The Heart & Mediastinum Flashcards
What is the mediastinum?
Broad central region that separates the two laterally placed pleural cavities extending from the sternum to the vertebrae bodies & from the superior thoracic aperture/inlet to the diaphragm (T1 -> T12)
Why is adipose tissue commonly found within the pericardium surrounding the heart?
Helps provide a cushion for the heart
How can you tell if an X-ray has been taken on inspiration?
Flattening of diaphragm
Corners of costodiaphragmatic recess
Can see middle rib sections
Lung fields sizeable
What 3 structures can you see directly above the heart on an X-ray?
Aortic notch
Pulmonary trunk
Lung hilum
What is the sternal plane?
Plane at sternal angle at rib 2 CC + ~ T4/5
Divides mediastinum into superior + inferior regions
How is the inferior region of the mediastinum further subdivided?
Anterior
Middle
Posterior
What can collect in the costodiaphragmatic recess?
Pleural effusion
Where is the posterior mediastinum?
Extends inferiorly to the 12th thoracic vertebrae
What must you be careful of if you are trying to access the costodiaphragmatic recess?
Liver
Kidneys
Where is the anterior mediastinum?
Narrow area between sternum + anterior pericardial sac
What is contained within the anterior mediastinum?
Internal thoracic vessels
Fat
Connective tissue
Some thymus (maybe)
What can the internal thoracic arteries be used for?
Coronary Artery Bypass Graft (CABG)
Where is the thymus?
In superior + sometimes anterior mediastinum
What happens to the thymus with age?
Relatively large in children causing a thymic sail sign on a CXR (looks like pathology) -> shrinks with age
What structures are contained within the superior mediastinum?
Arch of aorta Great vessels Trachea Oesophagus Thoracic duct Phrenic nerve Vagus nerve
What are the great vessels?
Subclavian veins Internal jugular veins Brachiocephalic veins Brachiocephalic trunk SVC Subclavian arteries Common carotid arteries
Veins sit ___ to the arteries.
Anterior
What is the ligamentum arteriosum a remnant of? What happens if it stays open?
Ductus arteriosis
Helps you bypass lungs in utero so should fuse shut but if it stays open you will have a mix of oxygenated + deoxygenated blood in systemic circulation
What is the cysterna chili?
Dilated sac in lower abdominal area that drains most lymphatics from most of body + major route into circulation
Branches off to form thoracic duct
Where is the SVC formed?
1st rib CC
Where does the phrenic nerve pass through the mediastinum?
Anterior
How does the vagus nerve travel from the mediastinum to the abdomen?
Posterior to hilum of lung + anterior to subclavian vessels descending through the mediastinum
Forms a plexus around trachea + oesophagus when oesophagus is immediately posterior to the LA of heart
L vagus travels through diaphragm anteriorly + R vagus travels through posterior surfaces of oesophagus to innervate the abdomen
What does the recurrent laryngeal nerve (RLN) do? What fibre type foes it carry?
Sensory fibres below vocal chords
Motor fibres to every muscle in the larynx apart from the cricothyroid
On what side would a hilar lymph node enlargement cause a hoarse voice?
Left because RLN can be compressed underneath the aortic arch
The left atrium of the heart is closely related to the oesophagus. What can this relationship be used for?
Transesophageal Echocardiogram (TOE) -> probe in oesophagus to image the heart
Where is the posterior mediastinum?
Behind the pericardial sac + anterior to the vertebral column
What structures are within the posterior mediastinum?
Oesophagus Vagal nerve plexus Descending aorta Thoracic duct Sympathetic chain Azygous system
What structures are within the middle mediastinum? What are they bound by?
Heart
Pericardium
Origins of great vessels (e.g. ascending aorta, pulmonary trunk + SVC)
Phrenic nerves
Bound by the pericardial sac
What is the fibrous pericardium bound to?
Central diaphragmatic tendon
Think of the heart shaped as a door wedge. What are its borders?
Diaphragmatic Left Right Base/posterior Apex (further corner away from base which is why it is also called the posterior surface)
The chambers of the heart tend to be named in a different direction to which they are facing. Why is this?
Heart is a midline structure that rotates left during development SO
R sided structures sit anteriorly
L sided structures sit posteriorly
What might form in the atrial appendages, especially in cases of atrial fibrillation?
Atrial appendages are dead ends of internal heart tissue so clots may form here + move to other parts of the body inc. head + neck - this is why AF can be so dangerous
What is the pericardium composed of?
- Fibrous pericardium: tough outer connective tissue layer
- Serous pericardium:
- Visceral (lines outside of heart forming epicardium) + parietal (lines inside of fibrous pericardium) layers
What is between the hearts parietal + visceral layers?
Pericardial cavity containing small amounts of lubricating pericardial fluid
How might haemopericardium lead to a cardiac tamponade?
Blood build up within tough fibrous pericardium reducing the heart’s ability to refill with blood from extremities + to contract due to high pressure -> impedes hearts ability to beat = irregular heart beats
Where are the reflections of the pericardial sac formed in the developing heart?
At great vessels
What 2 structures are formed when the heart tube and pericardial sac are developing?
- Transverse pericardial sinus: passageway between arterial outflows + venous inflow
- Oblique pericardial sinus: reflection of serous layer creating a blind ended sac posterior to heart behind LA
What can the transverse pericardial sinus be used for in surgery?
Can be used in surgery to clamp arterial outflow
Where is the atrioventricular valves (AV)? What do they do?
Valve formed by flap-like cusps anchored to the ventricle wall by tendons called chordae tendinae
Lie between atria + ventricles allowing for unidirectional flow of blood
What so papillary muscles do?
Extensions of ventricular wall that do not contract to open valves (this is passive) but contact to prevent cusps from being blown back into atria during ventricular systole
What might happen after a myocardial infarction with damage to the papillary muscle?
Cannot contract -> AV valve incompetence = blood regurgitation from ventricle to atrium causing a cardiac murmur
What is the fibrous cardiac skeleton made from?
Dense fibrous connective tissue
What are the main functions of the fibrous cardiac skeleton?
- Mechanical stability
- Electrical insulation (prevents free conduction of signal from atria -> ventricles)
- Attachment point for cardiac muscle + valve cusps
What structure is the ONLY route for signal conduction from atria to ventricles?
AV node + then bundle
What is the structure of the aortic and pulmonary valves?
Semi-lunar with 3 cusps with pocket-like sinuses behind each valve cusp
What is the function of aortic and pulmonary valve cusps?
Reverse flowing blood catches in the sinuses during ventricular diastole closing them - blood used to reperfuse myocardium itself
Cusps pushed toward vessel walls + open during ventricular systole
Why might aortic and pulmonary valve cusps have varying nomenclature?
Position alters from embryological -> adult position due to rotation of heart in development
Aortic: posterior -> anterior
Pulmonary: anterior -> posterior
How is the myocardium supplied with blood?
Coronary arteries arise from coronary sinus above aortic valve cusps -> main inflow during dyastole
What does the right coronary artery supply?
RA + RV
SA node
AV node
Posterior IV septum (minority of septum)
What is a right coronary artery (RCA)/left coronary artery (LCA) dominant heart? How common are they?
The dominant artery gives rise to PIVA
60% of individuals = RCA
40% of individuals = LCA
What are the branches of the right coronary artery? What do they supply?
SAN artery (supplies SA node, R + L atria)
Anterior ventricular arteries
Marginal artery (reaches apex)
PIVA (posterior 1/3 of septum)
What does the left coronary artery supply?
LA + LV
AV bundle
R + L bundle branches
Anterior IV septum (majority of septum)
What are the branches of the left coronary artery? What do they supply?
SAN artery (R + LA) PIVA Marginal artery (L ventricle to apex) LAD (R + LV + anterior 2/3rd of septum) Circumflex artery (LA + LV - continues as PIVA in 40% people)
What artery is a common place for atherosclerotic plaque build up?
LAD
Why might you image heart vessels on a angiogram?
Check for stenosis or atherosclerotic plaques
What is the venous drainage of the heart?
Coronary veins drain blood from myocardium -> majority of venous blood drains into RA via coronary sinus (inc. SVC + IVC)
What are the 4 surface anatomical points that map out the heart?
- 2rd R CC 1cm lateral to sternum (RA + SVC)
- 6th R CC 1cm lateral to sternum (RA + IVC)
- 2nd L CC 1cm lateral to sternum (auricle LA + PT)
- 5th L ICS medial to MCL(apex + LV)
Why is surface anatomy of the heart important?
Clinical examination
Interpreting medical images
Guiding surgical approach
Predicting injury
What are the auscultation points of the 4 heart valves?
- Pulmonary: 2nd L ICS lateral to sternum
- Aortic: 2nd 2 ICS lateral to sternum
- Mitral: 5th L ICS MCL
- Tricuspid: 4/5th ICS lateral to sternum
Why are valves listened to in a different place to their actual surface markings?
Listened to just downstream from surface marking as you want to hear how blood goes through the valve to see if its operating properly
What is the main function of the right atrium?
Receives venous blood from upper/lower body + the heart
Important for electrical conduction system of heart - SA + AV node initiate + continue conduction into ventricles
What are the rough bits of the right atrium made from?
Pectinate muscle
What is the fossa ovalis?
Shallow depression that is an embryological remnant of a hole called the foramen ovale from RA to LA that allowed blood to shunt avoiding the lungs as they are not functioning in utero -> when baby takes first birth as pressure changes in heart + lungs closing it
What is the main function of the left atrium?
Receives highly oxygenated blood from lungs via 4 pulmonary veins
Moderator band - component of electrical conduction system
What is the structure of the right ventricle?
Crescent-shaped + thinner wall than LV
Why is the left ventricular wall so much thicker than the right ventricular wall?
Must eject blood into aorta + then to rest of body so needs to be the most muscly
What are the rough parts of the left ventricle called?
Trabeculae carnae (embryological remnant)
What is the function of the conduction system of the heart?
Allows rapid coordinate delivery of cardiac impulse to atrial + ventricular muscles
Explain the electrical conduction system of the heart.
Originate in SA node (pacemaker) -> atria contract -> AV node -> ventricular septum -> R bundle branch -> purkinje fibres that contract ventricles -> atria + ventricles subsequently relax
What might be the consequence of a ventricular septal defect or infarct?
Hole: bundle branches impacted in trajectory or ability to send signal down one side of heart disrupted electrical signals
RCA infarct: necrotic heart tissue along diaphragmatic edge killing the purkinje fibres stopping electrical signal conduction
What is the parasympathetic supply to the heart?
Vagus nerve (CN X) - branches mainly arising in thorax
Postganglionic fibres arise from ganglia on heart
What is the sympathetic supply to the heart?
Top of sympathetic chain (T1-4) descend through neck to heart
Cardiac visceral sensory travel back to CNS with sympathetic nerves
What does the SNS and PNS do to the heart?
SNS: increases HR + contractility
PNS: decreases HR
Why can you get referred cardiac pain?
Cardiac sympathetic signals travel back to T1-4 spinal cord at same time as somatic sensory fibres from periphery causing signals to get crossed
Somatic sensory fibres come back to T1-4 from arm for e.g. causing arm pain in an MI
