1. Cardiac Cycle
Dr Sadath Pareed
13/01/2014

2. cardiac cycle
• Galen (200AD) the father of expirimental physiology
knew that the heart set the blood in motion
• Circulation of the left and right heart are separated and
grasped by Servetus ( 1511-1553)
• Modern concepts of the circulation laid by Harvey (15781657)

3. Definition :
Each cardiac contraction proceeds through
a series of electrical and mechanical events that
govern the opening and closing of the valves ,
the flow of blood into and out of the heart, and
the timing of the heart sounds.
Together these electrical and mechanical events
represent the cardiac cycle.
Complete cycle of events in the heart from the
beginning of one heart beat to the beginning of the
next.

4. CARDIAC CYCLE : 0.8 SEC
• Atrial Systole : 0.1 sec
• Atrial Diastole : 0.7 sec
• Ventricular systole : 0.3 sec
• Ventricular diastole : 0.5 sec

5. Ventricular Cycle
Systole
Diastole
I. Isovolumetric contraction 0.05s IV. Protodiastole
II. Rapid ejection
0.10s V. Isovolumetric relaxation
III. Reduced ejection
0.15s VI. Rapid filling phase
VII. Diastasis
VIII. Atrial systole
Total
0.3 s
Total
0.04 s
0.06 s
0.10 s
0.20 s
0.10 s
0.5 s

7.  Wiggers diagram is the graphic
representation of the various events of the
cardiac cycle
 Each cardiac cycle consists of 8 segments
represented by Roman numerals

9. VENTRICULAR CYCLE

10. Ventricular Cycle
Systole
Diastole
I. Isovolumetric contraction 0.05s IV. Protodiastole
II. Rapid ejection
0.10s V. Isovolumetric relaxation
III. Reduced ejection
0.15s VI. Rapid filling phase
VII. Diastasis
VIII. Atrial systole
Total
0.3 s
Total
0.04 s
0.06 s
0.10 s
0.20 s
0.10 s
0.5 s

11. I Isovolumetric contraction
•
•
•
•
Isovolumic.
Duration 50 mSec
LV pressure 8 – 80 mmg.
S1 occurs 20ms after pressure
crossover.
• M1 followed by T1.
• QRS complex begins slightly
before & the later half of R wave
occurs in this phase.
• C wave of JVP occurs during this
phase.

13. II Rapid ejection phase
• Duration 0.10 s
• Opening of aortic valve –rapid
ejection--2/3 of ejection occurs.
• Steep rise in aortic pressure
because blood is expelled faster
than peripheral run off into aorta.
• LV volume decreases rapidly.
• ST segment of ECG occurs.
• No heart sounds are heard during
ejection phase.-AoV opening
clinically silent event
• Left atrial pressure initially
decreases & then slowly rises.

14. III Reduced ejection Phase
• Ejection maintained by kinetic
energy of blood flow.
• Lasts for 0.15 s.
• One third of ejection.
• Aortic pressure falls because run
off is faster than inflow.
• Ventricular volume decreases at
slow rate.
• Coincides with T wave of ECG.
• Atrial pressure continues to rise
due to atrial filling.

15. IV Protodiastole
 0.04 s.
 Ventricle starts relaxing and
ventricular pressure begins to fall
below that of aorta.
 Semilunar valves are still open.
 Deceleration of column of blood
in the aorta hitting the aortic valve.
 Time interval between pressure
crossover & S2.
 Aortic closure occurs earlier.

16. V Isovolumetric relaxation
 Begins with the closure of
semilunar valves.
 AV valves are still closed
(Isovolumic).
 Active relaxation and sharp fall
in LV pressures.
 A characteristic notch (incisura
or dicrotic notch) in the aortic
pressure tracings (Valve closure)
 After valve closure, the aortic
and pulmonary artery pressures
rise slightly (dicrotic wave)
 V wave of JVP.

17. V Isovolumetric relaxation
• The volume of blood that
remains in a ventricle is called
the end-systolic volume and is
~50 ml in the left ventricle.
• The difference between the
end-diastolic volume and the
end-systolic volume is ~70 ml
and represents the stroke
volume.
• AV valves open at the end of
this phase .

18. VI
Rapid filling phase
 0.10 s.
 Begins with the opening of the
AV valves.
 70 – 80 % of filling.
 Sharp rise in ventricular volume.
 Fall in atrial pressure - Y descent.
 Ventricular filling is normally
silent.
 Audible third heart sound (S3)
represents tensing of chordae
tendineae and AV ring during
ventricular relaxation and filling.

19. 





VII Diastasis
Reduced filling phase; lasts for
0.20 s; 5 – 10 % of filling.
80% of ventricular filling occurs
before atrial contraction
Shortens with tachycardia.
Ventricular volume continues to
increase slowly.
Pressure rises gradually in both
atria and ventricles.
Corresponds with T – P segment
on ECG.

21. VIII Atrial systole
 Follows diastasis , lasts for 0.10s.
 Contributes 10 – 20 % of
ventricular inflow.
 Significant contribution ( 20 – 40
% ) in exercise , tachycardia ,
poor LV compliance.
 Coincides with fourth heart
sound.
 Causes slight rise of atrial
pressure curve ( 5 mmHg )
– a wave.
 P wave of ECG begins slightly
before atrial contraction.

22. • In children & young
adults ,the majority of
ventricular filling
occurs in early diastole
with prominent E
velocity &only small
contribution to
ventricular filling due
to atrial contraction

25. ATRIAL CYCLE

26. Atrial cycle
• Atrial systole
• Atrial diastole
• Atrial pressure
curve shows 3
pressure waves
- 0.1 s
- 0.7 s
a , c , v and
two falls in pressure called the
descents
x and y

27. Atrial cycle
A wave
 Reflects atrial systole.
 Follows P wave of ECG.
 Precedes upstroke of carotid
impulse and S1.
 Summit of A occurs 0.02 sec
after S4.
C wave
 Reflects the bulging of closed
AV valves into the atrium
during isovolumetric
contraction.

28. Atrial cycle
V wave
 Continuing venous in flow into
the atrium during ventricular
systole while the AV valve is
closed.
 Begins before S2& reaches its
peak after P2.
X descent
 Continuing atrial relaxation and
pulling of AV valves downward
by the contracting ventricle.

29. Atrial cycle
 Occurs during isovolumetric
contraction & systole. ( systolic
collapse)
Y descent
 Reflects the negative deflection
of atrial pressure when the AV
valve opens in early diastole.
( Diastolic collapse )
 It begins and ends during
diastole.

31. HEART SOUNDS

32. Heart Sounds
• Valve closure and rapid-filling
phases are audible with a
stethoscope placed on the chest.
• The first heart sound, results from
the closure of the AV valves,
heralds ventricular systole.
• The second heart sound, shorter
and composed of higher
frequencies than the first, is
associated with closure of the
semilunar valves at the end of
ventricular ejection.

34. Physiological Vs cardiological
systole and diastole
• Cardiological systole
demarcated by interval
between 1st and 2nd
heart sounds ,lasting
from M1 to A 2
• Physiological systole
lasts fom from start of
IVC to peak of
ejection phase, so that
physiological diastole
commences as LV
pressure starts to
fall(during reduced
ejection)

35. • Thus cardiological systole,demarcated by
heart sounds rather than physiological
events,starts fractionally later than
physiological systole and ends significantly
later

36. Heart Sounds
• Third and fourth heart sounds are
low-frequency vibrations caused
by early, rapid filling and late
diastolic atrial contractile filling
respectively.
• These sounds can be heard in
normal children but in adults
usually indicate disease.

37. VENTRICULAR
PRESSURE-VOLUME LOOP

38. •
•
•
•
Pressure-Volume loop
The cardiac cycle can be
divided into four basic
phases: .
Isovolumetric contraction
phase.
Ejection phase.
Isovolumetric relaxation
phase.
Ventricular filling phase

39. Pressure-Volume loop
Point 1 on the PV loop is
the pressure and volume
at the end of ventricular
filling (diastole), and
therefore represents the
end-diastolic pressure
and end-diastolic
volume (EDV) for the
ventricle.

40. Pressure-Volume loop
As the ventricle begins to
contract isovolumetrically
(phase b), the LVP increases
but the LV volume remains
the same, therefore resulting
in a vertical line (all valves
are closed).
Once LVP exceeds aortic
diastolic pressure, the aortic
valve opens (point 2) and
ejection (phase c) begins.

41. Pressure-Volume loop
During this phase the LV volume
decreases as LVP increases to a
peak value (peak systolic pressure)
and then decreases as the ventricle
begins to relax.
When the aortic valve closes
(point 3), ejection ceases and the
ventricle relaxes isovolumetrically
- that is, the LVP falls but the LV
volume remains unchanged,
therefore the line is vertical (all
valves are closed).

42. Pressure-Volume loop
The LV volume at this time is the
end-systolic volume (ESV).
When the LVP falls below left atrial
pressure, the mitral valve opens
(point 4) and the ventricle begins to
fill.
Initially, the LVP continues to fall as
the ventricle fills because the
ventricle is still relaxing.
However, once the ventricle is fully
relaxed, the LVP gradually increases
as the LV volume increases.

43. Pressure-Volume loop

44. Thank You