In the given passage, measurement of ECG has initiated at the point of wave of excitation within the heart. The baseline (isoelectric line) is a straight line on the EKG. It is the point of departure for the electrical activity of depolarizations and repolarizations of the cardiac cycles. The P wave results from atrial depolarization.
The QRS complex is a result of ventricular depolarization and indicates the start of ventricular contraction; simultaneous, smaller wave corresponding with the repolarization (relaxation) of the atria is obscured by this large QRS complex. The T wave results from ventricular repolarization and signals the beginning of ventricular relaxation. The electrical signal for atrial repolarization is masked by the larger QRS complex.
Just as the electrical activity of the pacemaker is communicated to the cardiac muscle, "echoes" of the depolarization and repolarization of the heart are sent through the rest of the body. By placing a pair of very sensitive receivers (electrodes) on other parts of the body, the echoes of the heart's electrical activity can be detected. The record of the electrical signal is called an electrocardiogram (EKG or ECG). You can infer the heart's mechanical activity from the EKG. Components of the EKG- The electrical events of the heart are usually recorded on the EKG as a pattern of a baseline broken by a P wave, a QRS complex, and a T wave.
Thus, the options (d), (c) and (a) are incorrect.
In the given passage, measurement of ECG has initiated at the point of wave of excitation within the heart. The baseline (isoelectric line) is a straight line on the EKG. It is the point of departure for the electrical activity of depolarizations and repolarizations of the cardiac cycles. The P wave results from atrial depolarization.
Therefore, the correct option is – b. The ECG systematically and quickly measures the stages at which the “wave of excitation” occurs within the heart and records them.