Cardiac Cycle

Cardiac events appearing from the beginning of one heart beat to the beginning of next heart beat and repeating themselves successively.

• Cardiac cycle time (H.Rate = 75/min) : 0.8 sec

Systole : 0.27 sec

Diastole: 0.53 sec

• Systole : Contraction and emptying

Muscle stimulated by action potential and contracting

• Diastole : Relaxation and filling

Muscle reestablishing Na+/K+/Ca++ gradient and is relaxing

Atria and ventricles go through separate cycles of

systole and diastole.

Atria contract prior to the ventricular contraction i.e.

when atria contract ventricles relax and vice versa.

 Each ventricle expels same volume of blood/beat.

Systole:

1) Isovolumic contraction

A-V valves close;

because (ventricular press > atrial press)

2) Aortic valve opens

3) Ejection phase

4) Aortic valve closes

Diastole

1) Isovolumic relaxation

2) A-V valves open

3) Rapid inflow

4) Diastasis – slow flow into ventricle

5) Atrial systole – extra blood in and this just

follows P wave. Accounts for 25% of filling

Atrial Pressure/Jugular Venous Pressure Waves

Atrial pressure waves:

a-wave = atrial contraction

c-wave = ventricular contraction

(A-V valves bulge)

v-wave = flow of blood into atria

x- descent = falling Rt atrial pressure due to atrial diastole

y- descent = falling Rt atrial pressure during ventricular filling

Ejection Fraction

• End diastolic volume = 120 ml

• End systolic volume = 50 ml

• Ejection volume (stroke volume) = 70 ml

• Ejection fraction = 70ml/120ml = 58% (normally 60%)

• If heart rate (HR) is 70 beats/minute, what is cardiac

output?

• Cardiac output = HR x stroke volume

= 70/min. x 70 ml

= 4900ml/min.

• If HR =100, end diastolic volume = 180 ml,

end systolic vol. = 20 ml, what is cardiac output?

• C.O. = 100/min. x 160 ml = 16,000 ml/min.

Aortic Pressure Curve

• Aortic pressure starts increasing during systole

after the aortic valve opens.

• Aortic pressure decreases toward the end of the

ejection phase.

• After the aortic valve closes, an incisura occurs

because of sudden cessation of back-flow toward

left ventricle.

• Aortic pressure decreases slowly during diastole

because of the elasticity of the aorta.

Valvular Function

• To prevent back-flow.

• Chordae tendineae are attached to A-V valves.

• Papillary muscle, attached to chordae tendineae, contract during systole and help prevent back-flow.

• Because of smaller opening, velocity through aortic and pulmonary valves exceeds that through the A-V valves.

Events in Cardiac cycle (Left ventricle)

Systole : 0.27 Sec or 0.3 sec

LV : 120 mmHg

RV : 25 mmHg

1. Onset of ventricular contraction.

2. A-V valves closure.

3. Isovolumetric ventricular contraction.

(LV = 60 msec, RV = 15 msec)

4. Semilunar valves open.

5. Ventricular ejection. (LV= 200 msec, RV= 270 m sec)

a. Rapid ejection 1/3rd (70%)

b. Slow ejection 2/3rd (30%)

ESV = 65 ml.

6. Semilunar valves close.

Events in Cardiac cycle (Left ventricle)

Diastole: 0.53 sec or 0.5 sec

7. Isovolumetric relaxation (100 msec)

8. A.V valves open

9. Ventricular filling (500 msec)

a. Rapid filling 60-65%

b. Slow filling (Diastasis) 5-10%

c. Rapid filling again (Atrial systole) 20-25%

‘Atrial kick’

• EDV = 135 ml

• Atrial Systole:

a. RA = 4-6 mmHg

b. LA = 7-8 mmHg