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1. CARDIAC CYCLE
Definition: The cyclical changes that take place in the heart during each beat (one systole and
one diastole)
Duration for one cycle = 0.8 sec
Phases:
◼ Atrial systole - 0.1 sec
◼ Atrial diastole- 0.7 sec
◼ Ventricular systole – 0.3 sec
◼ Ventricular diastole – 0.5 sec
ATRIAL SYSTOLE
◼ Contraction of atria & expulsion of blood into ventricles
◼ Contributes 25% of the ventricular filling
◼ Last phase of ventricular diastole
◼ Produces fourth heart sound
ATRIAL DIASTOLE
◼ Gradual filling of atria by blood brought by veins
VENTRICULAR SYSTOLE
◼ Contraction of ventricles & expulsion of blood into respective blood vessels
◼ Includes three phases
Isovolumetric contraction-0.05sec
Maximal ejection – 0.1 sec
Reduced ejection – 0.15 sec
Isovolumetric contraction
◼ Period between closure of AV valves & opening of semilunar valves
◼ Ventricles contract as closed chambers
◼ No change in the volume of blood in the ventricles
◼ Intraventricular pressure increases
Maximal Ejection phase
◼ Increase in intraventricular pressure
◼ Semilunar valves are forced to open
◼ Due to High Pressure gradient, blood is rapidly ejected out of ventricles
◼ About 2/3rd of stroke volume is ejected
Reduced ejection
◼ Due to decreased pressure gradient, the rate of ejection of blood is reduced
◼ About 1/3rd of stroke volume is ejected
VENTRICULAR DIASTOLE
◼ Filling of ventricles by the blood flowing from atria
◼ Includes five phases
Protodiastolic period – 0.04 Sec
Isovolumetric relaxation – 0.08 Sec
Rapid inflow – 0.11
Diastasis – 0.19
Atrial systole – 0.11
, 2
Protodiastolic phase
◼ Ventricle relaxes
◼ Intraventricular pressure in less than the pressure in the aorta/Pulmonary Arteries
◼ Semilunar valves close to prevent the back flow of blood from arteries into ventricles
◼ Closure of SLV produces second heart sound
Isovolumetric relaxation
◼ Period between closure of semilunar valves & opening of AV valves
◼ SLV and AV valves are closed
◼ Ventricle relaxes as closed chamber
◼ No change in the volume of blood in the ventricles
◼ Intraventricular pressure decreases
Rapid inflow phase
◼ Intraventricular pressure less than intra atrial pressure
◼ Hence AV valves open
◼ Blood flows from atria to ventricle at a faster rate
◼ Turbulence due to rapid flow produces third heart sound
Diastasis
◼ Increase in intraventricular pressure
◼ Blood flow from atria to ventricle at low rate or static
Atrial systole
◼ Last phase of ventricular diastole
◼ Contributes additional 25% of ventricular filling
HEART SOUNDS
4 recordable heart sounds (Phonocardiogram)
◼ First heart sound-S1 – Caused by closure of AV valves. Occurs at the beginning of
ventricular systole
◼ Second heart sound S2- Caused by closure of Semi Lunar Valves. Occurs at the end
of ventricular systole
◼ Third heart sound- Due to rapid ventricular filling
◼ Fourth heart sound- Caused by atrial systole
HEMODYNAMIC CHANGES
Pressure and volume changes in the atria & ventricle during cardiac cycle
◼ Intra atrial pressure curve
◼ Intraventricular pressure curve
◼ Aortic pressure curve
◼ Ventricular volume curve
Intra-atrial pressure curve
3 Positive waves – a, c & v (caused by increase in intraatrial pressure)
2 Negative waves - x & y (caused by decrease in intraatrial pressure)
◼ ‘a’ wave - due to atrial systole
◼ ‘c’ wave – due to bulging of AV valve into the ventricles during isovolumetric
contraction
◼ ‘v’ wave – due to filling of atria after the closure of AV valves
, 3
Intraventricular pressure curve: (Left ventricular pressure)
◼ During isovolumetric contraction phase – Pressure rises steeply due to a rise in
tension
◼ Maximum ejection phase – Maximum pressure (120 mmHg) develops as the ventricle
is contracting with a maximum force
◼ Reduced ejection phase – Pressure is less during this phase
Aortic pressure Curve:
◼ During diastole of heart, the aortic pressure is maintained at 80 mmHg
◼ During systole of the heart, it rises to 120 mmHg
Ventricular volume curve:
◼ End diastolic volume – During diastole, ventricular volume increases. The maximum
volume of blood in the ventricle at the end of diastole is called End Diastolic
volume. It is normally 130 ml.
◼ Stroke Volume: Volume of blood ejected out from ventricle during systole. It is 80 ml
◼ End Systolic Volume: The minimal volume of blood remaining in the heart at the end
of systole
ECG:
“P” wave = is due to atrial depolarization which occurs before atrial systole
“QRS” complex = is due to ventricular depolarization which occurs before ventricular
Systole
“T” wave is due to ventricular repolarization which occurs before ventricular diastole
Wiggers Chart
1. CARDIAC CYCLE
Definition: The cyclical changes that take place in the heart during each beat (one systole and
one diastole)
Duration for one cycle = 0.8 sec
Phases:
◼ Atrial systole - 0.1 sec
◼ Atrial diastole- 0.7 sec
◼ Ventricular systole – 0.3 sec
◼ Ventricular diastole – 0.5 sec
ATRIAL SYSTOLE
◼ Contraction of atria & expulsion of blood into ventricles
◼ Contributes 25% of the ventricular filling
◼ Last phase of ventricular diastole
◼ Produces fourth heart sound
ATRIAL DIASTOLE
◼ Gradual filling of atria by blood brought by veins
VENTRICULAR SYSTOLE
◼ Contraction of ventricles & expulsion of blood into respective blood vessels
◼ Includes three phases
Isovolumetric contraction-0.05sec
Maximal ejection – 0.1 sec
Reduced ejection – 0.15 sec
Isovolumetric contraction
◼ Period between closure of AV valves & opening of semilunar valves
◼ Ventricles contract as closed chambers
◼ No change in the volume of blood in the ventricles
◼ Intraventricular pressure increases
Maximal Ejection phase
◼ Increase in intraventricular pressure
◼ Semilunar valves are forced to open
◼ Due to High Pressure gradient, blood is rapidly ejected out of ventricles
◼ About 2/3rd of stroke volume is ejected
Reduced ejection
◼ Due to decreased pressure gradient, the rate of ejection of blood is reduced
◼ About 1/3rd of stroke volume is ejected
VENTRICULAR DIASTOLE
◼ Filling of ventricles by the blood flowing from atria
◼ Includes five phases
Protodiastolic period – 0.04 Sec
Isovolumetric relaxation – 0.08 Sec
Rapid inflow – 0.11
Diastasis – 0.19
Atrial systole – 0.11
, 2
Protodiastolic phase
◼ Ventricle relaxes
◼ Intraventricular pressure in less than the pressure in the aorta/Pulmonary Arteries
◼ Semilunar valves close to prevent the back flow of blood from arteries into ventricles
◼ Closure of SLV produces second heart sound
Isovolumetric relaxation
◼ Period between closure of semilunar valves & opening of AV valves
◼ SLV and AV valves are closed
◼ Ventricle relaxes as closed chamber
◼ No change in the volume of blood in the ventricles
◼ Intraventricular pressure decreases
Rapid inflow phase
◼ Intraventricular pressure less than intra atrial pressure
◼ Hence AV valves open
◼ Blood flows from atria to ventricle at a faster rate
◼ Turbulence due to rapid flow produces third heart sound
Diastasis
◼ Increase in intraventricular pressure
◼ Blood flow from atria to ventricle at low rate or static
Atrial systole
◼ Last phase of ventricular diastole
◼ Contributes additional 25% of ventricular filling
HEART SOUNDS
4 recordable heart sounds (Phonocardiogram)
◼ First heart sound-S1 – Caused by closure of AV valves. Occurs at the beginning of
ventricular systole
◼ Second heart sound S2- Caused by closure of Semi Lunar Valves. Occurs at the end
of ventricular systole
◼ Third heart sound- Due to rapid ventricular filling
◼ Fourth heart sound- Caused by atrial systole
HEMODYNAMIC CHANGES
Pressure and volume changes in the atria & ventricle during cardiac cycle
◼ Intra atrial pressure curve
◼ Intraventricular pressure curve
◼ Aortic pressure curve
◼ Ventricular volume curve
Intra-atrial pressure curve
3 Positive waves – a, c & v (caused by increase in intraatrial pressure)
2 Negative waves - x & y (caused by decrease in intraatrial pressure)
◼ ‘a’ wave - due to atrial systole
◼ ‘c’ wave – due to bulging of AV valve into the ventricles during isovolumetric
contraction
◼ ‘v’ wave – due to filling of atria after the closure of AV valves
, 3
Intraventricular pressure curve: (Left ventricular pressure)
◼ During isovolumetric contraction phase – Pressure rises steeply due to a rise in
tension
◼ Maximum ejection phase – Maximum pressure (120 mmHg) develops as the ventricle
is contracting with a maximum force
◼ Reduced ejection phase – Pressure is less during this phase
Aortic pressure Curve:
◼ During diastole of heart, the aortic pressure is maintained at 80 mmHg
◼ During systole of the heart, it rises to 120 mmHg
Ventricular volume curve:
◼ End diastolic volume – During diastole, ventricular volume increases. The maximum
volume of blood in the ventricle at the end of diastole is called End Diastolic
volume. It is normally 130 ml.
◼ Stroke Volume: Volume of blood ejected out from ventricle during systole. It is 80 ml
◼ End Systolic Volume: The minimal volume of blood remaining in the heart at the end
of systole
ECG:
“P” wave = is due to atrial depolarization which occurs before atrial systole
“QRS” complex = is due to ventricular depolarization which occurs before ventricular
Systole
“T” wave is due to ventricular repolarization which occurs before ventricular diastole
Wiggers Chart
