physiological event during cardiac cycle

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CARDIAC CYCLE
DR.PRIYANKA VERMA
MBBS, MD PHYSIOLOGY

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The heart acts as a –pump actually two separate pumps:
1. Right heart  pumps blood through the lungs
2. Left heart  pumps blood through the peripheral organs.
• A pulsatile two-chamber pump - an atrium and a ventricle.
• Each atrium is a weak primer pump for the ventricle.
• Pump  heart contracts and relaxes rhythmically.
• The terms systole (contractile phase) and diastole (relaxation
phase) usually refer to ventricular events
The Heart as a Pump

Cardiac Cycle
 Sequence of events taking place into the heart
during each heart beat is known as the cardiac cycle.
 Cardiac cycle is defined as the sequence of
electrical and mechanical events occurring in heart
during a single beat.

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•The events includes
1. Changes in the
pressures.
2. Changes in the
volume.
3. Changes in the
aortic, pulmonary
arteries.
4. Heart sounds
5. ECG changes

Phases of Cardiac Cycle
•Duration of each cardiac cycle at a normal heart
rate of 75 beats/min, is --- 60/75 = 0.8 s.
•During each cardiac cycle,
 Atrial cycle
 Ventricular cycle
But both atrial and ventricular events occurs
simultaneously

Atrial cycle (0.8 s)
1. Atrial systole or atrial contraction phase (0.1 s)
2. Atrial diastole (0.7 s).
Ventricular cycle (0.8 s)
3. Ventricular systole (0.3 s)
4. Ventricular diastole (0.5 s)
Phases of Cardiac Cycle

Ventricular systole (0.3 s) consisting of:
1.Isovolumic (isometric) contraction phase (0.05 s).
2.Phase of ventricular ejection which can be
further divided into rapid ejection phase (0.1 s)
and slow ejection phase (0.15 s).

Ventricular diastole (0.5 s) consisting of:
1.Protodiastole (0.04 s).
2.Isovolumic (isometric) relaxation phase
(0.06 s).
3.Rapid passive filling phase (0.11 s).
4.Reduced filling phase or diastasis (0.19 s)
5.Last rapid filling phase which coincides
with the atrial systole (0.1 s).

Cardiac Cycle
1. Atrial systole or atrial contraction phase (0.1 s)
2. Atrial diastole (0.7 s)
Ventricular systole (0.3 s) :
1. Isovolumic (isometric) contraction phase (0.05 s)
2. Phase of ventricular ejection which can be further divided into rapid
ejection phase (0.1 s) and slow ejection phase (0.15 s)
Ventricular diastole (0.5 s) consisting of:
1. Protodiastole (0.04 s)
2. Isovolumic (isometric) relaxation phase (0.06 s)
3. Rapid passive filling phase (0.11 s)
4. Reduced filling phase or diastasis (0.19 s)
5. Last rapid filling phase which coincides with the atrial systole (0.1 s)

physiological event during cardiac cycle

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Basic principle –
1. Blood flows from higher to lower pressure.
2. Contraction ↑ses the pressure with in a chamber while,
relaxation lowers the pressure.
3. Valves open/close according to pressure gradient :
AV valves open when atrial pressure > ventricular
pressure. And close when reversal.
Semilunar valves open when ventricular pressure > aortic
or pulmonary pressure. And close when reverse.

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Before atrial systole 
Ventricles relaxes and AV
Valves open.
Blood flows from great veins
into atria and from atria to
 ventricles
Thus atria and ventricles
forms continues cavity.

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Atrial systole
• [Impulse  SA Node  AV Node – represent  Atrial
depolarization
• Duration = 0.1 s
• Coincides with the last rapid filling phase of ventricular diastole.
• Both atria are contracting.
• Intra-atrial pressure increases
 RA pressure by 4-6 mmHg
 LA pressure by 7-8 mmHg.

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• ↑se in intra-atrial pressure
causes 'a' wave of JVP.
• 4TH
Heart sound  as blood
rush into ventricles.
• Contributes 20 % - 30 % to
ventricular filling.
• In ECG  as atrial systole –
peak of P wave.

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Blood pumps into
ventricles  slight ↑se
in ventricular pressure.
Mitral valve closes  at
the end of atrial systole
i.e. when ventricular
pressure exceeds atrial
pressure.

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•Duration = 0.7 sec
•Coincides with the ventricular systole and most of the
ventricular diastole.
•Atrial muscles relax  there occurs gradual filling of the
atria due to continuous venous return.
• the pressure gradually ↑ses in the atria  when AV
valves open dropping of pressure upto zero.
•Then the pressure again rises and follows the ventricular
pressure during the rest of atrial diastole.
Atrial diastole

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•Atrial diastole occurs during ventricular systole.
•Beginning of ventricular systole bulging of
atrioventricular valve into the atrium  results in ↑se in
atrial pressure  that produces ‘c’ wave in JVP.
•Venous return ↑ses atrial volume  ↑ses atrial
pressure. This produces ‘v’ wave in JVP.

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VENTRICULAR SYSTOLE
•After the atrial contraction phase is over 
•Begins with ventricular depolarization.
•i.e.. impulse SA node  AV node purkinje fiber 
ventricles start contracting.
•The ventricular systole lasts for 0.3 s and has following
phases:
1. Phase of isovolumic (isometric) contraction (0.05)
2. Phase of ventricular ejection (0.25)

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QRS wave, which represents electrical activation of
the ventricles.
Phase of isovolumic (isometric) contraction (0.05 S)

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With the beginning of ventricular contraction  ventricular
pressure exceeds rapidly ( >atrial pressure)
causing closure of AV valves production of 1st
heart sound.
Since the AV valves have closed and semilunar valves
have not opened.
so the ventricles contract as a closed chamber and the
pressure inside the ventricles rises rapidly to a high level.
Phase of isovolumic (isometric) contraction (0.05 S)

Stages of cardiac Cycle
-:
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Contraction of
Ventricles
AV Valves are closed
Semilunar valves
are closed
2
.
Isovolumic (isometric) ventricular contraction

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•As the ventricles contract, but the volume of blood in
the ventricles does not change, so this phase is called
isovolumic contraction phase.
•During this phase, due to sharp rise in the ventricular
pressure, there occurs bulging of AV valves into the atria
•Producing a small but sharp rise in the intra-atrial
pressure called c-wave.

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•This phase lasts for 0.05 s, until the pressure in the left
and right ventricles exceeds the pressure in the aorta
(80 mm Hg) and pulmonary artery (10 mm Hg)
And the aortic and pulmonary valves open

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Phase of ventricular ejection(0.25 sec)
1. Rapid ejection phase (0.1 sec)
2. Slow ejection phase. (0.15 sec)
1. Rapid ejection phase (0.1 sec)
left ventricular pressure rises slightly above 80 mm Hg and the
right ventricular pressure rises slightly above 8 – 10 mm Hg
The ventricular pressures push the semilunar valves
open.
Immediately, blood begins to pour out of the ventricles rapidly.

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The onset of the T wave, which represents repolarization of the
ventricles, marks the end of both ventricular contraction and
rapid ventricular ejection.
Rapid ejection of blood into the aorta (due to pressure gradient)
Ventricular volume ↓ses dramatically because most of the
stroke volume is ejected during this phase.
Atrial filling begins.

Stages of cardiac Cycle
-:
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Contraction of
Ventricles
AV Valves are closed
Semilunar valves
opened
3
.
Ejection phase

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Slow ejection phase(0.15 sec)
Inspite of change in pressure gradient, blood flow
continues from ventricle into the aorta due to the
momentum of forward flow of blood
Ejection of blood from the ventricle continues, but is
slower. Ventricular pressure begins to ↓se.
About 1/3rd
of the stroke volume is ejected during this
phase.

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Slow ejection phase(0.15 sec)
However, the aortic flow is significantly reduced
in this phase (hence, the name reduced
ejection phase).
Ventricular volume continues to ↓se and
reaches the end-systolic volume [ESV] at the end
of this phase

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Ventricular diastole (0.5 s) :
1.Protodiastole (0.04 s).
2.Isovolumic (isometric) relaxation phase
(0.06 s).
3.Rapid passive filling phase (0.11 s).
4.Reduced filling phase or diastasis (0.19 s)
5.Last rapid filling phase which coincides with
the atrial systole (0.1 s).

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The elevated pressure in the distended arteries (aorta and
pulmonary artery) immediately pushes the blood back
towards ventricles
1. Protodiastole (0.04 s)
Closure of semilunar (i.e. aortic and pulmonary) valves
(produces the 2nd
heart sound (S2)
Prevents the movement of blood back into the
ventricles

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This phase ends when the
AV valves open, as indicated
by the peak of v-wave .
2. Isovolumic or isometric relaxation phase (0.06 s).
semilunar valves [closed]
and the AV valves [not yet
opened] so the ventricles
continue to relax as closed
chambers .
This causes rapid fall of
ventricular pressure (from
80 mm Hg to 2−3 mm Hg in
the LV).
As the ventricular volume
remains constant, so called
as isovolumic or isometric
relaxation phase.

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1. During ventricular systole,
the atria are in diastole and
venous return continues so
that the atrial pressure is
high.
3. The rapid passive filling
phase produces the 3rd
heart sound (S3), which
is not normally audible.
RAPID PASSIVE FILLING PHASE (0.11 S)
2. When the AV valves open,
the high atrial pressure
causes a rapid, initial flow of
blood into the ventricles.
4. As AV valves open, the atria
and ventricles are a common
chamber and pressure in
both cavities falls --
ventricular relaxation
continues.

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Note. It is important to note that about 75- 80 % of blood
passes from the atria to the ventricles during rapid filling and
reduced filling phases of the ventricular diastole.
REDUCED FILLING AND DIASTASIS (0.19 S)
Pressure in the atria and
ventricles reduces slowly
and remains little above
zero.
Decreases the rate of blood
flow from the atria to
ventricle causing a very
slow filling called diastasis.

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•The last rapid filling phase of ventricular diastole
coincides with the atrial systole.
5. LAST RAPID FILLING PHASE (0.1 S)
1. The atrial systole brings
about the last rapid filling
phase and pushes the
additional 25% of the
blood in the ventricles.
2. With this phase,
the ventricular
cycle is
completed.

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Cardiac cycle: right versus left heart
 Both the ventricles pump the same volume of blood over
any significant time period.
 However, there exists a minor asynchronicity between the
two sides as:
 Right atrial systole precedes left atrial systole, but the
right ventricle starts contracting after the left ventricle.
 However, the right ventricular ejection begins before the
left ventricular ejection, because the pulmonary arteria
pressure is lower than the aortic pressure.

Phases Aortic
Pressure
1.
Isovolumetric
contraction
80 mmHg
2. Rapid
ejection
120 mmHg
due to
ejection
3.Slow
ejection
Pressure falls
slightly

Phases Aortic Pressure
4.
Protodiastole
Pressure is more
than 80 mmHg.
At the end of this
phase, pressure in
the ventricle is
less.
So blood tries to
enter but reflects
back due to
closure of the
aortic valve. This
produces incisura.

Phases Aortic Pressure
5.
Isovolumetric
relaxation
Pressure
reaches to 80
mmHg
6. 1st rapid
filling phase
Same as above
7. Slow filling
phase
Same as above
8. Last rapid
filling phase
Same as above

Phases Lt. Ventricular
Pressure
1.
Isovolumetric
contraction
Steep rise
2. Rapid
ejection
Peak level
3.Slow
ejection
Less than
previous
phase
Pressure changes during cardiac cycle

Phases Lt. Ventricular
Pressure
4. Protodiastole Fall in pressure
5. Isovolumetric
relaxation
Steep fall
6. 1st rapid
filling phase
Slight rise
7. Slow filling
phase
Slight rise
8. Last rapid
filling phase
Slight rise(atrial
systole)
Pressure changes during cardiac cycle

Atrial pressure
a wave = caused by atrial
contraction
c wave –Due to rise in atrial
pressure produced by the bulging
of the tricuspid valve into the right
atrium during isovolumetric
ventricular contraction phase.
v wave = Due to slow flow of
blood into the atria from the veins
while the A-V valves are closed
during ventricular contraction.

Que -A 50-year-old male patient comes with the
history of dyspnea. His JVP was raised. What is
JVP? Explain the waves. What does raise in JVP
signify?

JVP –JUGULAR VENOUS PRESSURE
•There is no valve at the
junction of superior vena
cava (SVC) and right atrium
(RA), therefore right atrial
pressure changes are
transmitted to the jugular
vein in the neck,- producing
'3' characteristic waves

(I) Positive waves
•‘a’ wave —Atrial systole
•‘c’ wave —Isometric ventricular
contraction, bulging of cusps of
tricuspid valve in atrium.
•v’ wave —Venous return in
atria against closed tricuspid
valve, that is passive rise in
pressure as venous return
continues in atria.

(II) Negative waves
• ‘x’ descent —Tricuspid cusps
descent back due to pull of papillary
muscles.
• ‘y’ descent — Lowering of right
atrial pressure due to opening of
tricuspid valve.
1.In tricuspid insufficiency, large c waves can be recorded.
2.Large ‘a’ waves are known as ‘cannon waves’ and are recorded
in complete heart block.

Significance of Raised JVP
• It is increased in hyperdynamic states like volume overload or renal
dysfunction.
• Also, when there is increased pressure on the right side of heart.
Tricuspid stenosis
Pulmonary hypertension
Congestive cardiac failure
Constrictive pericarditis
Superior vena caval obstruction

Cannon Wave
• When amplitude of ‘a‘ wave is abnormally big, it is called
giant ‘a’ wave or cannon wave. It occurs when right atrium
contracts against a closed tricuspid valve.
• Canon wave is seen in:
1. Complete heart block when atrial and ventricular
systoles coincide.
2. Nodal rhythm when the atrium and ventricle are
activated simultaneously.

Absence of ‘a’ Wave: in atrial fibrillation.
Prominent ‘v’ Wave: seen in tricuspid
regurgitation because when ventricle contracts
during systole blood enters into right atrium
through the incompetent tricuspid valve.

Volume changes
1. Atrial Systole =last rapid
filling phase of Vent Diast.
• When atrial contra -- begins.
→105 ml (75% )blood has
already flown into ventricles
• Atrial contrac  additional 25
ml (25%) filling of ventricles.
• at the end of VD  vent. vol
is about 130 ml-- End
diastolic vol

Volume changes
2. Vent Systole
 Isom vent contr- No change
in vent vol.
 Vent Ejection  About 70- 80
ml of the blood is ejected out
by Ventricles c/as stroke
vol.65% of EDV.
 Percentage of EDV that is
ejected with each heart beat
is called Ejection Fraction
(Normal: 65% of EDV).It is a
valuable measure of
ventricular contractility.

Volume changes
Vent diastole-
 Protodiastole + Isov ven
relaxation  no change
 Rapid & slow filling  vol
changes rapidly then
slowly.
 About 75 % of ventricular
filling.

Pressure–Volume Relationship
• (A–B) Diastolic filling of ventricle starts at
‘A’ as mitral valve opens and terminates
at ‘B’ as mitral valve closes. ventricular
volume ↑ses greatly without much
change in pressure (occurs during the
relaxation phase ).
• (B–C),With the onset of isovolumetric
contraction ventricular pressure rises
steeply without change in volume.
• At point C - Aortic valve opens that marks
the onset of ejection of the ventricle.

Pressure–Volume Relationship
• (C-D) - ventricular volume ↓ses, but
ventricular pressure continues to
rise, which reaches a peak at point
D (the rapid ejection phase ends)
and then ↓ses till point E (end of
slow ejection phase).
• (E–A) Then starts the isovolumetric
relaxation phase, during which
pressure falls abruptly to meet the
point A, which marks the opening of
the mitral valve.
• This completes one cardiac cycle.

E.C.G. CHANGES DURING CARDIAC CYCLE
• E.C.G. is the record of electrical changes
generated with each heart beat.
I. 'P' wave is due to atrial depolarization
and precedes atrial systole.
II. 'Q', 'R' and 'S' waves together
constitute the QRS complex and are
due to ventricular depolarization. It
precedes ventricular systole.
III. 'T' wave is due to ventricular
repolarization. It coincides with closure
of semilunar valves

HEART SOUNDS
• 1st
Heart Sound (HS1
)- due to closure
of 'AV valves' and marks the onset of
ventricular systole.
• 2nd
Heart Sound (HS2
)- due to closure
of semilunar valves and marks the
onset of ventricular diastole.
• 3rd
Heart Sound (HS3) : - due to
vibrations of the cardiac walls
produced by the rapid filling phase of
ventricular diastole proper.
• 4th
Heart Sound (HS4): - due to atrial
systole,

physiological event during cardiac cycle

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