The cardiac cycle is defined as the series of electromechanical events in the heart from one heartbeat to the next, mainly involving the sinoatrial node's action potentials initiating atrial and ventricular contractions. It consists of several phases including atrial contraction, isovolumetric contraction, and various ejection and filling phases, with corresponding electrical activity observable through an electrocardiogram. The document also discusses heart sounds, pressure-volume relationships, and disorders associated with central venous pressure waveforms.

1. THE CARDIAC CYCLE
PRESENTER: DR.
CHAMPAKA
MODERATOR:
DR.BHARATHI

2. DEFINITION
The cardiac cycle is the performance of
the human heart from the beginning of one
heartbeat to the beginning of the next.
It is a series of coordinated electromechanical
events that result in the ejection of blood from the
heart into the great vessels

3. MECHANISM
Each cycle is initiated by the spontaneous generation of an
action potential in the sino atrial node.
This node is located in the superior lateral wall of the right
atrium near the opening of the superior vena cava, and the
action potential travels from here rapidly through both atria and
then through the A-V bundle into the ventricles.

4. MECHANISM
Because of this special arrangement of the
conducting system from the atria into the
ventricles, there is a delay of more than 0.1
second during passage of the cardiac impulse
from the atria into the ventricles.
This delay allows the atria to contract ahead
of ventricular contraction, thereby pumping
blood into the ventricles before the strong
ventricular contraction begins. Thus, the atria
acts as primer pumps for the ventricles, and
the ventricles in turn provide the major source
of power for moving blood through the body’s

5. MECHANISM
The A-V valves (i.e., the tricuspid and mitral valves )
prevent backflow of blood from the ventricles to the atria
during systole,
And the semilunar valves (i.e., the aortic and pulmonary
artery valves ) prevent backflow from the aorta and
pulmonary arteries into the ventricles during diastole.

6. ACTION POTENTIAL
The types of action potential in the heart can be separated into
two categories:
1) Fast-response action potentials, which are found in the His-
Purkinje system and atrial or ventricular cardiomyocytes and
2) Slow-response action potentials, which are found in the
pacemaker cells in the SA and AV nodes.

8. THE CARDIAC CYCLE CONSISTS
OF
Electrical events ( generation of impulses, conduction
of the wave, ECG )
Mechanical events ( relaxation & contraction of atria &
ventricle )

9. WIGGERS’ DIAGRAM
Wiggers elegantly illustrated the mechanical,electrical
and acoustic events of the cardiac cycle.
His diagram depicts the aortic,ventricular and atrial
pressure tracings with concomitant ECG,ventricular
volume and auscultatory findings

10. WIGGERS’ DIAGRAM

11. PHASES OF THE CARDIAC
CYCLE
1. Phase of Atrial contraction
2. Phase of Isovolumic (isometric) contraction
3. Phase of rapid ejection
4. Phase of reduced ejection
5. Protodiastolic phase of the ventricle
6. Isovolumic (isometric) phase of relaxation of the ventricle
7. Rapid filling phase of the ventricle
8. Diastasis

12. PHASE OF ATRIAL CONTRACTION
75% of the blood flows
directly into the ventricles even
before the atria contracts.
Then atrial contraction causes
an additional 25-30% filling of
the ventricles which we also
call as “ATRIAL KICK”.
Pathologically fourth heart
sound (S4) can be heard.

13. FUNCTIONS OF VENTRICLES AS
PUMPS
 3 BASIC EVENTS :-
1. LV contraction
2. LV relaxation
3. LV filling

14. LV CONTRACTION
Can be divided into :-
Phase of isovolumic (isometric) contraction
Phase of rapid ejection
Phase of slow ejection

15. PHASE OF ISOVOLUMIC
(ISOMETRIC) CONTRACTION
As the ventricular contraction begins, the ventricular pressure
rises causing AV valves to close.
Then an additional 0.02-0.03 sec is required for the ventricle
to build up sufficient pressure to open the semilunar valves
against the pressure in aorta and pulmonary artery.
Therefore during this period, contraction is occurring in the
ventricle, but there is no emptying.
This term is not strictly true because there is apex to base
shortening & circumferential elongation.
1ST Heart sound is heard (S1)

16. PHASE OF RAPID EJECTION
When LV pressure rises
slightly above 80 mmHg and
RV pressure above 8 mmHg,
the ventricle pushes the
semilunar valves to open.
70% of the blood emptying
occur during first 1/3rd of the
period of ejection k/a PERIOD
OF RAPID EJECTION.

17. PHASE OF SLOW EJECTION
Rest 30% of blood emptying occur during the next 2/3rd of the
period of ejection k/a PHASE OF SLOW EJECTION.

18. VENTRICULAR VOLUME
Amount of blood ejected by each ventricle per stroke at
rest is 70-90 ml.
End diastolic ventricular volume is 130 ml
Therefore, end systolic ventricular volume is 50 ml.
Ejection fraction = 65%
The ejection fraction is a valuable index of ventricular
function.

19. LV RELAXATION
 Comprises of 5 phases :-
1. Early diastole (Protodiastole)
2. Late diastole (Period of isovolumic relaxation)
3. Rapid filling phase
4. Slow filling phase
5. Atrial systole

20. EARLY DIASTOLIC PHASE
At the end of the systole,
the already falling
ventricular pressure drops
more rapidly. This period
is k/a Protodiastole.
Lasts for 0.04 sec.

21. PHASE OF ISOVOLUMIC
(ISOMETRIC) RELAXATION
 Phase of late diastole
 AV valves & semilunar valves are closed.
 The ventricle muscle continues to relax for
another 0.03-0.06 sec.
 The ventricle volume does not change .
 The ventricular pressure falls rapidly back
to their low diastolic level.
 2nd Heart sound is heard (S2) due to
semilunar valve closure.

22. RAPID VENTRICLE FILLING
PHASE
 The A-V valves open due to the moderately increased
pressure in the atria.
 The blood flows rapidly into the ventricle.
 It is seen in first 1/3rd of the diastole.
 Ventricular volume – increases steeply.
 3rd heart sound is heard (S3)

23. DIASTASIS
During middle 1/3rd of the diastole, only small
amount of blood flows into the ventricle k/a diastasis.
This is the blood that continues to flow into the atria
through the veins & directly passes into the
ventricles.
Time – 0.2 sec
ECG – phase between end of T waves & next P wave.

24. During the last 1/3rd of the diastole, the atria contracts &
provides an additional 25% of blood to the ventricles.
Time – 0.1 sec

26. CENTRAL VENOUS
PRESSURE WAVEFORM

28. DISORDERS ASSOCIATED
WITH CHANGES IN CVP
WAVES
A Wave:
•Absent A wave: Atrial fibrillation
•Prominent A waves: First-degree A-V Block
•Giant A waves: Tricuspid stenosis, Right atrial myxoma,
Pulmonic stenosis,Pulmonary hypertension
•Cannon A Wave: A-V Dissociation,Ventricular
Tachycardia

29. X Descent
•Absent or diminished X Descent: Tricuspid regurgitation,
cardiomyopathy
•Prominent X Descent: Conditions causing giant A Waves
(i,e:Tricuspid stenosis, Right atrial myxoma, pulmonic
stenosis,pulmonary hypertension)

30. V Wave
•Large C-V Waves :Tricuspid regurgitation,Constrictive
pericarditis
Y Descent
• Absent Y Descent: Cardiac tamponade
•Slow Y Descent: Tricuspid stenosis, right atrial myxoma,
and other causes of giant A wave
•Rapid Y Descent-constrictive pancarditis, severe right heart
failure tricuspid regurgitation, atrial septal defects

31. RELATIONSHIP OF THE
ELECTROCARDIOGRAM TO THE
CARDIAC CYCLE
The electrocardiogram shows the P, Q, R, S, and T
waves.
These are electrical voltages generated by the heart
and recorded by the electrocardiogram from the
surface of the body.

32.  The P wave is caused by the spread of depolarization through
the atria and is followed by atrial contraction, which causes a
slight rise in the atrial pressure curve immediately after the
electrocardiographic P wave.
 About 0.16 second after the onset of the P wave, the QRS
waves appear as a result of electrical depolarization of the
ventricles, which initiates contraction of the ventricles and
causes the ventricular pressure to begin rising. Therefore, the
QRS complex begins slightly before the onset of ventricular
systole.
 Finally, the ventricular T wave represents the stage of
repolarization of the ventricles when the ventricular muscle
fibres begin to relax. Therefore, the T wave occurs slightly
before the end of ventricular contraction.

34. CARDIAC CYCLE AND
HEART SOUNDS

35. TIMINGS IN CARDIAC CYCLE
Although events on the 2
sides of the heart are similar
, they are somewhat
asynchronous.
RA systole precedes LA
systole.
Contraction of RV starts
after that of LV.
However since pulmonary
artery pressure is lower than
the aortic pressure , RV
ejection begins before LV
ejection.

36. TIMINGS IN VENTRICULAR
SYSTOLE
1. Isovolumetric contraction – 0.05 sec
2. Rapid ejection phase – 0.10 sec
3. Reduced ejection phase – 0.15 sec
4. TOTAL = 0.3 sec

37. TIMINGS IN VENTRICULAR
DIASTOLE
1. Protodiastole – 0.04 sec
2. Isovolumic relaxation – 0.06 sec
3. 1st rapid filling phase – 0.10 sec
4. Diastasis – 0.20 sec (depends on HR)
5. Last rapid filling phase – 0.10 sec
TOTAL = 0.5 sec

38. TIMINGS OF ATRIAL
FUNCTION
Atrial diastole – 0.7 sec
Atrial systole – 0.1 sec

39. PRESSURE - VOLUME
DIAGRAM

40. PRESSURE - VOLUME
DIAGRAM
Phase I: Period of Filling
Phase II: Period of Isovolumic Contraction
Phase III: Period of Ejection
Phase IV: Period of Isovolumic Relaxation

41. THANK
YOU!!