Cardiac Cycle : Cardiac Cycle Definition : Definition Cardiac cycle is defined as the sequence of coordinated events which take place during heartbeat. Each heartbeat consists of two major periods called systole and diastole.
During systole there is contraction of the cardiac muscle and pumping of blood from the heart through arteries. Slide 3: During diastole , there is relaxation of cardiac muscle and filling of blood. Various changes occur in different chambers of heart during each heartbeat. These changes are repeated during every heartbeat in a cyclic manner. Divisions of cardiac cycle : Divisions of cardiac cycle The contraction and relaxation of atria are called atrial systole and atrial diastole respectively. The contraction and relaxation of ventricles are called ventricular systole and ventricular diastole respectively. Slide 5: How ever, in clinical practice, the term ‘systole’ refers to ventricular systole and ‘diastole’ refers to ventricular diastole. Thus, the events of cardiac cycle classified in to two divisions.
2. Diastole. Sub divisions and duration of cardiac cycle : Sub divisions and duration of cardiac cycle When the heart beats at the normal rate of 72/minutes , the duration if each cardiac cycle is about 0.3second. The duration of systole is 0.27 second and that of diastole is 0.53 second. Generally, systole is divided in to two sub divisions and diastole is divided in to five subdivisions. systole : systole Time (second)
1. Isometric contraction = 0.05
2. Ejection period = 0.22
------ Diastole : Diastole Time(second)
1.Protodiastole = 0.04
2. Isometric relaxation = 0.08
3. Rapid filling = 0.11
4. Slow filling = 0.19
5. Atrial systole = 0.11
------- Slide 9: The total duration of cardiac cycle is 0.27 + 0.53 = 0.8 second.
Among the atrial events, systole occurs during the last phase of ventricular diastole. Atrial diastole is not considered as a separate phase, since it coincides with the ventricular systole and earlier part of ventricular diastole. The atrial systole extends for about 0.11 second and the duration of atrial diastole is about 0.69 second.s Description of events of cardiac cycle : Description of events of cardiac cycle For the sake of better understanding, the description of events of cardiac cycle is commenced with atrial systole.