Cardiac Cycle Flashcards
What is the cardiac cycle?
Series of consecutive contractions and relaxations of the heart, to ensure a continuous flow of blood & circulation around the body.
What is Ventricular diastole?
Diastole: Ventricular relaxation during which the ventricles fill with blood. Preload attributed to isometric contractions and stretching of an intracellular network of the cardiomyocyte.
How many phases are present during diastole?
4 phases
How many phases are present during systole?
3 phases
What is systole?
Systole: Ventricle contraction generates pressure, ejecting blood into the arteries for both pulmonary and systemic circulation.
What is an isovolumetric contraction?
Pressure builds up in ventricles, however ventricles do not expel blood until pressure overcomes afterload.
At what point does ventricular ejection proceed?
Pressure generated during isovolumetric contractions exceeds afterload
What phases occur after isovolumetric contraction?
Ventricular ejection and relaxation
What enables ventricular filling?
Passive filling of blood through pressure gradient into ventricle from atria. Atrial contraction (Systole)
What is End Diastolic volume (EDV)?
Volume of ventricles prior to systole
What is End-systolic volume (ESV)?
Volume in the ventricles after slow ejection (end stage of systole)
What is stroke volume?
The volume of blood expelled from the left ventricle during ventricular systole
EDV-ESV
What is the ejection fraction (EF)?
Proportion of the end diastolic volume that is ejected into systemic circulation during systole.
SV/EDV
What does EF illustrate?
The contractility of the heart
What is the normal ejection fraction?
52-72%
What is the typical EF for patients with heart failure?
35%
How does blood passively fill the ventricles?
Prior to atrial systole, the blood passively flows through the atrioventricular orifice through the mitral and tricuspid valve
What is the valve between the right atrium and right ventricle?
Tricuspid Valve
What is the left atrioventricular valve?
Mitral valve
What happens to the pressure during atrial filling (Atrial diastole)?
Pressure of atrium increases
P of atrium > p ventricle
How is atrial contraction stimulated?
Waves of excitation from the sinoatrial node
How is atrial systole depicted on the ECG?
P wave
What is the abnormal heart sound due to valve incompetency?
S4
What is S4?
Turbulent blood flow through dysfunctional valve closure.
What causes s4?
Pulmonary embolism,
Congestive heart failure
Tricuspid incompetennce
Which valves are closed during isovolumetric contraction?
Atrioventricular and semi lunar valves are closed
pressure is accumulating
Describe the pressure gradient during an isovolumetric contraction?
Ventricular pressure > atrial pressure
Describe the interval of the isovolumetric contraction?
Interval between the AV valves closing, and the semi-lunar valves opening
What signifies ventricular excitation on an ECG?
QRS complex
What heart sound is heard during the atrioventricular valve closure?
S1
What is S1?
The closure of the atrioventricular valves. (Lub)
What phase proceeds isovolumetric contraction?
Ventricular ejection phase
What is the ventricular ejection phase?
Period at which the ventricular pressure exceeds aortic and pulmonary pressure (afterload)
Semi lunar valves open
What type of contraction is associated with the ventricular ejection phase?
Isotonic contraction (Sarcomere shortening)
What volume resides post-ventricular ejection?
End-systolic volume
Residual volume in the ventricles
What is the C wave?
Atrial pressure caused by the right ventricular contraction *(Pushing tricuspid valve into atrium)
What type of electrical activity is demarcated on the ECG during the ventricular ejection phase?
None
No heart sounds, no valves are closing
What phase succeeds ventricular ejection?
Reduced ejection
What is reduced ejection?
END of ventricular systole.
Blood is ejected from the ventricles at a reducing rate as ventricular pressure decreased with volume reduction
What happens after reduced ejection?
Aortic and pulmonary pressure increases, exceeds ventricular pressure, and closes semi-lunar valves
How is reduced ejection depicted on an ECG?
T wave
Why is a T wave shown during reduced ejection?
Cardiac cells are undergoing repolarisation to resting potential
What phase succeeds reduced ejection?
Isovolumetric relaxation
What phase does isovolumetric ventricular relaxation belong to?
Diastole
What happens during isovolumetric relaxation?
Ventricular muscle relaxes, pressure on blood within the ventricles decrease.
What sounds is produced during isovolumetric relaxation?
Dicrotic notch
What is the dicrotic notch?
Caused by the rebound pressure against aortic valve as distended aortic wall relaxes./
What happens to semi-lunar valves during isovolumetric relaxation?
Semi-lunar valves (Aortic and pulmonary) close to prevent back flow to the ventricles
AV valves close
Why does the ventricular volume remain unchanged during isovolumetric relaxation?
The atrioventricular valves and semi-lunar valves are closed, thus there is no blood flow exchange between chambers
What is the second heart sound attributed to?
Closure of semi-lunar valves
What stage succeeds isovolumetric relaxation?
Rapid ventricular filling
What occurs during rapid ventricular filling?
Atrial pressure increases (ventricular pressure decreases via relaxation)
Generates pressure gradient,
Enables blood flow through atrioventricular orifice into the ventricles
This increases ventricular volume, simultaneously decreases atrial pressure
How does rapid ventricular filling occur?
Filling of ventricles is passive, not due to atrial systole.
Why does abnormal S3 occur?
Signifies turbulent ventricular filling, attributed to severe hypertension or mitral incompetence
What is s3 referred as to?
Ventricular Galloop
How is rapid ventricular filling depicted on an ECG?
Isoelectric ECG between cardiac cycles
What cardiac phase succeeds rapid ventricular filling?
Reduced passive filling
What are the changes to the ECG during reduced passive filling?
There are no changes to the ECG.
Atrial contraction is redundant
What occurs during passive ventricular filling?
Slow filling of ventricles (Diastasis), ventricular volume increases slowly (Reduction in pressure gradient)
How do the patterns of pulmonary circulation pressures compare on either side of the heart?
The patterns are identical, however quantitatively, the pressure in the right < left
Quantitatively, how does the volume ejected by the ventricles compare?
Identical ejection volumes between left and right ventricles
How can pressure changes in the pulmonary artery be detected?
Insertion of catheter with ballooon into the pulmonary artery, inflation of balloon prevents blood flow
Distal, pressure system of left atrium measured
What is pulmonary artery wedge pressure (PAWP)?
Possible to measure the preload on the left side
PAWP is elevated when there is left atrium or mitral valve dysfunction
What happens at Point A of the pressure-volume loop?
Mitral valve closure (increase in ventricular pressure) Isovolumetric contraction (Preload)
What occurs between A-B within pressure-volume loops?
Ventricular systole isovolumetric contractions:
Increase in left ventricular pressure, volume remains same
What occurs at stage B within pressure-volume loops?
Diastolic blood pressure
What occurs between B and C within the pressure-volume loops?
Ejection of blood during isotonic ventricular contraction
Ventricular systole.
How is pulse pressure measured on the pressure-volume loops?
Systolic blood pressure - Diastolic blood pressure
How is systolic blood pressure measured on a pressure-volume loop?
Peak of the loop
What occurs during point C on a pressure-volume loop?
Aortic valve closes (Dub)
When does the aortic valve open?
Point B
What happens between C and D on a pressure-volume loop?
Isovolumetric relaxation; Left ventricular pressure decreases for the same ventricular volume.
AV and semi-lunar valves closed.
