The electrocardiogram (ECG) is composed of a P-wave, a QRS complex, and a T-wave. These three components are measured:-once during each cardiac cycle.-three times during each cardiac cycle: during a contraction of the atria, a contraction of the ventricles, and when the heart is at rest.-twice during each cardiac cycle: during a contraction of the atria and a contraction of the ventricles.-independently of the cardiac cycle.
