15-09-22 – Coronary Circulation and Conduction System Flashcards
Learning outcomes
- Describe the origin, course and distribution of the right and left coronary arteries
- Explain the importance of the anastomoses that exist between the coronary arteries
- Describe the venous drainage of the heart
- Describe the anatomical position of the conducting system of the heart and how it controls heart rate
- List the arteries that supply the conduction system of the heart
- Describe the autonomic innervation of the heart
- Discuss the effects of ischaemia on the myocardium and how it may affect the conducting system of the heart
- Explain where pain originating from the heart is referred to and why
- Identify major branches of coronary arteries on angiograms
Is the cardiac muscle striated or smooth?
Is it voluntary or involuntary?
How do cells of the cardiac muscle connect?
What does this allow the heart to do?
What does tetanise mean?
Why does the heart not tetanise?
- The cardiac muscle is striated, but involuntary
- The cardiac cells branch and join with each other to form intercalated disks
- This connection allows the heart to work as a single functional organ/syncytium, which allows synchronized contraction of the heart to take place
- To tetanise means to throw into a state of permanent contraction
- The heart does not tetanise as this would prevent it from functioning like a pump
What do the following terms mean?
* Chronotropy
* Dromotropy
* Bathmotropy
* Inotropy
* Lusitropy
- Definitions for the following terms
- Chronotropy – chronotropic effects are those that change heart rate
- Dromotropy – dromotropic effects are those that affect the conduction in the AV node, and subsequently the rate of the electrical impulses in the heart
- Bathmotropy – Bathmotropic effects are those that change the excitability of irritability of the heart
- Inotropy – Inotropic effects are those that affect the contractility (strength of contraction) of the heart
- Lusitropy – lusitropic effects are those that affect the rate of myocardial relaxation
What are the arteries that supply the heart?
What are the coronary arteries the only branches of?
Where can the opening to the coronary arteries be found?
Where is a coronary artery opening not found?
Describe how the coronary arteries fills in 2 steps.
What is the nutrient supply to the endocardium?
- The heart is supplied by coronary arteries and their branches (right and left coronary arteries – RCA and LCA)
- The RCA and LCA are the only branches of the ascending aorta
- The opening of the RCA can be found on the aortic sinus of the right cusp of the aortic valve
- The opening of the LCA can be found on the aortic sinus (aka coronary sinus) of the left cusp of the aortic valve
- The posterior aortic sinus doesn’t have a coronary artery associated, so is called a non-coronary sinus
- How the coronary arteries fill:
1) Diastole begins with the closing of the aortic valve
2) When this occurs, blood moves from the coronary sinus of the left and right cusps of the aortic valve into the openings of the left and right coronary arteries - The endocardium (innermost layer of the heart) receives oxygen and nutrients directly from the chambers of the heart
Where does the right coronary sinus (RCA) arise from?
Where does it run from?
What 5 branches does the RCA give off?
What does each branch supply?
Which of these branches anastomose?
- The right coronary sinus (RCA) arises from the right aortic sinus
- The RCA runs posteriorly and inferiorly to the right side between the pulmonary trunk and the right auricle to the right ventricle
- 5 Branches of the RCA (Summary list of supply on later flash card):
1) SA nodal branch – Supplies SA node
2) Atrial branches – supply the right atrium
3) Right (acute) marginal branch – supplies lateral portion of right ventricle
4) Posterior interventricular branch (posterior descending artery) supplies:
* Posterior 1/3rd of interventricular septum (separates left and right ventricle)
* Inferior surface of right ventricle
* Some of the inferior surface of left ventricle
5) AV nodal branch
- The posterior interventricular branch anastomoses with branches of the left coronary artery at the apex of the heart (not proper anastomosis?)
What is an angiogram?
Label this sagittal angiogram of the right coronary artery (RCA)
- An angiogram is a type of x-ray used to check blood vessels
What is another name for the left coronary artery (LCA)?
Where does the LCA arise from?
How does the LCA compare in size and thickness to the RCA?
What 3 branches does the LCA divide into?
What do they each supply?
- The left coronary artery (LCA) is also known as the left main stem
- The LCA arises from the left aortic sinus between the left auricle and the pulmonary trunk
- The LCA is shorter, but thicker than the RCA
- The LCA divides into (Summary list of supply on later flash card):
1) Circumflex branches
* Encircles the heart muscle
* Supplies outer surface and back of heart
* Enters coronary sulcus (outer marking of where the atria separate from the ventricles) to the diaphragmatic surface of the heart
2) Anterior interventricular branches (left anterior descending branch (LAD)
* Supplies the anterior 2/3rds of the interventricular septum
* Supplies the AV bundle
* Supplies anterior surface of the heart, including left and right ventricle
* Supplies sternocostal surface of the heart
* Passes over diaphragmatic surface and becomes posterior
* Called ‘widow maker’ as it is blocked in 50% of myocardial infarction cases
3) Left (obtuse) marginal branch
* Supplies most lateral wall of the left ventricle
* Turns to diaphragmatic surface of the heart
* Anastomoses with branches of RCA
Label this coronary angiogram of the left coronary artery (LCA)
Summary.
What 5 structures does the right coronary artery supply?
What can obstruction of the right coronary artery cause?
What can mild cases cause?
What 3 structures does the left coronary artery supply?
What can obstruction of 2 branches of the left coronary artery cause?
What do anterior infarcts lead to?
- The right coronary artery supplies:
1) Walls of RA and RV
2) SA and AV node
3) Posterior part of interventricular septum
4) Proximal portion of AV bundle of His
5) Small areas of walls of LA and LV - Obstruction of the right coronary artery can lead to inferior infarct
- Mild cases are likely to cause arrhythmias, as the RCA supplies the SA and AV node
- The left coronary artery supplies:
1) Walls of LA and LV
2) Most of the interventricular septum
3) Part of the AV bundle of His - Obstruction of the left anterior descending artery of the LCA can cause anterolateral infarct
- Obstruction of the circumflex artery of the LCA can cause lateral infarct
- Anterior infarcts cause loss of left ventricle function, which can cause ventricular fibrillation (type of irregular heartbeat (vfib) – most common deadly heart rhythm)
How is coronary dominance determined?
Which side is most commonly coronary dominant?
Why is left coronary dominance more dangerous?
- Coronary dominance is decided by which coronary artery gives off the posterior interventricular (posterior descending) artery
- About 80% of people’s RCA is coronary dominant, with roughly 10% being left coronary dominant, and 10% being non-coronary dominant
- Left coronary dominance is dangerous because a blockage of the LCA in a left coronary dominant patient would lead to a greater area of the right and or left ventricle being exposed to ischaemia/infarction (blockage causing local death of tissue)
- Patients with left coronary dominance tend to have worse prognosis (likely cause of medical condition) when affected by acute coronary syndrome (term used to describe range of conditions associated with sudden reduced blood flow to the heart)
Label these branches of the RCA and LCA
What 3 vessel blockages cause MI?
What % of MI is caused by each blockage?
In what 2 ways might these blockages damage the conducting system of the heart?
What 2 conditions can these blockages lead to?
What process can be done on an occluded (obstructed) vessel?
How does CABG work? What vessels can be used for it?
- Myocardial Infarction can be cause by the following artery blockages:
1) LAD (Left anterior descending /Anterior interventricular) – 40-50% of MI
2) RCA – 30-40% of MI
3) Circumflex artery – 15-20% of MI - Conducting systems of the heart may be damaged as:
1) Septal branches of LAD supplies AV bundles
2) RCA supplies both SA and AV nodes and proximal AV bundle - These blockages of the conducting system can cause:
1) Heart block (causing bradycardia) – electrical impulses that control the beating of the heart are disrupted
2) Myocardial infarction/disruption - When we get an occluded (obstructed) vessel, we can bypass the occlusion via a Coronary artery bypass grafting (CABG)
- CABG shunts blood to either end of the blockage, which makes a bypass bridge
- Vessels that can be used to make a bypass graft for CABG:
1) ITA/LIMA (internal thoracic artery/Internal mammary artery)
2) Great saphenous vein – if 3 or more vessels are blocked so we can’t used ITA. Vessel needs to be moved so valves don’t prevent blood flow proximal to distal
What is a percutaneous transluminal coronary angioplasty used for?
What are the 2 ways this process can be done?
What medication can stents be coated with?
- A percutaneous transluminal coronary angioplasty is a process that widens the lumen of a blocked or narrow coronary artery
- This process can be done with or without a stent
- Percutaneous transluminal coronary angioplasty with stent
1) Placing deflated balloon catheter stent delivery system in place
2) Expanding the deflated balloon to expand the stent
3) Catheter removed and stent implanted - Without a stent, the balloon catheter is placed in the lumen of the vessel and expanded to crush the blockage and re-establish circulation
- A drug-eluting stent is coated with a slow-release anti-coagulant to help prevent blood clots from forming in the stent, as this could cause a future blockage
What do cardiac veins follow?
What is the coronary sinus?
What are the 4 cardiac veins?
How do each of them drain into the right atrium?
Where does most of the venous blood of the heart drain into the right atrium from?
Where does the remaining % drain in from?
- The cardiac veins accompany the coronary arteries and their branches
- The coronary sinus is a large venous structure
- It is located on the posterior aspect of the left atrium/between the left atrium and the right ventricle, within the atrioventricular groove (aka coronary sulcus)
- 60% of the venous blood drains into RA via coronary sinus
- 40% is drained by smallest
cardiac veins (thebesian
veins) and anterior cardiac
veins - The cardiac veins:
1) Great cardiac vein (interventricular vein)
* Joins the left side of the coronary sinus
* Follows LAD
2) Small cardiac vein – accompanies right marginal branch.
* This vein typically empties into the coronary sinus, but sometimes drains into the middle cardiac vein or directly into the right atrium
* Has bridging veins between myocardium (muscular layer of the heart) and the chamber
3) Middle cardiac vein (posterior interventricular vein)
* Drains into the right side of the coronary sinus
* Follows the posterior interventricular artery
4) Anterior cardiac veins
* Drains independently into the right atrium
* On the right coronary artery
5) Posterior vein of left ventricle
* The posterior vein of the left ventricle is a vein of the heart which courses over the inferior wall of the left ventricle and drains into the coronary sinus to the left of where the middle cardiac vein drains into the sinus.
* It drains the inferior wall of the left ventricle
* Follows the left marginal (obtuse) artery
- Most of the venous blood (60%) from the heart drains into the right atrium via the coronary sinus
- The remaining 40% is drained by smallest cardiac veins (aka thebesian veins) and anterior cardiac veins
What 2 networks does cardiac muscle fibres form?
What are they separated by?
Where can special modified cardiac muscle cells be found?
What is special about these cells?
What does this allow the heart to do?
What are the names given to these cells?
What is the role of the ANS in the heart?
- Cardiac muscle fibres (Myocardium) form atrial and ventricular networks that are separated by the fibrous skeleton
- Special modified cardiac muscle cells can be found immediately beneath the endocardium
- These cells are special as they can generate electrical pulses without stimuli and distribute them through the myocardium
- This allows the heart to contract in proper sequence
- These specialised calls are all of those that make up the conduction system (on next slide) i.e SA node all the way through to Purkinje fibres
- The role of the ANS in the heart is to shorten or prolong the duration of contraction
How big are the structures that make up the conduction system?
What are 6 the different structures that make up the conduction system?
Where are each of them found?
What arteries are the first 2 structures supplied by?
- Structures that make up the conduction system are microscopic
- Structures of the conduction system:
1) Sinoatrial (SA) node
* AKA Keith-Flack node
* Anterior to the opening of the SVC, and the upper end of crista terminalis (ridge in right atrium that extends between the orifice of SVC to the orifice of IVC)
* Basic depolarization of the SA node is 70-80 bpm
* Usually supplied by branches of the right coronary artery
2) AV (atrioventricular) node
* AKA Aschoff-Tawara node
* Located at the postero-inferior part of the IA septum, close to the opening of the coronary sinus
* Usually supplied by AV nodal branch of the right coronary artery
3) AV bundle of HIS
* Continuation of AV node
* Found in the right trigone between 3 fibrous rings of the cardiac fibrous skeleton
* Runs along the membranous part of the IV septum
* Splits into right and left bundle branches
4) Left bundle branch
* Descends on the left side of the membranous part of the IV septum towards the left ventricle
* Splits into Purkinje fibres
5) Right bundle branch
* Descends on the right side of the membranous part of the IV septum towards the right ventricle
* Enters septomarginal trabecula (moderator muscle found in the right ventricle) to reach base of the anterior papillary muscle
6) Purkinje fibres
* Starts at apex and moves superiorly
* Stimulates contraction of both ventricles
What does the AV bundle of His connect? How does it do this?
Where is the bundle of his found in relation to the fibrous skeleton of the heart?
What does this system ensure?
- The AV bundle of His serves as the only electrical connection between the atria and the ventricles
- It achieves this by being the only conductive route through the fibrous skeleton of the heart
- The AV bundle of His is found in the right trigone between the fibrous rings of the AV valves and the aortic valve, which is where the membranous portion of the IA, IV, and AV septum are found
- This system ensures synchronous contraction, in correct sequence, towards the outflow of each chamber
Describe the 6 steps in the electrical conduction pathway of the heart
Steps of the electrical conduction pathway of the heart:
1) SA node depolarises
2) Depolarisation spreads over the functional syncytium of the left and right atria
3) Electrical conduction goes down the internodal pathways
4) Coalesces round the AV node (only point of electrical conductivity between the atria and the ventricles) and slows down. This slowing down allows the atria to contract a fraction of a second before the ventricles, as this will allow the blood from the atria to enter into the ventricles before they contract.
5) Depolarisation gets into the AV bundle (bundle of His) branches at the midline of the heart and gets transmitted down them
6) Depolarisation comes up from the base of the heart through the purkinje fibres, which results in depolarisation of the deep ventricle tissue
What centres in the brain provide ANS innervation of the heart?
What do these ANS fibres form?
Where are superficial and deep cardiac plexus found?
What 3 structures do they supply?
Where do sympathetic fibres that supply the heart come from?
What is the role of sympathetic innervation in the heart?
How is this increase in workload accommodated?
Where do parasympathetic fibres that supply the heart come from?
What is the role of parasympathetic innervation in the heart?
How do they accommodate this reduction in workload?
What sensory innervation to the heart is there?
- Cardioacceleratory and Cardioinhibitory centres in the medullary reticular formation give off ANS fibres that innervate the heart (the hypothalamus is the main control center for the ANS, but the medulla controls some responses)
- These ANS fibres form superficial and deep cardiac plexuses around the heart
- These plexuses lie posterior to the aortic arch and adjacent to the bifurcation of both the pulmonary trunk and the trachea
- The superficial and deep plexus’ function is to innervate:
1) Conduction system,
2) Coronary blood vessels
3) Myocardium - Sympathetic innervation
- Pre-synaptic neruons that supply the heart are found in T1-T5 spinal segments, but they synapse somewhere in the cardiac plexus before going to the heart
- Sympathetic that innervate the heart increase heartbeat (chronotropic effect) and force of contraction (inotropic effect)
- Sympathetic also dilate coronary arteries to accommodate this extra workload
- Parasympathetic innervation
- Parasympathetic innervation of the heart comes from the right and left vagus nerve, which give off cardiac nerves
- Parasympathetics of the heart decrease heart rate (and force of contraction??? - controversy)
- They also constrict coronary arteries due to this decrease in workload
- Sensory innervation
- General visceral afferents (sensory) from the phrenic (?) are carried by the ANS to the heart
What does the ANS consist of?
What does the ANS produce a motor response to?
What do visceral pain afferents follow?
What do visceral reflex afferents follow?
When does referred pain occur?
What is referred pain?
Describe the 5 steps of the process of referred cardiac pain
- The ANS consists of general visceral efferent (GVE) fibres that create a motor response to general visceral afferent (GVA) fibre stimulation.
- Autonomic fibres accompany GVA fibres
- Although GVA fibres are part of the ANS, they are not classified as part of the sympathetic or parasympathetic system.
- Visceral pain afferents tend to follow the path of sympathetic supply
- Visceral reflex afferents follow the path of parasympathetic supply
- Referred pain occurs when we get visceral pain heading back to the CNS
- Referred pain is when our visceral pain afferent synapses onto the same second order sensor neurone as a somatic afferent
- This results in pain being felt in the skin e.g visceral pain being felt as somatic pain in the skin due to referred pain
- Process of referred cardiac pain:
1) Visceral (internal organs in midline) pain is caused through ischaemia/damage to the heart muscle
2) Visceral sensory nerve ending receptors are activated
3) General visceral afferents (GVA) fibres carrying the visceral pain signal travel back to the spinal cord and synapse onto the 2nd order neuron of T1-T5 segments, which is the same place somatic (skin) afferents synapse
4) Since visceral pain can’t be localised and somatic pain can, this results in the pain being referred to somatic areas (dermatomes in the skin) supplied by T1-T5 (anterior chest wall and possible medial aspect of arm)
5) This will result in visceral pain being felt in the skin e.g heart attack causes chest, neck and arm pain
