this content will be beneficial for b.sc nursing 1st year students.

1. CARDIAC CYCLE

2. Cardiac Cycle:
Definition:
The sequence of changes in the pressure and flow in
the heart chambers and blood vessels in between
the two subsequent cardiac contractions is known as
cardiac cycle.
• Normal duration: 0.8 second at heart rate of 75 per
minute.
• Atrial systole: 0.1 second
• Ventricular systole: 0.3 second
• Atrial diastole: 0.7 second
• Ventricular diastole: 0.5 second

3. Events in Cardiac Cycle:
• The parts of heart normally beat in an orderly
sequence- atrial systole, ventricular systole, atrial
diastole and ventricular diastole.

4. Events in Cardiac Cycle:

5. A. Atrial Systole:
1) Duration 0.1 second. It is seen following the
impulse generation in the SAN.
2) Atrial muscle contracts and atrial pressure rises
with ventricular pressure following it.
3) It propels approximately 30% additional blood
into the ventricles.

6. B. Ventricular Systole:
1) Total duration 0.3 second. It is seen after the
ventricles get invaded by the excitation process.
Ventricular contraction begins and ventricular
pressure exceeds atrial pressure very rapidly
causing closure of AV valves with production of
first heart sound (HS1).
2) The amount of blood ejected by each ventricle
per stroke at rest is 70-80 mL. this is called stroke
volume. This is approximately 65% of the end-
diastolic ventricular blood volume (EDV).

7. C. Atrial Diastole:
1) Duration 0.7 second.
2) During this phase, atrial muscles relax and atrial
pressure gradually increases due to continuous
venous return.

8. D. Ventricular Diastole:
1) Total duration 0.5 second. During ventricular
diastole the arterial pressure is better sustained
due to elastic recoil of the vessel wall and
immediately arterial pressure exceeds that in the
ventricle this results in closure of semilunar
valves causing sharp second heart sound (HS2).
2) The ventricular filling occurs passively during this
phase due to continuous blood return to the
heart (venous return) and due to atrial systole.

9. ELECTROCARDIOGRAM (ECG):

10. Electrocardiogram (ECG):
• Body is a volume conductor, i.e. body fluids are
good conductor of electricity. Therefore electrical
changes which occur in the heart with each heart
beat are conducted all over the body and can be
picked up from the body surface. The record of
these electrical fluctuations during cardiac cycle is
called electrocardiogram (ECG).

12. NORMAL ECG:
• The wave associated with electrical activity of the
various parts of the heart tissue during each cardiac
cycle are represented by letter P,Q,R,S and T.
1) P wave: It is due to atrial depolarisation and
represents the spread of impulse from SA node to
atrial muscles.
2) P-R segment: Following the P wave there is a brief
isoelectric period of 0.04 second called P-R segment.
3) QRS complex: It is due to ventricular depolarisation.

13. NORMAL ECG:
4) Q wave: Its duration less than 0.04 second,
beginning of Q wave represents invasion of mid-
portion of the interventricular septum by
excitation process.
5) R wave: It is a prominent and positive wave, it
represent excitation process, its height is directly
proportional to the functional activity of
ventricles.
6) S wave: It is negative deflection which follows
the ‘R’ wave, it represent excitation of more basal
parts of ventricles.

14. NORMAL ECG:
7) S-T segment: Following QRS complex there is
long isoelectric period which extend from the end
of S wave to the beginning T wave called S-T
segment. Its duration is 0.04 to 0.08 second.
8) T wave: Rounded positive deflection of duration
0.27 second and 0.5 mV height, It represents
ventricular repolarisation.