Cardiac Cycle

Dr Sadath Pareed

13/01/2014

cardiac cycle • Galen (200AD) the father of expirimental physiology

knew that the heart set the blood in motion• Circulation of the left and right heart are separated and

grasped by Servetus ( 1511-1553)• Modern concepts of the circulation laid by Harvey (1578-

1657)

Definition :

Each cardiac contraction proceeds through a series of electrical and mechanical events that govern the opening and closing of the valves , the flow of blood into and out of the heart, and the timing of the heart sounds. Together these electrical and mechanical events represent the cardiac cycle.

Complete cycle of events in the heart from the beginning of one heart beat to the beginning of the next.

CARDIAC CYCLE : 0.8 SEC

• Atrial Systole : 0.1 sec• Atrial Diastole : 0.7 sec

• Ventricular systole : 0.3 sec• Ventricular diastole : 0.5 sec

Ventricular Cycle Systole Diastole

I. Isovolumetric contraction 0.05s

II. Rapid ejection 0.10s

III. Reduced ejection 0.15s

Total 0.3 s

IV. Protodiastole 0.04 s

V. Isovolumetric relaxation 0.06 s

VI. Rapid filling phase 0.10 s

VII. Diastasis 0.20 s

VIII. Atrial systole 0.10 s

Total 0.5 s

Wiggers diagram is the graphic representation of the various events of the cardiac cycle

Each cardiac cycle consists of 8 segments represented by Roman numerals

VENTRICULAR CYCLE

Ventricular Cycle Systole Diastole

I. Isovolumetric contraction 0.05s

II. Rapid ejection 0.10s

III. Reduced ejection 0.15s

Total 0.3 s

IV. Protodiastole 0.04 s

V. Isovolumetric relaxation 0.06 s

VI. Rapid filling phase 0.10 s

VII. Diastasis 0.20 s

VIII. Atrial systole 0.10 s

Total 0.5 s

I Isovolumetric contraction

• Isovolumic.• Duration 50 mSec• LV pressure 8 – 80 mmg.• S1 occurs 20ms after pressure

crossover.• M1 followed by T1.• QRS complex begins slightly

before & the later half of R wave occurs in this phase.

• C wave of JVP occurs during this phase.

II Rapid ejection phase

• Duration 0.10 s• Opening of aortic valve –rapid

ejection--2/3 of ejection occurs.• Steep rise in aortic pressure

because blood is expelled faster than peripheral run off into aorta.

• LV volume decreases rapidly.• ST segment of ECG occurs. • No heart sounds are heard during

ejection phase.-AoV opening clinically silent event

• Left atrial pressure initially decreases & then slowly rises.

III Reduced ejection Phase

• Ejection maintained by kinetic energy of blood flow.

• Lasts for 0.15 s.• One third of ejection.• Aortic pressure falls because run

off is faster than inflow.• Ventricular volume decreases at

slow rate.• Coincides with T wave of ECG. • Atrial pressure continues to rise

due to atrial filling.

IV Protodiastole

0.04 s. Ventricle starts relaxing and

ventricular pressure begins to fall below that of aorta.

Semilunar valves are still open. Deceleration of column of blood

in the aorta hitting the aortic valve.

Time interval between pressure crossover & S2.

Aortic closure occurs earlier.

V Isovolumetric relaxation

Begins with the closure of semilunar valves.

AV valves are still closed (Isovolumic).

Active relaxation and sharp fall in LV pressures.

A characteristic notch (incisura or dicrotic notch) in the aortic pressure tracings (Valve closure)

After valve closure, the aortic and pulmonary artery pressures rise slightly (dicrotic wave)

V wave of JVP.

V Isovolumetric relaxation

• The volume of blood that remains in a ventricle is called the end-systolic volume and is ~50 ml in the left ventricle. 

• The difference between the end-diastolic volume and the end-systolic volume is ~70 ml and represents the stroke volume.

• AV valves open at the end of this phase .

VI Rapid filling phase 0.10 s. Begins with the opening of the

AV valves. 70 – 80 % of filling. Sharp rise in ventricular volume. Fall in atrial pressure - Y

descent. Ventricular filling is normally

silent. Audible third heart sound (S3)

represents tensing of chordae tendineae and AV ring during ventricular relaxation and filling. 

VII Diastasis Reduced filling phase; lasts for

0.20 s; 5 – 10 % of filling. 80% of ventricular filling occurs

before atrial contraction Shortens with tachycardia. Ventricular volume continues to

increase slowly. Pressure rises gradually in both

atria and ventricles. Corresponds with T – P segment

on ECG.

VIII Atrial systole

Follows diastasis , lasts for 0.10s. Contributes 10 – 20 % of

ventricular inflow. Significant contribution ( 20 – 40

% ) in exercise , tachycardia , poor LV compliance.

Coincides with fourth heart sound.

Causes slight rise of atrial pressure curve ( 5 mmHg ) – a wave.

P wave of ECG begins slightly before atrial contraction.

• In children & young adults ,the majority of ventricular filling occurs in early diastole with prominent E velocity &only small contribution to ventricular filling due to atrial contraction

ATRIAL CYCLE

Atrial cycle• Atrial systole - 0.1 s• Atrial diastole - 0.7 s• Atrial pressure

curve shows 3

pressure waves

a , c , v and

two falls in pressure called the x and y descents

Atrial cycleA wave Reflects atrial systole. Follows P wave of ECG. Precedes upstroke of carotid

impulse and S1. Summit of A occurs 0.02 sec

after S4.

C wave Reflects the bulging of closed

AV valves into the atrium during isovolumetric contraction.

Atrial cycle

V wave Continuing venous in flow into

the atrium during ventricular systole while the AV valve is closed.

Begins before S2& reaches its peak after P2.

X descent Continuing atrial relaxation and

pulling of AV valves downward by the contracting ventricle.

Atrial cycle Occurs during isovolumetric

contraction & systole. ( systolic collapse)

Y descent Reflects the negative deflection

of atrial pressure when the AV valve opens in early diastole. ( Diastolic collapse )

It begins and ends during diastole.

HEART SOUNDS

Heart Sounds• Valve closure and rapid-filling

phases are audible with a stethoscope placed on the chest.

• The first heart sound, results from the closure of the AV valves, heralds ventricular systole.

• The second heart sound, shorter and composed of higher frequencies than the first, is associated with closure of the semilunar valves at the end of ventricular ejection.

Physiological Vs cardiological systole and diastole

• Cardiological systole demarcated by interval between 1st and 2nd heart sounds ,lasting from M1 to A 2

• Physiological systole lasts fom from start of IVC to peak of ejection phase, so that physiological diastole commences as LV pressure starts to fall(during reduced ejection)

• Thus cardiological systole,demarcated by heart sounds rather than physiological events,starts fractionally later than physiological systole and ends significantly later

Heart Sounds

• Third and fourth heart sounds are low-frequency vibrations caused by early, rapid filling and late diastolic atrial contractile filling respectively.

• These sounds can be heard in normal children but in adults usually indicate disease.

PRESSURE-VOLUME LOOP

VENTRICULAR

Pressure-Volume loop

The cardiac cycle can be divided into four basic phases: .

• Isovolumetric contraction phase.

• Ejection phase.• Isovolumetric relaxation

phase.• Ventricular filling phase

Pressure-Volume loop

Point 1 on the PV loop is the pressure and volume at the end of ventricular filling (diastole), and therefore represents the end-diastolic pressure and end-diastolic volume (EDV) for the ventricle.

Pressure-Volume loop

As the ventricle begins to contract isovolumetrically (phase b), the LVP increases but the LV volume remains the same, therefore resulting in a vertical line (all valves are closed).

Once LVP exceeds aortic diastolic pressure, the aortic valve opens (point 2) and ejection (phase c) begins.

Pressure-Volume loopDuring this phase the LV volume decreases as LVP increases to a peak value (peak systolic pressure) and then decreases as the ventricle begins to relax.

When the aortic valve closes (point 3), ejection ceases and the ventricle relaxes isovolumetrically - that is, the LVP falls but the LV volume remains unchanged, therefore the line is vertical (all valves are closed).

Pressure-Volume loop

The LV volume at this time is the end-systolic volume (ESV).

When the LVP falls below left atrial pressure, the mitral valve opens (point 4) and the ventricle begins to fill.

Initially, the LVP continues to fall as the ventricle fills because the ventricle is still relaxing.

However, once the ventricle is fully relaxed, the LVP gradually increases as the LV volume increases.

Pressure-Volume loop

Thank You