Cancellation of electrocardiographic effects during ventricular excitation.

• The electrocardiographic effects of electrical activity in the heart are partially canceled by multidirectional spread of that activity. For example, the effect of excitation directed toward the right may be canceled by a similar process moving toward the left. The extent of such cancellation is of fundamental importance in electrocardiography. It is a measure of the extent to which cardiac electrical activity could be altered without corresponding electrocardiographic changes. It is also the basis for estimates of the degree of cardiac electrical alteration necessary to account for given changes in the electrocardiogram.