1. Applied anatomy of the heart Flashcards
Briefly describe an overview of the innervation of the heart and where these nerves lie
Innervated by the autonomic system
Supplied by cardiac plexus of nerves - lies anterior to the bifurcation of the trachea (carina) and posterior to the arch of the aorta
Contains parasympathetic from vagus, sympathetic from sympathetic trunk and visceral general afferents
These fibres extend from the plexus to the coronary vasculature and to the conducting system of the heart i.e. the SAN
Describe the parasympathetic innervation of the heart and give the pathway of innervation
Acts to slow the heart rate and reduce the force of contraction
Cardioinhibitory centre in the medulla
Release of Ach
Extends to primary neurone from cell bodies in the reticular formation of the medulla
These synapse with the vagus nerve
Post ganglionic neurones then extend to the SAN and the AVN
Describe the sympathetic innervation of the heart and give pathway of innervation
Acts to increase the heart rate and to increase the force of contraction
Via the cardioacceleratory centre in the medullary reticular formation
Descend down through white matter tracts in the lateral horn of the grey matter (the autonomic region)
Preganglionic sympathetic neurones then emerge from the thoracic spinal cord - from T1 to T4
Extend to SAN and AVN `
SO briefly compare the pathway of sympathetic and parasympathetic innervation of the heart
Parasympathetic synapses with and reaches the heart via the vagus nerve
Sympathetic is via the spinal cord - lateral horns of T1 to T4 and involves pre and post ganglionic neurones
Describe the medulla as the site of control for cardiac innervation
Medulla is the primary site in the brain to regulate sympathetic and parasympathetic outflow to the heart and blood vessels
Medullary centre is modified by the hypothalamus and higher centres
Describe the nuclei of the vagus nerve and where the parasympathetic outflow arises
Has three nuclei - dorsal motor nucleus, nucleus ambiguus, solitary nucleus
Parasympathetic outflow comes mainly from neurones in nucleus ambiguus and some from dorsal motor nucleus
Briefly describe cardiac pain (angina) and how it is felt
This is pain caused by ischaemia
Stimulate sensory nerve endings in the myocardium - nociceptors on the ends of visceral afferent nerve fibres can recognise a build up of lactate
These travel through teh sympathetic trunk and enter the spinal cord through T1 to T4
This means that the angina is not felt in the heart and is referred (T1 to T4)
Where can cardiac pain be referred?
Generally referred to the skin supplied by T1 to T4 i.e. the medial upper arm and the neck/jaw
Also to the epigastrium T5 to T9
What are the branches of the right coronary artery?
Right marginal
Posterior descending
What are the branches of the left coronary artery?
Left anterior descending (LAD)
Left marginal
Left circumflex
What region of the heart does the right coronary artery supply?
Right ventricle
Right atrium - SAN and AVN
What region of the heart does the left coronary artery supply?
Left ventricle
Left atrium
Interventricular septum
What is the interventricular septum and what is it’s structure?
The curved slanting wall that separates the right and left ventricles of the heart - composed of a muscular lower part and a thinner more membranous part
What is the blood supply to the interventricular septum?
Supplied by both the right and left coronary arteries - left anterior descending and the posterior descending
What is the most common variation of the coronary arteries?
The origin of the posterior descending artery - whether it originates from the right or left coronary artery (circumflex)
70-85% right dominance
8-15% left dominance
Give the location of chest leads for an ECG
V1 - right sternal edge, 4th intercostal space
V2 - left sternal edge, 4th intercostal space
V3 - halfway between V1 and V2, at the level of the left 5th rib
V4 - left 5th intercostal space midclavicular line
V5 - left intercostal space, mid-axillary line
V6 - left 5th intercostal space, mid axillary line
Which regions of the heart do the following leads correspond to?
- II, III, aVF
- I, aVL
- V1, V2,
- V3, V4
- V5, V6
- Inferior
- Lateral
- Septal
- Anterior
- Lateral
Which heart valves are open during diastole/systole?
Aortic and pulmonary and open during systole
Mitral and tricuspid are open during diastole
What is valvular disease and how can it be caused?
Any disease involving the loss of function of any of the heart valves
Inflammation of the valve e.g. due to infection (most common) Ageing, ischaemic heart disease Fibrosis and calcification (most common) Stenosis Regurgitation Rheumatic disease
What are the four types of valvular disease?
Mitral regurgitation
Aortic stenosis
Mitral valve stenosis
Aortic regurgitation
Describe mitral regurgitation
Most common type
Mitral valve does not close properly during systole
SO rather than all blood going up to the aorta from the ventricle, some goes back into the atrium
Leads to an overload of blood volume in the left atrium
Overall increased end diastolic volume and reduced cardiac output
This can lead to atrial enlargement and also to left ventricle dilation due to an increased preload
Describe aortic stenosis
Also occurs during systole
One of the loudest – heard at the right second intercostal space
The aortic valve is stenotic and so the left ventricle must generate an increased pressure to overcome the increased afterload created
Leads to left ventricular concentric hypertrophy due to the overload i.e. the wall of the left ventricle increases the size of the chamber decreases
Hypertrophied myocardium has a reduced compliance and a decreased coronary blood flow reserve – can lead to systolic and diastolic failure
Describe aortic regurgitation
During diastole
The aortic valve fails to close properly
So increased build up fluid in the left ventricle and the left ventricle dilates – the volume overload leads to an increased preload
The left ventricle becomes very dilated
Describe mitral valve stenosis
Diastolic murmur
Left atrium must generate a higher pressure to overcome the increased afterload
Leads to atrial enlargement and increased atrial pressure – can also cause pulmonary oedema and can lead to AF
The ventricular filling is reduced and this leads to a reduced cardiac output
Enlarged left atrium can lead to strokes and emboli entering the circulation
How is pulmonary oedema caused?
Left sided heart failure increases hydrostatic pressure the venous end and so all the blood is not drawn away from the arterial end to the venous end due to a lack of a pressure gradient - this results in pulmonary oedema
When might pulmonary vs. systemic oedema occur and how do these present?
Systemic oedema will occur in right sided heart failure and presents as swelling at the ankles
Pulmonary oedema will occur in left sided heart failure and presents as e.g. respiratory crackles and orthopnoea
How will congestive heart failure present in terms of oedema?
Patient will present with symptoms of both right and left sided failure i.e. pulmonary and systemic oedema
Define ‘chronotropic drug’ and give the different types
Chronotropic drugs alter the heart rate and rhythm by affecting the electrical conduction system of the heart e.g. altering the rhythm produced by the SAN
Positive chronotropes - increase the heart rate
Negative chronotropes - decrease the heart rate
Define ‘inotropic drugs’ and give the different types
These are drugs that alter the force of the contraction of the heart muscle
Positive inotropes - increased myocardial contractility
Negative inotropes - decrease myocardial contractility
Which region of the brain do parasympathetic neurones to the heart extend?
What do these neurones synapse to?
Medulla - the cardioinhibitory centre
Synapse onto the vagus nerve
From which region of the brain do the sympathetic neurones to the heart extend?
Medulla - cardioacceleratory centre in the reticular formation
Which part of the spinal cord to sympathetic neurones to the heart travel in?
Travels in the lateral horn of the grey matter - autonomic part
Which part of the grey matter in the spinal cord is the autonomic region?
Lateral horn
Which vertebral levels do the sympathetic neurones to the heart extend from?
Thoracic region - T1 to T4
What structure acts to modify the medulla in the brain?
The hypothalamus
Also other higher centres
Parasympathetic outflow to the heart comes from which of the vagus nuclei?
Nucleus ambiguus mainly
Small amount from the dorsal motor nucleus
What is the blood supply to the AVN?
From the posterior descending artery - variance of whether this is left or right coronary artery
Where is the left anterior descending artery located?
Right apex
What is the significance of an atheroma in the LAD?
An atheroma here will be of more dire consequences than anywhere else
