Lecture 21 Middle Mediastinum and Heart

Pericardium

Pericardium

serous membrane surrounding the heart

visceral pericardium (epicardium)

attached to the heart

parietal pericardium

attached to fibrous pericardium

amount of serous fluid between pericardium layers

about 15ml - 50ml

Fibrous pericardium

not serous
-third layer
-purpose it to anchor the heart inferiorly to the diaphragm and superiorly to the sternum

Pericardial Sac

surrounds the heart and helps prevent overfilling.
-superior attachment - the great vessels (pulmonary trunk, aorta, superior vena cava)
-inferior attachment - diaphragm

transverse pericardial sinus

used by the cardiac surgeons to pass a surgical clamp or placing a ligature around the great arteries
-Functional purpose is to allow the intrapericardial portion of the two great elastic arteries to expand posteriorly during cardiac systole

Oblique pericardial sinus

extends behind to left atrium and between the left and right pulmonary veins

blood supply to the pericardium

arterial supply comes primarily from the pericardiophrenic artery

innervation to the pericardium

from 3 sources
-Phrenic nerve - somatic sensory afferents (pain, pressure, temp)
- Sympathetic trunk - vasomotor input
- Vagus nerve - unclear function

Pericardial effusion

when normal levels of serous fluid exceed the normal range
-signs and symptoms depend on the accumulation rate of the serous fluid

fast pericardial effusion

puts large amount of pressure on the heart and causes heart failure or cardiac tamponade

slow pericardial effusion

time allow for a pericardiocentesis procedure

Pericarditis

inflammation of the pericardium, usually caused by a viral infection

Pericardiocentesis

surgical puncture to aspirate fluid from the sac surrounding the heart
-substernal approach - most common and direct access to the pericardial sac
-parasternal approach
-apical approach

what structures are they avoiding when accessing from the parasternal and apical approach?

Internal thoracic artery and phrenic nerve

Fossa ovalis

remnant of foramen ovale of fetal heart
in the septum of the atria (interatrial septum)

conus arteriosis

opening to big arteries

nodal tissue

initiates the heartbeat

conducting fibers

rapidly conducting the signal throughout the heart

Sinoatrial node

the heart beat is initiated here
-pacemaker of the heart
-sympathetic fibers increase the heart rate
-Parasympathetic fibers decrease the heart rate

stimulation of the SA node

-Sympathetic fibers from the T1-T6 synapse in cervical ganglion before passing to the cardiac plexus
-Parasympathetic fibers from the vagus nerve pass through the cardiac plexus

conduction of the heart

signal moves from the SA node through the muscles of the atria
-AV node is stimulated and then distributes the signal to the AV bundle (spreads to right and left)
-The bundles spread on each side of the interventricular septum
-Finally, signal spreads along the lateral sides of the ventricles (Purkinje fibers)

Electrocardiogram

used to measure electrical conduction of the heart

Heart block

damage to the conducting system of the heart
-location depends on severity of the block
-complete block or left or right bundle branch block

complete heart block

most severe
-a block between the SA and AV node

Cardiac pacemaker

treatment for arrhythmias
-can be dual chamber or in 3 chambers
-regulates conduction signal of heart
-Restores synchronous rhythm between atrial and ventricular chambers
(acts as a new AV node and can respond to small changes in the body)

Atrial fibrillation

uncoordinated twitching of the atria vs. rhythmic contractions
-Ventricles can follow with uncoordinated rhythms
-Can be treated with medication (Beta Blockers)

Ventricular fibrillation

uncoordinated twitching and lack of contractility of the ventricles; reduced blood flow
-Can be fatal due to loss of cardiac output and damage to the conducting system

Implantable cardioverter Defibrillator

treatment for defibrillator
-delivers a shock to stop all electrical activity and heart movement
-Seconds later the heart will "reset" and the SA node should deliver normal rhythm