The last conclusion of this passage is the measurement of ECG is initiated form the wave of excitation occurred within the heart. This wave of contraction is started from SA node to the AV node.
The intrinsic conduction system in the order that a depolarizing impulse travels during a normal heartbeat to record ECG: 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
Thus, the options (d), (b) and (a) are incorrect.
The last conclusion of this passage is the measurement of ECG is initiated form the wave of excitation occurred within the heart. This wave of contraction is started from SA node to the AV node.
Therefore, the correct option is – C. The ECG systematically and rather quickly measures the stages at which the “wave of excitation” occurs within the heart and records them. This wave has three distinct steps that spread from the SA node to the AV node.