Cardiac Cycle Flashcards
What is the cardiac cycle?
All events associated with the flow of blood through the heart during one heart beat
How long does one cycle last?
0.8 sec
What does cardiac cycle involve?
Series of coordinated Electrical and mechanical events resulting in volume and pressure changes within the heart
What are the left valves?
- Bicuspid / mitral valve
- Aortic valve
What does contraction of atria follow?
Depolarisation
What represents contraction of atria on ECG?
P wave
Why does atrial systole only contribute 20-30% of blood to ventricles?
At start of atrial systole, ventricles are normally filled with 70-80% capacity due to passive inflow during diastole
What direction do atrial muscles contract?
Contract from superior portion of atria toward atrioventricular septum
What happens to pressure in atria during atrial systole?
Pressure rises within atria and blood pumped into ventricles through open AV valve
What does ventricular systole follow?
Depolarisation of ventricles
What represents ventricular systole on ECG?
QRS complex
What 2 phases can ventricular systole be divided into?
- Isovolumic contraction (1st phase)
2. Ventricular ejection (2nd phase)
What happens in isovolumic contraction of ventricles and why does this mean volume of blood in chamber stays constant?
Pressure within chamber rises but not high enough to open SL valves and eject blood
Since blood is not being ejected from the ventricles at this early stage, the volume of blood within the chamber remains constant
Why does isovolumic contraction of ventricles cause AV valves to close?
- Pressure quickly rises above that of atria that are now relaxed (in diastole)
- Increase in pressure causes blood to flow back toward the atria, closing the tricuspid and mitral valves
Why do SL valves open and blood is ejected during ventricular ejection (2nd phase of ventricular systole)?
Contraction of ventricular muscle has raised pressure within ventricle to greater than pressures in pulmonary trunk and aorta. Blood pumped from heart, pushing SL valves open.
Why is pressure generated by left ventricle be greater than right?
Since the existing pressure in the aorta will be so much higher
Despite difference in pressure generated by ventricles, how does volume of blood pumped compare?
Both ventricles pump the same amount of blood. This quantity is referred to as stroke volume. Stroke volume will normally be in the range of 70–80 mL
What does ventricular diastolic follow?
Repolarisation of ventricles
What represents ventricular diastole on ECG?
T wave
What are 2 phases of ventricular diastole?
- Isovolumic ventricular relaxation phase (1st phase)
2. Late ventricular diastole (2nd phase)
What happens during isovolumic ventricular relaxation phase?
Pressure within the ventricles drops below pressure in both the pulmonary trunk and aorta, blood flows back toward the heart, producing the dicrotic notch (small dip) seen in blood pressure tracings
The semilunar valves close to prevent backflow into the heart
Why is there no change in volume of blood in ventricle during isovolumic ventricular relaxation phase?
Since the atrioventricular valves remain closed at this point
What occurs during late ventricular diastole?
As the ventricular muscle relaxes, pressure on the blood within the ventricles drops even further. Eventually, it drops below the pressure in the atria
What happens when ventricle pressure drops below atrial pressure?
Blood flows from atria to ventricles and pushes open AV valves.
Blows from major veins into relaxed atria and from there into ventricles
Both chambers are in diastole, the atrioventricular valves are open, and the semilunar valves remain closed
The cardiac cycle is complete.
