W2: Heart Flashcards
Discuss pericardium
The pericardium is a sac-like structure that surrounds the heart, fixing it within the middle mediastinum.
Superiorly, the pericardium is continuous with the tunica adventitia of the great vessels, and inferiorly with the dia- phragm.
The outermost layer is a fibrous layer consisting of dense collagenous tissue interspersed with elastic fibrils.
The inner surface of the fibrous pericardium is lined by simple squamous epithelium, called the serous parietal pericardium, which reflects onto the external surface of the heart to form the epicardium (or serous visceral pericardium).
The pericardium has a number of functions, including:
- Fixation of the heart in position
- Protection of the heart from bacterial/viral infection
- Lubrication of heart movement
- Resist over-distension of the heart
The pericardial cavity is a fluid-filled space between the parietal and visceral layers of the serous pericardium, and normally contains between 15-20ml of pericardial fluid. Pathological accumulation of fluid within this space is known as a pericardial effusion, which, when impairing cardiac function, is referred to as cardiac tamponade (occurs due to increase pressure on chambers causing reduced output).
Order can be remembered - Fart Police Smell Villains → Fibrous layer of pericardium, Parietal layer of serous, Serous fluid, Visceral layer
It is innervated by branches of the phrenic nerve - common source o freferred pain e.g. shoulder pain as a result of pericarditis
What is the transverse pericardial sinus?
Passgae through the pericardial cavity
Space between reflections of the serous pericardium, which is posterior to the ascending aorta and pulmonary trunk and anterior to the superior vena cava
It therefore separates the heart’s aterial outflow from its venous inflow
Clamping these vessels through this space completely stops ventricular outflow during cardiac operations - e.g. coronary artery bypass grafting
What is coronary artery bypass grafting?
CABG
Blood vessels can be taken from your leg (saphenous vein), inside your chest (internal mammary artery), or your arm (radial artery).
Once all the graft vessels have been removed, your surgeon will make a cut down the middle of your chest so they can divide your breastbone (sternum) and access your heart.
During the procedure, your blood may be rerouted to a heart-lung bypass machine. This takes over from your heart and lungs, pumping blood and oxygen through your body.
Your heart will be temporarily stopped using medicine while your surgeon attaches the new grafts to divert the blood supply around the blocked artery.
After the grafts have been attached, your heart will be started again using controlled electrical shocks.
Your breastbone will then be fixed together using permanent metal wires and the skin on your chest sewn up using dissolvable stitches.
Which side oxygenated and which deoxygenated?
Right = deoxygenated
Left - oxygenated
Describe the internal divisions forming the 5 surfaces of the heart
Anterior (or sternocostal) – Right ventricle.
Posterior (or base) – Left atrium.
Inferior (or diaphragmatic) – Left and right ventricles.
Right pulmonary – Right atrium.
Left pulmonary – Left ventricle.
Heart sulci
The coronary sulcus (or atrioventricular groove) runs transversely around the heart – it represents the wall dividing the atria from the ventricles. The sulcus contains important vasculature such as the right coronary artery.
The anterior and posterior interventricular sulci can be found running vertically on their respective sides of the heart. They represent the wall separating the ventricles.
Discuss walls of the heart
Can be divided into three distinct layers: the endocardium, myocardium, and epicardium
Endo - lines cavities - loose connective and simple squamous epithlielial
Subendocardial layer - joins endo and myo - vessels and nerves of heart conductive system - e.g. purkinje fibres
Myo - involuntary striated
Epicardium - formed by visceral layer of pericardium - connective tissue and fat
What is the musculature of the heart built upon?
Underlying fibrous skeleton
Forms outflow tracts and creates a non-conducting band - anulus fibrosis between atria and ventricles
What does the right atrium do? Discuss right atrium generally
Drains blood from superior and inferior vena cavae (& coronary veins via coronary sinus orifice) and transmits blood to right ventricle through tricuspid valve
Internal anterior wall is trabeculated, formed of pectinate muscle
Right atrial appendage (auricle) curves around the origin of the aorta - increases total volume
Interior can be divided into two:
- The posterior wall is smooth, forms a region known as the sinus venarum
- Atrium proper - anterior, includes right auricle - rough muscular walls formed by pectinate muscles
These two regions are separated by the crescent shaped crista terminalis (muscular ridge)
Discuss interatrial septum?
Separates atria
In the right atrium = fossa ovalis - remnant of foramen ovale which allowed blood to bypass the lungs
Closes upon first breath
Can cause atrial septal defect - patent foramen ovale - can lead to right heart failure
Discuss right ventricle
The right ventricle, which forms much of the anterior surface of the heart, collects blood from the right atrium after it passes through the tricuspid valve, which has three cusps.
Blood goes to pulmonary artery
Can be separated into an inflow and an outflow portion
The inflow tract of the right ventricle is trabeculated with muscular ridges known as the trabeculae carnae.
Three sets of papillary muscles attach to the inferior surfaces of the tricuspid valve leaflets via chordae tendinae, which contract to prevent the valve cusps prolapsing into the right atrium during ventricular contraction.
The smooth walled outflow tract terminates at the pulmonary (semilunar) valve at the level of the 3rd costal cartila
Discuss left atrium
Recieve oxygenated blood
The left atrium, located on the posterior surface of the heart, drains blood from the four pulmonary veins and is predominantly smooth walled, aside from the trabeculated wall within the left atrial appendage.
Due to the stagnant nature of blood within this appendage, blood clots may form. As such, the left atrial appendage is a common source of thrombi that cause strokes and other blockages of the vascular tree
Discuss left ventricle
The left ventricle, which forms the cardiac apex, receives blood from the left atrium via the mitral (bicuspid) valve.The mitral valve has 2 cusps.
Like the right ventricle, the left ventricle is trabeculated by trabeculae carnae and contains papillary muscles that prevent mitral valve prolapse during ventricular contraction.The aortic outflow tract is non-muscular and terminates at the aortic (semilunar) valve at the level of the 3rd intercostal space.
Discuss heart sounds, including surface points where they are best heard
When examining the cardiovascular system, it is essential to listen to the heart sounds with a good stethoscope to identify pathology affecting the heart valves.The first heart sound (S1) is produced by vibrations generated by closure of the mitral and tricuspid valves, corresponding to the end of diastole and beginning of ventricular systole. S1 is typically high-pitched and described as a “lub”.The mitral valve is best heard over the apex of the heart, whilst the tricuspid valve is best heard over the fourth intercostal space at the left sternal edge.
The second heart sound (S2) is produced by the closure of the aortic and pulmonary valves at the end of systole, as the arterial; blood pressure starts to exceed the ventricular pressure.The aortic valve is best heard at the second right intercostal space whilst the pulmonary valve is best heard at the second left intercostal space.The sound is described as a “dub”.
What are valves formed from?
Connective tissue and endocardium
Describe AV valves
The mitral and tricuspid valves are supported by the attachment of fibrous cords (chordae tendineae) to the free edges of the valve cusps. The chordae tendineae are, in turn, attached to papillary muscles, located on the interior surface of the ventricles – these muscles contract during ventricular systole to prevent prolapse of the valve leaflets into the atria.
There are five papillary muscles in total. Three are located in the right ventricle, and support the tricuspid valve. The remaining two are located within the left ventricle, and act on the mitral valve.
Discuss semilumar valves
- Close at the beginning of ventricular diastole
- Both have 3 cusps
Discuss innervation of heart
The cardiac plexuses supply autonomic innervation to the heart via the cardiac nerves from the Vagus and recurrent laryngeal nerves (parasympathetic) and the cervical and upper thoracic sympathetic ganglia (sympathetic,T1-T5).
The sympathetic fibres cause an increase in heart rate and contractile force, whereas the para- sympathetic fibres act to slow the heart rate.
Where is the SAN? What does it do and what artery supplies it?
The sinoatrial (SA) node is located in the crista terminalis, which separates the smooth and rough walls of atria
This node acts as the pacemaker of the heart and is usually supplied by an atrial branch of the right coronary artery
Where is the AVN? What happens after?
Atrioventricular septum (by anulus fibrosus) → Bundle of His → along left and right bundle branches → Purkinje fibres (in subendocardial surface) which spread across the ventricular myocardium
Located near opening of coronary sinus
Delays impulses by 120ms
Discuss cardiac pain
Sensory fibres innervating the heart pass along the sympathetic nerves to terminate in the upper thoracic spinal cord. As such, ischaemic pain from the heart is referred to the dermatomes of T1-T5, sensed as a severe, crushing central chest paint that classically spreads to the inner aspect of the left arm and occa- sionally the left neck and jaw.
Where do the coronary arteries arise from?
The right and left aortic sinuses
Small openings in the aorta behind right and left flaps of aortic valve
Describe and draw the branching structure of the coronary arteries
LCA branches into left anterior descending (also known as anterior interventricular artery). This is the artery most likely to be occluded
LCA also gives off left marginal artery (LMA) and left circumflex artery (Cx). In 25% people left circumflex also contributes to the posterior interventricular artery
The RCA branches to form the right marginal artery anteriorly
In 80-85% of people, it also branches to form the posterior interventricular artery posteriorly
What is the venous drainage of the heart mostly due to? Where does this empty into?
Mainly through the coronary sinus - large venous structure in posterior aspect of the heart
Cardiac veins → coronary sinus → right atrium
What are the main tributaries of the coronary sinus?
Great cardiac vein (anterior interventricular vein) – the largest tributary of the coronary sinus. It originates at the apex of the heart and ascends in the anterior interventricular groove. It then curves to the left and continues onto the posterior surface of the heart. Here, it gradually enlarges to form the coronary sinus.
Small cardiac vein – located on the anterior surface of the heart, in a groove between the right atrium and right ventricle. It travels within this groove onto the posterior surface of the heart, where it empties into the coronary sinus.
Middle cardiac vein (posterior interventricular vein) – begins at the apex of the heart and ascends in the posterior interventricular groove to empty into the coronary sinus.
What is coronary dominance?
Coronary dominance is determined by the coronary artery that gives rise to the posterior interven- tricular artery.The right coronary artery is dominant in 70% of the population, whereas the left coronary artery is dominant in around 10% of the population.Approximatively 20% of people have co-dominance, meaning that both the right coronary artery and the circumflex branch of the left coronary artery supply the posterior interventricular artery
At what phase of the cardiac cycle is the heart recieving its oxygen?
Diastole, when the semilunar valves are closed
What is the coronary sulcus?
Groove separating atria from ventricles
Describe distribution of arteries branching from the RCA
The RCA passes to the right of the pulmonary trunk and runs along the coronary sulcus before branching. The right marginal artery arises from the RCA and moves along the right and inferior border of the heart towards the apex. The RCA continues to the posterior surface of the heart, still running along the coronary sulcus. The posterior interventricular artery then arises from the RCA and follows the posterior interventricular groove towards the apex of the heart.
Describe the distribution of branches from the LCA
The LCA passes between the left side of the pulmonary trunk and the left auricle. The LCA divides into the anterior interventricular branch and the circumflex branch. The anterior interventricular branch (LAD) follows the anterior interventricular groove towards the apex of the heart where it continues on the posterior surface to anastomose with the posterior interventricular branch. The circumflex branch follows the coronary sulcus to the left border and onto the posterior surface of the heart. This gives rise to the left marginal branch which follows the left border of the heart.
Where is the apex beat usually?
5th space, midclavicular line
Describe shunts in foetal heart
Foramen ovale – shunts highly oxygenated blood (from the umbilical veins) from the right atrium to the left atrium.
Ductus venosus – connects the umbilical vein to the inferior vena cava, therefore carries highly oxygenated blood. Allows it to bypass the liver. Shunting oxygenated blood to the brain. Occurs because most of the critical functions of the liver are effectively undertaken by the placenta.
Ductus arteriosus – passes between the pulmonary trunk and the arch of the aorta. Functions to protect the developing lungs from circulatory overload and carries moderately oxygenated blood. The foetus’ lungs are fluid filled and non-functioning - allows blood to bypass
Describe changes to foetal blood flow at birth
The foramen ovale closes to form the fossa ovalis – this closure forces the entire right heart’s output tothe lungs.
- When the pulmonary circulation opens, pressure in left atrium increases
The ductus arteriosus constricts – this occurs when the blood PO2 exceeds 50mmHg, as the foetus takesits first breaths.
- Forms the ligamentum arteriosum
- Thought to be due to increased bradykinin in the circulating blood which causes muscular contraction in the walls
The umbilical vein constricts – this prevents blood loss via the umbilicus.The ductus venosus forms the ligamentum venosum (liver), whilst the umbilical vein forms the ligamentum teres, the free edge of the falciform ligament of the liver
Atrial Septal Defects
Characterised by a defect within the inter-atrial septum, allowing blood to pass from the left atrium back into the right atrium.
These defects may result from a failure of adhesion between the flap valve of the foramen ovale and the septum secundum at birth, or due to a failure of fusion of the septum primum with the endocardial cushions.
Depending on the size of the shunt, this can lead to right sided overload, pulmonary hypertension and atrial arrhythmias.
Ventricular Septal Defects
Characterised by a defect in the interventricular septum, most commonly within the membranous por- tion of the septum. Shunting of blood from the left ventricle to the right ventricle may lead to increased pulmonary blood flow, reduced cardiac output and raised pulmonary artery pressure.
The left and right Bundles of His may be at risk.
Tetralogy of Fallot
One of the most common cyanotic heart conditions, characterised by a combination of four related heart defects that commonly occur together:
1) Large ventricular septal defect
2) Overriding aorta - aorta is positioned directly over a ventricular septal defect, instead of over the left ventricle - looks like deoxygenated blood is going into the aorta
3) Pulmonary stenosis - narrowing of pulmonary valve
4) Right ventricular hypertrophy
Severe cyanosis may be present at birth. Full surgical repair is required within the first year of life.
What is a sign of cardiac hypertrophy?
Displacement of apex beat
At what stage does the foramen ovale form and what does it form from?
7 weeks
Perforaitons in the dorsal part of the septum primum called foramen secundum
The septum secundum grows
The edges of the septum secundum fuse with cushion tissue leaving an oval aperture, the foramen ovale, which, with the foramen secundum, remains patent until birth, forming a flap-like valve.
Explain why the left recurrent laryngeal nerve is found in the thorax?
During development, the link between the branchial arch arteries descends into the thorax and ends up as the ductus areteriosus connecting the aortic arch to the pulmonary trunk.
What are the circulatory consequences of the first breath?
Expansion of the lung and the associated rise in alveolar oxygen concentration causes loss of pulmonary vascular hypoxic vasoconstriction. As a result of this, there is a dramatic fall in pulmonary arterial pressure and hence in the pressure on the right side of the heart.
Coarctation of the Aorta
A narrowing of the aorta, which typically occurs at the junction of the aortic arch and the descending aorta. This constriction forces the heart to pump harder than usual, in order to propel blood beyond the stenosis. This results in high blood pressure in the head, neck and upper limbs, and low blood pressure in the lower limbs. Consequences of coarctation include premature heart disease, cerebral aneurysms, organ failure, arterial rupture and death.
Thoracic Aortic Aneurysm
This is a ballooning of the aorta above the diaphragm, which predisposes the vessel to rupture due to weakening of the vessel wall. If a rupture occurs, the mortality rate is as high as 80%. 20% of these aneurysms are linked to family history. Aneurysms may be treated using either open surgery or endovascular stent graft insertion.
Abdominal Aortic Aneurysms
As in the thorax, the aorta can balloon outwards to form aneurysms within the abdomen. Abdominal aortic aneurysms (AAA, “Triple As”) are far more common than thoracic aortic aneurysms and all men aged 65 are invited to an ultrasound screening scan to identify those at risk. Aneurysms can interfere with the blood supply of many of the structures reliant on the abdominal aorta, including the kidneys and GI tract. Rupture of these aneurysms can be rapidly fatal.
Coronary Artery Bypass Graft (CABG)
The left internal thoracic (mammary) artery can be used for a coronary artery bypass operation. This can involve freeing the distal part of the artery and then anastomosing it to the coronary artery distal to the blockage, re-perfusing the myocardium with blood.
Where is the best place to listen to sounds from the left AV valve?
Apex
What is the azygos vein and where is it seen on an axial CT?
Either side of vertebral column
Drains viscera in mediastinum
2 main tributaries are hemiazygos vein and accessory hemiazygos vein
The apex of the heart is formed by…
The left ventricle
During a routine check-up, a doctor discovers a heart murmur in a 53-year-old male patient. He refers the patient to a cardiologist who decides to perform a transoe- sophageal echocardiogram (TOE).Which of the following structures is located closest to the oesophagus?
Apex of the heart
Ascending aorta
Pulmonary valve
Left atrium
Right auricle
Left atrium
How many pulmonary veins are there?
4
Draw heart valves looking down on the heart
The vertebral level at which the inferior vena cava pierces the diaphragm to enter the right atrium
T8
