are likely to be appreciated and more accurate diagnosis can be made in disease of the myocardium. The innocent nature of certain variations from the accepted normal tracing cannot be overemphasized, because an incorrect interpretation may lead to the premature termination of a career, unnecessary restriction of day-to-day activities, and unreasonable anxiety to the family of the unfortunate victim. It is, therefore, of the utmost importance to establish the significance of these minor abnormalities in the light of our increasing knowledge of the appearance of the normal tracing. This investigation is concerned with the appearance of certain aspects of the tracing in apparently healthy males, especially with regard to the influence of respiration on the Q wave and the configuration of the S-T segment and the T wave in lead III, the appearance of the T wave in the bipolar CR and the "unipolar" V chest leads, and the possible usefulness of a transthoracic lead.