Cardiovascular - Anatomy + Physio Flashcards
Which coronary artery branches off the posterior aortic sinus?
Left coronary artery
Which coronary artery branches off the anterior aortic sinus?
Right coronary artery
What is the route of the left coronary artery?
LCA
1. Left Anterior Descending / Anterior Interventricular Artery (anterior)
–> Diagonal branches
2.** Left circumflex (posterior)**
—–> 3 Left Marginal Arteries
What is the route of the right coronary artery?
RCA
1. RCA comes down anterior (anterior)
–> Right marginal artery
2. Posterior inter-ventricular artery (posterior)
Where does the SAN artery branch off?
Right coronary artery
Which 2 arteries meet at the apex of the heart?
- Left Anterior Descending
- Posterior Interventricular Artery
Which artery supplies the inferior wall of the heart?
Left circumflex artery
Which artery supplies the antero-lateral wall of the heart?
Left Anterior Descending Artery
Distal - V3 + V4
Which artery supplies the antero-septal wall of the heart?
Left Anterior Descending Artery
Proximal - V1 + V2
What is right dominance of the heart?
Posterior descending artery supplied by the RCA
Most common
What is left dominance of the heart?
Posterior descending artery supplied by the LCA
Worst prognosis in MI - loss of anterior and posterior blood supply
What is co-dominance?
Posterior descending artery supplied by both the RCA and LCA
Best prognosis but least common
What is a myocardial bridge?
Myocardial muscle covering a major coronary artery
runs through the heart, only branches visible externally
What are the 3 things in the carotid sheath?
- Common carotid artery
- Internal jugular vein
- Vagus nerve
At what level of the spinal cord do the common carotids bifurcate into internal and external carotids?
C3-4
Level of the posterior hyoid bone
What level of the spinal cord do the phrenic nerve branch off?
Phrenic nerve branches off at C3,4,5
Comes down mediastinum, contributes to cardiac plexus and innervates the diaphragm
How does referred pain work in heart injury?
When heart injury - phrenic nerve sends afferent signals to CNS
Phrenic nerve originates at C3,4,5 - so CNS cannot localise the pain and instead gives response of pain in whole region
C3,4,5 also supplies shoulder, neck and jaw = referred pain in MI
What structures lie in the superior mediastinum?
Trachea
Oesophagus
Arch of aorta
SVC
Vagus and phrenic nerves
Left recurrent laryngeal nerve
At what point of the spinal cord is the mediastinum split into superior and inferior?
T4-5
Sternal Angle
What lies in the anterior inferior mediastinum?
Thymus
What structures lie in the middle inferior mediastinum?
Heart
Pericardium
Phrenic nerves
Ascending aorta
Pulmonary trunk
What structures lie in the posterior inferior mediastinum?
Oesophagus
Sympathetic chain
Azygous vein
Descending aorta
Vagus nerve
Thoracic duct
What is the relation of the left recurrent laryngeal nerve to the aortic branch?
LRLN heads behinds arch of aorta and loops around right sublavian artery to head back up to larynx
Left laryngeal nerve branches off the vagus nerve
LRLN provides motor innervation to the intrinsic muscles of the larynx
What are the 3 functions of the pericardium?
- Anchor heart to surrounding structures
- Protect heart from trauma, damage etcccc
- Prevent heart from overfilling and stretching
What are the layers of the heart?
From in to out
- Endocardium
- Myocardium
- Epicardium - Visceral layer of serous pericardium
- Pericardial cavity - Serous Fluid - prevent friction
- Parietal Layer of serous pericardium
- Fibrous pericardium - dense irregular connective tissue
Which vein is suitable for a central venous line to monitor central venous pressure and why?
Right Internal jugular vein
- Direct route to right atrium
- No valves
What vessel is best used for a autograft in a CABG?
Internal thoracic / internal mammory
Why is a thoracic artery better than a vein from the leg for autograft in a CABG?
Artery already adapted to carry high pressure blood so less likely to become dilated.
Can provide alternative source of blood supply - only have to change one side and leave the other intact
Do not have valves
Where is the coronary sinus located?
Posterior aspect of the heart
What does the coronary sinus drain into?
Right atrium
85% of venous drainage occurs via coronary sinus
What are the thesbian veins?
Smallest cardiac veins
Drain into the 4 chambers of the heart
Why is the blood in the left ventricle less saturated with oxygen than the blood it originally receives from the pulmonary veins?
Left ventricle receives blood from thesbian vein = mixing venous blood = physiological shunting
What is the vessel course of the arch of aorta?
Brachiocephalic trunk
- Right common carotid
- Right subclavian artery
Left common carotid
Left subclavian artery
Where does the azygous vein drain into?
Posteriorly in to inferior vena cava
What are aortic sinuses?
Small swelling in aortic artery
- Stops valves sticking to the aortic wall so they can still close
- Allows blood to pool in the sinuses after systole to allow valves to shut before flowing out arteries
What are the atrio-ventricular valves?
Left - Mitral/bicuspid
Right - Tricuspid
Between atria + ventricle - Closed at start of ventricular contraction
What 3 strucutres help atrio-ventricular valves work?
Chordae tendinae reinforce valves by tethering to papillary muscle
Papillary muscle gets electrical signal from bundle branches via moderator band to contract when the ventricles will contract
Papillary muscles contract to prevent prolapse of valves to stop backflow of blood into atria during ventricular contraction
What are the semi-lunar valves?
Left - aortic valve
Right - pulmonary valve
Between ventricles + arteries - close during ventricular relaxation
How many papillary muscles are there in the heart?
5 papillary muscles
3 in the right ventricule supporting tricuspid valve
2 in the left ventricle suppporting mitral valve
What is the AV valve structure within the heart?
Tricuspid - 3 cusps
Mitral - 2 cusps
Base of each cusp anchored to a fibrous ring that surrounds the orifice
How do the semi-lunar valves ensure they close and not leak open?
At the beginning of ventricular diastole - blood in artery falls back on to the valve via gravity = filling the sinuses and pushing valve cusps together
No tethering muscles
How does blood enter the left and right coronary arteries?
LCA - fills from left aortic sinus in the left cusp of aorta
RCA - fills from right aortic sinus in the right cusp of aorta
Blood recoils during ventricular diastole into aortic sinuses
What is the route of blood on the left side of the heart?
Pulmonary veins pump oxygenated blood from lungs into left atrium → left ventricle → aortic arch → supply whole body (except lungs)
Left ventricle wall thicker to pump blood round whole body
What is the route of blood on the right side of the heart?
SVC pumps deoxygenated blood from upper limbs/head/neck/thorax and IVC pumps deoxygenated blood from below diaphragm into right atrium → right ventricle → pulmonary trunk → pulmonary arteries → 1 to each lung
Which valve is most likely to wear down over time?
Mitral Valve
Blood flows on both sides of the anterior/septal cusp during atrial and ventricular systole = more likely to wear down
What is the function of the moderator bands?
Conduct impulses from the interventricular bundle to the base of the anterior papillary muscle
Ensure the papillary muscles can contract to shut AV valves at the same time as ventricular systole to prevent backflow of blood
What part of the autonomic nervous system is predominantly responsibke for innervating SA node to generate an impulse
Sympathetic nervous sytem
What is cardiac output?
CO = the volume of blood ejected by left or right ventricle in 1 minute
CO = Heart Rate x Stroke Volume
CO = 70bpm x 75ml = 5L/min
How much can cardiac output increase in exercise?
x4-6 increase
What is stroke volume and what affects it?
SV = the volume of blood ejected from the ventricle from 1 contraction
SV = ESV - EDV
What has a positive correlative affect on stroke volume?
Preload
Contractility
What has a negative correlative affect on stroke volume?
Afterload
What is preload?
The amount of stretch of the cardiac myocytes in the ventricles at the end of diastole, prior to systole
How is preload measured?
**End diastolic volume or pressure **
Equivalent to atrial volume/pressure - which is the same as venous return
What affects preload?
Central venous pressure
Heart rate
Ventricular compliance
Atrial contractilty
Valvular disease
What factors affect central venous pressure?
- Circulating volume - haemorrhage, dehydration = decrease CVP
- Respiratory pump
- Skeletal muscle pump - pressure from muscles constricting on veins = increase CVP
- Gravity - blood pooling in peripheral vein = decrease CVP
- Sympathetic nerve - constriction of veins = increase CVP
How does the respiratory pump affect central venous pressure?
Negative pressure in throacic cavity compared to below diaphgram -
- pressure difference enhanced in inspiration (very negative in lungs and positive in abdomen)
Pressure gradient = blood pulled back to lungs with negative pressure to enhance venous return
How does compliance affect preload?
Increase compliance = more stretched = higher EDV but at lower EDP
Decreased compliance = less ability to stretch = lower EDV but at higher EDP
Increase compliance in dilated cardiomyopathy, regurgitation
Decrease compliance in HOCM, hypertrophy
What is the affect of heart rate on preload?
Low heart rate = more filling time of ventricles = increase in preload
What is the frank-starling law of the heart?
The more a ventricle is filled during diastole = greater stretch = greater force of contraction = greater stroke volume
What is contractility and what affects it?
Force of contraction that is independant on initial fibre length
Dependant on intraceullar free calcium during systole affected by positive and negative inotropic agents
What are inotropic agents and how do they work?
Agents that increase or decrease contractility of the heart by affecting free intracellular calcium levels or sensitivity of receptor proteins to calcium
What are positive inotropic agents?
Drugs
- Dopamine, atropine, dobutamine, digoxin, milrinone, epinephrine, norepinephrine, isoprenaline, caffeine
Ions
- High calcium
Hormones
- glucagon, insulin, T3 + T4
What are negative inotropic agents?
Drugs
- Verapimil, diltiazem, beta blockers, anti-arrhythmics
Parasympathetic stimulation
- Acetylcholine
Ions
- Low calcium, high potassium and sodium
What is afterload?
Reflects the resistance that the ventricle must overcome when ejecting blood
Increased after load = less blood able to be ejected = decreased stroke volume
Law of Laplace - ventricular wall stress at start of systole
Hugely dependant on aortic pressure - ventricular pressure has to be greater than this to eject blood
What are factors decreasing afterload?
Ventricular hypertrophy - thicker wall means shared tension = less tension experienced by each sarcomere unit = less wall stress = reduced afterload
What increases afterload?
Aortic valve stenosis
Atherosclerosis in aorta and proximal arteries
Hypertension
Vasoconstriction
What are chronotropic agents?
Agents that affect the heart rate - by altering the electrical impulse at the SAN that regulate the heart’s rhythm
What are physiological causes of low HR?
Endurance athletes
Sleeping
Sedatives
What are physiological causes of high HR?
Exercise
Stress
Caffeine
Female > Male
Age - babies and elderly
What are negative chronotopic agents?
Acetylcholine - parasympathetic
Digoxin
Beta blockers
Verapmil
Diltiazem
Hypothyroidism
Hypothermia
What are positive chronotropic agents?
Adrenaline, Noradrenaline - sympathetic
Atropine, isoprenaline
Hyperthyroidism - T3/4
When do the coronary arteries get their blood flow?
Diastole
Coronary arterial tree is intramural so get compressed during systole - 80% of blood flow occurs when ventricles are relaxed
What is the functional adaptation of the myocardium to meet high oxygen demand?
HIgh blood flow in coronary arteries
Myocardium extracts 75% of the oxygen it receives in the blood
The rest of the bosdy extracts 25% of the oxygen it receieves in the blood
What is a structural adaptation of the myocardium?
High myocardial capillary density
Distance that oxygen and nutrients travel from blood to the myocyte is shorter
What is metabolic hyperaemia?
Metabolites released in exercise have vasodilative effects on necessary muscles
Whilst systemic vasoconstriction in other organs to redirect their blood supply where needed
How is cardiac output increased during exercise?
SV and HR
Increase in stroke volume
Increased preload
- Skeletal muscle pump
- Peripheral venoconstriction - in veins not being used
Increased contractility
- Increased sympathetic activity
Increase in heart rate
- Increase sympathetic activity - stimulate cardiac sympathetic fibres
- Decreased parasympathetic activity - normally inhibit SAN
What are the demands on the CVS during exercise?
- Increase oxygen and remove carbon dioxide
- Increase blood flow to active muscles
- Stabilise blood pressure
- Keep core temperature cool
How is cardiac output different in athletes?
Same cardiac output
- Lower HR
- Higher SV (heart muscle hypertrophy = reduce afterload, more responsive to catecholamines = increase contractility) (lower HR = increase filling time = increase preload)
How is cardiac output increased during exercise?
Increase in HR (main factor at high work loads)
Increase in SV (eventually plateus at high work loads)
Stroke volumes eventually plateaus and falls at very high work rates(less time for filling of ventricles) → increased heart rate becomes more important at high work loads to maintain increased CO
How does stroke volume response differ in a supine exercise like swimming vs upright exercise like cycling?
Swimming = high SV at beginning due to lack of gravity working on venous pressure = increased CVP –> so increase HR is main way of increasing CO
Cycling = sudden burts of exposive exercise - increase in preload from skeletal muscle pump - large increase in SV + along with increase in HR
Why can heavy weight lifting be dangerous in uncontrolled hypertension?
BP = CO X TPR
Massive increase in total peripheral resistance due to muscle contraction against vessels
Leads to large increase in blood pressure
Also avoid in ischaemic heart disease
How does the total peripheral resistance affect the blood pressure in exercise?
Dilation in blood vessels in active muscles = lower vascular resistance - risk of hypotension
Vasoconstriction in inactive tissues - gut, kidneys, inactive muscles = increase vascular resistance = to compensate for risk of hypotension
Balance between the two to allow net fall in TPR to match rise in CO to maintain BP
BP = CO X TPR
What is the difference between blood flow to the skin during light and moderate exercise?
Light exercise = vasoconstriction
Moderate exercise = vasodilation to allow heat loss through skin to reduce core temp (less blood back to heart = reduced preload —> increase HR to maintain CO)
How can heavy exercise in hot weather lead to heat stroke?
Vasodilation for heat loss through skin but cannot increase heart rate to maintain CO → reduced CO detected by baroreceptors in heart → activates sympathetic nervous system = vasoconstriction to maintain blood pressure (at expense of cooling function) → elevation in core body temp
How long is 1 cardiac cycle and how is the time split?
0.8 seconds
0.3 - ventricular contraction
0.5 - ventricular relaxation
What occurs in the cardiac cycle during ventricular contraction?
1. Isovolumetric contraction
- Ventricle full of blood
- Ventricle Pressure > Atria Pressure = closure of AV valve = S1 sound LUB
- Ventricular contraction = massive increase in pressure but no movement of blood as all valves closed
- QRS complex
2.Ventricular Ejection
* Arterial pressure > Ventricular Pressure = SL valves open
* Ejection of bloof from ventricle
* Ventricular volume decreases
* ST complex
What occurs in the cardiac cycle during ventricular relaxation?
1.Isovolumetric relaxation
* Relaxation of ventricles
* Residual volume after ejection = ESV
* Ventricle repolarises = T wave
* Artery pressure > Ventricle pressure = SL valve shut = S2 sound DUB
* All valve shut so no movement of blood in ventricle
2.Ventricular filling
* Atria filling so atria pressure > ventricle pressure = AV valves open
* Passive filling of ventricles - 70/80% of blood volume
3.Atrial contraction
* SAN fires for contraction of atria
* Remaining blood pushed into ventricles 10/20%
* P wave
* EDV of ventricle
When and how is a S4 heart sound heard?
During Atrial Systole - just before S1 (closure of AV valve)
Active blood filling in ventricle against non-compliant, stiffened ventricle
Best heard in apex
Heard in HCM, ventricular hypertrophy
Atrial Gallop
When and how is a S3 heart sound heard?
During ventricular filling, just after S2 (before atrial contraction)
Passive filling of blood in ventricle against a very compliant ventricle wall
Heard in congestive heart failure, dilated cardiomyopathy
May be normal in children,
Ventricular Gallop
What are the 3 pressure changes in the atria and what waveforms represent these?
Wigger’s diagram
V wave - atria fill with blood
A wave - contraction of atria
C wave - bulging of AV valves into the atria during ventricular contraction
