Coronary Circulation and Conduction Flashcards
Learning outcomes
- Describe the origin, course and distribution of the coronary arteries
- Explain the importance of the anastomoses 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 of the myocardium and how it may affect the conducting system
- Explain where pain originating from the heart is referred to and why
- Identify major branches of coronary arteries on angiograms
Spit some facts about the heart
It never sleeps (hopefully!). • How is it innervated? It changes gear. • Who/what controls this? How? It cannot use the oxygenated blood in its chambers • Why? • Is it “all truth and nothing but the truth”? Has its own very reliable blood supply
Describe cardiac muscle
striated but involuntary
Fibres branch and join with each other with intercalated discs
work as a single functional organ or syncytium
synchronized contraction
does not tetanize
What are the 5 different effects that can be had on the heart?
Chronotropy Dromotropy (conduction) Bathmotropy (excitability) Inotropy (contractility) Lusitropy (relaxation)
Describe the course of the blood supply to the heart
Supplied by coronary arteries and their branches
Right coronary artery (RCA)
Left coronary artery (LCA)
The endocardium receives oxygen and nutrients directly from the chambers of the heart
Describe the source of the coronary arteries
Are the only branches of the ascending aorta
Emerge in aortic sinuses
Describe the right coronary artery
Arises from the right aortic sinus
SA nodal branch
Supplies the SA node of the conduction system
Atrial branches supply the right atrium
Right (acute) marginal branch
Usually gives off the posterior
interventricular branch
(aka posterior descending artery)
Anastomoses with branches of Left coronary artery at the apex
Describe the left coronary artery
LEFT MAIN STEM
Arises from the left aortic sinus between left auricle and the pulmonary trunk
Shorter but thicker than right coronary artery
Enters the coronary sulcus
Divides into circumflex and anterior interventricular branches
Anterior interventricular branch (left anterior descending, LAD)
− Supplies the sternocostal surface
− Anastomoses with posterior interventricular branch of RCA at the apex
− “Artery of sudden death”
Circumflex branch
Left (obtuse) marginal branch
Anastomoses with the branches of RCA
Summarise coronary blood supply in regards to the RCA and its branches
Walls of RA and RV
Sino-atrial and Atrioventricular nodes
Posterior part of interventricular septum (proximal portion of atrioventricular bundle of His)
Small areas of the walls of LA and LV
Summarise coronary blood supply in regards to the LCA and its branches
Walls of LA, LV
Most of the interventricular septum including part of the atrioventricular (AV) bundle
What is coronary dominance?
The artery that gives off the posterior interventricular/posterior descending artery determines the coronary dominance
In ~80% of the people RCA is dominant
Where are the most likely places for a myocardial infarction to occur?
- LAD 40-50%
- RCA30-40%
- Circumflex 15-20%
How may a MI damage the conduction system of the heart?
• LAD (septal branches) supplies AV bundles • RCA supplies both SA and AV nodes • Heart block (bradycardia)
What are potential sources of vessels for CABG?
Internal thoracic artery
(Internal Mammary Artery (LIMA))
Great Saphenous Vein***
What is CABG?
Coronary Artery Bypass Grafting
- Bypass of the occluded portion of the vessel in a myocardial infarction
What is coronary angioplasty?
Surgical repair of a damaged or blocked vessel in the heart
- Percutaneous Transluminal Coronary Angioplasty
- With or without stent (drug-eluting v bare-metal stents)
- Anticoagulation medication
What are cardiac veins
Cardiac veins accompany the coronary arteries and their branches
Most of the venous blood drains into RA via coronary sinus
What is the source of venous return from the coronary arteries?
Cardiac veins
Most of the venous blood drains into RA via coronary sinus
Name the cardiac veins
Great cardiac (anterior interventricular) vein joins the coronary sinus
Small cardiac vein accompanies right marginal branch
Middle cardiac (posterior interventricular) vein drains into coronary sinus
Anterior cardiac veins drain independently into the RA
Describe the coronary sinus
Lies between the LA and LV
Surrounded by muscle fibers
from LA
Drains 60% of the venous blood of the heart into the RA
40% is drained by smallest cardiac veins (the besian veins) and anterior cardiac veins
Describe the cardiac conduction system
Cardiac muscle fibers form 2 networks separated by fibrous skeleton: Atrial and ventricular networks
There is a group of specialized, modified cardiac muscle cells that
− lie immediately beneath the endocardium
− can generate electrical impulses without external stimuli
Cardiac muscle cells distribute electrical impulses through the myocardium,
– causing the heart to contract in the proper sequence
Autonomic nervous system shortens or prolongs the duration of a cardiac cycle
What are the components of the cardiac conduction system?
− Sinu-atrial node (SA node) − Atrioventricular node (AV node) − Atrioventricular bundle (bundle of His) • Left bundle branch • Right bundle branch − Purkinje fibers.
None of these are macroscopic
Describe the sino-atrial node
Keith-Flack node
Pace-maker
The basic depolarization rate of the SA node is 70 to 80 beats per minute
Located anterior to the opening of the SVC, upper end of crista terminalis
Usually supplied by branches of the right coronary artery
Describe the atrioventricular node
Aschoff-Tawara node
Located at the postero- inferior part of IA septum, close to the opening of the coronary sinus
Usually supplied by AV nodal branch of the right coronary artery
Describe the atrioventricular bundle
Bundle of His
− Continuation of the AV node
− Runs along the membranous part of the IV septum.
− Splits into right and left bundle branches
Describe the right bundle branch of the atrioventricular bundle
− Descends on the right side of the
membranous part of the IV septum.
− Enters the septomarginal trabecula to reach the base of the anterior papillary muscle
− Splits into Purkinje fibres which spread out into the ventricular walls
Describe the left bundle branch of the atrioventricular bundle
− Descends on the left side of the
membranous part of the IV septum.
− Splits into Purkinje fibres
How may conduction pass from the atria to the ventricles through the skeleton?
The AV bundle of His is (and should be) the only conductive route through the fibrous skeleton
This system ensures synchronous contraction, in the correct sequence, toward the outflow of each chamber
Describe nerve supply to the heart
Cardioacceleratory and Cardioinhibitory centers in the Medullary reticular formation
Superficial and deep cardiac plexus
− Lie inferior to the aortic arch, adjacent to the bifurcation of both the
pulmonary trunk and the trachea
− Supply conduction system, coronary blood vessels, and myocardium
1. Presynaptic sympathetic fibres travel in T1-5(6) spinal nerves
− Increase the heart beat and force of contraction
− Dilate coronary arteries
2. Parasympathetic fibres reach in vagus
− Decrease the heart beat (and force of contraction * Controversy)
− Constrict coronary arteries
3. General visceral afferents
Discuss cardiac pain and how it may be referred
Pain caused by ischaemia and damage to cardiac muscle
Visceral sensory nerve endings are activated
GVA (General Visceral afferent) (sympathetic) fibers carrying the sense travel with sympathetics in T1-5 spinal nerves
Pain fibres from organ and skin travel to spinal cord together
Pain not felt in heart but referred to somatic areas (skin) supplied by T1-5 (anterior chest wall and possibly medial aspect of the left arm
