The Cardiac Cycle Flashcards
How many phases is each heart beat split into. How long does each phase last?
Diastole (ventricular relaxation); lasts approximately 2/3 of each beat.
Systole (ventricular contraction); lasts approximately 1/3 of each beat.
How many phases are present in diastole and systole. Name each phase in the correct order.
Diastole - 4 phases
Systole - 3 phases
Atrial systole (part of diastolic phase) Isovolumetric contraction Rapid Ejection Slow Ejection Isovolumetric relaxation Rapid passive filling Slow passive filling
Equation for SV?
SV = EDV (~120ml) - ESV (~50ml) = 70ml
How do you calculate ejection fraction?
EF = (SV/EDV) x 100 = 70/120 x 100 = 58%
Normal range is 52-72%
What valve is between the RA and RV?
Tricuspid valve
What valve is between the LA and LV?
Mitral (bicuspid) valve
What valves are between the RV and pulmonary artery and the LV and aorta?
Right side - pulmonary valve
Left side - aortic valve
What wave on an ECG signifies start of atrial systole?
P-wave
What happens during atrial systole?
Electrical activity signified by P-wave on ECG stimulates atrial muscle to contract.
Atria already almost full from passive filling driven by pressure gradient. Atria contract to ‘top-up’ the volume of the blood ventricle.
(Atrial systole through atrial contraction stimulated by waves of excitation from the SAN causes ventricles to fill with max capacity of blood (EDV).)
What abnormal heart sound can be heard in during atrial systole?
4th Heart sound - occurs with congestive HF, PE or tricuspid incompetence.
What is the relationship between atrial contribution to ventricular filling to the duration of diastolic filling?
Inversely proportional
The longer the diastolic period the greater the ventricle will fill passively with blood hence the atrial contribution will decrease.
Roughly what percentage of ventricular filling does atrial systole account for?
~10%
High HR affects this value as there is less time for passive ventricular filling. Hence the atrial systole may account for 40% of ventricular filling.
What happens to the atrial contribution to ventricular filling when the diastolic interval is shortened?
Increases
Is the pressure greater in the atria or ventricles during atrial systole?
Atria
What marks the start of ventricular depolarisation and hence the start of isovolumetric contraction?
QRS complex - electrical event
What is isovolumetric contraction phase?
Isovolumetric contraction is the interval between AV valves (tricuspid and mitral) closing, and the semi-lunar valves (pulmonary and aortic) opening.
Ventricular contraction proceeds against closed valves; therefore ventricles contract with no change in volume (Isovolumic). Contraction contributes to significant increase in pressure.
CONTRACTION OF VENTRICLES WITH NO CHANGE IN VOLUME
What heart sound is heard during isovolumetric contraction and what is it caused by?
1st Heart Sound (Lub) due to the closure of the AV valves.
What type of contraction occurs in the ventricular muscles during isovolumetric contraction?
Isometric - don’t change length/stretch and pressure inside ventricles increases.
What is rapid ejection?
Period at which the ventricular pressure > aortic and pulmonary pressure (afterload), semi-lunar (pulmonary and aortic) valves open, demarcating the initiation of this phase. Ventricular pressure is achieved through isometric contraction. Isotonic contraction (sarcomere shortening) assists expulsion. ESV (residual volume present in ventricles) succeeds the ventricular/rapid ejection phase. Opening of the semi-lunar valves facilitates blood ejection (Stroke volume) through the pressure gradient into systemic and pulmonary circulation → Decreasing ventricular volume.
Are there any hearts sounds during rapid ejection?
No heart sounds.
No valves closing.
What initiates the rapid ejection phase?
Inter-ventricular pressures exceed the pressure in aorta and PA.
What phase marks the end of systole?
Reduced ejection
What wave on an ECG represents reduced ejection?
T-wave - ventricular muscle cells repolarised.
Cardiac cells being to repolarise (AP returns to resting potential) illustrated by T wave.
What is the reduced ejection phase?
Marks end of ventricular systole. Blood ejected from ventricles at a reducing rate, and ventricular pressure decreases simultaneously with volume reduction → aortic and pulmonary pressure eventually exceeds ventricular pressure, stimulating closure of semi-lunar valves.
However, this phase doesn’t’ contain any heart sounds.
What sound can be heard during isovolumetric relaxation?
2nd Heart Sound (dub) due to closure of semi-lunar valves and associated vibrations.
What is the isovolumetric relaxation phase?
Ventricular muscle relaxes, pressure on remaining blood within ventricle begins to decrease.
Pressure within ventricles < aorta and pulmonary trunk, blood flows back towards heart, producing dicrotic notch (small dip) seen in blood pressure tracings.
What phase is the dichrotic notch a part of?
Isovolumetric relaxation
Does the ventricular volume change during isovolumetric relaxation?
No
What causes the dichrotic notch to appear on the aortic pressure curve?
Caused by rebound pressure against aortic valve as distended aortic wall relaxes. (Sharp increase)
What volume is present in the ventricles during the isovolumetric relaxation phase?
ESV (so ~50ml)
What does an ECG look like during the rapid passive filling phase?
Flat
Rapid passive filling occurs during isoelectric ECG between cardiac cycles.
What is the rapid passive filling phase?
Atrial pressure ^ (ventricular decreases via relaxation) to the extent that AV valves open → enables blood flow along pressure gradient through AV into ventricles.
Subsequently increases ventricular volume and simultaneously decreases atrial pressure.
Filling of ventricles is PASSIVE, not due to atrial systole.
What may be heard during rapid passive filling?
3rd Heart Sound - Signify turbulent ventricular filling; attributed to severe hypertension or mitral incompetence; referred to as ventricular gallop.
What can reduced passive filling also be called?
Diastasis
What is reduced passive filling?
Slow filling of ventricles (Diastasis); ventricular volume ^ slowly (reduction in pressure gradient). Ventricles are able to fill considerably without the contraction of the atria.
No changes in ECG, no subsequent heart sounds..
Compare the pressures in the right and left heart.
Patterns of pressure changes in the right side of heart → identical to those on the left. Quantitatively, pressures in the right heart and pulmonary circulation are relatively lower (peak systole -25mmHg in PA).
Compare the volume of blood pumped by each side of the heart.
Both same volume (it is simply pumping the same quantity of blood into a lower pressure circuit)
BP valve values in systemic and pulmonary circuits?
Systemic = 120/80 mmHg
Pulmonary = 25/5 mmHg
What does a raised pulmonary artery wedge pressure indicate?
Problem on the left side of the heart (LA)
Mitral valve dysfunction
What might a raised PCWP indicate?
LV failure or severe mitral valve stenosis.
On a pressure-volume loop what does the difference between point C and B represent (or even point A and D)?
Stroke Volume
What valve closes at point A on a pressure-volume loop?
What volume is represented by point A on the loop?
Lub - 1st HS therefore it is the Mitral valve closing
EDV
What valve closes at point C on a pressure-volume loop?
What volume is represented by point C on the loop?
Dub - 2nd HS therefore it is the aortic valve closing.
ESV
What happens between point B and C on a pressure-volume loop?
Ventricle begins to expel blood, therefore the volume of the blood in the ventricle fall, ventricular pressure rises then falls. The semi-lunar valves are open.
What happens from point A to point B on a pressure-volume loop?
Isovolumetric contraction - volume of blood within the ventricle is unchanged, however there is a large ^ in pressure (Preload). At this point, ventricular pressure is equivalent to the aortic pressure (afterload), just above to overcome it.
Name the process that occurs from point C to D on a pressure-volume loop.
Isovolumetric relaxation
What point on a pressure-volume loop is representative of preload on a P-V loop?
Point A
EDV is reflective preload - associated with volume of blood filling the ventricles, and stretching the resting ventricular muscle.
What is preload in terms of the P-V loop?
Determines stretch on muscle fibres, associated with isometric contractions and influenced with end-diastolic ventricular volume.
What is afterload in terms of the P-V loop?
Pressure in aorta that the ventricle has to overcome to eject blood. Afterload is realised beyond point B, whereby the aortic valve opens; LV encounters the aortic pressure.
How do an increase in preload and afterload affect SV?
^ Preload = ^ SV (Frank-Starling Relationship)
^ Afterload = Decreased SV
Explain why an increased afterload decreases SV.
Increasing the afterload > more pressure is required to open the aortic valve, point B moves in a positive Y direction.
Point A remains same, identical EDV.
Increase in afterload means less shortening can occur, stroke volume decrease.
Define CO
Contractile capability (or strength of contraction) of the heart.
CO = HR x SV
What type of nervous activity increases CO and explain the extrinsic mechanism?
Sympathetic stimulation
Changes Ca2+ delivery to myofilaments. Changes amount of cAMP in cells.
What does ESPVR stand for?
End-systolic pressure volume relationship
How does an increase in contractility affect the ESPVR lines on a pressure volume loop?
Makes it steeper > generates more force due to more CO2.
