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LECTURE – 3 DR. ZAHOOR ALI SHAIKH 2

CARDIAC CYCLE  Cardiac events occurring during one beat (systole & diastole) are repeated during the next beat  Cardiac cycle time : 0.8 second when heart rate is 75 beats per minute. 3

CARDIAC CYCLE  Atria and Ventricle go through separate cycles of systole and diastole.  When we use the term Systole and Diastole, we refer to ventricles, until unless specified for atria. 4

We will discuss mechanical & electrical changes during Cardiac Cycle Mechanical changes: 1. Phases of cardiac cycle 2. Pressure changes during cardiac cycle 3. Volume changes during cardiac cycle 4. Heart sounds Electrical Changes 5. Electrocardiogram (ECG) 5

6 ECG ECG ( Electrocardiogram) – These electrical events can be recorded by putting electrodes on the surface of body P wave – Atrial depolarization QRS - Ventricular Depolarization T wave – Ventricular Repolarization We will discuss ECG in detail in coming lectures.

MECHANICAL CHANGES 1. PHASES OF CARDIAC CYCLE 7

PHASES OF CARDIAC CYCLE  Atrial systole: 0.1 second  Atrial diastole : 0.7 seconds  Ventricular systole : 0.3 seconds  Ventricular diastole : 0.5 seconds 8

ADAS VSVD CARDIAC CYCLE Atrial Cycle ( 0.8 Sec.) Ventricular Cycle (0.8 Sec.) 0.7 Sec. 0.1 sec. 0.3Sec.0.5 sec. AS – Atrial Systole; AD – Atrial Diastole ; VS – Ventricular systole; VD – Ventricular diastole 9

Ventricular events  Ventricular systole 1. Isovolumetric contraction 2. Ejection phase Rapid ejection Slow ejection  Protodiastolic phase  Ventricular Diastole 1. Isovolumetric relaxation phase 2. Filling phase Rapid filling Slow filling Last rapid filling 10

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Ventricular events Ventricular systole 1. Isovolumetric Contraction  When blood has come from Atria into the ventricle, ventricle will start contracting, when pressure increases in ventricle than atria, AV valves close.  This phase of ventricular contraction when all valves are closed is called ISOVOLUMETRIC CONTRACTION. 12

Ventricular systole  During Isovolumetric Contraction, volume remains same, but pressure in the ventricle must continue to increase till it exceeds aortic pressure. 13

Ventricular systole 2. Ejection Phase  When ventricular pressure increases, semi-lunar valve [aortic and pulmonary valves] will open and blood will flow into aorta and pulmonary artery. This is Ejection Phase [pumping of blood out].  Ejection is rapid first and then slow. 14

Protodiastolic phase  Once ventricle muscle is fully contracted, than it will relax and ventricular pressure will drop rapidly.  When ventricles are relaxing, but aortic and pulmonary valves have not closed yet, this period is called Protodiastole.  It lasts for 0.04 sec.  It ends when aortic and pulmonary valve close. 15

Ventricular Diastole 1. Isovolumetric Relaxation During diastole, When ventricular pressure falls below the Aortic pressure, aortic valve closes, and AV valves are not open yet, ventricle is close cavity with all valves closed. This phase is called Isovolumetric Relaxation (means volume remains same but pressure is decreasing). 16

Ventricular Diastole 2. Filling phase When ventricular pressure falls below the atrial pressure, AV valve open and blood moves rapidly from the atria into the ventricles – first rapid filling phase [causes 3 rd heart sound]. Then blood comes slowly – slow filling phase. Then atria contract for 0.1sec and blood comes fast into the ventricle – last rapid filling phase [causes 4 th heart sound]. NOTE Last rapid filling phase is due to atrial systole and contributes to 20-30% of ventricular filling. After atrial systole, cardiac cycle will re-start. 17

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ADAS VSVD Relation Of Heart Sounds With Phases Of Cardiac Cycle HEART SOUNDS 0.7 Sec. 0.1 sec. 0.3Sec.0.5 sec. 1 st Heart Sound 2 nd Heart Sound3 rd Heart Sound4 th Heart Sound AS – Atrial Systole; AD – Atrial Diastole ; VS – Ventricular systole; VD – Ventricular diastole 19

Tachycardia, Effect on Cardiac Cycle  During Tachycardia, when heart rate is increased, both systole and diastole time decreases.  Diastole length (time) is shortened much more than systole length. Therefore it reduces the time for ventricular relaxation and filling. 20

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2. PRESSURE CHANGES DURING CARDIAC CYCLE 22

Pressure changes during cardiac cycle Rt- Atrium = 0-7mm Hg. Lt- Atrium = 2-10 mm Hg. Rt – Ventricle = 25 / 6(2-8) mm Hg. Lt – ventricle = 120 / 8(2-10) mm Hg. Aorta = 120 / 80 mm Hg. Pul. Artery = 25 / 10 mm Hg. 23

 Draw pressure curve for Lt.ventricle, Aorta & Lt. Atrium  Draw pressure curve for Rt. Ventricle & Pul. Artery. 24

Events of cardiac cycle showing pressure changes in left ventricle, aortic pressure, atrial pressure, ECG & phonocardiogram 25

pressure curves for Rt. ventricle. & Pulmonary Artery 26

3. VOLUME CHANGES DURING CARDIAC CYCLE 27

 Define Stroke Volume (SV)  Define End Diastolic Volume (EDV)  Define End Systolic Volume (ESV)  Define Ejection Fraction (EF) 28

 Stroke Volume: It is a volume of blood pumped out by each ventricle per beat. It is about ml. Stroke volume (SV) = EDV – ESV  End Diastolic Volume: Volume of blood in each ventricle at the end of diastole. It is about 120 – 130 ml.  End Systolic Volume: Volume of blood in each ventricle at the end of Systole. It is about 50 to 60 ml 29

Volume changes during cardiac cycle 30

Events of cardiac cycle showing left ventricular pressure, volume changes, & phonocardiogram 31

 Ejection fraction (EF) is the percentage of ventricular end diastolic volume (EDV) which is ejected with each stroke. EF = SV (EDV – ESV) EDV X X 100 = 62.5% Normal ejection fraction is about 60 – 65 %. Ejection fraction is good index of ventricular function. 32

Heart Sounds  We will discuss Heart Sounds in next lecture. 33

What You Should Know From This Lecture  Cardiac Cycle – Definition  Phases of Cardiac Cycle  Pressure Changes  Volume Changes  Period of Systole & Diastole During Tachycardia  Relationship of Heart sounds with Cardiac Cycle 34

Thank you 35