Dr. David Lyness
Stage 1 = Diastole - P&A Close, T&M Open
Stage 2 = Atrial Systole - T&M Open
Stage 3 = Isovolumetric Contraction - APTM closed
Stage 4 = Ventricular Ejection - P&A Open
Stage 5 = Isovolumetric Relaxation - P&A Close
P wave – atrial depolarisation
PR interval – spread of excitation through the atria, AV node and bundle of His
QRS complex – spread of excitation through the ventricles
T wave – ventricular repolarisation
Pressure differentials promote through flow of blood!
Mechanical contraction occurs after depolarisation, therefore systole starts at the end of the QRS complex and ends during the T wave.
Heart Sounds = CLOSING valves
1st = Mitral & Tricuspid
2nd = Aortic & Pulmonary
The cardiac cycle describes each heart beat, incorporating relaxation and contraction.
Phase one describes diastole and you can see above that atrial & ventricular pressure are both low but atrial pressure is higher than ventricular pressure - this sets up the through through of blood when the atria end up contracting.
You can also see how the ventricular pressure ends up below the atrial pressure after isovolumetric relaxation.
The ventricular volume rises slightly during diastole and then to its peak at the end of atrial systole.
Aortic pressure is always high but falls during diastole, then peaks during ventricular systole.
There is a dicrotic notch after the first fall after peak aortic pressure - this is when the aortic valve closes and a backup of pressure (aorta > LV) leads to a second, smaller peak.
During rapid inflow, the ventricular volume, but not pressure increases.
>40yo, a 3rd heart sound can be linked to cardiac dysfunction or volume overload of the ventricles (GALLOP rhythm)