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MRCS Part B > Thorax > Flashcards

Thorax Flashcards

1
Q

What are the main muscles of the thorax?

A

External intercostals, internal intercostals, innermost intercostals, transversus thosacis

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2
Q

Describe the layout of the intercostal muscles.

A

External intercostals: run infero-laterally from the rib above to the rib below. It is continuous with the external oblique.
Acts to elevate the ribs and increase the thoracic volume.
Innervates by intercostal nerves T1-T11.

Internal intercostals: run infero-posteriorly, continuous with the internal oblique.
Acts to reduce the thoracic volume.

Innermost intercostals: they are separated from the internal intercostals by the neuro vascular bundles.

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3
Q

What are the attachments and the action of the transversus thoracis?

A

Attach from the posterior surface of the inferior sternum to the internal surface of costal cartilages 2-6.
Acts to weakly depress the ribs

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4
Q

What are the 3 attachments of the diaphragm?

A
  • Lumbar vertebra via the arcuate ligament.
  • costal cartilage 7-10 & ribs 11-12
  • xiphoid process of the sternum
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5
Q

Describe the origin of the right and left crura.

A

R crus arises from L1-L3. The fibres surround the oesophageal opening acting as a physiological sphincter.

The L crus arises from L1-2.

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6
Q

What are the openings in the diaphragm and what passes through them?

A

Cabal Hiatus (T8)
- IVC
- Phrenic nerve

Oesophageal Hiatus (T10)
- oesophagus
- vagus nerve
- L gastric branches to oesophagus

Aortic hiatus (T12):
- aorta
- thoracic duct
- azygous vein

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7
Q

What is the innervation to the diaphragm?

A

The phrenic nerve (C3-5)

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8
Q

What is the arterial supply to the diaphragm?

A
  • Inferior phrenic arteries (from aorta)
  • superior phrenic
  • pericardiacophrenic
  • musculophrenic
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9
Q

What are the signs of diaphragm paralysis and what are the causes?

A

It causes paradoxical movement where the affected side moves up on inspiration and down on expiration.

Causes:
- mechanical trauma to nerve or diaphragm itself
- compression to nerve (tumour)
- myopathy such as myasthenia
- neuropathy such as diabetes

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10
Q

How can the mediastinum be divided?

A

Into superior and inferior. The inferior is then further divided into anterior, middle and posterior.

The superior and inferior are divided by an imaginary like passing between the sternal angle and T4 vertebra.

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11
Q

What are the borders of the superior mediastinum?

A

Superior: thoracic inlet
Inferior: line from sternal angle to T4
Anterior: manubrium of sternum
Posterior: T1-T4
Lateral: pleura of lungs

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12
Q

What are the contents of the superior mediastinum?

A

Aortic arch (and branches)
SVC (and tributaries including brachiocephalic, azygous, L superior intercostal)
Phrenic nerve
Vagus nerve
Cardiac plexus
Sympathetic trunk
Trachea
Oesophagus
Thoracic duct
Thymus
Infrahyoid muscles

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13
Q

What are the borders and the contents of the anterior mediastinum?

A

Superior: line from sternal angle - T4
Anterior: body of sternum/ transversus thoracis
Posterior: pericardium
Lateral: parietal pleura

Contents: no major structures in adults, contains loose connective tissue. In children the thymus extends inferiorly.

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14
Q

What are the parts and the branches of the subclavian artery?

A

Divided into 3 parts: proximal, deep and distal to the scalenus anterior.

Branches:

Vertebral
Internal thoracic
Thyrocervical trunk

Costocervical trunk

Dorsal scapula

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15
Q

What are the boundaries and the contents of the middle mediastinum?

A

Boundaries:
Anterior and Posterior: pericardium
Lateral: pleura
Inferior: diaphragm
Superior: line from sternal angle to T4

Contents:
- heart
- tracheal bifurcation
- ascending aorta
- pulmonary trunk
- SVC
- cardiac plexus
- phrenic nerve
- lymph nodes

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16
Q

Describe the path of the phrenic nerve.

A

Travels down the neck on the anterior aspect of the scalenus anterior. Enters the thoracic inlet between the subclavian artery and vein. Runs along the surface of the pericardium anterior to the lung hilum.

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17
Q

What are the contents of the posterior mediastinum?

A
  • thoracic descending aorta and branches (posterior intercostals x9, bronchial arteries, oesophageal arteries, superior phrenic)
  • oesophagus
  • oesophageal plexus
  • thoracic duct
  • azygous system (azygous vein, hemi azygous, accessory azygous)
  • sympathetic trunk
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18
Q

Describe the azygous system.

A

Ascends to the right of the vertebral column (causing a groove in the R lung). It drains into the SVC.

It is initially formed by the combination of the ascending lumbar and R sub costal vein.
It receives tributaries from the hemi-azygous vein, accessory azygous veins from the left and the right 2nd-12th intercostal veins, bronchial veins and the pericardial veins.

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19
Q

What are the branches of the thoracic aorta?

A

Ascending:
- L and R coronary arteries

Arch (ends at the level of T4):
- brachiocephalic
- left carotid
- left subclavian

Thoracic Descending: T4-T12
- bronchial arteries
- mediastinal arteries
- oesophageal artieries
- pericardial arteries
- superior phrenic arteries
- intercostal arteries

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20
Q

What is the ductus venosus?

A

Embryological vessel that allows shunting of blood from the umbilical vein to the IVC, bypassing the liver.
Closes to become the ligamentum venosum.

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21
Q

What is the ductus arteriosus?

A

Vessel allowing shunting of blood from the pulmonary artery to the descending aorta (bypassing the lungs).
Closes to form the ligamentum arteriosum.

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22
Q

What are the functions of the umbilical artery and vein?

A

Umbilical artery: takes deoxygenated blood from the umbilical cord to the placenta

Umbilical vein: takes oxygenated blood from the placenta to the liver. This closes to become the ligamentum teres at birth

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23
Q

What are the tributaries of the SVC?

A

Forms from the union of the L and R brachiocephalic veins (at the level of the 1st costal cartilage)
Tributaries include;
Azygous vein
Mediastinal veins
Oesophageal veins
Pericardial veins

It drains into the R atrium at the level of the 3rd costal cartilage

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24
Q

How can you classify thoracic aortic aneurysms?

A
  1. Ascending
  2. Arch
  3. Descending
  4. Thoraco-abdominal
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25
What is the Crawford classification?
I: subclavian- renal II: subclavian - infrarenal III: distal descending - infrarenal IV: above diaphragm to bifurcation
26
What are the indications for management in a thoracic aortic aneurysm?
- >5.5 in ascending - >6.5 in descending - if >1cm/year in growth - symptomatic
27
What is an aortic dissection?
Initial tear causing a false lumen which propagates.
28
What causes traumatic dissection?
May be caused by a deceleration injury. The thoracic aorta is anchored by the ligamentum arteriosum, brachiocephalic and vertebral arteries. In deceleration this part stays fixed whilst the rest moves forward and therefore dissection occurs.
29
What are the atraumatic causes of dissection?
HTN Media degeneration Aortitis CT disorders
30
How can you classify aortic dissection?
DeBakey: 1. Ascending- Descending 2. Ascending only 3. Descending only Stanford: A: ascending B: descending
31
How do you manage aortic dissection?
Permissive hypotension Stanford A and DeBakey 1/2 need surgical repair Stanford B and DeBakey 3 can be medically managed unless high risk of rupture or evidence of end organ ischaemia
32
What are the locations and function of the chemoreceptors?
Peripheral: carotid body and aortic body Central: medulla oblongata The peripheral receptors act in response to partial pressures of O2 and CO2. The central only react to CO2. An increased CO2 stimulates an increased resp rate.
33
Where are the baroreceptors located and what do they do?
Located at the carotid Sonys and the aortic arch. A sudden rise in BP stimulates an impulse to be sent via the tractus solitaries to the vasoconstrictor tract of the midbrain. This leads to inhibition of the sympathetic system (reduced vasoconstriction) and increased vagal tone at the SA node
34
What are the layers of the pericardium?
Fibrous layer (continuous with central tendon of the diaphragm) Parietal layer of serous Serous fluid Serous pericardium (also known as the epicardium)
35
What is the function of the pericardium?
- fixed heart in the middle mediastinum - prevents overfilling - lubrication - protection from infection
36
What is cardiac tamponade?
Accumulation of fluid under non distensible fibrous pericardium causing compression of the heart and therefore reduced cardiac output
37
What layers would you go through in a parasternal approach of pericardiocentesis?
1. Skin 2. Fascia 3. Pec Major 4. Intercostals (x3) 5. Transversus thoracis 6. Fibrous pericardium 7. Parietal layer of serous pericardium
38
What are the layers of the heart wall?
Innermost: endocardium Loose connective tissue and squamous epithelium. Myocardium: involuntary striated muscle Epicardium: visceral layer of the serous pericardium
39
Describe the surface anatomy of the heart.
Draw a line from; 1. The lower border of the 3rd costal cartilage on the right edge of the sternum. 2. The lower border of the 6th costal cartilage on the right edge of the sternum 3. 5th intercostal space, mid clavicular line 4. 2nd intercostal space, L border of the sternum
40
Describe the location and contents of the sulci of the heart.
Coronary sulcus: atriventricular groove. Contains the RCA, circumflex branch of LCA, small cardiac vein and coronary sinus. Anterior interventricular sulcus: Contains the LAD and the great cardiac vein Posterior interventricular sulcus: Contains the posterior interventricular artery and the middle cardiac vein
41
Describe the coronary artery anatomy.
The left coronary artery arises from the left posterior articular sinus. It branches into the left anterior descending, the left marginal and the left circumflex. The right coronary artery (from the anterior aortic sinus) branches to form the right marginal and the posterior interventricular
42
Describe the venous drainage of the heart.
All veins drain into the R atrium via the coronary sinus. This sits in the posterior coronary sulcus and enters the RA near to the tricuspid valve and it has its own valve to prevent reflux - the Thebesion valve. It receives tributaries from: - great cardiac vein (sits by LAD in the anterior interventricular groove) - small cardiac vein (in the coronary sulcus) - middle cardiac vein (posterior interventricular sulcus) - posterior cardiac vein (on posterior aspect of L ventricle)
43
What are the features of the RA?
Receives blood from the IVC, SVC and coronary sinus. It’s inner surface has two cavities separated by the muscular ridge called the crista terminalis. The sinus venosum is smooth walled and receives blood from the SVC and IVC The atrium proper is anterior and has rough walls due to the pectinate muscles. The interventricular septum has a depression for the fossa ovale.
44
What are the features of the right ventricle?
Triangular in shape, forms the anterior heart border. The inflow portion has trabeculae carnae which form ridges, bridges and pillows. The papillary muscles are attached to the tricuspid valve by the chorda tendinae The outflow portion (superior aspect) is smooth walled.
45
What are the features of the interventricular septum?
The superior aspect is membranous The inferior part is muscular
46
What is the typical cardiac output?
5-6L / minute
47
What is Laplace Law?
Wall tension = circumference x thickness
48
What is Starling’s Law?
Larger end diastolic volume = higher stroke volume due to increased stretch in cardiac fibres.
49
Describe the conducting system of the heart?
1. Action potential is created by the SA node 2. Spreads across the atria causing contraction. 3. Reaches the AV node which delays the signal 4. Conducted via the bundle of His down the interventricular septum 5. Spreads via the Purkinje Fibres causing the ventricles to contract
50
Where does the SA node sit?
In the right atrium where the SVC enters
51
Where does the AV node sit?
At the atrioventricular septum near the opening of the coronary sinus
52
What are the signs of an atrial septal defect?
Parasternal heave Split S2 Mid systolic murmur
53
What are the indications for repair of an atrial septal defect?
- L > R shunt - AF - CCF - emboli causing CVA
54
What are the signs of a ventricular septal defect?
Systolic murmur Tachypnoea Hepatomegaly/Cardiomegaly Poor feeding
55
When would you repair a VSD?
Always needs surgical management
56
What is a patient ductus arteriosus and what are the features?
This is a connection between the pulmonary artery and aortic arch. Normally closes at birth due to the reduction in maternal prostaglandins. Features include: Tachycardia Tachypnoea Pulmonary oedema Pansystolic murmur Hepatomegaly Failure to thrive
57
How do you manage a patent ductus arteriosum?
Medical: indomethacin Surgical: ligation
58
What is tetralogy of Fallot?
1. VSD 2. Pulmonary stenosis 3. Overriding aorta 4. RV hypertrophy
59
What is coarctation of the aorta?
Stenosis of the aorta at the site of the ligamentum arteriosum. May present with syncope/claudication or BP mismatch
60
How do atherosclerotic plaques form?
Endothelial injury. LDL accumulates. Platelet adhesion causes the release of plt derived growth factor attracting monocytes. Monocytes engulf cholesterol causing oxidation of LDL and then forms foam cells. This stimulates smooth muscle and fibroblast proliferation. The smooth muscles migrate into the intima and fibroblasts lay down collagen and elastin. Plaque forms
61
How do you manage an MI?
Morphine, nitrates, aspirin, clopidogrel PCI
62
Which ECG leads would show changes in an RCA artery infarct?
Leads II, III, aVF (Inferior location)
63
If leads V1-V4 show ecg changes where would the infarct be?
Septal - LAD artery
64
If ecg changes were present in leads I, aVL, V5, V6 which vessel is affected?
The circumflex (anterolateral)
65
How do you manage VT?
If they are unstable then need immediate cardio version. If stable then: - amiodarone (via central line) - lidocaine - procanamide NOT verapamil
66
What are the risk factors for aortic stenosis?
Age Rheumatic fever High calcium Bicuspid valve
67
What are the eponymous signs for aortic regurgitation?
Quinkes: visible pulsation in capillary bed Mullers: pulsation of the uvula Traubes: pistol shot femoral auscultation Corrigons pulse: collapsing pulse DeMussets: pulsatile head bobbing
68
What are the causes of aortic regurgitation?
Rheumatic fever Marfans Endocarditis Vasculitis Type A dissection
69
What are the features of aortic regurgitation?
Dyspnoea Orthopnoea Pulmonary oedema Angina Wide pulse pressure Early diastolic murmer Syncope
70
What are the common organisms causing endocarditis?
Staph A and Staph Epidermis are the most common. Strep Viridans and enterococcus Then the HÁČEK group: (commensals or the oral cavity). Haemophilis, cariobacterium, eikenella, kingella
71
What is the patho physiology of infective endocarditis?
Causes vegetation containing fibrin, inflammatory cells and microbes on the heart valves which may erode, embolise or produce and abscess
72
What is the diagnostic criteria for infective endocarditis?
Dukes criteria. Need to have 2 major, or 1 major and 3 minor, or 5 minor Major: - +ve blood culture - involvement of the endocardium on echo - new murmur Minor: - fever >38 - +ve blood cultures but atypical - predisposing factors (IVDU) - vascular/immune signs - +ve echo but atypical
73
What are the peripheral signs of infective endocarditis?
Splinter haemorrhages Oslers nodes Jane way lesions Roth spits Vasculitic rash
74
What are the indications for surgery in infective endocarditis?
- haemodynamic compromise - CCF - Valve obstruction - Abscess formation - Septic emboli - Fungal - Failure to respond to medical treatment
75
Describe the path of the vagus nerve from its origin to the diaphragm.
The vagus nerve arises from the medulla and exits the cranium via the jugular foramen. It travels within the carotid sheath between the CCA and the IJV. The L side loops around the ligamentum arteriosum. The R side loops around the subclavian artery
76
What does the vagus nerve supply in the abdomen?
Anterior= stomach, pylorus, liver, hand pancreas, D1/2 of duodenum
77
How do inotropes work?
They act via: - alpha 1 receptors in the peripheries causing vasoconstriction - beta 1 receptors in the heart cause +ve chronotropic and +ve inotropic affect - beta 2 receptors in the coronary vasc causing vasodilation
78
What is cardiac output?
Stroke volume x Heart rate
79
What can affect cardiac output?
Preload After load Heart rate Contractility
80
What is pulse pressure?
Systolic - diastolic
81
What is MAP?
1/3x systolic + 2/3x diastolic
82
Give some examples of positive inotropes and how they work.
Noradrenaline - acts on alpha receptors causing vasoconstriction Adrenaline - acts on alpha 1, beta 1 and beta 2 Dobutamine - acts in beta 1 and beta 2 (strong inotrope, weak chronotrope) Metaraminol - acts on alpha 1 to increase SVR Need to be aware can cause low flow to kidneys
83
What is a pulmonary artery catheter?
This is a multi-lumen catheter with an inflatable balloon at its proximal tip. It inserts into the pulmonary artery via the IJV.
84
What are the functions of the lumens in a pulmonary artery catheter?
Balloon inflation Delivery of IV or pacing wires Measure pressure in proximal RA and pulmonary artery Measure the CO via thermodilution Therefore it can measure the CVP, PCWP, CO, ppO2 And indirectly measure: SVR, stroke volume and ventricular pressure
85
What are the complications of inserting a pulmonary artery catheter?
Pneumothorax Infection Valve damage Thrombus Perforation Arrhythmia Incorrect placement leading to incorrect results
86
What is a normal CVP?
2-6mmHg or 2-10cmH2O
87
Why is CVP useful?
It is a measure of RA pressure and therefore indirectly LA pressure. It is useful in managing shock as it measures the preload. The response of the CVP to fluid is diagnostic. If the CVP rises and stays high then giving more fluid will not change CO. If it rises then falls it suggests the fluid is being redistributed and if it rises very transiently it suggests the patient is very underfilled.
88
Describe the steps of a median sternotomy.
1. Incision 2cm below sternal notch to xiphoid 2. Divide the suprastenal ligament 3. Divide and he xiphoid with scissors and saw the sternum 4. Retract and apply bone wax 5. Finger sweep the thymus away 6. Identify the brachiocephalic vein 7. Divide the pericardium and apply stay sutures
89
What are the complications of a sternotomy?
Vessel injury (brachiocephalic artery and vein and right ventricle) Sternal dehiscence Osteomyelitis Wire sinus
90
What is cardioplegia?
This is a K+ rich solution which is given into the aortic root to flow into the coronaries.
91
What are the complications of cardiopulmonary bypass?
- coagulopathy due to hypothermia and heparin - CVA due to air/ calcium embolism - Cardiogenic shock leading to Low CO
92
What are the complications of a CABG?
- bleeding (due to dehiscence, coagulopathy, cannula site leak) - reduced CO (due to cardiogenic shock, incomplete revascularisation) - CVA - nerve damage - infection (sternal infection, endocarditis, leg infection) - renal failure - AF
93
What are the causes of pneumothorax?
Primary: - Spontaneous - Marfans - Bulla/blebs Secondary: - Trauma - Pathological (asthma, COPD, infection, malignancy) - Iatrogenic (Central line) - post operative
94
What is the management of pneumothorax?
PRIMARY: If stable then consider simple aspiration, if fails then consider chest drain. SECONDARY: If breathless, >2cm, >50 then chest drain.
95
How do you insert chest tube?
Informed consent Gather equipment (blade, underwater seal chest tube, artery forceps) Clean field Insert into triangle of safety: 4-5th intercostal space, just anterior to the mid-axillary line. Inject LA, cut overlying skin, finger thoracotomy, insert chest drain ensuring all holes are inside the chest cavity, connect to water seal system secure drain re-examine and chest XR

MRCS Part B (14 decks)

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