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:
⇒ P-wave – electrical excitation (depolarisation) of the atria, which leads to contraction of both the atria.
⇒ QRS complex – depolarisation of the ventricles, which initiates ventricular contraction.
⇒ T-wave – 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)