Middle Mediastinum & Heart Flashcards
Contents of the middle mediastinum
1) Heart
2) Pericardium
3) Great vessels
4) Phrenic nerves with vessels
Name the 3 layers of the pericardium
Outer = fibrous Middle = parietal serous Inner = visceral serous
Name the attachments of the pericardium.
- Sternal
- Diaphragmatic
- Adventitia of great vessels
Pericardial cavity
Potential space btwn parietal serous + visceral serous pericardium
Pericardial effusion
Excess fluid in pericardial cavity
*can occur if heart is perforated
Cardiac tamponade
Rapid accumulation of fluid in the pericardial cavity that compresses the heart
Pericardiocentesis
- Drainage of fluid (-centesis) from the pericardial cavity
* Wide-bore needle inserted through the 5th or 6th intercostal space near the sternum or infrasternally
Transverse pericardial sinus
Recess just behind aorta + pulmonary trunk
Oblique pericardial sinus
Recess between pulmonary veins (posterior side)
Name the 4 borders of the heart.
Superior:
- Right & left atria
Right:
- Right atrium
Inferior:
- Mostly right ventricle
- Some left ventricle
Left:
- Mostly left ventricle
- Some left atrium
Surface anatomy of superior border of heart
Inferior of 2nd right rib to superior of 3rd left rib
Surface anatomy of right border of heart
3rd right costal cartilage to 6th right costal cartilage
Surface anatomy of inferior border of heart
6th right costal cartilage to 5th left intercostal space
Surface anatomy of left border of heart
Line connecting superior & inferior borders
Point of Maximal Impulse (PMI)
Apex of heart being forced against anterior thoracic wall during contraction
Where is the PMI located?
5th left intercostal space at mid-clavicular line
Aortic valve auscultation
Right upper sternal border
Pulmonary valve auscultation
Left upper sternal border
Tricuspid valve auscultation
Left sternal border (4th intercostal space)
Mitral valve auscultation
5th intercostal space around at PMI (midclavicular line)
Right atrium (RA)
- Forms right border of heart
- SVC + IVC + coronary veins drain into RA
- Has smooth wall (sinus vernarum) + rough, muscular wall (pectinate muscles)
Crista terminalis
Internal separation of sinus veranrum (smooth part of RA) from right auricle
Coronary sinus
- Where coronary veins drain into RA
- Located between IVC orifice & AV orifice
Pectinate muscles
Muscles lining RA (+ right auricle)
Tricuspid valve
- Guards right AV orifice
- Between RA + RV
- 3 cusps
*Septal, anterior, posterior
Fossa ovalis
- Remnant of foramen ovale & its valve during fetal development
- If doesn’t close –> patent foramen ovale (PFO)
Chordate tendinae
Attach tricuspid cusps to papillary muscles
Papillary muscles
- Contract to prevent prolapse of tricuspid valves
- Connect to valves via chorade tendinae
- 3 total (corresponding to tricuspid cusps)
Trabeculae carnae
Irregular muscular ridges lining RV + LV
Conus arteriosus
Part of RV that tapers into arterial cone
Supraventricular crest
Thick muscular ridge separating ridged muscular wall of inflow chamber from smooth wall of conus arteriosus in outflow chamber in RV
Septomarginal trabecula (moderator band)
- Curved muscular bundle running from inferior part of IV septum to base of anterior papillary muscle
- Contains part of right bundle branches of AV bundle
- Allows for coordinated contraction of anterior papillary muscle
Pulmonary valve
- Located at apex of conus arteriosus
- Leads into pulmonary trunk
- 3 cusps
*R, L, anterior –> opposite of aortic valve
Pulmonary trunk
- Carries deoxygenated blood to lungs
- Bifurcates into R&L pulmonary arteries
- Level of T4
Right auricle
- Small muscular pouch in RA
- Overlaps aorta
- Increases capacity of RA
*Look here for origin of RCA
Left auricle
- Small muscular pouch in LA
- Overlaps pulmonary trunk
- Has pectinate muscles in its walls
*Look here for origin of LCA
Left atrium (LA)
- Makes up most of left border of heart
- Has large smooth wall & small muscular part (left auricle w/ pectinate muscles)
- Pulmonary veins (4 - R&L superior, R&L inferior) drain into LA
- Slightly thicker than RA
Right ventricle (RV)
- Forms most anterior & inferior border of heart
- Gets blood from RA through right AV orifice
Interatrial septum
- Separates atria
- Where fossa ovalis is located
Right AV orifice
RA –> RV
Left AV orifice
LA –> LV
Left ventricle (LV)
- Forms apex & left border of heart
- Most of diaphragmatic surface
- 2-3x thicker & does more work than RV due to higher BP
- Gets blood from LA through left AV orifice
Aortic vestibule
Area leading to aortic orifice
Aortic orifice
LV –> aorta
Aortic valve
- Opens into aorta
- 3 cusps
*R, L, posterior
Mitral valve
- Bicuspid valve from LA –> LV
- Also attached to chordae tendinae & papillary muscles
*Anterior, posterior
Aortic sinuses
- Spaces between wall of aorta & each cusp of aortic valve
- R&L contain openings into RCA & LCA
*Posterior sinus is NONCORONARY
Name components of blood flow in relation to the heart.
- SVC + IVC + coronary veins drain doxy blood into RA
- RA to RV through tricuspid valve
- RV U-shaped turn to pulmonary trunk through pulmonary valve
- Bring deoxy blood to lungs
- Pulmonary veins bring oxy blood to LA
- LA to LV through mitral valve
- LV U-shaped turn to aorta through aortic valve
- Oxy blood to rest of body through aorta
- RCA & LCA at aortic sinuses bring oxy blood to heart
Four main functions of fibrous skeleton of heart
1) Hold valves open
2) Site of attachment of leaflets and cusps
3) Electrical insulation
4) Site of attachment of myocardium
Name 3 layers of the heart wall
1) Epicardium (thin external - formed by visceral serous pericardium)
2) Myocardium (thick middle - cardiac muscle)
3) Endocardium (thin internal - lining membrane that also covers valves)
Review conduction pathway of heart
1) SA node initiates impulse + causes atria to contract
2) Impulse travels to AV node by myogenic conduction
3) Then travels down AV bundle
4) Divides into R+L bundle branches at junction of muscular + membranous parts of IV septum
5) Proceed on each side of muscular IV septum deep to endocardium
6) Ramify into subendocardial branches (Purkinje fibers)
7) Stimulate ventricle walls & papillary muscles to contract
*Own conduction system - no need to connect nerves in heart transplant
SA node
- Pacemaker of heart
- Initiates heartbeat
- Located heart junction of SVC + RA
AV node
- Located near opening of coronary sinus in the interatrial septum
- Receives impulse from SA node & distributes to AV node bundle
AV node bundle
- Only bridge of conduction between atrial + ventricular myocardium
- Through fibrous skeleton of of heart
- Along membranous part of IV septum
Interventricular (IV) septum
- Strong separation between ventricles
- Both muscular + membranous
Right & left bundle branches
- Proceed on each side of muscular IV septum deep to endocardium
Subendocardial branches (Purkinje fibers)
- Extend into walls of ventricles
- Stimulate ventricle walls + papillary muscles to contract
Describe the cardiac cycle
- Begins w/ ventricular elongation + filling (diastole)
- Ends w/ ventricular shortening + emptying (systole)
Lub-dub sounds
- Lub = blood from atria to ventricles
- Dub = ventricles expelling blood from heart
When does blood flow into the coronary arteries?
Only during diastole
Right coronary artery (RCA)
What are its 4 main branches?
What does it supply?
- Arises from right aortic sinus
4 branches:
1) SA nodal branch
2) Right marginal branch
3) AV nodal branch
4) PDA
Supplies:
1) RA
2) Most RV + some LV
3) IV septum
4) SA node
5) AV node
SA nodal branch
- 1st ascending off of RCA
- Supplies SA node
Right marginal branch
- Branch off of RCA that runs along acute angle of heart
- Does not reach apex of heart
- Supplies right border of heart
AV nodal branch
- Branch off of RCA at crux of heart
- Supplies AV node
Posterior descending artery (PDA)
- Posterior branch off of RCA (or LCA depending on dominance)
- Goes towards apex
- Supplies both ventricles + IV septum
Left coronary artery (LCA)
What are its 2 main branches?
What does it supply?
- Arises from left aortic sinus
Branches:
1) Left anterior descending (LAD)
2) Left circumflex (LCX)
Supplies:
1) LA
2) Most of LV + some RV
3) Most of IV septum including AV bundle
* SA node (in 40% of people
Left anterior descending (LAD) branch
- Anterior branch of LCA
- Passes along IV sulcus to apex
- Supplies both ventricles + IV septum
*Sometimes branches into lateral diagonal branch
Left circumflex (LCX) branch
- Branch of LCA
- Follows coronary sulcus around left border to posterior surface
- Terminates before reaching crux
*Sometimes branches into left marginal branch
How does blood drain from coronary veins into heart?
- Small + middle drain into great
- Great drains into coronary sinus –> RA
Pericardiacophrenic arteries
- Supplies pericardium, diaphragm, & phrenic nerve
- Runs w/ phrenic nerve
Total arterial revascularization (bilateral IMA + radial artery)
- Use IMAs/radial artery to bypass blockage
- Right IMA usually routed behind aorta + pulmonary arteries through transverse sinus
Arterial dominance
- Origin of PDA
- Could be from RCA, LCA, or both
Where should you insert a needle for pericardiocentesis?
Wide-bore needle inserted through the 5th or 6th intercostal space near the sternum or infrasternally
