Final answer:
The deflections on an ECG are labeled with the letters P, Q, R, S, and T, representing the electrical activity of the heart during a cardiac cycle.
Step-by-step explanation:
The deflections that occur on an Electrocardiogram (ECG) are labeled with the letters P, Q, R, S, and T. These deflections correspond to specific electrical events in the heart. The P wave represents the depolarization of the atria, which precedes atrial contraction. The QRS complex, which is a series of three waves, represents the depolarization of the ventricles, indicating the preparation for ventricular contraction. Finally, the T wave signifies the repolarization of the ventricles, a necessary step for the ventricles to relax and prepare for the next heartbeat.
In summary, the lead II potential, measured between the right arm and left leg, is usually the most graphed and analyzed in ECGs. It provides significant insight into heart-muscle function and its coordination with arterial blood pressure.