phases of cardiac cycle

What controls the opening & closing of heart valves during the cardiac cycle?

Pressure changes in the heart chambers

When does MV open & close?

• Open- LA pressure > LV pressure

• Close- LA pressure < LV pressure

General rule for all heart valves

Valves open when pressure behind the valve is higher & close when pressure in front of the valve is higher, preventing backflow

4 phases of ventricular diastole

1. Isovolumic relaxation

2. Rapid early diastolic filling (80%)

3. Diastasis (reduced filling/mid diastole)

4. Atrial systole (late filling, 20%)

When does most ventricular filling occur during diastole?

About 80% of ventricular filling occurs during rapid early diastolic filling

What happens during atrial systole (late diastolic filling)

The atria contract & provide the remaining 20% of ventricular filling

Isovolumic relaxation

Phase between SL valve closure & AV valve opening when ventricles begin to relax

What happens to the valves during Isovolumic relaxation?

Both SL & AV valves close

Why is it called Isovolumic relaxation?

Ventricular pressure decreased while ventricular volume stays the same because all valves are closed

What is being shown?

Isovolumic relaxation

What is rapid passive filling during ventricular diastole?

The phase when the ventricles rapidly fill with blood after the AV valves open

When does ventricular diastole occur on the EKG?

Begins at the end of T wave & ends with start of QRS complex

What is the valve status during rapid passive filling?

• AV valves- OPEN

• SL valves- CLOSED

Diastasis

Mid diastole there is equalization of pressure & MV & TV close

When does atrial systole occurs & what does it do?

• occurs at end of ventricular diastole with start of the P wave

• pushes remaining blood into ventricles (atrial kick)

What is the valve status during atrial systole?

• AV valves- OPEN

• SL valves- CLOSED

How much does atrial systole contribute to ventricular filling?

Atrial systole contributes about 20% of ventricular filling (atrial kick)

Isovolumic contraction

Phase between AV closure & SL opening

What happens to the valves during Isovolumic contraction?

All valves are closed

Why is is called Isovolumic contraction?

Ventricular pressure increases while ventricular volume stays same

What is being shown?

Isovolumic contraction

Ventricular systole

Phase when ventricles contract & eject blood into great arteries

When does ventricular systole occur on EKG

Begins with QRS & ends with T

Valve status during ventricular systole

• AV- CLOSED

• SL- OPEN

What happens during the ejection phase of ventricular systole?

Blood is ejected from the ventricles into the great arteries. The phase includes rapid and reduced ejection, and ventricular volume is lowest at peak systole