CVS Session 2: cardiac cycle Flashcards
Why is the heart described as 2 pumps acting in series?
Left heart-goes to systemic circulation, high pressure
Right heart-goes to pulmonary circulation, low pressure
Output of both sides over time must be equal
Describe the conduction system of the heart
Pacemaker cells of the SA node generate APs spontaneously at regular intervals
Activity spreads over atria (atrial systole)
Reaches AV node, delayed for ~120ms
Spreads down septum between ventricles down the bundle of his and purkinje fibres
Spreads through ventricular myocardium from endocardial to epicardial surface
Ventricle contracts from the apex upwards, forcing blood through the outflow valves
Function of valvular cusps?
Ensure blood only flows in one direction: pushed open to allow blood flow and close together to seal to prevent backflow
Describe the four cardiac valves
Atrioventricular valves:
Tricuspid (right, 3 cusps)
Mitral (left, 2 cusps)
Cusps attach to papillary muscles via chordae tendinae to prevent inversion of the valves in systole
Semilunar/outflow valves:
Pulmonary (right ventricle into pulmonary artery)
Aortic (left ventricle to aorta)
Function of AV node delay of 120ms?
Ensures the atria have ejected their blood before the ventricles contract
Describe the cellular changes in the course of the myocardial action potential
Rapid depolarisation: Na+ channels open causing rapid influx
Initial rapid repolarisation: inactivation of Na+ channels
Plateau: Ca2+ influx through slowly-opening channels
Repolarisation to resting potential: net K+ efflux
Changes in aortic pressure over one depolarisation/heart beat
Increases gradually during atrial systole, drops to initial level during ventricular systole then rises slightly during isovolumetric relaxation, then plateaus during later stages
Changes in atrial pressure over one depolarisation
Rises slightly during atrial systole
Changes in ventricular pressure over one depolarisation
Increases dramatically during ventricular contraction, falls back to level of start during isovolumetric relaxation
Name the 7 stages of the cardiac cycle
- Atrial contraction
- Isovolumetric contraction
- Rapid ejection
- Reduced ejection
- Isovolumetric relaxation
- Rapid filling
- Reduced filling
In which stages are the AV valves open?
Atrial contraction
Rapid filling
Reduced filling
In which stages are the AV valves closed?
Isovolumetric contraction
Rapid ejection
Reduced ejection
Isovolumetric relaxation
In which stages are the semilunar valves open?
Rapid ejection
Reduced ejection
In which stages are the semilunar valves closed?
Atrial contraction Isovolumetric contraction Isovolumetric relaxation Rapid filling Reduced filling
Events in atrial contraction?
Atrial pressure rises
Causes the final 10% of left ventricular filling
Narrows SVC, IVC and PV so not much blood regurgitates
AV valves are open, semilunar valves are closed
What is end diastolic volume?
The max. ventricular volume at the end of atrial contraction
~120ml
Events in isovolumetric contraction? (diastole)
AV valves close as intraventricular pressure exceeds atrial pressure (semilunar stay shut)
No change in ventricular volume as all valves closed
Events in rapid ejection? (systole)
Intraventricular pressure > aortic pressure, so aortic valve opens (others shut). Lowest aortic pressure
Atrial pressure initially decreases as ventricles contract, then rises as blood continues to flow into atria from venous inputs
Rapid decrease in ventricular volume as blood is ejected into the aorta
Events in reduced ejection? (systole)
Repolarisation of ventricle-decreased rate of ejection
Atrial pressure gradually rises due to continued venous return
(AV valves closed, SL open)
Events in isovolumetric relaxation? (systole)
Intraventricular pressure
What is end systolic volume?
The volume at the end of systole in the ventricles
~50ml
What is stroke volume?
The blood that is ejected during systole
Calculated by EDV-ESV
~80ml
Events in rapid filling? (diastole)
Intraventricular pressure
Events in reduced filling? (diastole)
Rate of filling decreases-IV pressure rises,
Heart about 90% filled by now
Further filling by atrial systole
Aortic and pulmonary arterial pressures falling
Heart sound S3?
During rapid ventricular filling-normally silent, can happen in children but if in adults usually pathological (ventricular dilation)
May represent tensing of chordae tendineae and AV ring during ventricular relaxation and filling
Occurs ~1/3 of the way during diastole
Heart sound S4?
Caused by vibration of ventricular wall during atrial contraction
Occurs in left ventricular hypertrophy
Route of blood flow during diastole?
Blood passively flows from the pulmonary veins, into the left atrium, then into the left ventricle through the open mitral valve
What is ‘atrial kick’ and when does it occur?
Occurs at high heart rates when less time for ventricular filling (shortened diastole)
Atrial contraction accounts for about 40% of ventricular filling (rather than the usual last 10%)
Heart sound S2?
Closure of outflow valves
In isovolumetric relaxation
Sound is shorter, high pitch, lower intensity “dub”
Heart sound S1?
Closer of AV valves
In isovolumetric contraction
Longer, louder “lub”
Usually split, as mitral valve closes slightly before tricuspid
Between which heart sounds do systole and diastole occur respectively?
S1-S2
S2-S1
What is a heart murmur?
Abnormal heart sounds due to turbulent blood flow (normal, laminar flow is silent)
‘Whooshing’ noise
Main cause is valvular disease
Stenosis causing murmur?
Narrowing of a valve
Aortic/pulmonary: systolic murmur
Mitral/tricuspid: diastolic murmur
Regurgitation causing murmur?
Incompetent valve causing some backward blood flow
Aortic/pulmonary: diastolic murmur
Mital/tricuspid: systolic murmur
Patent ductus arteriosus causing murmur?
Continuous murmur throughout systole and diastole
From where does blood flow into the right atrium?
SVC (head, thorax, arm)
IVC (abdomen and lower body) [most from here]
Coronary sinus
When are AV valves open and closed?
Open in diastole
Closed in systole
When are outflow valves open and closed?
Open during rapid ejection (systole), close in isovolumetric relaxation
How can stroke volume increase?
Stronger contraction of fibres therefore stronger ventricular contraction
If heart rate increases from 60 to 120bpm, what will happen to the length of diastole?
Will fall by ~ 2/3
What does the first 100ms of diastole represent?
75-80% of ventricular filling
Driven by pressure gradient from venous system
Length of systole and diastole?
Length of systole more fixed than diastole
Increased heart rate decreases length of diastole
Important because at a very high heart rate filling may be compromised
What are the aortic sinuses?
Left and right
Arise from aorta roof, superior to aortic valve, pass around opposite sides of PT
Give rise to the left and right coronary arteries
Right coronary artery origin, course, supply and branches?
Origin: right aortic sinus
Course: follows coronary sulcus
Supplies: RA, SA node, AV node, posterior part of IVS
Brances: SA nodal branch, right marginal branch, AV nodal branch, posterior IV branch
SA nodal branch of RCA?
In anterior heart, AV groove
Supplies SA node
Right marginal branch of RCA?
In anterior heart, AV groove, towards apex
Supplies right border of heart
AV nodal branch of RCA?
Near origin of posterior IV branch
Supplies AV node
Posterior IV branch of RCA?
Supplies RV and LV and posterior 1/3 of IVS
Left coronary artery?
Origin: left aortic sinus
Course: runs in AV groove and gives off branches
Supplies: most of LA and LV, IVS, AV bundle, some AV node
SA branch of LCA?
Only in 40%; supplies LA and SA node
Circumflex branch of LCA?
Passes to left in AV sulcus and runs to posterior surface
SUpplies LA and LV
Left marginal branch of LCA?
Supplies LV, follows left border
Anterior IV branch of LCA? aka LAD
Supplies RV, LV, anterior 2/3 of IVS
Venous drainage of the heart?
- Veins that empty into the coronary sinus (main vein running around circumference in middle) (e.g. great cardiac vein, middle and small cardiac veins, left marginal vein)
- Partly by small veins draining into the RA without coronary sinus (e.g. anterior cardiac veins
Right atrium structure
Venous supply: SVC, IVC and coronary sinus
Forms the right border of the heart
Right auricle: muscular pouch that increases capacity
Crista terminalis: verticle ridge that divides the interior structures:
- Sinus venarum: thin, smooth posterior part on which venous vessels open, derived from sinus venosus
- Pectinate muscles: anterior part, contains R. auricle
Recieves deox blood from venae cavae and drainage from coronary sinus, pumps into RV through right AV orifice (guards tricuspid valve)
Interatrial septum?
Separates atria
Fossa ovalis on RA side: closed form of foetal foramen ovale
Left atrium structure
Forms the posterior border of the heart
Receives oxygenated blood from 2 superior and 2 inferior pulmonary veins
Left AV orifice guards mitral valve, blood flows into LV
Interior:
- Smooth inflow portion receives blood from PV
- Muscular outflow portion: anterior, made of pectinate muslces and left auricle
Right ventricle structure
Largest part of anterior surface and most of inferior border. Superiorly meets conus arteriosus
Receives deoxygenated blood from RA and pumps into pulmonary trunk (gives rise to pulmonary arteries)
Inflow part: irregular muscle-trabeculae carnae:
- Ventricle wall at both ends forming a bridge
- Ventricle wall on length forming a ridge to separate inflow from outflow
- Base of ventricle wall with chordae tendinae at other end, forming papillary muscles
Moderator band between IVS and anterior wall of RV containing right bundle branches
Outflow part:
- aka. conus arteriosus
- smooth walls: no trabeculae carnae
- pulmonary semilunar valve enters pulmonary trunk
Right ventricle contraction?
Papillary muscles begin to contract before ventricles, draw cusps of tricuspid valves together. 3 muscles corresponding to the 3 cusps. Pull on chordae tendinae, prevent regurgitation
Left ventricle structure?
Anterior to LA, contributes to anterior aspect of heart and apex
Oxygenated blood from LA and expels into the aorta
Walls thicker than RV as arterial pressure higher in systemic than pulmonary circulation, so more work to pump. Trabeculae carnae more numerous than RV. Anterior and posterior papillary muscles,more than RV, attached to chordae tendinae that attach to mitral valve (double leafed so A and P)
Outflow: aortic vestibule
- smooth walled
- derived from bulbis cordis
- leads to the aortic semilunar valve
What are cardiac valves made from?
Connective tissue and endocardium
AV valves close in systole by papillary muscles attached to chordae tendinae, causing S1
Semi lunar valves close in diastole by backflow of blood forcing shut, causing S2
