In lead I of an EKG, the electrical activity is measured from which two points?

In lead I of an EKG, the electrical activity is measured from the right arm to the left arm. This lead is oriented horizontally across the chest and provides a view of the heart's electrical activity in a left-to-right direction.

The difference in electrical potential between the two arms allows for an assessment of how effectively the heart's electrical impulses are traveling, particularly through the atria and ventricles. The output from this lead is crucial for identifying various cardiac conditions, such as arrhythmias or myocardial infarctions, as it provides insight into the overall electrical axis of the heart.

Each of the other options involves different combinations of extremities that do not align with how lead I is defined. Understanding that lead I specifically uses the right and left arms helps differentiate it from the other leads, which measure electrical activity across different points in the body.