Cardiac cycle made easy

cardiac cycle and its different phases explained in a easily understandable way for all

1. Cardiac Cycle Dr. Md. Mostafizur Rahman Bhuiyan Resident (Phase: A) Dept. of Paediatric Cardiology

2. Definition: The cardiac events that occur from the beginning of one heartbeat to the beginning of the next are called the cardiac cycle. Cardiac Cycle

3. Events in cardiac cycle : Electrocardiogram Mechanical changes Atrial systole & diastole Ventricular systole & diastole Pressure Changes Aortic pressure Ventricular pressure Atrial pressure Pulmonary artery pressure Volume changes Heart sounds  A   Wiggers diagram , named after its developer,  Dr. Carl J. Wiggers , is a standard diagram used in teaching  cardiac physiology .  In the Wiggers diagram, the X axis is used to plot time, while the Y axis contains all of the following on a single grid.

4. Relationship of the Electrocardiogram to the Cardiac Cycle Each cardiac cycle is initiated by spontaneous generation of an action potential in the SA node . The P wave Is caused by spread of depolarization through the atria It is followed by atrial contraction It causes a slight rise in the atrial pressure curve immediately after the P wave. About 0.16 s after the P wave, the QRS appear

5. Relationship of the Electrocardiogram to the Cardiac Cycle QRS complex: Caused by electrical depolarization of the ventricles It initiates contraction of the ventricles i.e ventricular systole T wave: It represents the stage of repolarization of the ventricles when the ventricular muscle fibers begin to relax. Therefore , the T wave occurs slightly before the end of ventricular contraction.

6. A-V Valves Open; Semilunar Valves Closed Atrial systole (1): About 80% of blood normally flows continually from the great veins into the atria. Then, atrial contraction causes an additional 20% filling of the ventricles. Atrial diastole : At the end of systole diastole occurs and during this period blood enters into atria from great veins. Atrial systole occurs during the last phase of ventricular diastole. Atrial diastole is not considered as a separate phase, since it coincides with the whole of ventricular systole and earlier part of ventricular diastole. Mechanical events in Cardiac cycle

7. Ventricular systole: starts at the end of atrial sytole . Isovolumic contraction (2): Immediately after ventricular contraction begins, the ventricular pressure rises abruptly, causing the A-V valves to close, produces the 1 st heart sound during this period, ventricle contracts but muscle does not shorten and no blood passes out of ventricle, thus pressure increases. It strarts from the closure of AV valve and terminated by opening of semilunar valve

8. Period of rapid ejection (3) : the first third of ejection is called the period of rapid ejection as 70 per cent of the blood emptying occurring during this time. Period of slow ejection (4): remaining 30 per cent emptying occurs during the last two third of cardiac cycle known as the period of slow ejection. Period of Ejection: When the left ventricular pressure rises slightly above 80 mm Hg (and the right ventricular pressure slightly above 8 mm Hg), the ventricular pressures push the semilunar valves open. Immediately, blood begins to pour out of the ventricles.

9. Ventricular diastole: Protodiastolic phase : pressure in ventricles falls semilunar valve closes due to high aortic pressure produces 2 nd heart sound  

10. Isovolumic relaxation (5) : interval between closure of semilunar valve and opening of AV valve At the end of systole, ventricular relaxation begins suddenly, allowing both the right and left intraventricular pressures to decrease rapidly. The elevated pressures in the distended large arteries that have just been filled with blood from the contracted ventricles immediately push blood back toward the ventricles, which snaps the aortic and pulmonary valves closed. For another 0.03 to 0.06 second, the ventricular muscle continues to relax, even though the ventricular volume does not change, giving rise to the period of isovolumic or isometric relaxation. During this period, the intraventricular pressures decrease rapidly back to their low diastolic levels. Then the A-V valves open to begin a new cycle of ventricular pumping.

11. Rapid filling phase(6): ventricular pressure fall markedly and the blood rushes from atria to ventricle. Blood was accumulated in the rt & lt atria during ventricular systole for the closed A-V valves & the moderately increased atrial pressure push the A-V valves open and allow blood to flow rapidly into the ventricles 3 rd heart sound produces Slow filling phase / diastasis (7): amount of filling is minimum (blood from the veins and passes through the atria directly into the ventricles) ventricular pressure slowly rises Last rapid filling (Atrial systole): due to atrial contraction blood rushes from atria to ventricle. It accounts for about 20 per cent of the filling of the ventricles during each cardiac cycle.

12. Mechanical events in Cardiac cycle DIVISIONS AND DURATION   OF CARDIAC CYCLE When the heart beats at a normal rate of 72/minute , duration of each cardiac cycle is about 0.8 second . ATRIAL EVENTS Time VENTRICULAR EVENTS Time Atrial systole 0.11 (0.1) Ventricular systole 0.27 (0.3) 1.Isovolumetric contraction 0.05 2. Ejection period          0.22 Atrial diastole = 0.69 (0.7) Ventricular diastole 0.53 (0.5) 1. Protodiastole 0.04 2. Isometric relaxation 0.08 3. Rapid filling 0.11 4. Slow filling / diastasis 0.19 5. atrial systole / Last rapid filling 0.11

13. Atrial Events Vs Ventricular Events Out of 0.7 sec of atrial diastole, first 0.3 sec (0.27 sec accurately) coincides with ventricular systole. Then, ventricular diastole starts and it lasts for about 0.5 sec (0.53 sec accurately). Later part of atrial diastole coincides with ventricular diastole for about 0.4 sec. So , the heart relaxes as a whole for 0.4 sec.

14. Pressure Changes in the Atria In the atrial pressure curve three minor elevations , called the a, c, and v atrial pressure waves, are noted. The a wave caused by atrial contraction. right atrial pressure increases 4 to 6 mm Hg during atrial contraction, and the left atrial pressure increases about 7 to 8 mm Hg. The c wave occurs when the ventricles begin to contract; it is caused partly by slight backflow of blood into the atria at the onset of ventricular contraction and mainly by bulging of the A-V valves backward toward the atria because of increasing pressure in the ventricles. The v wave occurs toward the end of ventricular contraction; it results from slow flow of blood into the atria from the veins while the A-V valves are closed during ventricular contraction

15. Pressure change in Ventricle: Intra ventricular Pressure Change During Ventricular Systole: When the heart is in  diastole , pressure in the  systemic arteries  averages about 80 mmHg.   In Isometric contraction period, intraventricular pressure sharply rises as ventricle contracts in a closed cavity due to closure of both AV & Semilunar valve. In maximum ejection phase, pressure in the lt ventricle and aorta rises about 120 mmHg, when blood passage out & volume decreases But the force of contraction is stronger than out flow, so intraventricular pressure rises .

16. Pressure change in ventriular diastole: In protodiastolic phase, pressure continue to fall. In isomertic relaxation phase, LV pressure sharply falls blow the pressure in Aorta, semilunar valves snap shut. The pressure in the aorta falls to 80 mmHg, while pressure in the left ventricle falls to 0 mmHg. Rapid filling phase: When the pressure in the ventricles falls below the pressure in the atria, the AV valves open and a phase of rapid filling of the ventricles occurs. last rapid filling phase, corresponds with atrial systole, blood pumps into ventricle & pressure suddenly rises. Pressure change in Ventricle:

17. Pressure changes during cardiac cycle Pressures observed within cardiac chambers during systole and diastole Heart region Pressure (mmHg) Right atrium 0-4 Right ventricle 25 systolic; 4 diastolic Pulmonary artery 25 systolic; 10 diastolic Left atrium 8-10 Left ventricle 120 systolic; 10 diastolic Aorta 120 systolic; 80 diastolic

18. During diastole, normal filling of the ventricles increases the volume of each ventricle to about 110 to 120 milliliters. This volume is called the end-diastolic volume. Then, as the ventricles empty during systole, the volume decreases about 70 milliliters, which is called the stroke volume. SV=EDV −ESV The remaining volume in each ventricle, about 40 to 50 milliliters, is called the end-systolic volume. The fraction of the end-diastolic volume that is ejected is called the ejection fraction - usually equal to about 60 per cent. ejection fraction (EF) is used to evaluate stroke volume and contractility . It is described as: EF=(SV / EDV)×100%   A higher EF suggests more efficient heart activity. Volume changes in ventricles:

19. Phonocardiogram A graphic recording of cardiac sound A specially designed microphone on the chest wall. Sound waves amplified, filtered and recorded. Doppler Echocardiography has replaced the phonocardiography

20. 1 st heart sound( lubb ) The 1st heart sound, marks the beginning of systole (end of diastole). Related to the closure of the mitral and tricuspid valves. 2 nd heart sound (Dub) The 2nd heart sound, marks the end of systole (beginning of diastole). Related to the closure of the aortic and pulmonic valves Heart sound in cardiac cycle

21. Heart sound in cardiac cycle Third Heart Sound The third heart sound (S 3 ) is a low-pitched, early diastolic sound audible during the rapid entry of blood from the atrium to the ventricle Fourth Heart Sound The fourth heart sound (S 4 ) is a late diastolic sound that corresponds to late ventricular filling through active atrial contraction. It is a low-intensity sound heard best with the bell of the stethoscope.