Mechanical Heart Functioning

MECHANICAL HEART FUNCTIONING

09 - Mechanical Heart Function – Introduction to anatomy

Heart is pump that beat 10000 times per day. During a lifetime the pumped volume equals that

of 3 supertankers.

HEART LOCATION - Heart is located in the mediastinum, area from the sternum to the vertebral

column and between the lungs. Superior right point at the superior border of the 3rd right costal

cartilage; Superior left point at the inferior border of the 2nd left costal cartilage 3 cm to the left

of midline; Inferior left point at the 5th intercostal space, 9 cm from the midline; Inferior right

point at superior border of the 6th right costal cartilage, 3 cm from the midline

Frontal view

Transversal view

Apex - directed anteriorly, inferiorly and to the left. Base - directed posteriorly, superiorly and to

the right. Anterior surface - close to sternum and ribs. Inferior surface - rests on the diaphragm

Right border - faces right lung. Left border - faces left lung.

SURFACE ANATOMY

Sulci separates the grooves on surface of heart containing coronary blood vessels and fat

- coronary sulcus: encircles the heart and marks the boundary between the atria and the

ventricles

- anterior interventricular sulcus: marks the boundary between the ventricles anteriorly

- posterior interventricular sulcus marks the boundary between the ventricles posteriorly

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Pericardium - The heart can freely move within the pericardium. Each layer is made up of a single

sheet of epithelial cells, known as mesothelium.

Outer layer that surrounds the heart. Continuous with the

central tendon of the diaphragm, the fibrous pericardium

is made of tough connective tissue and is relatively non-

distensible. Its rigid structure prevents rapid overfilling of

the heart, but can contribute to serious clinical

consequences.

Fibrous pericardium - protects and anchors the heart, prevents overstretching (if pressure on

the hearts starts to increase, heart try to distend and fibrous pericardium stop it). Serous

pericardium - thin delicate membrane that contains: parietal layer (outer layer) lines the internal

surface of the fibrous pericardium; pericardial cavity with pericardial fluid and visceral layer

(epicardium). It is needed to lubricates the heart to prevent friction.Epicardium: visceral layer of

serous pericardium. Myocardium: cardiac muscle layer is the bulk of the heart and

Endocardium: chamber lining & valves.

Cardiac tamponade (pathology) - is caused by pericardial effusion (build-up of fluid inside the

pericardium). This hampers cardiac filling (because the fibrous pericardium does not stretch),

and this may lead to an emergency situation. There are several causes, e.g., pericarditis, or

myocardial rupture in the setting of acute myocardial infarction.

Chambers – Heart is divided in 4 chambers: 2 chambers called atria, 2 lower called ventricles.

RIGHT ATRIUM - Receives blood from three sources - superior vena cava, inferior vena cava and

coronary sinus. The coronary sinus collects the majority of the cardiac venous blood. It receives

the blood from the myocardium, a thick layer of muscle within the heart, and facilitates the

movement of the blood into the right atrium. Interatrial septum: partitions the atria from the

ventricle. Here we found the fossa ovalis: is a remnant of the foetal foramen ovale. The foramen

should close after birth, if it remains, there’s a communication between the two atria and this

could lead to different pathologies. Tricuspid valve: blood flows through into right ventricle. It

has three cusps composed of dense cartilage covered by endocardium.

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RIGHT VENTRICLE – Forms most of anterior surface of heart. Papillary muscle: are cone shaped

trabeculae carneae (raised bundles of cardiac muscle) it serves to contract when the right

ventricle is also contracting and help avoid of back flow. Chordae tendineae: cords between

valve cusps and papillary muscles. Interventricular septum: partitions ventricles. Pulmonary

semilunar valve: blood flows into the trunk of the pulmonary artery.

Fossa Ovalis - The fossa ovalis is an oval depression on the septal wall of the atrium, and

corresponds to the situation of the foramen ovale in the fetus. It is situated at the lower part of

the septum, above and to the left of the orifice of the inferior vena cava. This septum is less thick.

It is used by cardiologist to access the left atrium with catheters.

LEFT ATRIUM – Receives blood from lungs through 4 pulmonary veins (2 right + 2 left). Around

the valves of pulmonary vein there’s often an ectopic electrical activity causing atrial fibrillation.

Bicuspid valve: blood passes through into left ventricle. It has two cusps to remember names of

this valve, remember the mnemonic LAMB: Left Atrioventricular, Mitral, or Bicuspid valve. To

prevents the back flow through the mitral valve to the left atrium the left ventricle is contracting.

LEFT VENTRICLE – Forms the apex of heart. Chordae tendineae anchor bicuspid valve to papillary

muscles (also has trabeculae carneae like right ventricle). Aortic semilunar valve: blood passes

through valve into the ascending aorta when the ventricle contracts just above valve are the

openings to the coronary arteries.

To conclude the anatomy of the hear we have to mention: Ventricular Myocardial Band

(Torrent-Guasp) and the Fibrous skeleton of the heart - It is the attachment for the leaflets and

cusps of the valves. Also the myocardium it is attached. Act as an electrical insulator between

the atria and the ventricle. It also patency of the AV and semilunar valves, prevention of

overdistension.

Valves

A-V valves open and allow blood to flow from atria into ventricles when ventricular pressure is

lower than atrial pressure (a form of passive opening). It occurs when ventricles are relaxed,

chordae tendineae are slack and papillary muscles are relaxed. A-V valves close preventing

backflow of blood into atria - occurs when ventricles contract, pushing valve cusps closed,

chordae tendinae are pulled taut and papillary muscles contract to pull cords and prevent cusps

from reverting (prevents the backflow from the ventricle to the atria).

Semilunar (SL) valves open with ventricular contraction - allow blood to flow into pulmonary

trunk and aorta. SL valves close with ventricular relaxation - prevents blood from returning to

ventricles, blood fills valve cusps, tightly closing the SL valves.

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VALVES DURING SYSTOLE

VALVES DURING

DIASTOLE

PHASES OF THE HEARTBEAT

1. SL valves close “dub”: AV valves open and filling of atria and ventricles begins

2. AV valves open; passive filling of ventricles, ventricular filling stage and contraction of atria

(atrial kick) contraction of ventricles

3. AV valves close “lub”: SL valves open and blood goes to lungs and body **Heart Murmur**

The atria also contract and this an hemodynamic significance because contribute to the cardiac

output, to the pump punction of the heart. The atria contracts and push some blood into the

right ventricle and to the left ventricle before the right and left ventricle contracts themselves.

It is called Atrial kick (concours as the atria contract prior to ventricular contraction, it

contributes to the cardiac output. atrial kick contributes 15-35% to the volume of blood in the

ventricle. This extra volume in turn increases cardiac output by a similar 15-35%. Note: as we

age, atrial kick tends to be a more significant contributor to cardiac output (closer to 35%).

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Heart Sounds - Auscultation is performer through the Stethoscope. This technique listen for

sounds of heartbeat coming from turbulence in blood flow caused by valve closure. First heart

sound (LUB) is created with the closing of the atrioventricular valves. We hear the tricuspid valve

and the ventricle start to contract. Second heart sound (DUB) is created with the closing of

semilunar valves. When the contraction is over, the pulmonary and aortic valves are closed in

order to prevent the back flow from the aorta and from pulmonary artery

Heart sound in a normal subject: LUB-DUB

At the end of the ejection

phase the semilunar

valves (the aortic valve –

here not visible – and the When the ventricular

pulmonary valve) close. contraction begins, the

Heart sound BUB. AV valves (mitral and

tricuspid valves) close.

Heart sound LUB

Coronary Arteries and Veins

Coronary Arteries- Branches of aorta above aortic semilunar valve

Left coronary artery is splitted into: circumflex branch (LCx): in coronary sulcus, supplies left

- atrium and left ventricle; anterior interventricular artery (LAD): supplies both ventricles

Right coronary artery (RCA) is splitted into: marginal branch: in coronary sulcus, supplies

- right ventricle and posterior interventricular artery: supplies both ventricles.

If there are some problems connected to the coronary artery, part of the heart has a lack of

blood and this phenomena Is called ISCHEMIA.

Coronary Veins - Collects wastes from cardiac muscle. Drains into a large sinus on posterior

surface of heart called the coronary sinus. Coronary sinus is important for the introduction of

electrodes during electrophysiological studies. Coronary sinus empties into right atrium.

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Coronary arteries and veins – learn to recognise following patterns

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Innervation of the Heart

Information about blood pressure, generated by baroreceptors in the carotid sinuses and in the

aortic arch, travels via afferent fibers in cranial nerves IX and X to the cardiovascular centre of

the autonomic nervous system in the brain stem. This centre responds dynamically by adjusting

efferent sympathetic outflow (travelling to the heart via the spinal cord), and adjusting efferent

parasympathetic outflow (travelling to the heart via cranial nerve X).

Thus, heart rate and cardiac contractility are adjusted to counteract blood pressure changes.

From the book: Autonomic innervation of the heart plays an important role in regulating cardiac

function. The heart is innervated by parasympathetics (vagal) and sympathetic efferent fibers.

The right vagus nerve preferentially innervates the sinoatrial (SA) node, whereas the left vagus

nerve innervates the AV node; however, significant over- lap can occur in the anatomical

distribution. Atrial muscle is also innervated by vagal efferent; the ventricular myocardium is

only sparsely innervated by vagal efferent. Sympathetic efferent nerves are present throughout

the atria (especially in the SA node) and ventricles, and in the conduction system of the heat

Vagal activation of the heart decreases heart rate (negative chronotropy), decreases conduction

velocity (negative dromotropy), and decreases contractility (negative inotropy) of the heart

Vagal-mediated inotropic influences are moderate in the atria and relatively weak in the

ventricles. Activation of the sympathetic nerves to the heart increases heart rate, conduction

velocity, and inotropy. Sympathetic influences are pronounced in both the atria and ventricles.

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10 - Mechanical Heart Function: Contraction Mechanism

The contraction mechanism is one of the determinants of the mechanical heart functions. Cardiac functions

are determinate by different factors:

1. Contraction mechanism

2. Excitation-Contraction: calcium influences on the contraction.

3. Electrical activity

4. Neurohormonal systems: they exert their influence on contractility.

5. Cardiovascular interactions & Loading conditions: are pre-load after-load so

how will the heart fill, which pressure will the heart see when it pumps the

blood in the aorta and pulmonary arteries. These are all together called the

loading conditions and they have an important impact in ca