Cardiac cycle. Cardiology, Spandana

1. CARDIAC CYCLE
MO!Z

2.  CARDIAC CYCLE / THE LEWIS CYCLE / WIGGERS CYCLE
( First conceived by Wiggers / fully assembled by LEWIS )
 Gives Sequence of events ( pressure / volume / electrographic / valvular movements )
occurring in heart during systolic and diastolic periods
 One cycle consist of 1SYSTOLE + 1DIASTOLE
 Similar mechanical events occurring in both right side and left side of heart ( with only
pressure and volume difference)

3.  The total duration of the cardiac cycle, including systole and diastole, is the reciprocal of the heart
rate.
- if heart rate is 72 beats/min –
the duration of the cardiac cycle - 1/72 min/beat
- about 0.0139 minutes per beat
- or 0.833 second per beat.
systole comprises about 0.4 of the entire cardiac cycle.
 For heart rate around 75 / min
cardiac cycle is total duration of 0.8 sec
- Atrial systole (0.1sec) atrial diastole(0.7 sec)
- Ventricular systole (0.3 sec) ventricular diastole(0.5 sec)

4. Atrial events
( atrial systole 0.1 sec, atrial diastole 0.7 sec)
Ventricular events
( ventricular systole 0.3 sec, ventricular diastole 0.5 sec)
At point when atrial systole ends , ventricle systole begins
For 0,4 sec both atrium and ventricle are in diastole
(Joint diastole)
when HR increases joint diastole time mainly comes down

5.  With Increasing Heart Rate
The duration of the action potential decreases
Decreases Duration of Cardiac Cycle including the contraction and
relaxation phases
Duration of Diastole decrease > systole
Thus shortens time for diastolic filling.
Thus to maintain or augment LV stroke volume LV filling rate must increase .
This is accompanied by enhancement of LV relaxation
and lower early diastolic LV pressure

6.  Cardiac cycle Often explained in relation to left ventricle –
with three basic events –
1) LV contraction
2) LV relaxation
3) LV filling phases

7.  LEFT VENTRICULAR CONTRACTION –
ISOVOLUMIC CONTRACTION (b)
MAXIMUMAL EJECTION / phase of rapid ejection (c)
 LEFT VENTRICULAR RELAXATION -
START OF RELAXATION & phase of REDUCED EJECTION (d)
ISOVOLUMIC RELAXATION (e)
LV FILLING RAPID PHASE (f)
SLOW LV FILLING ( DIASTASIS) (g)
ATRIAL SYSTOLE OR KICK (a)

8. Physiologic
 Physiologic systole includes-
isovolumetric contraction
peak of ejection phase
 Physiologic diastole includes-
reduced ejection phase
isovolumetric relaxation
filling phase
Cardiologic
 Cardiologic systole - M1 to A2
Longer than physiologic systole
Includes-
Major part of isovolumetric contraction
Maximal ejection
Reduced ejection
 Cardiac diastole – A2 to M1
Isovolumetric relaxation,
filling phases,
isovolumetric contraction

10. THE LEWIS or WIGGERS CYCLE - Mechanical events in cardiac cycle
depicted as pressure vs time

11.  LV contraction-
During this phase - Atria relaxing - receives blood from pulmonary veins
Pressure start rising in LV ..
MV closes...but pressure not so high to open AV.
Thus ventricle will continue contract as close chamber
(isovolumetric contraction) (b)
On further rise in pressure leads to open of AV

12. Isovolumetric contraction – a/w QRS complex of ECG
useful in septal defect assessment
in regurgitant lesions there is no true isovolumetric contraction
use to calculate myocardial perfusion index
( isovolumetric contraction time + isovolumetric relxation time )
---------------------------------------------------------------------------------
--------------
ejection time

13.  As AV open
- termination of isovolumetric contraction
- Period of rapid ejection start
- LV continues to contract & Pressure in
ventricle keeps on increasing,
- Aorta will receive blood and will stretch out
- LV and aortic chamber will behave as single chamber
- & pressure changes occurring in LV will be transferred
into aorta
( At this phase LA Still in relaxing phase )

14. Pressure in LV start following ..
but AV still open..
ejection will become slow
----- Slow ventricular ejection phase.
As pressure In LV start following
pressure in aorta also start following ..
but as aorta is elastic - wind kessel effect –
it will keep on squeezing the blood
and blood moves forward

15. When pressure in aorta still more d/t elastic recoil
than relaxing LV –-- AV closes
but MV is still close as though LV start relaxing
pressure in LV is still more than LA..
Isovolumetric relaxation

16. Atria still relaxing and receiving blood
While relaxing, when pressure in LV becomes less
than atrium MV opens
Blood will rapidly flow into LV…
rapid passive ventricular filling phase. 50% of atrial
blood
Accounts for most of increase in LV volume during diastole

17. Ventricular diastole continues..
blood coming to LA will directly flow to LV ..
LV act as conduit….
slow passive ventricular filling/ diastasis
30% of atrial blood
( longest phase of diastole)

18. SA node fires & Atria contracts …
Phase of atrial contraction-
during this phase - Pressure in atrium rises,
Mitral Valve open
Pressure and volume transferred to the LV
Aortic Valve remains closed
(as pressure in aorta > ventricle)
80% of ventricular filling passive (50 + 30 )
& already done before atrial contraction )
atrial contraction add 20% of ventricular filling
more valuable when physically active i.e. during
exercise/ In stenotic lesion/ HF patient etc

19. Normal pressures

20.  Pressure volume loop of RV is same as that of LV ,
however the area is only 1/5th of LV because pressure so much lower on right
LVEDV ~ 110- 120 ml
LVESV ~ 40- 50 ml
SV ~ 70 ml

21. THE LEWIS or WIGGERS CYCLE - Mechanical events in cardiac cycle depicted as
pressure vs volume

22. Uses of pressure volume loop
 Work done by heart = total area under curve
 Width indicates stroke volume = EDV – ESV
 Height  s/o afterload, ventricular activity
SV
 Ejection fraction = ---------- x 100
EDV
ESV
 EDV = ------------------
1-EF

23. work done
Cardiac efficiency of heart = -------------------------------------------
chemical expenditure
normally 20 – 25%
in patient with heart failure < 5%
Potential energy of heart –- energy present in heart when end systolic volume is zero
(i.e after removing all blood from heart)

24. Pressure Volume Loop In MS
 MS -- EDV reduced
 Reduction in Preload
 SV decreases – width of graph-- shifted to left
 CO decreases -Reduction in afterload ,,
reduction in height

25. Pressure Volume Loop In MR
 MR -- EDV will increase
 Preload increased –
 SV increase – width of graph will increase
 No true isovolumetric relaxation
or isovolumetric contraction will be seen
 Afterload decrease – Height decrease

26. Pressure Volume Loop In AS
 Aortic stenosis – EDV & ESV will be high
 SV decreases – width reduces
 Afterload high – height increases

27. Pressure Volume Loop In AR
 AR – NO true isovolumetric relaxation or contraction
 EDV increase – shift to right
 Volume increases - Afterload increases
– height increases

28. 