Cardiac cycle by doctor deb kumar Bhakat .pptx

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 .

6. 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.

7. 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.  

8. Phases of Cardiac cycle

9. 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

10. 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.

11. 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.

12. 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 .

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

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

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

16. 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 .

17. 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.

18. 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.

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

20. 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.

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

22. 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.