1
Q
What is the Mediastinum
A
- Broad Central region that separates the two laterally placed pleural cavities
2
Q
Where is the Mediastinum found?
A
- Extends from Sternum to bodies of verterbra A-P axis
- From Superior Thoracic Aperture to the Diaphragm S-I axis
3
Q
What Vertebral Level does the Sternal Place Sit?
A
- T4/T5 intervertebral disc
4
Q
How are the Mediastinum regions divided?
A
- Sternal plane (T4/T5 IV disc), divides Superior and Inferior
- Inferior region further subdivided: Anterior, Middle, Posterior Regions by the Pericardial sac
- Middle Mediastinum - Where the heart sits
- Anterior Mediastinum is very narrow
- Posterior Mediastinum extends inferiorly to 12th Thoracic vertebra –> to Costodiaphragmatic recess
5
Q
What Structures come off the Aorta at the Aortic Arch
A
- Right side - Brachiocephalic trunk
- Left side - Left common carotid artery
6
Q
What structures form the Superior Vena Cava?
A
- Left and Right Brachiocephalic veins
7
Q
Where do the Mediastinal Veins sit relative to the arteries
A
- Veins sit anterior to arteries
8
Q
Where are the Left and Right Brachiocephalic Veins formed?
A
- Immediately posterior to the sternal clavicular joint
- Where Subclavian vein + Internal jugular vein meet
9
Q
Where is the Superior Vena Cava formed?
A
- Behind right costal cartilage of rib 2
10
Q
What are the Arteries coming off of the Aortic Arch in order as it passes posteriorly and laterally?
A
- Brachiocephalic trunk - Branches into R. Common Carotid a. (right head & neck) and R. Subclavian a. (right upper limb)
- Left Common Carotid a. (left head and neck)
- Left Subclavian a. (left upper limb)
11
Q
What is Ligamentum Arteriosum
A
- In embryonic circulation - Ductus Arteriosus, Connected pulmonary trunk to arch of aorta, Allowed blood to bypass lungs during development.
- Closes soon after birth to become a ligamentous connection
- If fails to close, have mixing of low oxygenated blood from pulmonary trunk into highly oxygenated within aorta, Decreasing O2 content of blood to systemic circulation
12
Q
What structures can be found in the Superior Mediastinum?
A
- Arch of aorta, great vessels, trachea, oesophagus, thoracic duct, phrenic & vagus nerves
13
Q
What structures can be found within the Anterior Inferior Mediastinum?
A
- Internal thoracic vessels
- Fat
- Connective tissue
- Part of Thymus gland
14
Q
Where is the Anterior portion of the Inferior Mediastinum found?
A
- Between sternum and anterior pericardial sac down to diaphragm
15
Q
Describe CABG Procedure and its relevance to the Internal Thoracic arteries
A
- Coronary Arterial Bypass Graft procedure
- Can harvest part of an internal thoracic artery to replace/support coronary vessels in the heart which have become blocked/damaged beyond repair
16
Q
Describe the Internal Thoracic Arteries, where they arise and their connections
A
- Arise from R + L Subclavian Arteries
- Pass Veins posteriorly and then pass anteriorly to anterior mediastinum region
- Give off some segmental anterior intercostal arteries that course within intercostal grooves to anastomose with posterior intercostal arteries that come off aorta.
- Resists atherosclerotic plaque build up better than any other artery
- Great anastomotic connections - CABG Procedure
17
Q
What happens to the thymus with age?
A
- Involved in early development of immune system
- As age, atrophies after puberty into leftover fatty tissue
18
Q
Where is the Thymus gland found?
A
- Located in superior & sometimes anterior mediastinum
19
Q
What can be seen in the anterior mediastinum of children on CXR?
A
- Thymus is relatively large in children
- Can lead to thymic sail sign on CXR on right side of chest - Normal
20
Q
What structures can be found in the posterior Inferior Mediastinum region?
A
- Oesophagus, Vagus nerves and Plexus, Descending aorta, Thoracic duct, Sympathetic Autonomic chain, Azygous venous system
21
Q
What is the Function of the Azygous Venous System?
A
- Drain thoracic wall + overlying tissues
22
Q
Where do the Oesophagus and Trachea sit in the Mediastinum?
A
- Sit in Superior & Posterior Mediastinum
23
Q
What is the Innervation of the oesophagus
A
- Motor and Sensory - Vagus nerve
24
Q
How can you visualise the left atrium of the heart via Ultrasound?
A
- Due to close relation of oesophagus to heart
- Can pass US probe down oesophagus + visualise left atrium of heart
25
What structures are found within the Middle Inferior Mediastinum?
- Heart
- Pericardium
- Origins of the great vessels: Superior Vena Cava, Pulmonary Trunk, Ascending Aorta
- Phrenic nerves - Passing very close to pericardium on either side of mediastinum. Contain fibres from C3,4,5 spinal nerves. Innervate diaphragm but also bring sensory innervation to fibrous pericardium
26
What is the connection of the Fibrous Pericardium to the Diaphragm?
- Binds to the central Diaphragmatic tendon
| - So does not change shape that much with respiration, provides support
27
What can occur if there is compression or blockage of the SVC?
- Extrinsic compression by tumour/metastasis to mediastinal lymph nodes
- Block of venous return from areas draining into SVC
- Can see congestion of venous blood unable to drain (purple discolouration of pt in severe case)
28
What structure does the left recurrent laryngeal nerve swing immediately underneath as it heads back up towards the larynx
- Under the Aortic Arch
29
Where do the Vagus Nerves pass structures in the chest?
- Passes Posterior to hilum of the lungs
- But, Runs Anterior to the Subclavian Vessels & descends through mediastinum
- Right side, Recurs under the Right Subclavian artery posteriorly by apex of lung into Right Recurrent Laryngeal n. into Internal Larynx
- Left side, Recurs between pulmonary a. and aortic arch into Left Recurrent Laryngeal n.
- Rest of Vagal n. (R+L) continue down forming plexuses around trachea and inferior oesophagus
- Into diaphragm and abdominal cavity
- Vagal / Parasympathetic Autonomic Nerve Supply to gut viscera
30
What is the Aorto-Pulmonary Window
- Clinical Region between Pulmonary a. and Aortic Arch
| - Where Vagus nerve recurs into left Recurrent Laryngeal n.
31
On what side would a hilar lymph node enlargement cause a hoarse voice?
- Left side
| - L RLN recurs close to this region and may be compressed
32
Describe the Cardiac Plexus
- Cardiac plexus is a mix of BOTH Cardiac branches of vagus nerve (Parasympathetic) and Sympathetic Chain Fibres froom T1-T4 levels (Sympathetic system)
- Located Behind heart, between trachea and aorta
33
Describe the Parasympathetic and Sympathetic Nerve Supplies to the Heart
- Parasympathetic - Left & Right Vagus Nerves
| - Sympathetic - Sympathetic Chain T1-T4 level fibres, mainly left side.
34
Describe the Sensory nerve supply to the heart
- Cardiac Visceral sensory fibres travel back to CNS along with sympathetic nerves
- Sense Stretch, Inflammation, Hypoxia
- Referred Cardiac Pain occurs in the T1-T4 dermatomes mainly on left
- E.g. left arm and left jaw as well as chest pain
35
Why might a myocardial infarction cause pain which is perceived as being in your left arm or jaw?
- Due to the Visceral sensory nerve supply to the heart being derived from T1-T4 dermatomes which also supply the arm and jaw. Stimulation of one may cause perceived stimulation of another.
36
Describe the Base of the Heart
- True posterior surface of the heart
- Sits against oesophagus
- Composed primarily of left atrium
37
Explain the Orientation of the heart
- Heart is a midline structure that rotates to the left during development
- Means right-sides structures sit anteriorly while left-sided structures sit posteriorly
- Heart is also encased by fibrous pericardium
38
What completely encases the heart?
- Pericardium
- Fibrous pericardium: Outer
- Serous pericardium: Parietal & Visceral (Epicardium)
- Pericardial cavity between Serous pericardium layers, containing pericardial fluid
39
Describe the Fibrous Pericardium
- Tough outer connective tissue layer
- Does not allow sudden fast changes in heart size/volume within pericardial cavity
- Relatively inflexible, thus, inflammation or changes in fluid surrounding the heart can have large consequences
40
What is the function of Pericardial Fluid?
- Found between Visceral Serous Pericardium and Parietal Serous Pericardium
- Roughly 50cc Normally
- Reduces friction between heart epicardium + surrounding layers
41
Describe Pericarditis
- Inflammation + Swelling of the coverings of the heart
- Can be very painful due to phrenic nerve sensory innervation of the fibrous pericardium
- Can have purulent pericarditis, Pus in the pericardial space
42
What is Haemopericardium
Blood seeping into pericardial space
43
How might a Haemopericardium lead to a cardiac tamponade?
- Rapid increase in pressure within pericardial space due to blood entering
- Can compress ventricle spaces
- = Restricted cardiac filling
- Can lead to cardiac tamponade
44
What is Pericardial Effusion?
- Under certain conditions pericardial cavity may become distended by accumulations of Serous fluid
45
What innervates the fibrous pericardium
Phrenic nerve - Sensory innervation
46
what is inflammation of the pericardium called
Pericarditis
47
What are possible causes of pericardial effusion?
- Congestive heart failure
- Blunt chest trauma
- Malignancy
- Ruptured MI
- Aortic Dissection
- Mediastinal Lymphatic Obstruction
48
Compare Chronic Pericardial Effusion with Acute Pericardial Effusion
- Chronic - Slowly accumulating fluid within pericardial sac, pericardium has time to dilate, permits effusion to become large without interfering with cardiac function. Pt w/ less 500cc Chronic effusion only clinical significance is characteristic enlargement of heart shadow on chest radiograph
- Acute - Rapidly accumulating fluid within pericardial sac, pericardium has no time to expand to accommodate, 2-300cc over short amount of time can have clinically devastating consequences (cardiac tamponade), and pain due to rapid pressure increase
49
Describe the development of sinuses in the Pericardium
- During development the heart start as a tube
- This tube becomes surrounded by pericardial sac with reflections at the great vessels
- Folding of heart tube creates a passageway between arterial outflows & venous input (Transverse pericardial sinus)
- Reflection of serous layer creates blind ended sac posterior to heart (Oblique Pericardial sinus)
50
What is the Clinical Significance of the Transverse Pericardial Sinus
- Can be used in surgery to clamp arterial outflow
- Finger can go through sinus and clamp put on
- Followed by putting heart on bypass machine
- E.g. Used if repairing via CABG procedure
51
What venous drainage does the right atrium receive?
- Venous from upper body - SVC
- Venous from lower body - IVC
- Venous from Heart walls - Coronary sinus
52
Describe the valve that sits between right atrium and right ventricle
- Tricuspid valve
- Faces forward and medially
- Closed during ventricular systole/contraction
- Stops blood flowing back up into right atrium
53
Describe the division of the right atrium
- Inferior of RA divided into 2 continuous spaces
- Externally indicated - Sulcus terminalis - from R. side SVC opening to R. side IVC opening
- Internally indicated - Crista terminalis
- Posterior to Crista terminalis = Openings of IVC & SVC, V. smooth and thin walls
- Anterior to Crista terminalis = Opening of Coronary sinus, walls covered in pectinate muscles, Atrial appendage, Tricuspid valve in right ventricle
54
Describe the Atrial Appendage and Explain its clinical relevance
- Ear-like muscular pouch that externally overlap the ascending aorta, covered in pectinate muscles
- Potential space for blood clots to form especially in irregular heartbeats
- Blood may get caught there if taking longer to contract + clot may form in dead-ended space.
55
Describe the Inter-atrial septum
- Separating RA from LA
- Faces forward and right - Medial wall of RA
- Depression in inter-atrial septum = Fossa ovalis
56
What is the Fossa ovalis
- Depression in inter-atrial septum
- Marks location of embryonic foramen ovale which allowed oxygenated blood entering RA through IVC to pass directly into LA so as to bypass lungs
57
Where are the SAN and AVN located in the heart?
- Embedded within Superior Atrium
| - Part of heart conduction system
58
What might form in the atrial appendages, especially in cases of atrial fibrillation?
- Blood clots
59
Describe the Right Ventricular walls
- RA opening where tricuspid valve located
- Numerous muscular irregular structures = Trabeculae Carnae
- Attached to ventricular walls throughout length/form bridges across and between ventricular wall
- Trabeculae Carnae muscles with one end attached to ventricular surface and other attachment point for tendon-like fibrous cords = Chordae tendinae
- Papillary muscles - Chordae tendinae - Connect to free edges of cusps of tricuspid valve
- Superior portion of ventricle with opening into pulmonary trunk via pulmonary semilunar valve = Conus Arteriosus (Infundibulum)
60
What is the Infundibulum
- Conus Arteriosus
- Superior right ventricle smooth surface
- Pulmonary semilunar valve here
61
What are the Trabeculae carnae
- Numerous irregular muscular structures in the wall of the right ventricle
- Attached to ventricular walls throughout length of right ventricle. Form small bridges/ridges across ventricular wall
- Few = Papillary Muscles - One end attached to ventricular wall, other attachment = tendon-like fibrous cord (Chordae tendinae) which attaches to free edges of cusp of tricuspid valve
62
Describe the structure of the left atrium
- Anterior portion, smooth thin walls, openings of all 4 pulmonary veins.
- Inter-atrial septum - Fossa ovalis
- Anterior portion, pectinate muscles, continuous with left atrial appendage.
- Blood passes through Mitral (bicuspid) valve into left ventricle
63
How does the Ventricular wall reflect its function?
- Wall is 3x THICKER than right ventricular wall --> Reflects function
64
Describe the Left Ventricle
- Lies anterior to LA
- Forms apex of heart
- Blood enters through mitral valve and exits superiorly through aortic semilunar valve
- Trabeculae carnae present with
- some papillary muscles extending off trabeculae carnae to anchor bottom of Chordae tendinae to secure bottom of mitral valve cusps
65
Describe the Papillary muscles of the Heart Ventricles
- Papillary muscles are extensions of ventricular wall
- Attach to Chordae Tendinae which attach to bottom of a Cusp of the Tricuspid/Bicuspid Valve
- Contract to prevent cusps from being blown back into Atria during Ventricular Systole
- Cusps open passively
66
Describe the Atrioventricular valves
- Lie between atria and ventricles and allow for unidirectional flow of blood
- Valves formed by flap-like cusps that are anchored to the ventricle wall by tendons
- Tricuspid - Between RA + RV
- Bicuspid/Mitral - Between LA + LV
67
What might happen after a MI with damage to the papillary muscle?
- May necrotise
- Have AV valve incompetence/regurgitation
- No longer able to contract during ventricular sytole
- Can develop cardiac murmur
68
What is the Dense Fibrous Cardiac Skeleton?
- Dense fibrous connective tissue of the heart
69
What is the Function of the Fibrous Skeleton of the Heart
- Provides ANCHOR point for cardiac muscle and heart valve cusps
- Mechanical stability
- Electrical insulation, Prevents 'free' conduction of electrical signal from atria to ventricles
- AV node found embedded within it
70
Describe how the Aortic and Pulmonary Valves Function
- Found in outflow tracts of the aorta & pulmonary trunk
- Are semilunar & each have 3x cusps
- Pocket like spaces (sinuses are located behind each valve cusp
- During Ventricular systole - Ventricles contract, value cusps pushed toward vessel walls and OPEN up
- During Ventricular diastole - Ventricles relax, reverse-flowing blood catches in the pockets of aortic and pulmonary valves, and CLOSES the valve.
71
State the Aortic Semi-lumar Valve Nomenclature
- New names reflect position relative to the coronary arteries
- Right Coronary leaflet - Right Coronary a. opens behind
- Left Coronary leaflet - Left Coronary a. opens behind
- Non-adjacent leaflet
72
State the Pulmonary Semilumar Valve Nomenclature
- New names reflect position relative to coronary arteries
- Right-adjacent leaflet
- Left-adjacent leaflet
- Non-adjacent leaflet
73
What is Stenosis in regards to the Heart valves?
- Valvular Heart disease
- Failure of valve to open fully
- Slows blood from leaving a chamber
74
What is Valvular Insufficiency?
- Regurgitation or failure of valve to close completely
| - Results in Backflow
75
What are the most commonly affected Valves in Valvular Heart Disease (Stenosis or Insufficiency)
- Mitral and Aortic Valve
- Commonly
- Mitral Valve Prolapse - Most common type of congenital heart disease in adults
- Aortic Stenosis - Most frequent valve abnormality, often result of degenerative calcification
76
Describe Mitral Valve Prolapse
- One of both leaflets are enlarger, redundant, or FLOPPY
- Most common type of congenital heart disease in adults
- Results in leaflets extending back into LA during systole
- Blood regurgitates into LA, when LV contracts = Late systolic murmur
- Clinically:
- LV Hypertrophy
- LA dilation
- Increased pulmonary pressure + Pulmonary Oedema
- Shortness of breath
- Right sided heart failure
77
Describe Aortic Stenosis
- Often result of Degenerative calcification
- Valve cannot open fully, blood cannot enter aorta easily
- Results in LV hypertrophy (thickness & enlargement of left ventricle trying to compensate for reduced blood supply to body)
- Pt may experience dizziness, syncope, episodes of fainting, angina chest pain
78
Where does the myocardium get its blood supply from?
- Coronary arteries which arise from the coronary sinus above the cusps of aortic values
79
When does the heart receive its blood supply?
- Main inflow is during Ventricular diastole
- Blood backflow closes semilunar valves + opens coronary arteries
- During systole, valves opened and pressed against openings of arteries
80
What is a Right Coronary Artery Dominant heart?
- When a heart is RCA dominant it gives rise to the Inferior Interventricular Artery
- Can also give rise to Sinuatrial Nodal Artery
- Also a number of Anterior Ventricular arteries
- Artery along its margin = Right Marginal Artery
81
What does the Right Coronary Artery Supply?
- Right atrium & Right Ventricles
- SA node & AV node
- Conduction system up to AV bundles
- Posterior 1/3rd of IV septum
82
What can occur in a MI in the right coronary artery
Can affect the conduction of signal propagation across heart's tissues, SA/AV node knock out
83
What determines the Coronary Artery Dominance of the heart?
Which artery gives rise to the inferior interventricular artery
84
What is a Left Coronary Artery Dominant Heart?
- Left coronary artery gives rise to the inferior interventricular artery
- Will arise off termination of the Circumflex artery
85
What arteries arise off of the LCA of the heart?
- If LCA dominant - Inferior Interventricular artery
- Sometimes Sinuatrial Nodal artery
- Branches into
- Circumflex artery
- And Anterior Interventricular artery
- Marginal artery
86
What does the LCA normally supply?
- Left atrium & Left Ventricle
- Anterior 2/3rds of IV septum
- AV bundle
- Right & Left Bundle Branches
87
What can occur in a MI in the LCA
- If Supply of AV bundle +/ Right & Left bundle branches compromised
- Can cease to have electrical signal propagation of heart in these areas
88
Describe the Cardiac Veins
- Great, Middle & Small Cardiac veins
- Drain blood from myocardium of the heart
- Majority of venous blood drains into the Right Atrium via the Coronary sinus
89
Describe the Surface anatomy of the heart
1. 3rd Rib Costal Cartilage - Right Lateral to Sternum. Junction of SVC & RA
2. 6th Rib Costal Cartilage - Right Lateral to Sternum. Junction of RA & IVC
3. 2nd Rib Costal Cartilage - Left Lateral to Sternum. Site of Left Atrial Appendage meets Pulmonary trunk
4. 5th ICS - Left mid-clavicular line. Site of Apex of lung & LV
90
Describe the Auscultation points of the Heart
- Heart sounds results from valves closing and pathologies affecting heart, sounds tend to travel in direction of flow
- 1. Aortic Valve - 2nd R ICS lateral to sternum
- 2. Pulmoary Valve - 2nd L ICS lateral to sternum
- 3. Tricuspid Valve - 5th L ICS lateral to sternum
- 4. Mitral Valve - 5th L ICS MCL
91
Describe the Conduction system of the heart
- Allows rapid coordinated delivery of cardiac impulse to atrial & ventricular muscles
- Impulse originates in SA node (Pacemaker)
- Propagates to AV node - Cardiac skeleton helps electrically insulate atria from ventricles.
- Electrical signal can only travel to ventricles via AV node and bundle
- Splits into R + L bundle branches
- Course down either side of interventricular septum
- Along ventricular floors via Purkinje fibres
Block 2
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