2. Cardiac Cycle
The cardiac events that occur from beginning of one heart beat to the beginning of the next.
The cardiac cycle, fully assembled by Dr. Lewis but first conceived by Dr Carl. J.Wiggers.(1883-
1963)
Electrical
Mechanical
Haemodynamics , Pressure and Flow Volume changes.
3. Cardiac Cycle Initiation: Action potential in the sinus node
Action potentials originating
in the sinus node travel to
AV node (1m/s) in 0.03 sec
atrial muscle is about 0.3 m/sec
small bands of atrial fibers about 1 m/sec
4. 1.AV nodal delay of 0.09 sec before the impulse
enters the penetrating portion of the A-V bundle
2. A final delay of another 0.04 sec occurs mainly in
this penetrating A-V bundle
A total delay of 0.16 sec occurs before the excitatory
signal finally reaches the contracting muscle of the
ventricles from its origin in sinus node.
5. Special Purkinje fibers
Transmit action potentials at a velocity of 1.5 to 4.0 m/sec
About 6x that in ventricular muscle
About 150x that in A-V nodal fibers
Allowing almost instantaneous transmission of the cardiac
impulse throughout the ventricular muscle
6. Duration Of cardiac Cycle:
(Duration of Systole + Duration of Diastole)
It is the reciprocal of Heart Rate
Example:
Heart Rate = 72 beats /minute
Cardiacl cycle duration is 1/72 = 0.833 sec/beat
1 Beat = 0.8 sec (800 msec)
Systole = 0.3 sec
Diastole = 0.5 sec
In tachycardia, Diastolic phase decreases more than systolic phase.
7. ventricular pressures fall to
their low diastolic
values(lower than atrial
pressure)
A-V valves open ,Rapid
Ventricular filling ,followed
by Atrial contraction/ kick
During Ventricular Systole
Continuous flow from great veins into Atria
the closed A-V valves
Increase pressure in Atria, V wave
RA
Mean 5mm
(2-7)
LA
Mean 12
(6-21)
8. The ‘a” wave is caused by atrial contraction
RA
6mm
(2-7)
LA
10mm
(4-16
RVEDP
4mm
(1-7)
LVEDP
8mm
(5-12)
9. Wiggers' diagram
of
Cardiac cycle
Left Ventricular Contraction
Isovolumic contraction (b)
Maximal ejection (c)
Left Ventricular Relaxation
Start of relaxation and reduced ejection (d)
Isovolumic relaxation (e)
Left Ventricular Filling
LV filling: rapid phase (f)
Slow LV filling (diastasis) (g)
Atrial systole or kick (a)
10. THE PHASE OF ISOVOLUMIC CONTRACTION (b)
Contraction is occurring in the ventricles, against closed AV valves and Semilunar
Valves, the Ventricular volume remains same. This period is called the period of
isovolumic or isometric contraction
Steep rise in pressure from
C wave of JVP
Left Ventricular Contraction
Isovolumic contraction (b)
Maximal ejection (c)
Left Ventricular Relaxation
Start of relaxation and reduced
ejection (d) LV filling: rapid phase
(f
Isovolumic relaxation (e)
Left Ventricular Filling
)
Slow LV filling (diastasis) (g)
Atrial systole or kick (a)
LVEDP
(5-12mm)
to Ao P(70-105)
RVEDP
(1-7)
to
Pul A P( 9-19
RA
6mm
(2-7)
LA
10mm
(4-16
RVEDP
4mm
(1-7)
LVEDP
8mm
(5-12)
11. Left Ventricular Contraction
Isovolumic contraction (b)
Maximal ejection (c)
Left Ventricular Relaxation
Start of relaxation and reduced
ejection (d)
Isovolumic relaxation (e)
Left Ventricular Filling
LV filling: rapid phase (f)
Slow LV filling (diastasis) (g)
Atrial systole or kick (a)
13. Maximal Ejection ( c) Early 1/3rd
continuing isovolumic contraction causes Steep rise in Ventricular pressure
( LV pressure rises above Aortic pressure (70-105
(RV pressure of above Pulmonary Artery pressure( 9 -19mm)
Ventricular pressures push the semilunar valves open and ejection starts
LV and Aortic Peak Systolic Pressure Mean 130 Range 90-140
RV and Pulmonary trunk Peak Systolic Pressure Mean 25 mm range 15-30mm
70% of the total ejection volume flows out during the first third
of the ejection period,
Left Ventricular Contraction
Isovolumic contraction (b)
Maximal ejection (c)
Left Ventricular Relaxation
Start of relaxation and reduced
ejection (d)
Isovolumic relaxation (e)
Left Ventricular Filling
LV filling: rapid phase (f)
Slow LV filling (diastasis) (g)
Atrial systole or kick (a)
X descent is due to downward movement of the lateral
annulus of the tricuspid valve during RV contraction and
atrial relaxation, It coincides with ST segment on
electrocardiogram
14. LV Pressure and Aorta Pressure
Mean 130 Range 90-140
RV and PA Pressure
Mean 25 mm range 15-30mm
Maximal Ejection ( c) Early 1/3rd
15. Left Ventricular Contraction
Isovolumic contraction (b)
Maximal ejection (c)
Left Ventricular Relaxation
Start of relaxation and reduced
ejection (d)
Isovolumic relaxation (e)
Left Ventricular Filling
LV filling: rapid phase (f)
Slow LV filling (diastasis) (g)
Atrial systole or kick (a)
16. Start of relaxation and reduced ejection (d)
(2/3rd of the ejection phase)
Myocyte [Ca2+] starts to decline because of SR Ca2+ uptake
Relaxation progresses, rate of
Ventricular ejection of blood into the
Aorta , PA falls
Blood flow from the left
ventricle to the aorta rapidly diminishes but is
maintained by
aortic recoil—the Windkessel effect
17. Windkessel Effect:
Interaction between the stroke volume and the compliance of
the aorta and large elastic arteries.
Helps in damping the fluctuation in blood
pressure (pulse pressure)
Assists in the maintenance of organ perfusion
during diastole when cardiac ejection ceases.
18. pressure in the aorta(60-90mm)
significantly exceeds the falling LV
pressure, the aortic valve closes, which
creates the first component of the
second sound, A2
closure of the pulmonic valve as
pulmonary artery pressure exceeds RV
pressure, producing P2 component
19. Left Ventricular Contraction
Isovolumic contraction (b)
Maximal ejection (c)
Left Ventricular Relaxation
Start of relaxation and reduced ejection (d)
Isovolumic relaxation (e)
Left Ventricular Filling
LV filling: rapid phase (f)
Slow LV filling (diastasis) (g)
Atrial systole or kick (a)
20. Isovolumic relaxation (e)
Left Ventricular Contraction
Isovolumic contraction (b)
Maximal ejection (c)
Left Ventricular Relaxation
Start of relaxation and reduced
ejection (d)
Isovolumic relaxation (e)
Left Ventricular Filling
LV filling: rapid phase (f)
Slow LV filling (diastasis) (g)
Atrial systole or kick (a)
ventricular muscle continues to relax,( against closed AV valves
and Semilunar valves) so the ventricular volume does not
change, giving rise to the period of isovolumic or isometric
relaxation(0.03 to 0.06 seconds)
Intraventricular pressures rapidly decrease back
to their low diastolic levels
21. LV filling: rapid phase (f)
Left Ventricular Contraction
Isovolumic contraction (b)
Maximal ejection (c)
Left Ventricular Relaxation
Start of relaxation and reduced
ejection (d)
Isovolumic relaxation (e)
Left Ventricular Filling
LV filling: rapid phase (f)
Slow LV filling (diastasis) (g)
Atrial systole or kick (a)
caused by a negative pressure gradient from
atrium to the LV apex, creating a suction effect
rapid filling may cause the physiologic third heart sound
(S3)
pathologic S3 when left atrial and LV diastolic
pressures are elevated in congestive heart failure
22. As pressures in the atrium and ventricle equalize, LV filling
virtually stops (diastasis, separation).
Left Ventricular Contraction
Isovolumic contraction (b)
Maximal ejection (c)
Left Ventricular Relaxation
Start of relaxation and reduced
ejection (d)
Isovolumic relaxation (e)
Left Ventricular Filling
LV filling: rapid phase (f)
Slow LV filling (diastasis) (g)
Atrial systole or kick (a)
Slow LV filling (diastasis) (g)
Renewed filling requires that atrial pressure exceed LV
pressure. This is achieved by atrial systole (or the “left atrial
kick”),
Atrial systole or kick (a)
Atrial systole or kick corresponding to the A wave on JVP
23. Physiological systole starts from
isovolumic contraction to the peak of
ejection phase
Physiological diastole is from calcium
uptake by SR, ventricular relaxation and
reduced ejection.
24. Total ventricular systole 0.3 sec
Isovolumic contraction (b) 0.05 sec (0.015sec for RV)
Maximal ejection (c) 0.10sec
Reduced ejection (d) 0.15 sec
Total ventricular diastole 0.5 sec
Isovolumic relaxation (e) 0.1 sec
Rapid filling phase (f) 0.1 sec
Slow filling (diastasis) (g) 0.2 sec
Atrial systole or booster (a) 0.1 sec
GRAND TOTAL (Syst+Diast) = 0.8 sec
25. Normal Pressure Waveforms
The cardiac cycle starts with the electrocardiographic P wave, which initiates atrial
contraction. The pressure waves of atrial systole and diastole are denoted as the a
wave (see Fig. 22.15) and x descent, respectively
LV pressure at the end of the a wave is called the end-diastolic
pressure (also known as LVEDP). The LVEDP corresponds to the
ECG R wave
When the LV pressure falls below the
aortic pressure, the AV closes,
forming the dicrotic notch on the
aortic
26. Pressures in the various Portions of the circulation in a person lying horizontal
