Basic Cardiac Anatomy:

Patrick J. Lynch, medical illustrator; C. Carl Jaffe, MD, cardiologist http://creativecommons.org/licenses/by/2.5/ transesophageal echocardiography; TEE; heart anatomy; cardiac anatomy; left ventricle; ultrasound; four chamber view; 4C
Cardiac Structures:

3. Right Atrium

4. Right Ventricle

5. Left Ventricle

6. Conduction System

7. Cardiac Valves

8. Left Ventricular Outflow Tract

9. Ventricular Band (Torrent-Guasp)

10. Coronary Arteries

11. Descriptive Variables

12. Descriptive Variables

Extended Outline

1. Cardiac Skeleton

2. Coronary Arteries

3. Cardiovascular Silhouette

Cardiac Surface Anatomy

Surgical Anatomy Of The Mitral Valve

The mitral apparatus includes the leaflets, annulus, chordae tendineae, papillary muscles, and left ventricle.

A. Leaflets

• The mitral valve has two leaflets, the anterior (aortic) and posterior (mural) leaflets.
• The leaflets are attached directly to the mitral annulus and to the papillary muscles by primary and secondary chordae.

1.Anterior mitral leaflet:

• Is in direct continuity with the fibrous skeleton of the heart.
• This leaflet is contiguous with the left and noncoronary cusps of the aortic valve and the area beneath the intervening aortic commissure, termed the fibrous subaortic curtain.
• Although the anterior leaflet occupies only 35% to 45% of the annular circumference, its leaflet area is almost identical to that of the posterior leaflet.

2.Posterior Leaflet:

• Has two variable indentations or clefts that divide the posterior leaflet into three scallops: the largest or middle scallop, the posteromedial scallop, and the anterolateral scallop.
• Fan-shaped chordae insert into and define the clefts between the individual posterior scallops.
• Motion of the posterior leaflet is more restricted than that of the anterior leaflet; however, both mitral leaflets contribute importantly to effective valve closure.

The surface of the mitral leaflet is divided into three zones corresponding to areas of chordal insertion and leaflet coaptation.

1. The rough zone: is the leading edge of the anterior and posterior mitral leaflets. This zone is the contact surface of the mitral leaflets during systole.
2. The clear zone: is peripheral to the rough zone and represents most of the body of the leaflet; this portion of the mitral valve billows into the atrium during ventricular contraction.
3. The basal zone: between the clear zone and the annulus, receives the insertion of the basal chordae tendineae (tertiary chordae), which originate directly from the trabeculae of the left ventricle. The basal zone is found only on the posterior leaflet.

B. Annulus

• The mitral annulus is the site of leaflet attachment to muscular fibers of the atrium and ventricle.
• The annulus is flexible and decreases in diameter during each systolic contraction by approximately 26%.
• The orifice of the mitral valve also changes shape, from elliptical during ventricular systole to circular during late diastole. This flexibility increases leaflet coaptation during systole and maximizes orifice area during diastole.
• Anteriorly, the annulus is attached to the fibrous skeleton of the heart. This limits its flexibility and its capacity to dilate with mitral regurgitation (MR). The posterior annulus is more flexible and is not attached to rigid surrounding structures. This accounts for the clinical observation that dilation of the annulus occurs posteriorly with MR.
• Important Anatomic Landmarks:

1. The circumflex coronary artery courses laterally around the mitral annulus in the posterior atrioventricular groove.
2. The coronary sinus runs more medially in the same groove.
3. The artery to the atrioventricular node, usually a branch of the right coronary artery, runs a course parallel and close to the annulus of the anterior leaflet near the posteromedial commissure.
4. The aortic valve is situated between the anterior and posterior fibrous trigones. The bundle of His is located near the posterior trigone.

C. Chordae Tendineae

• The chordae tendineae are chords of fibrous connective tissue that attach the mitral leaflets to either the papillary muscles or the left ventricular free wall.
• They often subdivide and interconnect before they attach to the leaflets. The chordae are divided into:

1. Primary chordae: attach directly to the fibrous band running along the free edge of the leaflets. These chordae ensure that the contact surfaces (rough zone) of the leaflets coapt without leaflet prolapse or flail.
2. Secondary chordae: attach to the ventricular surface of the leaflets at the junction between the rough and clear zones. These chordae contribute to ventricular function. Secondary chordae enable the ventricle to contract in an efficient cone-shaped fashion; when secondary chordae are excised, the left ventricle assumes a globular shape.
3. Tertiary chordae: are unique to the posterior leaflet. They arise as strands directly from the left ventricular wall or from small trabeculae to insert into the ventricular surface of the leaflet near the annulus.

D. Papillary Muscles

• The anterolateral and posteromedial papillary muscles each supply chordae tendineae to both leaflets.
• The two groups of papillary muscles subtend the anterolateral and posteromedial commissures and arise from the junction of the apical and middle thirds of the ventricular wall.
• The anterolateral papillary muscle receives a dual blood supply from the anterior descending coronary artery and either a diagonal branch or a marginal branch of the left circumflex artery.
• The posteromedial papillary muscle receives its blood supply from either the left circumflex artery or a distal branch of the right coronary artery.
• Because of the single blood supply to the posteromedial papillary muscle, infarction of the posteromedial papillary muscle is much more common.

E. Left Ventricle

• The posterior left ventricular wall and papillary muscles play an important role in leaflet coaptation and valve competence.
• Papillary muscles are aligned parallel to the ventricular wall and attach via chordae to the free edges of the valve leaflets. These muscles project from the trabeculae and may be single, bifid, or a row of muscles arising from the ventricular wall.
• During isovolumetric contraction the mitral leaflets are pulled downward and together by this interaction. Ventricular dilatation may affect the alignment and tension on the papillary muscles and valve competence.

Cardiac Cellular Structures:

SA NODE:

1. Specialized cells high in the right atrium next to the superior vena cava
2. Pacemaker of the heart with an inherent rate of 60 – 100 beats per minute
3. Richly innervated by parasymapthetic (vagus nerve) and sympathetic system

BACHMANN”S BUNDLE:

1. Intra-atrial tract connecting right and left atrium
2. Conducts impulse from the right to the left atrium

AV JUNCTION:

1. Situated at the anterosuperior portion of the interatrial septum near the tricuspid annulus,  the AV Junction is comprised of the compact AV node and the fast and slow AV nodal pathways on the  atrial side along with the Bundle of HIS on the ventricular side.
2. Inherent rate is 40 -60
3. Innervation by sympathetic as well as parasympathetic nervous system.
4. Slows conduction to allow atrial contents to empty into ventricles before ventricular contraction.

BUNDLE OF HIS AND BUNDLE BRANCHES:

1. Two main branches of the Bundle of HIS – Right and Left Bundle Branches
2. Right Bundle Branch is long and slender.
3. Left Bundle Branch is broad and fans out with 3 fascicles generally.  a. posterior   b.  anterior superior  c.  intraventricular septum
4. Conduction velocity through the HIS-Purkinje system is 3-4 times faster   than through the myocardium
5. HIS and Bundle Branches are supplied by the Left Anterior Descending  and the Posterior Descending coronary arteries.

ACCESSORY  ATRIOVENTRICULAR  CONNECTIONS:

Rapidly conducting accessory AV pathways exist on either right or left side

1.  Usually capable of antegrade and retrograde conduction – about 75% of patients exhibit pre-escitation (manifest bypass tract) on 12 lead ECG in sinus rhythm while 25% conduct retrograde only (concealed bypass tract) and < 2-4% conduct antegrade only.
2. Clinical syndrome: Wolff-Parkinson-White (WPW)  

Slowly conducting accessory AV pathways exist only on the right side

1. Antegrade only conduction via Mahaim fibers – pre-excitation evident on 12 lead only during PSVT – Mahaim PSVT
2. Retrograde only conduction – pre-excitation is NEVER evident on 12 lead ECG is sinus rhythm or in PSVT – Permanent form of Junctional Reciprocating Tachycardia (PJRT)

To see animation of the conduction system of the heart  Click Here .  

There are also several quizes on the cardiac cycle.  Click Here and look at the menu on the left for the quizes.

Labeling exercise of the internal structures of the heart Click Here