Cardiac cycle
Dr. shafali singh
Learning Objectives
• Describe the sequence of events that occur during one cardiac cycle
• Identify the intervals of isovolumic contraction, rapid ejection,
reduced ejection, isovolumic relaxation, rapid ventricle filling,
reduced ventricular filling and atrial contraction.
• Interpret in correct temporal relationship, the pressure, volume,
heart sound, and ECG changes in the cardiac cycle.
• Contrast the relationship between pressure and flow into and out
of the left and right ventricles during each phase of the cardiac
cycle.
• Describe and explain the atrial and central venous pressure waves.
• Interpret ventricular pressure-volume loop and on it label the
phases and events of the cardiac cycle (ECG, valve movement).
CARDIAC CYCLE
1. ELECTRICAL CHANGE
2. MECHANICAL CHANGE
3. HEMODYNAMIC CHANGE
4. HEART SOUNDS
Cardiac cycle
The cardiac events that occur from beginning of
one heart beat to the next are called the cardiac
cycle
Atria
Atrial systole
Atrial diastole
Ventricle
Ventricular systole
Ventricular diastole
Heart beat duration (rate is 75 beat/min)
Duration of cardiac cycle
• HEART RATE : 75/MIN
• HENCE DURATION FOR ONE CYCLE IS: 60/75 =
0.8 Sec
• ATRIAL CYCLE
– ATRIAL SYSTOLE – ATRIAL DIASTOLE-
0.1 SEC
0.7 SEC
• VENTRICULAR CYCLE
– VENTRICULAR SYSTOLE – 0.3 SEC
– VENTRICULAR DIASTOLE – 0.5 SEC
What happens to time spent and
systole and diastole with tachycardia?
• Under Normal condition:n1/3rd time in
systole and 2/3rd in diastole
• Tachycardia : time spent in diastole
decreases dramatically whereas time
spent in systole falls to lesser extent.
CARDIAC CYCLE
•
•
•
•
•
IF HR ↑ - 150 / MIN
CARDIAC CYCLE – 0.4 Sec
SYSTOLE 0.25 Sec
DIASTOLE 0.15 Sec
HENCE LITTLE TIME FOR VENTRICULAR
FILLING
Mechanical Events of Cardiac cycle
1.
2.
3.
4.
5.
6.
7.
8.
Atrial systole
Isovolumic contraction phase
Rapid ejection phase
Reduced ejection phase
Isovolumic relaxation phase
Rapid filling phase
Reduced filling phase (Diastasis)
Last rapid filling phase
ATRIAL SYSTOLE
• Last phase of ventricular diastole
• Drives some more blood into the ventricles
• Increases the ventricular filling by 35%
• 0.1 Sec
• Coincides with ‘a‘ wave of JVP
• Contraction of atria-Fourth Heart sound
VENTRICULAR SYSTOLE
1.ISOVOLUMETRIC CONTRACTION
•
•
•
•
•
•
•
Coincides with ‘c ‘wave in JVP
Semilunar valve : remain closed
AV valves close – First Heart sound
Closed chamber – Contracts
No change in the volume
BLOOD INCOMPRESSIBLE
Intraventricular pressure ↑
2.EJECTION PHASE
• ↑ Intraventricular pressure
• > 80mm Hg- Diastolic pressure of
Aorta
Or > 10mmHg- Diastolic pressure of
Pulmonary arteries
• Semilunar valves forced to open
• Blood flows into arteries from
ventricle
EJECTION PHASE
• MAXIMAL EJECTION –
• Due to High Pressure gradient - Blood is ejected
into Aorta/Pul. Art.
• REDUCED EJECTION –
• Due to decreased Pressure gradient
• STROKE VOLUME – 70 ml
• END SYSTOLIC VOLUME = 40-50 ml
• EDV – SV = ESV [120 – 70 = 50]
Ventricular diastole
1.Protodiastolic period –
2.Isovolumetric relaxation –
3.Rapid filling phase –
4.Reduced filling phase (Diastasis)
5.Last rapid filling phase/ Atrial
systole follows
1.PROTODIASTOLIC PHASE
• Ventricle relaxes
• Intraventricular pressure
< pressure in the aorta/Pul.Arteries
• Blood flows back from aorta/pul art
into ventricle
• SLV closes -Second heart sound
2.ISOVOLUMETRIC RELAXATION
• SLV and AV valves closed
• Ventricle relaxes as closed
chamber
• No volume change
• Intraventricular pressure ↓
3.RAPID INFLOW PHASE
• ↓Intraventricular pressure< intra
atrial pressure
• Hence AV valves open
• Blood flows from atria to ventricle
• Third heart sound
4.DIASTASIS
• ↑ in intraventricular pressure due to
↑blood flow from atria
• Blood flow from atria to ventricle at
low rate or static
• Duration of diastasis variable
During diastole there is passive filling of the relaxed left
ventricle. The ventricle does not suck blood into the lumen.
Filling is by the venous pressure.
The first sign of activity in the heart is the atrial contraction.
This weak structure pushes a small amount of blood into the
ventricle (atrial kick)
Blood is also propelled back into the veins giving
rise to the A-wave.
Not vital.
Isovolumetric contraction occurs as the ventricle starts to
contract. The mitral valve closes The ventricular pressure rises
toward aortic pressure .
The mitral valve bulges into the atrium causing the C wave in
venous pressure
Ejection phase starts as the aortic valve opens. The ventricular
contents are ejected during this time.
Isovolumetric relaxation begins as the aortic valve closes.
Ventricular pressure falls from aortic to left atrial during this
period.
Diastolic filling begins again as the mitral valve opens
Accumulated blood in the atrium rushes into the ventricle
Movement of blood into the ventricle causes venous pressure to
drop suddenly causing the V wave
EKG
EVENT
VALVULAR
EVENT
SOUND
P wave
Atrial
depolarisation
S4
(S3 prior to P
wave)
PR interval
AV Node
conduction
Mitral valve
open
(ventricle is
filling)
-
QRS
Ventricular
depolarization
Mitral valve
close
S1
QT interval
Ejection phase
Aortic valve is
open
No sound
T wave
Ventricular
repolarization
Aortic valve
closure
S2
-
HEMODYNAMIC CHANGES
• Pressure and volume changes in the atria &
ventricle during cardiac cycle
• Intra atrial pressure curve
• Intraventricular pressure curve
• Aortic pressure curve
• Ventricular volume curve
INTRA-ATRIAL PRESSURE CURVE
• Pressure changes in the atria is reflected in the
veins near the heart, eg.jugular vein
• acv curve – Jugular Phlebogram - JVP
PHLEBOGRAM
• 3 Positive waves – a,c &v
• 2 Negative waves x &y
3
2
a
1 c
4
v
y
x
AS
VS
VD
Venous Pulse
a wave
Highest deflection of the venous pulse and
produced by the contraction of the right
atrium
Correlates with the PR interval
Is prominent in a stiff ventricle, pulmonic
stenosis and insufficiency
Is absent in atrial fibrillation and other
atrial arrhythmias
Venous Pulse
c wave
Mainly due to the bulging of the tricuspid
valve into the atrium (rise in right atrial
pressure)
Occurs near the beginning of ventricular
contraction (is coincident with right
ventricular isovolumic contraction)
Venous Pulse
x descent
Produced by a decreasing atrial pressure during atrial
relaxation
Separated into two segments when the c wave is
recorded
v wave
Produced by the filling of the atrium during ventricular
systole when the tricuspid valve is closed
Follows T wave of the EKG
A prominent v wave would occur in tricuspid
insufficiency and right heart failure
Venous Pulse
y descent
Produced by the rapid emptying of the right
atrium immediately after the opening of the
tricuspid valve
A more prominent wave in tricuspid insufficiency
and a blunted wave in tricuspid stenosis
• A common diagnostic technique is to place
catheters at various points in the
cardiovascular system and record their
pressures.
INTRAVENTRICULAR PRESSURE CURVE
Ejection phase
Closure of SLV
4
SLV opens
Protodiastole
3
5
Isovolumetric Relax
Isovolumetric contr
Atrial systole
1
6 AV valves open
7 VD
2
Closure of AV Valve
AS
VS
VD
AORTIC PRESSURE CURVE
1
2
2-3
3
4
5
2
120
5
3
4
100
Incisura
1
80
VS
VD
– SLV open
– Max. Ej. Phase
– Reduced Ej. Phase
– End of Vent. Diastole
- SLV closes
– Small positive wave
VENTRICULAR VOLUME CHANGES
120
60ml
I
V
R
I
V
C
VS
A
S
VD
A is atrial systole.
Causes the A wave in
atrial pressure.
Helps fill the ventricle.
B is Isovolumic
contraction.
It starts with mitral
valve closure
Both the aortic and
mitral valves are closed
so the ventricle’s
volume is constant.
C is rapid ejection
period.
It starts with aortic valve
opening.
Ventricular pressure leads
aortic.
Flow out of the ventricle
is accelerating.
D is the reduced ejection
period.
Aortic pressure leads
ventricular.
Flow out of the ventricle
is decelerating.
E is the isovolumetric
relaxation period.
Begins with aortic valve
closure.
Ventricular volume is
constant
Gives rise to the V wave
as blood accumulate in
the atrium
F is the rapid filling
period.
Begins with opening of
the mitral valve.
Gives rise to the y wave
as blood accumulated in
the atrium rushes into the
ventricle.
y
G is the reduced filling
period(diastasis).
Ventricular filling is now
in equilibrium with
venous return.
Events on the right
side are the same
except the pressure
is lower.
Left ventricular enddiastolic volume (LVEDV)
Left ventricular end-systolic
volume (LVESV)
stroke volume= LVEDV-LVESV
cardiac output = stroke volume x heart rate
Since there are no
valves between the
atrium and veins atrial
pressure is essentially
equal to venous
pressure.
Notice the venous
pressure trace with
A, C and V waves
Ventri
Q1. Ventricular filling begins at point?
Q2. Closure of mitral valve begins at point?
• The volume and pressure tracings for the left
ventricle of a 34 year old male are shown
below. Which of the following points
correspond to aortic valve opening?
A
B
C
D
E
PRESSURE-VOLUME LOOPS
Q.On the graph showing left ventricular volume and
pressure, isovolumetric contraction occurs from point
(A) 4 → 1
(B) 1 → 2
(C) 2 → 3
(D) 3 → 4
Q The aortic valve closes
at point
(A) 1
(B) 2
(C) 3
(D) 4
Q The first heart sound corresponds to point
(A) 1
(B) 2
(C) 3
(D) 4
If the heart rate is 70 beats/min, then the
cardiac output of this ventricle is closest to
(A) 3.45 L/min
(B) 4.55 L/min
(C) 5.25 L/min
(D) 4.90 L/min
(E) 9.85 L/min
70
140
The ejection fraction equals
a. 0.50
b. 0.55
c. 0.60
d. 0.65
e. 0.70
Mechanically Altered States
•
•
•
•
•
•
•
•
•
Preload
Afterload
Increased contractility
Exercise
Heart failure
Aortic stenosis
Aortic insufficiency
Mitral stenosis
Mitral insufficiency