Relevent points of heart related to one cardiac cycle

1. Cardiac Cycle
Arjun MS
Assistant Professor , AHS , MTMC

2. Cardiac cycle
• It’s the sequences of changes in the pressure and flow
between two subsequent contraction in the cardiac
chambers and the blood vessels is called as Cardiac cycle
.
• Normal duration – 0.8s at an heart rate of 75 bpm .

3. • These pressure changes originate as conductive
electrochemical changes within the myocardium that result
in the concentric contraction of cardiac muscle.
• Valves within the heart direct blood movement, which leads
to the organized propulsion of blood to the next chamber.

4. Phases of Cardiac cycle
• Atrial Diastole
• Atrial Systole
• Ventricular Diastole
• Ventricular Systole

5. • The period of contraction that the heart undergoes while it
pumps blood into circulation is called systole.
• The period of relaxation that occurs as the chambers fill with
blood is called diastole.

7. Pressures and Flow
“Fluids, whether gases or liquids, are materials that flow
according to pressure gradients—that is, they move from
regions that are higher in pressure to regions that are lower
in pressure.”
• Accordingly, when the heart chambers are relaxed (diastole),
blood will flow into the atria from the veins, which are
higher in pressure.

8. • As blood flows into the atria, the pressure will rise, so the blood
will initially move passively from the atria into the ventricles.
• When the action potential triggers the muscles in the atria to
contract (atrial systole), the pressure within the atria rises
further, pumping blood into the ventricles.
• During ventricular systole, pressure rises in the ventricles,
pumping blood into the pulmonary trunk from the right
ventricle and into the aorta from the left ventricle.

9. Phases of Cardiac cycle

11. VENTRICULAR SYSTOLE
It is associated with ejection of blood out of the ventricles. It
consists of:
• Isovolumetric (isovolumic or isochoric) contraction: 0.05 s
• Rapid ventricular ejection phase: 0.10 s
• Slow ventricular ejection phase: 0.15 s

12. Isovolumic Contraction :
• It is the first phase of ventricular systole. This phase begins
with the rise of pressure in the ventricles .
• Although ventricular contraction occurs during this phase,
there is no ventricular emptying and hence this phase is known
as isovolumic contraction.

13. This phase is associated with:
• Initial mitral component (M1) of the first sound as the
ventricular pressure exceeds the atrial pressure causing
closure of the atrioventricular (AV) valves and
• Beginning of the isovolumic contraction (IC) wave of the apex
cardiogram.

14. • Rapid Ventricular Ejection Phase :
• This phase begins with the opening of the semilunar valves
(aortic and pulmonary) when the LV pressure exceeds the aortic
pressure and RV pressure exceeds the pulmonary artery (PA)
pressure.

15. It is associated with:
1. Rise in arterial pressure (aorta and PA) as blood enters the great
vessels much faster than it can escape into the peripheral
branches
2. Decrease in ventricular volume
3. About 2/3rd of the stroke volume is ejected during this phase
4. Peak of ejection E wave of the apex cardiogram.

16. Slow or Reduced Ventricular Ejection Phase
• This phase occurs before the closure of the semilunar (SL) valves.
• It is associated with :
1. Decline in the ventricular pressure as ventricular contraction
begins to subside with slow ejection of blood .
2. During this phase, blood flows out of the aorta and PA more
rapidly than it enters from the ventricles.
3. The blood flow in the aorta is maintained by the aortic
distensibility, known as Windkessel effect.

17. VENTRICULAR DIASTOLE
It consists of:
1. Protodiastole : 0.04 s
2. Isovolumetric (isovolumic) ventricular relaxation phase : 0.08 s
3. Rapid ventricular filling phase : 0.10–0.12 s
4. Slow ventricular filling phase or diastasis : 0.18–0.20 s
5. Last rapid ventricular filling phase (due to atrial systole) : 0.06–
0.10 s

18. Protodiastole :
• At the end of ventricular systole, the ventricular pressure drops
more rapidly but the pressure in the great arteries is sustained
by the elastic recoil of the vessel wall which exceeds that in the
ventricles, resulting in the closure of the SL valves producing
second heart sound .

19. • Isovolumic Relaxation Phase :
• It begins after the closure of the SL valves and the intraventricular
pressure continues to decline rapidly and ventricular muscle
continues to relax without any change in the ventricular volume.
• Hence, this phase is known as isovolumic relaxation phase.
• It lasts until the ventricular pressure falls below the atrial pressure
and AV valve opens.

20. Rapid Ventricular Filling Phase :
• It accounts for most of the ventricular filling.
• It begins with the opening of the AV valves when the
intraventricular pressure falls below that of atrial pressure and
blood begins to flow from the atria into the ventricles.

21. Slow Ventricular Filling Phase:
During this phase, the intraventricular pressures slowly rises as
the ventricles are passively filled from the atria with decreased
rate.

22. ATRIAL SYSTOLE
• It occurs following the impulse generation in the SA node.
• With atrial contraction (‘atrial kick’), the increased atrial
pressure results in an increase in the ventricular volume i.e.
the last rapid ventricular filling phase which constitutes
about 30% of the ventricular filling.

23. • It produces:
• a wave in the atrial pressure tracing and in JVP
• Outward a wave of apex cardiogram

24. ATRIAL DIASTOLE
• During this phase, atrial muscles relax and atrial pressure
gradually increases due to the continuous venous return
until the opening of the AV valves.