Cardiology

1. 1
THE CARDIAC CYCLE
The Cardiac cycle.
 Is the period from the END of
one cardiac contraction to the
END of the next contraction
One cardiac cycle is reflected by
ELECTRICAL & MECHANICAL
changes

2. 2
ELECTRICAL & MECHANICAL
CHANGES
Electrical changes are recorded by
an ELECTROCARDIOGRAM (ECG).
Mechanical changes are reflected
by:
 Pressure
 Volume
 Heart sounds &
 Blood flow changes

3. 3
CARDIAC CYCLE CONT.
One cardiac cycle consists of:
 A period of Ventricular Systole or
Systolic phase (ie a period of
ventricular contraction) &
 A period of Ventricular Diastole or
Diastole phase (ie a period of
ventricular relaxation)

4. 4
ELECTRICAL CHANGES
Electrocardiogram (ECG).
 This records the Electrical voltages
generated by the heart and recorded
from the surface of the body.
 The waves recorded are P, QRS
complex & T.
P wave is due to spread of depolarization
through the Lt and Rt atrium leading
to atrial contraction

5. 5
ECG WAVES CONT.
QRS complex is due to the spread
of depolarization through the Lt &
Rt ventricles leading to
ventricular contraction.
T wave is due to repolarization of
the ventricles ie Lt & Rt
ventricular relaxation.

6. 6
MECHANICAL FUNCTION OF
THE ATRIA
There are two mechanical phases of
atria
 Passive phase where 70% of
blood passes directly from the
atria to the ventricles
 Active phase where 20 to 30% of
the blood enters the ventricles
due to atria contraction

7. 7
STAGES OF VENTRICULAR
FILLING
There are three stages of
ventricular filling:
 Rapid filling which occurs in the
first 1/3
 Diastasis phase - middle 1/3
 Additional filling – last 1/3 due to
atria contraction

8. 8
EMPTYING OF THE VENTRICLES
During ventricular emptying (systole),
the ATRIA/VENTRICULAR (A-V) valves
ie mitral and tricuspid closes then
semilunar valves (Aortic & Pulmonary)
open.
This causes:
 Rapid ejection of blood ie 70% of
blood is ejected rapidly
 Slow ejection of blood ie 30% is
ejected slowly

9. 9
TIME FOR VENTRICULAR
FILLING AND EMPTYING
 Time for ventricular filling (diastole) = 0.5
sec
 Time for ventricular emptying (systole) = 0.3
sec
 Total time for filling & emptying = 0.8 sec
 0.8 sec is one cardiac cycle ie diastole +
systole
 ie 0.8 sec is one beat
 Therefore one min (60 sec) 60/0.8 = 75
cycles or beats per min.

10. 10
ISOVOLUMETRIC
CONTRACTION
Isovolumetric contraction ie contraction
or systole is occurring but no emptying
of the blood ( the same volume).
This is the period between mitral &
tricuspid valves closure and opening of
aortic & pulmonary valves only
TENSION is increasing but no
shortening of the muscles

11. 11
THE ISOVOLUMETRIC
RELAXATION
The relaxation is occuring but there
is no change in blood volume.
This is the period between aortic &
pulmonary valves closure and
opening of mitral & tricuspid
valves ie only TENSION is
decreasing but no lengthening of
the muscles

12. 12
Lt VENTRICULAR
VOLUME CHANGES
 The volume of blood in the left ventricle at
the end of relaxation (diastole) is 120 -130
mls
 The amount of blood in the Lt ventricle at the
end of contraction (systole) is 50 – 60 mls
 Therefore the amount of blood pumped
(ejected) out or stroke volume (SV) is about
70 mls
Stroke volume (70mls) is the amount of blood
ejected from the ventricle during a single
heart beat

13. 13
CARDIAC OUTPUT
The cardiac output (CO) can be defined as the
amount of blood ejected or pumped out of
the heart per min.
 Mathematically CO = SV times HR
= 70 times 75 = about
5000ml per min or 5l. However stroke
volume (SV) IS influenced by
 Preload
 Contractility &
 Afterload

14. 14
CARDIAC OUTPUT CONT.
Cardiac output (CO) can therefore be
altered by factors that alter SV and HR.
 Preload is determined by the volume
of blood in the ventricle at the end of
diastole ie the Left Ventricular End
Diastolic Volume (LVEDV)
 An increased LVEDV increases the SV
ejected which obeys Frank Starling law
of the heart ie increased stretching of
fibres increases their contractile power

15. 15
STROKE VOLUME CONT
Stroke volume is also influenced by
 Contractility which is the force of
ventricular contraction and is
independent of ventricular loading.
Contractility depends on the
interaction of the contractile proteins
MYOSIN & ACTIN found in the THICK
& THIN filament of the myocardial
sarcomere.

16. 16
STROKE VOLUME CONT.
Stroke volume is influenced by
 Afterload which is an expression of the
resistance which a ventricle must
overcome to eject the stroke volume.
Factors that affect Afterload:
 The resistance in the aorta
 The peripheral resistance
 The mass of blood in the aorta
 The viscosity of the blood

17. 17
ECG WAVES