Question 2

Outline the anatomy of the cardiac ventricles including the chambers, valves and conduction
elements.

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College Answer

This question expected an outline of the anatomy of the cardiac ventricles. Candidates that broke down the anatomy into subsections with correct and clear descriptions of each component were most
successful. A potential structure to approach this question is included below; 
- position, orientation, relations and characteristics of the chambers including ventricular
interdepence
- internal ventricular structures including muscle type, septum, trabeculae, papillary muscules,
infundibulum and moderator band
- valves and valvular rings’ position, structure and attachments
- conduction elements position and divisions
- blood and nerve supply

Discussion

The structure suggested by the college is excellent, but to fully answer this question with those headings would require a regurgitation of Last's which would probably be beyond most trainees, and in fact this time 89% of them were unable to manage it. What follows is just such a regurgitation, organised according to the college structure. As one can plainly see it would be impossible to do this in ten minutes. What follows after it is an attempt to answer this question within the timeframe, using the absolute minimum of detail.

Position 

  • Right border: from the lower border of the right 3rd costal cartilage to the lower border of the right 6th costal cartilage; it extends just beyond the right margin of the sternum
  • Inferior border: from the right 6th costal cartilage to the apex
  • Apex: normally in the left fifth intercostal space about 9 cm from the midline. 
  • Left border: from apex to lower border of the left 2nd costal cartilage, about 2 cm from the sternal margin.

Orientation

  • Fixed by the greater vessels, but free to move in the pericardium
  • The ventricles are narrower and slightly rotated during systole
  • During full inspiration, the apex descends more than the base, and the heart become more vertical in position

Basic structural anatomy

  • Atria and ventricles are separated by the fibrous skeleton
  • Muscular fibres encircle the chambers in spirals
  • The conducting system is the only connection between the two muscular systems
  • Right atrium:
    • lies between the superior and inferior venae cavae, and forms the right border of the heart
    • Receives the coronary sinus and the venae cava
    • One auricle
  • Left atrium
    • Two auricles
    • Entered by four pulmonary veins
  • Right ventricle:
    • Irregular concave shape
    • Contains the tricuspid valve, which is attached to the fibrous skeleton
  • Left ventricle
    • Conical shape
    • Three times as thick as the right ventricle
  • Interdependence
    • Distension of one ventricle (eg. right) affects the distensibility of the other, impacting on its ability to fill

Internal ventricular structures

  • The septa:
    • Interatrial septum is a thin wall of atrial muscle forming the posterior  wall of the right atrium above the opening of the coronary sinus.
    • Interventricular septum is  a thick muscular wall (equal in thickness to the rest of the left ventricle) attached to the conjoined atrioventricular rings, and is thinner and more fibrous at this attachment (the membranous portion)
  • Trabeculae are irregular muscular columns which project from the inner surface of the ventricles.
  • Papillary muscles are extended trabeculae that are attached to the cusps of the tricuspid and mitral valve by chordae tendinae, and their role is to prevent regurgitation by bracing the mitral and tricuspid valves against prolapse during systole.
  • The infundibulum is a funnel-like sleeve of right ventricular muscle that  forms the RV outflow tract and forms the fibrous ring that serves as the attachment for ther pulmonary valve. 
  • The moderator band, also referred to as the septomarginal trabecula, is a condensation of trabeculae which lies fee from the wall, in the cavity of the RV, attached by its two ends to the interventricular septum and the anterior papillary muscle. It contains part of the right bundle branch of the His system.

Valvular structures

  • Tricuspid valve
    • Position: behind the midline of the lower sternum
    • Structure: three cusps, anterior posterior and septal
    • Attachments: 
      • Fibrous ring that attaches to the cardiac fibrous skeleton
      • The edges and ventricular surfaces of the cusps attach to the chordae tendineae
  • Pulmonary valve
    • Position: behind the left border of the sternum, at the third costal cartilage, slightly above the position of the aortic valve
    • Structure: three cusps, anterior, right and left
    • Attachments: fibrous ring at the top of the infundibulum attaches to the crescent-shaped arches of the cardiac skeleton at the root of the pulmonary artery 
  • Mitral valve
    • Position: behind the midline of the lower sternum, but higher and to the left of the tricuspid valve
    • Structure: two cusps, anterior and posterior; the anterior cusp sits between the mitral and aortic orifices; thicker and smaller than the tricuspid
    • Attachments:
      • fibrous ring formed by the anterior and posterior fila coronaria arising from the corresponding left and right fibrous trigone of the cardiac fibrous skeleton
      • Chrodae tendinae insert into the edges of the leaflets
  • Aortic valve
    • Position: behind the left border of the sternum, at the third costal cartilage, slightly below the position of the pulmonary valve
    • Structure: three cusps, right left and posterior 
    • Attachments: no specific fibrous ring; instead three fibrous triangular arches act as points of attachment for the cusps.

Conductive elements

  • SA node: small bundle of cells in the superior right atrium
  • Internodal tracts: lines of minimally modified myocytes arranged in parallel along the atrial wall
  • AV node: small bundle of cells at the septal part of the right atrial base
  • His-Purkinje system: parallel-aligned large heavily modified myocytes, spreading out from the central Bundle of His, along two bundle branches, and into hundreds of terminal ramifications. Insulated by fibrous tissue until the last divisions.

Blood supply

  • Right coronary artery: lies in the groove between the right ventricle and the right atrium; runs anteriorly, and then posteriorly to encircle the heart
  • Left main: short; divides into tow branches:
    • Left anterior descending (descends anteriorly, as the name suggests)
    • Left circumflex (descends posteriorly in the atrioventricular groove)
  • Anastomosis between the arteries exists at the arteriolar level

Venous drainage

  • Coronary sinus:
    • Lies in the posterior part of the atrioventricular groove
    • Receive tributaries from the five cardiac veins, which lie next to the coronary arteries:
      • The great cardiac vein (next to the LAD)
      • The middle cardiac vein (next to the PDA)
      • The small cardiac vein (next to the RCA)
      • the posterior vein of the left ventricle
      • the oblique vein of the left atrium (along the posterior surface of the left atrium)
  • The anterior cardiac vein is separate from the coronary sinus, and contributes minimally (the sinus gets almost all of the blood)
  • Also, there are venae cordis minimae or Thebesian veins, which are small veins in the walls of all four chambers of the heart that open directly into the respective chambers. They have trivial relevance, except to be mentioned by students of physiology when they discuss the causes of shunt. 

Lymphatic drainage

  • Lymph channels drain back along the coronary arteries
  • They emerge from the fibrous pericardium along with the aorta and pulmonary trunk
  • Ultimately, empty into the tracheobronchial lymph nodes and mediastinal lymph trunks

Nerve supply

  • The heart is innervated by the cardiac plexus:
    • Multiple contributions from multiple nerves:
      • The superficial part of the cardiac plexus is formed by the union of the inferior cervical cardiac branch of the left vagus and the cardiac branch of the left cervical sympathetic ganglion
      • The deep part of the cardiac plexus receives contributions from:
        • the right vagus
        • the left vagus
        • a branch from each recurrent laryngeal nerve
        • sympathetic fibres from the remaining five cervical sympathetic ganglia
        • from the upper five or six thoracic sympathetic ganglia of both sides
  • Supplied territories include:
    • SA node (accelerator or depressor of the heart rate)
    • AV node 
    • Bundle of His
    • Vasomotor to coronary arteries

Now: this description is 1076 words, or 6769 characters, which according to the speed records described by Hardcastle & Matthews (1991) would take 42 minutes to put down on paper. What follows is a more achievable description, which eshews the suggested college structure in favour of something more condensed which still answers the question

  • Right ventricle: 
    • Irregular concave shape
    • Forms the right border of the heart
    • Anterior, retrosternal
    • Moderator band (contains right bundle branch) connects the septum and the anterior papillary muscle
    • Infundibulum (RV outflow tract) forms the orifice for attachment the pulmonary valve
  • Left ventricle: 
    • Conical shape, three times as thick as the RV
    • Forms the left border and apex of the heart
    • Lays posteriorly and to the left
  • Both ventricles:
    • Trabeculated (internal musclualr ridges)
    • Papillary muscles connect to tricuspid and mitral valve edges  by chordae tendinae
    • Interdependence: increased filling of one ventricle decreases the filling of the other
  • Valves:
    • Tricuspid: 3-leaflet, attached to fibrous ring 
    • Pulmonary: 3-leaflet, attached to infundibulum
    • Mitral: 2-leaflet, attached to anterior and posterior fila coronaria
    • Aortic: 3-leaflets attach to  three fibrous triangular arches (no ring)
    • Chordae tendinae tether the leaflets of the tricuspid and mitral valves
  • Condictuing system:
    • from superior right atrium (SA node),
    • via internodal tracts along the atrial wall, 
    • to AV node in the interatrial septum, 
    • down to the bundle of His in the ventricular septum,
    • along bundle branches and their ramifications to the ventricular muscle
  • Blood supply:
    • Right coronary artery 
      Left main: short; divides into two branches: left anterior descending and left circumflex 
      Anastomosis between the arteries exists at the arteriolar level
    • Venous drainage into the coronary sinus 
  • Nerve supply:
    • Cardiac plexus (both vagus nerves, recurrent laryngeal nerve, sympathetic fibres from five cervical ganglie ad upper thoracic sympathetic ganglia)

That version is 234 words, or 1599 characters, which means that a veteran police interviewer in North Birmingham of the early 1990s would have been able to just squeeze this into ten minutes, writing legibly at a speed of about 160 characters per minute.

References

Hardcastle, R. A., and C. J. Matthews. "Speed of writing." Journal of the Forensic Science Society 31.1 (1991): 21-29.

LE WALD, LEON T. "The Relation of the Heart, Pericardium and the Heart Valves to the Anterior Chest Wall." Archives of Surgery 6.1_PART_I (1923): 89-100.

Weinhaus, Anthony J., and Kenneth P. Roberts. "Anatomy of the human heart." Handbook of cardiac anatomy, physiology, and devices. Humana Press, 2005. 51-79.

Plus whatever anatomy textbook you've currently got propping up the wonky edge of the washing machine.