Cardiac Functional Anatomy

Atrial and ventricles separated by fibrous skeleton of heart (dense irregular connective tissue). They are only electrically connected by the conducting system.

Right atrium:

1. Forms right aspect of heart
2. IVC, SVC, and coronary sinus drain here
3. One auricle

Left atrium:

1. Forms posterobasal aspect of heart
2. 4x pulmonary veins drain here
3. One auricle

These are separated by the interatrial septum which bears the fossa ovalis

Right ventricle:

1. Concave in shape
2. Contains moderator band (trabeculum containing the RBB)
3. Smooth-walled outflow tract "infundibulum"

Left ventricle:

1. Conical in shape
2. 3x thicker than the RV

Both contain trabeculae (thick outcroppings of myocardium), the largest of which are called papillary muscles and attach to the AV valves with chordae tendinae, preventing regurgitation.

Ventricles separated by the interventricular septum

1. Membranous portion superiorly (thinnest part)
2. Thicker muscular portion basally
3. This causes ventricular interdependence (when one ventricle is distended, the septum bulges into the other ventricle and decreases ventricular compliance)

Tricuspid valve:

1. Deep to the sternum in the midline
2. Anterior, posterior and septal cusps
3. Fibrous ring

Mitral valve:

1. Deep to the sternum in the midline, just superior and left of the tricuspid valve
2. Anterior and posterior cusps
3. Fibrous ring

Pulmonic valve:

1. At the lower border of the 3rd rib at the left sternal edge.
2. Anterior, right, and left cusps
3. Fibrous ring

Aortic valve:

1. At the lower border of the third rib, inferior and to the right of the pulmonic valve
2. Left, right, and noncoronary cusps
3. No fibrous ring; 3 triangular fibrous arches

Cardiac plexus

1. T1-T4 sympathetics
2. Vagus

Left coronary

1. Arises from aorta just distal to the left coronary cusp of aortic valve
2. quickly bifurcates into anterior interventricular (LAD) and left circumflex
3. LCx gives off obtuse marginals
4. LAD gives off diagonals and forms anastomosis with PDA at the apex

Right coronary

1. Arises from the aorta, just distal to right coronary cusp
2. Supplies the SA node in 60%
3. Travels down the right margin of the heart then circles posteriorly
4. Supplies the AV node in 90%
5. Forms the posterior interventricular artery in 85% of people (right-dominance; the remaining 15% are split between arising from the LCx, LAD, or a combination of vessels)

AV node: small group of cells in the superior right atrium

1. Primary pacemaker; regular depolarizations regulated by the \(I_K\) funny current
2. Intrinsic rate: 60-100bpm
3. Regulated by parasympathetics from the cardiac plexus (except post-transplant) and serum catecholamines

Internodal tracts: barely-modified myocardiocytes that aid atrial conduction

AV node: modified myocardial cells at the basoseptal part of the right atrium

1. Central part of AV node slows conduction to allow for AV synchrony; accomplishes this due to lack of fast sodium channels
2. Prolonged refractory period, limiting AV conduction to ~220 beats per minute; this is also under autonomic control by hyper-polarization of cells
3. Automaticity, with an intrinsic rate ~40bpm (these 'junctional' rhythms result in cannon a-waves)

Bundle of His -> right bundle branch and left bundle branch (which becomes left anterior and posterior fascicle) -> Purkinje fibers are all heavily modified myocytes, insulated by fibrous tissue.