Cardiac Anatomy for Surgeons

DR. REZWANUL HOQUEMBBS, MS, FCPS, FRCSG, FRCSEd

Associate Professor

Department of Cardiac Surgery

BSMMU

The Cardiovascular System: • Consists of the heart plus all the blood vessels • Transports blood to all parts of the body in two 'circulations': pulmonary

(lungs) & systemic (the rest of the body)

Heart• Hollow, muscular organ • 4 chambers: 2 atria (right & left) & 2 ventricles (right & left)

Blood returning from the body enters the right atrium (via the inferior & superior vena cavas). From there, blood flows into the right ventricle, which then pumps blood to the lungs (via the pulmonary artery). Blood returning from the lungs enters the left atrium (via pulmonary veins), then the left ventricle. The left ventricle then pumps blood to the rest of the body (systemic circulation) via the aorta.  

Pathway of Blood Through the Heart and Lungs

Structure of outer layer

• Fibrous pericardium• Serous pericardium• Parietal pericardium• Visceral pericardium ( epicardium)

Pericardium is the coelomic sac around the heart

Pericardial cavity

PericardiumProtects and anchors the heart

Prevents overfilling of the heart with blood

Allows for the heart to work in a relatively friction-free environment

Common diseases- Pericarditis, Pericardial effusion, Constrictive pericarditis

Pericardial reflection• The parietal layer of serous pericardium is

continuous with the visceral layers of serous pericardium around the roots of the great vessels. These reflections of serous pericardium occur in two locations:

• one superiorly, surrounding the arteries, the aorta and pulmonary trunk;

• the second more posteriorly, surrounding the veins, the superior and inferior vena cava and the pulmonary veins.

• The zone of reflection surrounding the veins is 'J-shaped' and the cul-de-sac formed within the 'J', posterior to the left atrium, is the oblique pericardial sinus.

• A passage between the two sites of reflected serous pericardium is the transverse pericardial sinus. This sinus lies posteriorly to the ascending aorta and the pulmonary trunk, anteriorly to the superior vena cava, and superiorly to the left atrium.

Heart-introduction

• The heart is a hollow muscular organ of a somewhat conical form; it lies between the lungs in the middle mediastinum and is enclosed in the pericardium. It is placed obliquely in the chest behind the body of the sternum and adjoining parts of the rib cartilages, and projects farther into the left than into the right half of the thoracic cavity, so that about one-third of it is situated on the right and two-thirds on the left of the median plane.

• The heart, in the adult, measures about 12 cm. in length, 8 to 9 cm.

in breadth at the broadest part, and 6 cm. in thickness. Its weight, in the male, varies from 280 to 340 grams; in the female, from 230 to 280 grams. The heart continues to increase in weight and size up to an advanced period of life; this increase is more marked in men than in women.

Heart Wall

Epicardium – visceral layer of the serous pericardium

Myocardium – cardiac muscle layer forming the bulk of the heart

Fibrous skeleton of the heart – crisscrossing, interlacing layer of connective tissue

Endocardium – endothelial layer of the inner myocardial surface

External heart –Anterior view

External heart-posterior view

Cardiac chamber-right atrium

• Inlet vessels (3): inferior vena cava, superior vena cava, coronary sinus

• Crista terminalis• Right auricle• Musculi pectinate ( pectinate muscles)

( primitive atrium)• Sinus venarum• Interatrial septum• Fossa ovalis ( foramen ovale)• SA and AV nodes• Tricuspid valve ( right ventricle)• Triangle of Koch

· Tendon of Todaro · Inferior isthmusTendon of Todaro

Interatrial septum

Schematic drawing showing the location of different types of ASD, the view is into an opened right atrium. HV: right ventricle; VCS: superior caval vein; VCI: inferior caval vein; 1: upper sinus venosus defect; 2: lower sinus venosus defect; 3: secundum defect; 4: defect involving coronary sinus; 5; primum defect.

Cardiac chamber- left atrium• Left Atrium• Left auricle ( pectinate muscles)• Valvule of foramen ovale• Bicuspid valve ( mitral valve)• ( left ventricle)• Anterior and posterior cusps

Cardiac chamber-right ventricle

• Conus arterious ( infundibulum) ( pulmonary trunk)

• Trabeculae carneae• Septaomarginal trabeculae (moderator

band) ( anterior papillary muscle)• Papillary muscles• Anterior papillary anterior and

posterior cusps of tricuspid• Posterior papillary posterior and

septal cusps of tricuspid• Septal papillary anterior and septal

cusps of tricuspid• Chordae tendineae• Pulmonary valve ( pulmonary trunk

lungs pulmonary veins left atrium)

 

Right ventricle• a) Inlet portion supports tricuspid valve

b) Trabecular sinus portion (main body of the RV) · Moderator band · Medial papillary muscle (of conus) c) Outlet portion · Infundibular (Conal) septum (separates semilunar valves) · Crista supra ventricularis - separates sinus (chamber) from outlet portion of the ventricle · Septal band (tabecula septomarginalis)

• · Parietal band (ventriculo-infundibular fold) · Pulmonary valve

Anatomic positions of VSD Outlet defect (a)Papillary muscle of the conus (b)Perimembranous defect (c);Marginal muscular defects (d); Central muscular defects (e); Inlet defect (f);Apical muscular defects (g).

The crista supraventricularis gives origin to two large muscular bands, the septal band (SB), which courses along the interventricular septum and the parietal band (PB), which is located along the free wall of the right ventricle. The septal band is shown as a prominent muscle trabecula along the upper portion of the interventricular septum. The septal band also gives rise to the medial tricuspid papillary muscle and continues toward the apical region as the moderator band. Together, the septal and moderator bands make up the septomarginal trabecula along which the right bundle branch travels. The moderator band inserts into the base of the anterior papillary muscle. 

Parietal band

• A schematic presentation of the three main anatomic components of the interventricular septum as seen from the morphologic left ventricle (A) and the morphologic right ventricle (B).

• septum of the atrioventricular canal;

• septum of the muscular septum; and

• parietal band or distal conal septum.

VSD

Anatomic drawing showing the location of the different types of ventricular septal defects. Sub-pulmonary defects are caused by deficiency of the conal septum. Membranous defects are located behind the septal leaflet of the tricuspid valve. Atrio-ventricular (AV) canal type defects are caused by deficiency of the endocardial cushion component of the inter-ventricular septum. Muscular defects can occur in any portion of the muscular septum.

Pulmonary valve

Pulmonary valve - consists of three semilunar cusps with free edges projecting upward into the lumen of the pulmonary trunk.

The free superior edge of each cusp has a middle, thickened portion, the nodule of the semilunar cusp, and a thin lateral portion, the lunule of the semilunar cusp.

Left Ventricle

• Thick wall Inlet portion supports mitral valve Anterior and posterior papillary muscles Outlet portion beneath aortic valve

• Trabeculae carnae• Chordae tendinae• Aortic valve (contrast

structure/function with atrioventricular valves)

• Left, right, noncoronary semilunar cusps

• Nodules

Aortic valve

• The opening from the left ventricle into the aorta is closed by the aortic valve. It consists of three semilunar cusps with the free edge of each projecting upward into the lumen of the ascending aorta..

• Between the semilunar cusps and the

wall of the ascending aorta are pocket-like sinuses-the right, left, and posterior aortic sinuses. The right and left coronary arteries originate from the right and left aortic sinuses. Because of this, the posterior aortic sinus and cusp are sometimes referred to as the noncoronary sinus and cusp.

Aortic root

• The aortic root may be defined as the portion of the left ventricular outflow tract which supports the leaflets of the aortic valve, delineated by the sinotubular ridge superiorly and the bases of the valve leaflets inferiorly. It comprises the sinuses, the aortic valve leaflets, the commissures, and the interleaflet triangles.

• The sinuses are expanded portions of the aortic root which are confined proximally by the attachments of the valve leaflets and distally by the sinotubular junction. They are named according to the coronary arteries arising from them—right, left, and non-coronary. The sinotubular junction, delineating the superior aspect of the aortic root, is circular and composed of primarily elastic tissue, and it supports the peripheral attachments of the valve leaflets

Diagrammatical representation of the aortic root: (a) sinotubular junction; (b) basal ring (surgical annulus); (c) the sinuses of Valsalva.

Underwood M J et al. Heart 2000;83:376-380

Copyright © BMJ Publishing Group Ltd & British Cardiovascular Society. All rights reserved.

Aortic root

Cardiac Valvesa) Aortic valve- wedged between mitral and tricuspid, pulmonary

valve separated b) Mitral valve

· Anterior leaflet wide, short, 1/3 of annular circumference

· Posterior leaflet narrow, long, 2/3 of annular circumference

· Papillary muscles and chordae tendineae

c) Tricuspid valve · Anterior, posterior, septal

leaflets d) Aortic and pulmonary valves

· 3 cusp, semilunar · Sinuses of Valsalva

· Nodulus Aranti and lunulae

Marginal chordae, rough zone chordae, basal chordae, fan shaped commissural chordae.The major chordae supporting a leaflet insert either into its free edge, or the area beyond the free edge on the ventricular aspect up to the line of closure of the leaflet. This area between the free edge and the line of closure is termed the rough zone in contradistinction to the area between the line of closure and the basal attachment of the leaflet which is easily trans illuminated and is smooth. It is important to remember that the line of closure of a leaflet is not its free edge.

Chordae tendineae

Fibrous skeleton of the Heart

The fibrous skeleton of the heart is a connective tissue frame which functions to electrically isolate the atria from the ventricles. The atrioventricular conducting system is the only electrical connection between the atria and the ventricles in a normal heart. Also, it provides rigidity to prevent the dilatation of individual valves or outflow tracts. Finally, it provides a point of attachment for valve leaflets and the myocardium. The myocardium extends from the fibrous skeleton in a series of spirals that progress to the apex.

Atrioventricular Valve Function

Semilunar Valve Function

Left Ventricular Outflow Tract · Semilunar aortic valve· Fibrous annulus is not a ring · Interleaflet triangles · Aortoventricular junction · Sinuses of Valsalva · Sinotubular junction (sinus rim) = junction of sinus of Valsalva and ascending aorta · Posterior commissure relates to mid point of anterior leaflet of mitral valve

Ventricular Band (Torrent-Guasp)· Biventricular myocardial band extending from pulmonary artery to aorta.· Two loops: basal and apical· Double helix derived from spiral fold· Apex has figure-8 configuration

Myocardial band

Function of myocardial band

Conduction System· Sinoatrial node - anterolateral RA

· Interatrial conduction pathways- not well defined and somewhat controversial

· Atrioventricular node - triangle of Koch · Bundle of His - AV node to membranous septum, usually located on the inferior/posterior wall of the

membranous septum· Left bundle branch - left ventricular septal surface into

multiple branches · Right bundle branch - below medial papillary muscle

via septal and moderator bands to anterior papillary muscle

· Inferior isthmus (right atrium)· Bachman's bundle (left atrium)

Coronary Arteries · Right and left coronary arteries · Dominance is determined by origin of posterior descending artery· Dominance is usually right or balanced; 10-15% prevalence of left dominance· Balanced pattern occurs when there is no particular dominance · Septal blood supply 2/3 left anterior descending, 1/3 posterior descending · Sinus node artery from RCA - 55% · AV node artery from U bend at crux, just beyond the takeoff of the PDA if circulation is right dominant

Coronary Arteries a) Right and Left coronary arteries originate from proximal aorta via respective ostiab) Common branches from main coronary arteries· Left main– LAD, LCX, Ramus intermedius· Left anterior descending-- septal and diagonal arteries· Circumflex– Obtuse marginal arteries (and PDA in left dominant hearts)· Right coronary artery-- acute marginal, AV nodal, sinus node arteries (and PDA in right dominant hearts)

Ven

ou

s d

rain

age

of

Hea

rt

Branches from both the parasympathetic and sympathetic systems contribute to the formation of the cardiac plexus. This plexus consists of a superficial part, inferior to the aortic arch and between it and the pulmonary trunk, and a deep part, between the aortic arch and the tracheal bifurcation. Sympathetic fibers reach the heart through the cardiac nerves from the sympathetic trunk. Preganglionic sympathetic fibers from the upper four or five segments of the thoracic spinal cord enter and move through the sympathetic trunk. They synapse in cervical and upper thoracic sympathetic ganglia, and postganglionic fibers proceed as bilateral branches from the sympathetic trunk to the cardiac plexus. From the cardiac plexus small branches, which are mixed nerves containing both sympathetic and parasympathetic fibers, supply the heart.

Innervation of Heart

Cardiovascular Silhouette a) Mediastinal Border· Right atrium· Superior vena cavab) Left Border· Aortic arch· Pulmonary trunk· Left atrial appendage· Left ventricle

Microscopic Anatomy of Heart Muscle

• Cardiac muscle is striated, short, fat, branched, and interconnected

• The connective tissue endomysium acts as both tendon and insertion

• Intercalated discs anchor cardiac cells together and allow free passage of ions

• Heart muscle behaves as a functional syncytium

Microscopic Anatomy of Heart Muscle

Figure 18.11

• Cardiac muscle tissue: • Striated-consists of sarcomeres just like skeletal muscle• Cells contain numerous mitochondria (up to 40% of cell volume) • Adjacent cells join end-to-end at structures called intercalated discs

Intercalated discs-contain two types of specialized junctions: • desmosomes (which act like rivets & hold the cells tightly together) and • gap junctions (which permit action potentials to easily spread from one

cardiac muscle cell to adjacent cells).

• Cardiac muscle tissue forms 2 functional syncytia or units:

• the atria being one & • the ventricles the other. Because of the presence of gap junctions, if any cell is stimulated

within a syncytium, then the impulse will spread to all cells. In other words, the 2 atria always function as a unit & the 2 ventricles always function as a unit. However, there are no gap junctions between atrial & ventricular contractile cells. In addition, the atria & ventricles are separated by the electrically nonconductive tissue that surrounds the valves. So, a special conducting system is needed to permit transmission of impulses from the atria to the ventricles.

drrhbulbul@yahoo.com+8801711560305