Middle Mediastinum, Heart Flashcards
What are the boundaries of the middle mediastinum?
Within the inferior mediastinum, it is between the transverse thoracic plane (sternal angle to disc between T4 and T5) and the diaphragm
What are the contents of the middle mediastinum?
Pericardium + heart, roots of great vessels (ascending aorta, pulmonary trunk, SVC), arch of azygos vein, main bronchi, and phrenic nerves accompanied by pericardiacophrenic vessels
What is the fibrous pericardium? What is it attached to?
The external sac of dense connective tissue which lies deep to mediastinal parietal pleura. It is bound to central tendon of diaphragm and is fused with tunica adventitia of great vessels at level of sternal angle
What is the functional significance of the fibrous pericardium?
Protects against abrupt overfilling of the heart, as in pericardial effusion.
What is the serous pericardium / what are its two layers?
The internal sac filled with pericardial fluid, it is a single epithelial layer composing two layers - parietal + visceral
Parietal - lines the internal surface of the fibrous pericardium
Visceral - lines external surface of heart - it is the epicardium
What is the epicardium?
The visceral layer of serous pericardium which sits ontop of the myocardium
What is the pericardial cavity?
A potential space between the parietal and visceral layers of serous pericardium which allows the heart to move freely within the sac
What two sinuses does the reflection of serous pericardium onto the great vessels make?
transverse pericardial sinus - runs anterior to superior vena cava and posterior to pulmonary trunk (artery) + aortic arch
oblique pericardial sinus - runs between pulmonary veins and inferior vena cava where you get stuck as a cul-de-sac
What is the primary blood supply to the pericardium? Secondary supply?
Pericardiacophrenic - branch of ITA running with phrenic nerve
Smaller contributions from: musculophrenic, as well as bronchial, esophageal, and superior phrenic branches from thoracic aorta
Coronary arteries from aortic arch supply visceral layer of serous pericardium only
What is the venous drainage of the pericardium?
Mainly pericardiacophrenic veins
- tributaries of brachiocephalic or internal thoracic
- azygos venous system
What is the innervation of the pericardium?
Phrenic nerve - primary source of sensory fibers, can lead to referred paid in supraclavicular region
Vagus nerve - function unknown
Sympathetic trunks - vasomotor
What is the clinical importance of the transverse pericardial sinus?
It is the place where a surgical clamp or ligature can be placed around aorta & pulmonary trunk, while tubes of coronary bypass machine are inserted to divert circulation of blood during cardiac surgery
What is pericarditis?
Inflammation of pericardium, can cause chest pain and result in pericardial friction rub
What is pericardial effusion?
Leaking of fluid from pericardial capillaries into pericardial cavity, building up fluid and leading to cardiac tamponade because the heart cannot expand and ventricles will have limited bloodflow
What is cardiac tamponade?
compression of the heart by an accumulation of fluid in the pericardial sac
What is cardiomegaly?
Heart slowly increasing in size, allowing for enlargement to occur without compression
What is hemopericardium?
Blood enters the pericardial cavity via stab wound or weakened area of heart muscle after heart attack. Compression can lead to cardiac tamponade and also engorged veins in face / neck when the superior vena cava compresses
What is pericardiocentesis?
Drainage of serous fluid from pericardial cavity, relieving cardiac tamponade
What are the three layers of the heart?
Epicardium - Visceral layer of serous pericardium
Myocardium - Cardiac muscle
Endocardium - Endothelium + subendothelial connective tissue, also covers valves
Where does the heart sit anatomically?
Posterior to sternum, costal cartilages, and medial ends of ribs 3-5 on left side. It sits obliquely, with 2/3 to left and 1/3 to right of median plane
What is the apex of the heart and where is it?
Left inferolateral part of left ventricle, posterior to left 5th intercostal space. It points at a 45 degree angle to medial plane and more anteriorly than base
What is the base of the heart and where is it?
It is the posterior aspect of the heart, mainly composed of left atrium, faces towards vertebral bodies of T6-T9, between the bifurcation of the pulmonary trunk called the coronary groove
What are the right, left, inferior, and superior borders of the heart?
Right - right atrium, between SVC and IVC
Left - left ventricle and left auricle
Inferior - right ventricle
Superior - right and left atria + auricles
What is the sternocostal surface of the heart?
Anterior surface - Mainly the right ventricle
What is the diaphragmatic surface of the heart?
Inferior surface - mainly left ventricle, related to central tendon
What is the pulmonary surface of the heart?
Left surface - mainly left ventricle
What are the sources of blood to the right atrium? Where do they open to (what level)
SVC - 3rd costal cartilage
IVC - 5th costal cartilage
Coronary sinus - between right AV opening and IVC opening - receives venous drainage from heart vessels
Anterior cardiac veins of right atrium - minor contribution
What are the pectinate muscles? What is their division point?
Muscles forming the rough, anterior wall of the right atrium. They extend into the right auricle, a muscular pouch increasing the capacity of the atrium.
Division point: Terminal sulcus, internally existing as the crista terminalis
What is the sinus venarum and what does it form?
It the primordial right atrium, forms the smooth, thin-walled posterior part of right atrium, separated from muscular part by terminal sulcus.
What structure is in the interatrial septum and what is it a remnant of?
Fossa ovalis - remnant of foramen ovale which opened the right atrium to the left atrium in the fetus
What is the conus arteriosus?
The superior taper of the right ventricule into arterial cone which leads to pulmonary trunk via pulmonary semilunar valve
What are trabeculae carneae?
Irregular muscular elevations in the left and right ventricles
What is the supraventricular crest?
The ridge separating muscular (rough) inflow area from smooth conus arteriosus (outflow)
Where is the right AV orifice and how is backflow prevented?
4/5th intercostal level. Backflow is prevented by tricuspid valve. The three cusps are held by tendinous cords attached to papillary muscles, which attach to the ventricular wall and will contract during systole to prevent prolapse of the valve into the right atrium due to high pressures.
What are the two parts of the interventricular septum and why?
Membranous - continuous with fibrous skeleton, posterior 1/3 of IV septum
Muscular - Thick portion the will bulge into the right ventricle because of higher blood pressure in the left ventricle. Anterior 2/3 of IV septum
What does the septomarginal trabecula form?
The moderator band, it is attached to inferior interventricular septum and the base of the anterior papillary muscle. It acts as a shortcut for the right bundle of the AV bundle, thus playing a role in the conduction system of the heart
What are ventricular septal defects? Where do they happen and what do they cause?
Most common site is the membranous part of the IV septum, where it would combine with the muscular part
Represents 25% of all congenital heart disease, and can be of varying size.
Since BP is higher in left ventricle, blood will be shunted back into right ventricle and lead to increased pulmonary BP and ultimately pulmonary disease
What is pulmonary stenosis?
Valve cusps of semilunar valve can fuse, leading to a narrowing. This restricts pulmonary outflow
What is the blood flow into the left atrium, and how does its auricle compare to the right atrium?
4 pulmonary veins (2 from each side)
The muscular auricle is smaller,
Left atrium has smooth wall and muscular portion similar to the right atrium.
Why is the left atrium clinically important?
It is the site of thrombi (immobile blood clots) formation on the wall of the left atrium. They can become emboli (mobile blood clots) which can occlude an artery
How does the left ventricle compare to the right ventricle with respect to size, location, and shape?
Left ventricle walls are 2-3x thicker since arterial pressure is higher in systemic vs pulmonary circulation, and left ventricle does more work than right
Left ventricle forms the apex of the heart, and makes up almost all of the left border + diaphragmatic surface.
Left is more round. Right is more crescent shaped
How do the papillary muscles compare in left vs right ventricles?
There are only 2 in the left, since it has the mitral (biscupid) valve, but they are MUCH bigger than the right ventricle because the pressure is so much higher in the left.
What is the name for the left semilunar valve, and where does it open into?
Known as the aortic valve, opens into aortic orifice which supplies the ascending aorta
What are the aortic sinuses and what do they give rise to?
They are three recesses in the ascending aorta just superior to the aortic valve.
Left and right coronary arteries arise from the aortic sinuses, the posterior sinus has nothing which arises from it
What is the most frequently disease valve of the heart? How can this happen?
The mitral (biscupid valve) Nodules on valve - irregular blood flow Scarring / shortening of valve - leads to blood regurgitating into left atrium (mitral insufficiency) during systole and heart murmur
What is aortic insufficiency?
Defective aortic valve - blood regurgitates back into left ventricle. Leads to heart murmur and collapsing pulse
What is the one cusp of the triscupid valve you need to remember?
The septal cusp. Both bicuspid and tricuspid valves have anterior and posterior cusps.
What are the cusps of the aortic + pulmonary valves?
Aortic = left, right, posterior Pulmonary = left, right, anterior
What are the branches of the right coronary artery?
SA nodal branch - supplies SA node - 60%
Right marginal branch - supplies right border of heart
AV nodal branch - supplies AV node - 80%
Posterior interventricular branch (posterior descending)
What does the right coronary artery supply?
Right atrium, most of right ventricle, part of left ventricle + IV septum, SA node (60%), AV node (80%)
What does the left coronary artery supply?
Left atrium, most of left ventricle + IV septum, part of right ventricle, and SA node (40%)
What are the branches of the left coronary artery?
SA nodal branch - SA node (40%)
Anterior IV artery - supplies left ventricle and IV septum
Circumflex branch - supplies posterior surface, runs along coronary groove
Left marginal branch - branches from the circumflex branch and supplies left ventricle
Where does the posterior IV branch arise from normally, and when would this be different?
normally arises from right coronary artery
15% of the time the left coronary artery is dominant, and it arises from the circumflex branch
Where can the circumflex artery come off sometimes directly from?
Normally it’s from the left coronary artery, but it can sometimes arise directly from the right aortic sinus
Why are coronary artery branches considered end arteries?
They supply the myocardium without functional overlap
Small branches do anastomose, however, and this may be important in coronary artery disease
What is coronary insufficency?
Insufficient blood flow to coronary arteries, can lead to ischemic heart disease, often characterized by angina pectoris - chest pain in substernal region and down medial side of left arm + forearm
What is the venous drainage of the heart?
Drains via coronary sinus (primary), as well as anterior cardiac veins of right ventricle, which also drain directly into right atrium.
Coronary sinus receives blood from great cardiac vein anteriorly, and middle and small cardiac veins posteriorly.
How is lymph drained from the heart?
Myocardium and subepithelial connective tissue drains into the subepicardial lymphatic plexus, travels in coronary groove and empties into inferior tracheobronchial lymph nodes
What is the SA node? Where is it?
The pacemaker of the heart, located just deep to the epicardium, at junction of superior vena cava and right atrium. Sends impulse 70x per minute
Sends impulses to atria first
What is the AV node? Where is it?
Just posteriorinferor of interatrial septum, near the opening of the coronary sinus. It is ABOVE the tricuspid valve
Will send impulses through the ventricles second, since it sends fibers to both ventricles
What is diastole and what valves are opened / closed during that time?
Diastole - ventricular filling
AV valves - open
Semilunar valves - closed
What occurs in the final moments of diastole?
Atria contract to expel final blood into the ventricles
What is the isovolumetric contraction? What sound does this cause?
Ventricles first contraction in systole, which closes the AV valves.
This causes the “lub”
What is systole and what valves are opened / closed during that time?
Systole - ventricular ejection
AV valves - closed
Semilunar valves - opened
What is the isovolumetric relaxation and what sound does that does that cause?
The end of systole, when the semilunar valves close
causes the “dub” sound
What marks the beginning of diastole?
Closure of semilunar valves. There is a subsequent opening of AV valves to let blood start flowing back into ventricles
What does sympathetic stimulation of the heart do?
Increases the heart’s rate and force of contraction, dilates coronary arteries (inhibits parasympathetic constriction), thus supplying more oxygen and nutrients to myocardium during increased activity
What does parasympathetic stimulation of the heart do?
Slows the heart rate, reduces the force of the heartbeat, and constricts the coronary arteries, saving energy
Why does ischemia (lack of blood supply) of the heart lead to pain of skin on medial aspect of upper limb?
Ischemia causes sensory pain endings to be stimulated in the myocardium, although the heart is insensitive to touch and temperature.
Afferent pain fibers enter the spin at T1 - T4/T5, especially on the right side, and your brain sometimes thinks this is coming from upper limb or chest
What are the cardiac plexuses?
The sympathetic / parasympathetic stimulation to heart. Located anterior to tracheal bifurcation, posterior to ascending aorta, and superior to the bifurcation of the pulmonary trunk
