T1 L7: Middle mediastinum

• Boundaries of the middle mediastinum?

  anterior and posterior: pericardium

  lateral: mediastinal pleura

  superior: transverse thoracic plane

  inferior: diaphragm

  
• Middle mediastinum contents

  Organs: Heart, pericardium

  Nerves: Phrenic

  Veins: vena cavae, pulmonary veins, cardiac veins

  Arteries: ascending aorta, pulmonary trunk, coronary arteries

  
• Right atrium structures

  Vessels: superior and inferior vena cava

  Crista terminalis: boundary between smooth and rough area (muscle)

  Fossa ovalis: remnant of foetal foramen ovale

  Coronary sinus: return of all coronary deoxygenated blood

  Sinoatrial node: located in junction between atrial wall and superior vena cava. site of generation of initial cardiac pulse

  
• Right ventricle structures

  Tricuspid valve

  Chordae tendineae (heart strings)

  Papillary muscles (valve muscles)

  Trabeculae carneae (tissue attached to heart strings to aid in valve closure)

  Moderator band (pathway within muscle which allows perkunjee fibres to contract evenly)

  Pulmonary valve (semilunar)

  
• Left atrium structures

  pulmonary veins (4 expected, but variations occur)

  Fossa ovalis: embryological remnant of foramen ovale

  Bicuspid (mitral) valve

  
• Left ventricle structures

  Bicuspid valve - left atrioventricular

  Chordae tendineae - heart strings

  Papillary muscles - valve muscles

  Trabeculae carneae - tissue attached to heart strings

  Aortic valve

  
• Coronary artery branches

  Right coronary artery branches:

  • right marginal
  • posterior interventricular

  Left coronary artery branches:

  • anterior interventricular
  • circumflex
  • left marginal

  
• Potential anatomical variance

  • anastomoses of anterior interventricular artery and posterior interventricular artery
  • coronary artery dominance (the coronary artery that provides blood flow to the posterior interventricular artery, and hence majority of the ventricles). Can be RCA, LCA or both dominant.
• Cardiac veins

  mirror a similar path to the coronary arteries

  transport blood to coronary sinus

  blood emptied into right atrium

  
• Clinical interventions to blockage in myocardium?

  Bypass surgery

  vessels used:

  Great saphenous vein

  • similar diameter to coronary arteries
  • can easily be harvested due to its superficial location
  • minimal number of valves

  Internal thoracic artery

  • local to the area
  • arterial vessel

  
• Pericardium

  attached to great vessels superiorly

  phrenic nerve travels over surface

  attached to diaphragm inferiorly

  Functions:

  protects heart from overfilling (cardiac distension)

  retains heart in position (pericardio-sternal ligaments)

  
• Layers of the pericardium

  from out to in:

  Fibrous pericardium (external)

  Serous pericardium (internal):

  • parietal (wall) layer
  • Pericardial cavity - contains serous fluid, allows frictionless movement during heart beats
  • visceral layer / epicardium

  
• Clinical relevance of the pericardium

  Transverse Sinus:

  cavity located between outflow and inflow vessels of the heart

  used in surgery to clamp the outflow of blood from heart

  
• Cardiac innervation - conduction

  Sinoatrial (SA/pacemaker) Node

  location: junction between SVC and right atrium

  Atrioventricular (AV) node

  location: interatrial septum close to coronary sinus opening

  
• Fibrous skeleton of the heart

  provides insulation between atria and ventricles

  adds delay to conduction of impulses

  only site of conduction is the AV node

  allows adequate filling of ventricles before contraction

  
• Autonomic innervation of the heart

  Sympathetic fibres from sympathetic trunk levels T1 - T4 enter cardiac plexus

  travel to SA node

  Parasympathetic fibres from Vagus nerve enter cardiac plexus and then travel to SA node
• Cardiac plexuses

  Superficial cardiac plexus (inferior to aortic arch, anterior to pulmonary arteries)

  Deep cardiac plexus (anterior to bifurcation of trachea)

  
• Which blood vessels converge to form the superior vena cava?

  braciocephalic veins
• How does the organisation of the right ventricle go?

  tricuspid valve → chordae tendinae → papillary muscles → trabecular carnae → moderator band
• Cusps of the aortic valve?

  left

  right

  posterior
• Cusps of the pulmonary valve?

  left

  right

  anterior
• Where do coronary arteries arise from?

  aortic valves

  right coronary artery from right cusp

  left coronary artery from left cusp
• How does the left coronary artery go?

  left coronary artery:

  • circumflex branch → left marginal branch
  • anterior interventricular branch
• How does the right coronary artery go?

  right coronary artery:

  • right marginal branch
  • posterior interventricular branch
• What two branches of the coronary arteries form anastamoses in 90% of people?

  anterior interventricular branch of left coronary artery and posterior interventricular branch of right coronary artery

  
• What is coronary artery dominance?

  coronary artery which gives rise to the posterior interventricular artery

  anatomical variance

  70% individuals - RCA

  15% individuals - LCA

  15% individuals - RCA/LCA codominant

  
• Where do the coronary veins transport blood to?

  coronary sinus

  emptied into right atrium

  
• Conduction through heart pathway?

  SAN → AVN → AV bundle (bundle of His) → moderator branch → purkinjee fibres