Abstract
The electrocardiogram as ordinarily taken is a record of the differences of potential occurring between various parts of the body remote from the heart. While these differences of potential can be shown to be due to a primary electrical effect in the heart muscle itself, it is evident that they also depend on the nature of the body tissue as a conducting medium. Thus, if the body were composed of a non-conducting material, it is obvious that the primary cardiac electrical effect would not give rise to differences of potential in remote parts, while, on the other hand, if the body possessed the property of a good conductor, such as copper, it can be shown that the difference of potential between parts remote from the heart would be infinitesimal.
These considerations led us to believe that the presence of a large effusion surrounding the heart, especially a large pericardial effusion, might manifest itself by a lowering of the voltage of the electrocardiogram. This belief has been reinforced by our observation of seven cases of low voltage associated with large pericardial or pleuropericardial effusions. In some of these cases the markedly low voltage of the electrocardiogram led to a suspicion of effusion, which was later confirmed by X-ray examination, aspiration or autopsy finding.
The characteristic finding in the electrocardiogram is a decided lowering of voltage of the main deflection in all three leads. This is not necessarily associated with any constant alteration in the shape of the various waves, although it is quite conceivable that the effusion may also alter the electrical axis of the hear in some cases, or cause other changes in the propagation of the electrical disturbance.
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