The cardiac cycle

What is the cardiac cycle

The sequence of mechanical and electrical events that occur form the start of one heart beat to the start of the next, including the systole and diastole of both atria and ventricles

What are the two main phases of the cardiac cycle

Systole and diastole

What happens during ventricular diastole

Ventricles relax, AV valves open, blood flows passively form atria to ventricles

What is isovolumetric contraction

Early systole when ventricles contract with all valves closed → pressure rises but volumes stays constant

What triggers ventricular ejection

Ventricular pressure exceeding aortic/pulmonary artery pressure → semilunar valves open

What happens during isovolumetric relaxation

Ventricles relax with all valves closed, causing rapid fall in pressure

Which valves open during ventricular filling

AV valves open

Which valves are open during ventricular ejection

Semilunar valves open

What causes the S1 heart sound

Closure of the AV valves

What causes the S2 heart sound

Closure of semilunar valves

Why does atrial pressure not fall to zero during diastole

because of elastic recoil

Define stroke volume (SV)

SV = EDV - ESV

Define cardiac output (CO)

CO = SV x HR

What is jugular venous pressure (JVP)

An estimate of right atrial pressure, reflecting right heart function and venous return

What does the ‘a wave’ in the JVP represent

Right atrial contraction

What does the ‘c wave’ in the JVP represent

Bulging of the tricuspid valve during early ventricular systole

What does the ‘v wave’ in the JVP represent

Passive filling of the right atrium when tricuspid valve is closed

What causes the JVP ‘x descent’

Atrial relaxation and downward movement of the tricuspid valve during ventricular systole

What causes the JVP ‘y descent’

Opening of the tricuspid valve and rapid ventricular filling

When in the cardiac cycle does ventricular pressure peak

during mid-to-late systole

What initiates the cardiac cycle

Depolarisation of the SA node → atrial contraction