Given below is the ECG of a normal human. Which one of its components is correctly interpreted below? [figure]
- Complex QRS - one complete pulse
- Peak T - initiation of total cardiac contraction
- Peak P and peak R together - systolic and diastolic blood pressures
- Peak P - initiation of left atrial contraction only
Answer
(1) Complex QRS - one complete pulse
Solution
As per NCERT, the P-wave represents the electrical excitation (depolarisation) of the atria, which leads to contraction of both the atria.
The QRS complex represents depolarisation of the ventricles, which initiates ventricular contraction, and the T-wave represents the return of the ventricles from excited to normal state (repolarisation); its end marks the end of systole.
By counting the number of QRS complexes in a given time period, the heart beat rate of an individual is determined.
∴ One QRS complex represents one complete pulse (heart beat).
Answer: (1)