Cardiac Cycle Flashcards
What are the different stages of the cardiac cycle?
Systole:
Atrial systole
Isovolumetric contraction
Rapid ejection
Reduced ejection
Diastole:
Isovolumetric relaxation
Rapid filling
Reduced filling
What is a U wave thought to represent on an ECG?
Thought to perhaps represent the slow repolarisation of the papillary muscles.
What is the proportion of left ventricular filling occurs during diastole/systole?
60-80% of ventricular filling occurs during diastole
20-40% of ventricular filling occurs during atrial systole
Draw a pressure/time graph of the cardiac cycle, labelling the left atria, left ventricle and aorta?
Label an ECG over this?
Google image
Describe what happens during atrial systole in terms of: valves, ECG, pressure and blood flow?
Valves:
AV valves open
Aortic/pulmonary valves closed
ECG:
P wave represents atrial depolarisation which leads to atrial contraction
Pressure:
Atrial contraction causes a small increase in pressure which is seen as the A wave.
On completion of atrial contraction the atrial pressures fall, as seen in the x descent and the atrioventicular valves float upwards and close.
Blood flow:
During atrial contraction the pressure within them increases to the point where the pressure forces blood through the atrioventricular valves into the ventricles.
Atrial contraction at rest normally accounts for only 20% of ventricular filling but can be as much as 40% during an increase in heart rate, due to a relative decrease in passive diastolic ventricular filling.
What is diastasis?
It is the second phase of diastole when there is a reduced pressure gradient between the left atria and ventricle, resulting reduced flow across the mitral valve.
Aka reduced filling
What is the flow velocity across the mitral valve in a young healthy adult?
0.7m/s
Describe what happens during isovolumetric contraction in terms of: valves, ECG, pressure and blood flow?
Valves: All valves closed.
ECG: The QRS complex represents ventricular depolarisation (Fig 1).
Blood flow: There is no flow of blood during this phase.
Pressure:
Ventricular depolarisation causes ventricular contraction and a rapid increase in ventricular pressure. This increase in pressure results in the mitral and tricuspid valves closing and generation of the 1st heart sound
This phase is said to be isovolumetric because in the time between the atrioventricular (AV) valves closing and the semilunar valves opening the pressure continues to increase with no change in the volume of the heart
Atrial pressures also increase as the AV valves bulge back into the atrial chambers. This is seen as the c wave in the jugular pulse
Describe what happens during isovolumetric contraction in terms of: valves, ECG, blood flow and pressure?
Valves:
All valves closed.
ECG:
The QRS complex represents ventricular depolarisation.
Blood flow:
There is no flow of blood during this phase.
Pressure:
Ventricular depolarisation causes ventricular contraction and a rapid increase in ventricular pressure. This increase in pressure results in the mitral and tricuspid valves closing and generation of the 1st heart sound.
This phase is said to be isovolumetric because in the time between the atrioventricular (AV) valves closing and the semilunar valves opening the pressure continues to increase with no change in the volume of the heart.
Atrial pressures also increase as the AV valves bulge back into the atrial chambers. This is seen as the c wave in the jugular pulse.
Describe what happens during rapid ejection in terms of: valves, ECG, blood flow and pressure?
Valves:
Aortic and pulmonary valves open
Mitral and tricuspid valves remain closed.
Blood flow:
When the intraventricular pressure is greater than that in the aorta and pulmonary artery, the aortic and pulmonary valves open.
Consequent to this pressure gradient, blood is ejected out of the ventricles into the aorta and pulmonary artery. The maximum velocity of the blood flow is reached early in the ejection phase and the ventricular volume decreases.
During this time the atria continue to fill with blood returning from the lungs and systemic circulation and their volume increases (Fig 1).
Pressure: Atrial pressures initially decrease during ventricular contraction because the base of the atria is pulled downward and so the atrial size expands. The pressure in the ventricle and aorta continue to rise but at less of a gradient until it reaches a plateau.
Describe what happens during reduced ejection in terms of: valves, ECG, blood flow and pressure?
Valves:
Aortic and pulmonary valves open
Mitral and tricuspid valves remain closed
ECG: The T wave represents ventricular repolarisation.
Blood flow:
Ventricular repolarisation initiates ventricular relaxation and the rate of ventricular emptying falls.
Pressure: Ventricular pressure falls to slightly less than that of the aorta and pulmonary artery, however ventricular emptying continues due to the kinetic energy propelling blood forward. Atrial pressures rise as a result of continued venous return of blood into the atria.
What is the normal flow velocity across the aortic valve?
0.9-1.7m/s
Describe what happens during isovolumetric relaxation in terms of: valves, ECG, blood flow and pressure?
Valves: All valves closed.
Blood flow: Ventricular repolarisation initiates ventricular relaxation and the rate of ventricular emptying falls. As the ventricles empty there is reversal of the pressure gradient between the ventricles and aorta/pulmonary aa causing the valves to shut.
Pressure:
Continued relaxation of the ventricles results in a continued decrease in intra-ventricular pressures.
The energy of blood in the ventricles is no longer greater than that of the outflow tract.
This reversal of pressure gradient across the aortic and pulmonary valves causes them to close.
The closure of the aortic and pulmonary valves is associated with a characteristic notch, or incisura in the aortic and pulmonary pressure tracings.
As diastole commences, there is a brief reversal of the blood flow, which causes closure of the valves. The small pressure increase, indicated by the dicrotic notch, is caused by the elastic recoil of the vessel walls.
The ventricular volume remains constant throughout this phase. The left ventricle residual volume, or end-systolic volume, remains approximately 50 ml.
The atria continue to fill and the back flow of blood against the closed AV valves creates the v wave of the jugular pulse.
Heart sound: The closure of the aortic and pulmonary valves gives the second heart sound.
Describe what happens during rapid filling in terms of: valves, ECG, blood flow and pressure?
Valves:
Mitral and tricuspid valves open
Aortic and pulmonary remain closed
Blood flow: Blood flow into the ventricles is rapid and the ventricular volume increases.
Pressure: As the ventricular pressures become lower than the atrial pressures the atrioventricular valves open. Despite being passive, the flow is rapid because the atria are maximally filled before the AV valves open. Diastolic suction aids initial filling of the left ventricle. This occurs when the left ventricle actively relaxes and creates a more rapid fall in left ventricular pressure than the existing fall in atrial pressure (Fig 1a). The rapid fall in atrial volume and hence atrial pressure is represented by the y decent on the jugular pulse waveform (Fig 1b).
Heart sound: A third heart sound may be heard due to tensing of the chordae tendinae and the atrioventricular ring which support the valve leaflets. This is pathological except in children.
Describe what happens during reduced filling ECG, blood flow and pressure?
Valves:
Mitral and tricuspid valves open.
Aortic and pulmonary valves closed.
Blood flow: As the ventricles fill with blood and become nearly full their compliance decreases.
Pressure: Ventricular pressure increases and the subsequent decrease in the pressure gradient between the atria and the ventricles causes them to fill more slowly (Fig 1).
