| Autor: |
Wilson, Frank N., Macleod, A. Garrard, Barker, Paul S., Wilson, F N, Macleod, A G, Barker, P S |
| Zdroj: |
Annals of Noninvasive Electrocardiology; Jul2001, Vol. 6 Issue 3, p246-271, 26p |
| Abstrakt: |
IN previous articles from this laboratory1,2 it has been pointed out that, in accordance with the laws which govern the flow of electric currents in volume conductors, the potential variations produced by the cardiac muscle are very much greater in magnitude in the immediate neighborhood of the heart than at a distance from it. It has been shown that when one electrode of the string galvanometer is placed upon the pre-cordium, the position of the second electrode, so long as it is distant from the heart, has comparatively little influence upon the form of the ventricular electrocardiogram. Attention has been called to certain resemblances between leads of this type and direct leads of the kind employed by Lewis and Rothschild3 in which one electrode is placed in actual contact with the ventricular muscle and the other upon the chest wall. In both cases the form of the ventricular complex is determined in a very large measure, although not to quite the same extent in the former as in the latter, by the potential variations of the exploring electrode; in both cases the muscle units which lie nearest this electrode exert individually a much greater effect upon its potential than those which are more distant from it. Curves obtained by leading from points on or near the heart to one of the extremities utilized in taking the three standard indirect leads may be freed from the influence exerted by potential variations of the indifferent electrode by a method which we have recently described.4 When this electrode is placed upon the left leg the correction is made by subtracting from each ordinate of the recorded curve one-third of the sum of the deflections, measured in. millivolts, inscribed in Leads II and III at the corresponding instant in the cardiac cycle. It is possible in this way to determine, at least approximately, the time course of the potential of the exploring electrode, and thus to eliminate any difference beween direct and semidirect leads for which potential variations of the indifferent electrode are responsible. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
|
