THE HUMAN HEART

DR. NWOSU C.I.A., MSc,MBBS,MD.

LEARNING OBJECTIVES• The heart is a 3-layered, 4-chambered double pump that, in the

embryo invaginated into a preexisting sac,• The surfaces and borders in the surface anatomy of the heart enables

accurate diagnosis in trauma and diseases,• The knowledge of the heart layers is helpful in the appreciation of

such diseases as rheumatic carditis,• The fibrous skeleton is dense connective tissue to which structures of

the heart are attached,• There are 4 heart valves, 2 A-V valves & 2 semilunar valves: PAMT,• All 4 heart valves are located directly behind the sternum, but the

sound of their closure is heard in areas different from their anatomical location,

• The closure of the A-V valves is responsible for the first heart sound, whereas the closure of the semilunar valves is responsible for the second heart sound,

• Venous return, stroke volume & cardiac output,• The cardiac cycle describes events from the beginning of one beat to

the beginning of the next,

THE HEART IN MIDDLE MEDIASTINUM

SURFACES & BORDERS 3 SURFACES: Anterior or sternocostal : RT atrium , Rt ventricle & AVG Posterior or base : mostly left atrium, Diaphragmatic surface : RT & LT ventricles, and PIG, 3 BORDERS: Superior border :from 3rd Rt CC to 2nd LT CC Inferior border : RT atrium & RT ventricle; from 6th CC to AB, Rt border : Rt atrium ; from 3rd RT CC to 6th RT CC Lt border : LT ventricle & LT auricle ;from 2nd LT CC to AB AB = apex beat = where maximum cardiac impulse is felt; it is

located on the 5TH left intercostal space, mid-clavicular line (5th LT ICS, MCL)

CRUX = point of intersection between IAG, Iinter-atrial & interventricular grooves/sunci ; AV nodal artery from RT coronary artery takes off from here,

The Rt heart lies anteriorly & the left posteriorly, as a result of cardiac folding in the 4th week of intrauterine life which brings the arterial and venous ends together,

STERNOCOSTAL SURFACE & THE 4 BORDERS

DIAPHRAGMATIC & POSTERIOR SURFACES

Posterior surface or base

Diaphragmatic surface

SURFACE ANATOMY OF THE BORDERS OF THE HEART/CARDIAC APEX

HEART FIBROUS SKELETON• Embryologically, the cardiac jelly forms the fibrous skeleton of

the heart : dense connective tissue to which structures of the heart are attached

• The fibrous skeleton consists of 4 rings (which encircle 4 valves), 2 trigones, and membranous portions of inter - atrial and inter - ventricular septa, tendon of Todaro, and supraventricular crest,

• The trigones connect the rings to the inter - atrial and inter - ventricular septa

• Functionally the fibrous skeleton - keeps the valves open , - keeps the valves from being overstretched by large volumes, - provides attachment points for the myocardium, - provides electrical insulation to atria & ventricles = separates atria from ventricles

so they can contract independently - membranous IVS provides a passageway for the AV bundle of His,

THE FIBROUS SKELETON OF THE HEART

EACH OF THE 4 HEART CHAMBERS HAS A SMOOTH & A ROUGH PART

HEART CHAMBERS

RIGHT ATRIUM• Crista terminalis lies between sinus venerium & musculi pectinati,

and between the openings of SVC & IVC,• At the junction of SVC opening & superior end of crista terminalis is

the location of sinoatrial node (SAN),• OPENINGS :Superior vena cava, inferior vena cava (with valve of

Eustace), coronary sinus (with valve of Thebesius), & tricuspid valve,• Fossa ovalis & annulus ovalis on inter-atrial septum,• Opening of coronary sinus lies between 3 structures : fossa ovalis, IVC

opening & tricuspid valve opening,• Tendon of Todaro runs from between the 2 valve to the top part of

septal leaflet of tricuspid valve,• Boundaries of triangle of Koch - the site of AVN : - tendon of Todaro - attachment of septal leaflet of tricuspid valve, - anteromedial margin of orifice of coronary sinus

TENDON OF TODARO• Tendon of Todaro runs from the valve of coronary sinus to the margin of

fossa ovalis ,• Is an extension of the fibrous skeleton of the heart,• this tendinous structure forms one of the boundaries of the surgically

important triangle of Koch

Tendon of Todaro

Membranous part of IVS

Septal leaflet of tricuspid

Fossa ovalis in IAS

Valve of IVC (Eustace) Valve of coronary sinus

(Thebesius)Crista terminalis

Pectinate muscle

RIGHT VENTRICLE Inlet & outlet valves, Inlet part is roughened by trabeculae carnae, ridges, 3 papillary

muscles attached to tendinous cords, Outlet part is the smooth, arterial infundibulum = conus

arteriosus Supraventricular crest supports the following structures - anterosuperior leaflet of tricuspid valve, - septomarginal band (septomarginal trabecula = moderator band) - separating the attachments of tricuspid & pulmonary valves, Moderator band (septomarginal trabecula) =a curved muscular

bundle that stretches from the inferior part of IVS to anterior papillary muscle

Functions of Moderator band : - re-inforces the septal surface and anterior papillary muscle, - conveys the Rt bundle branch (or part of it) to the anterior wall, - embraces & is strengthened by the supraventricular crest, - may prevent overdistension of RT ventricle

When the ventricular muscle contracts during the second phase (ejection) of systole, the ventricular volume reduces, and there is a tendency for the atrio-ventricular valves

to prolapse into the atria. The papillary muscles prevent this.

RIGHT VENTRICULAR OUTFLOW = CONUS ARTERIOSUS = INFUNDIBULUM

Supporting & separating the ridged inflow part from the smooth arterial outflow part is a thick, arched muscular structure, the supraventricular crest,

Supraventricular crest : a muscular arch/ridge between the smooth and rough parts of RT ventricle that accommodates the 140 degrees change of direction of flow of blood between the inflow & outflow of RT ventricle

INTERVENTRICULAR SEPTUM Indicated externally by AIVG and PIVG, In cross section, the interventricular septum bulges into the RT ventricle

Left ventricle

Right ventricle

Interventricular septum

LEFT ATRIUM & LEFT AURICLE

auricle

atrium

LEFT VENTRICLE• Rough inlet and smooth outlet (aortic vestibule)• Like the Rt ventricle, the inlet is roughened by

trabeculae carnae, ridges,and 2 papillary muscles attached to their tendinous cords,

• No Moderator band,• Wall 3 X as thick as the wall of the Rt ventricle• During systole, the papillary muscle begins to

contract before the general myocardium: a mechanism to tighten the cords & pull together the valve cusps to avoid prolapse

Trabeculae carnae

HEART VALVES

• VALVE ANAT. LOCATION AUSCULTATION SITE• P 3rd CC 2nd LT ICS• A 3rd ICS 2nd RT ICS• M 4th CC cardiac apex (5th Lt ICS MCL)• T 4th ICS Rt inferiormost ST (? 5th RT ICS)• (3344) (2255)

• The cardiac valves are 2 ATRIOVENTRICULAR & 2 SEMILUNAR,• Each heart valve consists of a core of connective tissues covered by endocardium ; thus whatever affects the endocardium affects the heart valves e.g bacterial endocarditis

A 10 YO boy had group A beta heamolytic streptococcal pharyngitis and in 6 weeks developed pan-carditis and arthritis. What does that mean to you in terms of heart structure?

RT coronary ostium

LT coronary ostium

Coronary sinuses

Ascending aorta

HEART VALVES

HEART VALVES & HEART SOUNDS• Normal heart valves

produce sounds only when they close

• Where might specific valves be best heard?– remember that the

sounds are produced by BLOOD FLOW hitting/moving each structure

– project the most likely passage of soundwaves ie. the direction of blood flow through each “gate”

HEART VASCULATURE & INNERVATION

• VESSELS: 2 coronary arteries, cardiac veins/coronary sinus, and cardiac lymphatics,

• NERVES: autonomic & visceral afferents; - sympathetic from all cervical ganglia and T1-5, - parasympathetic by the 2 vagus nerves - both form the superficial (on the ligamentum arteriosum) and

deep (posterior to arch) cardiac plexuses, - from here mixed autonomic nerves innervate the conducting

tissue of the heart ; the right supplies the SAN, while the left supplies the AVN

THE HEART IN HEALTH & DISEASE

THE HEART IN HEALTH & DISEASE

CARDIAC CYCLE Describes events from the beginning of one beat to the beginning of the

next, It consists of diastole (ventricular filling) and systole (ventricular

emptying), The cardiac cycle is best begun from diastole : DIASTOLE : Step 1 : semilunar valves close, Step 2 : the atrio-ventricular valves open to receive venous return, Step 3 : atrial; contraction : the atria squeeze out the last drops, SYSTOLE : Step 4 : ventricles begin to contract thereby causing the closure of atri-

ventricular valves, Step 5 : isometric contraction of ventricles when all 4 valves are closed, Step 6 : further increase in ventricular pressure forces open the semilunar

valves, 1st & 2nd Heart Sounds are caused by valve closure : atrio-ventricular, then

semilunar.

Cardiac referred pain

THANK YOU

PRACTICE QUESTIONS• What mediates the anginal pain of cardiac origin that radiates across the

precordium, neck, shoulder, medial arm?• Where is the mitral valve sounds best heard, and why is this different from

the location of the valve itself?• What are the circulatory changes that occur at birth?• What is the location of the apex beat?• An injury that damages the interventricular septum involves which cardiac

valve?• An artificial pacemaker is implanted to remedy the function of which

conducting tissue of the heart?• Which veins open into the right ventricle?• What are the unique characteristics of the right atrium and right ventricle?• Looking at the A-P radiagraph of the chest, what structures form the right

boundary of the cardiac silhouette from the clavicle downward?• Describe the events of the cardiac cycle.

EMBRYOLOGIC SUMMARY

• Begins as angiogenic cell clusters in splanchnic mesoderm ; these become 2 endocardial tubes which fuse during body foldings,

• The single endocardial tube which emerges becomes segmented into 5 dilatations : TBVAS,

• The segmented dilated endocardial tube folds into a U-shaped structure with the arterial and venous ends moving upward and the venous end moving caudally and to the left,

• T = truncus arteriosus, becomes ascending aorta and pulmonary trunk,• B = bulbus cordis forms conus arteriosus & aortic vestibule,• V = primitive ventricle, forms the rough part of the 2 definitive ventricles,• A = primitive atrium, forms the rough part of the 2 definitive atria and the

auricles,• S = sinus venosus, forms sinus venerium, coronary sinus and oblique vein of left

atrium,• The smooth part of left ventricle is formed from absorption of the primitive

pulmonary vein into the left atrium

EKG BASICS

• When one part of cardiac muscle depolarizes and becomes electronegative relative to other parts,electrical current also spreads from the electronegative part into adjacent tissues (electropositive) all the way to the surface ; recordable on electrocardiograph,

• Electrocardiographic leads are bipolar limb leads, precordial (chest) leads & augmented unipolar limb leads,

• The basic electrocardiographic waves are :• P due to atrial depolarization,• QRS complex due to ventricular depolarization, contraction, and atrial

repolarization (atrial T wave obscured by QRS complex) ,• T wave due to ventricular repolarization,• P-R interval is about 0.16 second.

VALVULAR INSUFFICIENCY• Common causes of valvular insufficiency are rheumatic fever, ischemic heart disease,

congestive cardiac failure, prolapse, degerative or age-related(as in calcific aortic stenosis),infective endocarditis, non-bacterial thrombotic endocarditis etc, etc.

• Rheumatic fever affects mostly the left heart valves; mitral valve is the most frequently damaged by disease processes,

• Age –related changes occur most commonly in the aortic valve,• Non-bacterial thrombotic endocarditis results from deposition of blood products on previously

normal valves: common in malignancies, especially adenocarcinoma,• Bacterial endocarditis occurs in previously damaged valves ; acute type by high virulence

bacteria e.g Staph. aureus, whereas subacute is by low virulence organisms e.g @-hemolytic Strep.

• Libman-Sacks endocarditis consists of sterile vegetation on cardiac valves of SLE patients,• MECHANISM : the disease process usually excites an endocardial inflammation, which

produces necrosis with deposits e.g. Aschoff bodies in rheumatic pan-carditis; healing produces fibrosis that deforms the valve(s) +++, and predisposis to formation of vegetation & embolization.