What does an ECG measure? Mark all that apply. (2 points) 1. Electrical activity in atrial muscle 2. Contraction of the atrial muscle 3. Relaxation of the atrial muscle 4. Electrical activity in ventricular mu
A. Electrical activity in atrial muscle
B. Contraction of the atrial muscle
C. Relaxation of the atrial muscle
D. Electrical activity in ventricular muscle