In the above given passage, author has described the movement of the Electrocardiogram (EKG) as the wave of excitation is proceeding.
The following is the order of ventricular depolarization wave follows,
The intrinsic conduction system in the order that a depolarizing impulse travels during a normal heartbeat: from first to last (top to bottom).
Sino-articular node (SA node) -----> internodal pathway,-----> Arterio-ventricular node (AV-node) -----> Arterio-ventricular bundle situated in the septum of the heart --> Bundle of His ------> right and left bundle branches,-----> Purkinje fibers
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), (b) and (a) are incorrect.
In the above given passage, author has described the movement The Electrocardiogram (EKG) has shown as the wave of excitation is proceedings with electrical currents of heart.
Therefore, the correct option is – c. To inform the reader how an electrocardiograph reads the electric currents emitted by the heart.