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The Heart Illustrations are taken from: J. Malmivuo, R. Plonsey, Bioelectromagnetism, Oxford Press, 1995 http://butler.cc.tut.fi/~malmivuo/bem/book/ Location of the Heart The heart is located in the chest between the lungs behind the sternum and above the diaphragm.

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the heart
The Heart

Illustrations are taken from:

J. Malmivuo, R. Plonsey, Bioelectromagnetism, Oxford Press, 1995

http://butler.cc.tut.fi/~malmivuo/bem/book/

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

location of the heart
Location of the Heart

The heart is located in the chest between the lungs behind the

sternum and above the diaphragm.

It is surrounded by the pericardium.

Its size is about that of a fist, and its weight is about 250-300 g.

Its center is located about 1.5 cm to the left of the midsagittal plane.

Located above the heart are the great vessels: the superior and inferior vena cava, the pulmonary artery and vein, as well as the aorta.

The aortic arch lies behind the heart.

The esophagus and the spine lie further behind the heart.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

location of the heart in the thorax
Location of the heart in the thorax

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

the anatomy of the heart and associated vessels
The anatomy of the heart and associated vessels

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

anatomy of the heart
Anatomy of the Heart

The heart is oriented so that the anterior aspect is the right

ventricle while the posterior aspect shows the left atrium.

The atria form one unit and the ventricles another.

The left ventricular free wall and the septum are much thicker

than the right ventricular wall. This is logical since the left

ventricle pumps blood to the systemic circulation, where the

pressure is considerably higher than for the pulmonary

circulation, which arises from right ventricular outflow.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

orientation of cardiac muscle fibers
Orientation of cardiac muscle fibers

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

anatomy of striated muscle
Anatomy of striated muscle

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

blood circulation via heart
Blood circulation via Heart

The blood returns from the systemic circulation to

the right atrium and from there goes through the

tricuspid valve to the right ventricle.

It is ejected from the right ventricle through the

pulmonary valve to the lungs. Oxygenated blood returns

from the lungs to the left atrium, and from there

through the mitral valve to the left ventricle.

Finally blood is pumped through the aortic valve to

the aorta and the systemic circulation..

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

electrophysiology of cardiac muscle cell
Electrophysiologyof Cardiac Muscle Cell

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

electrical activation of the heart
Electrical activation of the Heart

In the heart muscle cell, or myocyte , electric activation takes place

by means of the same mechanism as in the nerve cell -

that is, from the inflow of sodium ions across the cell membrane.

The amplitude of the action potential is also similar, being about

100 mV for both nerve and muscle. The duration of the cardiac

muscle impulse is, however, two orders of magnitude longer than

that in either nerve cell or skeletal muscle. A plateau phase follows

cardiac depolarization, and thereafter repolarization takes place.

As in the nerve cell, repolarization is a consequence of the outflow

of potassium ions.

The duration of the action impulse is about 300 ms (Netter, 1971).

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

mechanical contraction of cardiac muscle
Mechanical contraction of Cardiac Muscle

Associated with the electric activation of cardiac muscle cell

is its mechanical contraction, which occurs a little later.

An important distinction between cardiac muscle tissue and

skeletal muscle is that in cardiac muscle, activation can propagate

from one cell to another in any direction.

As a result, the activation wavefronts are of rather complex shape.

The only exception is the boundary between the atria and ventricles,

which the activation wave normally cannot cross except along a

special conduction system, since a nonconducting barrier of fibrous

tissue is present..

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

slide13

Electric and mechanical activity in(A) frog sartorius muscle cell, (B) frog cardiac muscle cell, (C) rat uterus wall smooth muscle cell.In each section the upper curve shows the transmembrane voltage behavior, whereas the lower one describes the mechanical contraction associated with it.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

the conduction system of the heart
The conduction system of the heart.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

conduction on the heart
Conduction on the Heart

The sinoatrial node in humans is in the shape of a crescent and

is about 15 mm long and 5 mm wide.

The SA nodal cells are self-excitatory, pacemaker cells.

They generate an action potential at the rate of about 70 per minute.

From the sinus node, activation propagates throughout the atria,

but cannot propagate directly across the boundary between atria

and ventricles.

The atrioventricular node (AV node) is located at the boundary

between the atria and ventricles; it has an intrinsic frequency of

about 50 pulses/min. However, if the AV node is triggered with

a higher pulse frequency, it follows this higher frequency.

In a normal heart, the AV node provides the only conducting

path from the atria to the ventricles. Thus, under normal conditions,

the latter can be excited only by pulses that propagate through it.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

slide16

Propagation from the AV node to the ventricles is provided by a

specialized conduction system.

Proximally, this system is composed of a common bundle, called the

bundle of His (after German physician Wilhelm His, Jr., 1863-1934).

More distally, it separates into two bundle branches propagating along

each side of the septum, constituting the right and left bundle

branches. (The left bundle subsequently divides into an anterior and

posterior branch.) Even more distally the bundles ramify into Purkinje

fibers (named after Jan Evangelista Purkinje (Czech; 1787-1869))

that diverge to the inner sides of the ventricular walls. Propagation

along the conduction system takes place at a relatively high speed

once it is within the ventricular region, but prior to this (through the

AV node) the velocity is extremely slow.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

slide17

Propagation on ventricular wall

From the inner side of the ventricular wall, the many activation sites

cause the formation of a wavefront which propagates through the

ventricular mass toward the outer wall.

This process results from cell-to-cell activation. After each ventricular

muscle region has depolarized, repolarization occurs.

Repolarization is not a propagating phenomenon, and because the

duration of the action impulse is much shorter at the epicardium (the

outer side of the cardiac muscle) than at the endocardium (the inner

side of the cardiac muscle), the termination of activity appears as if

it were propagating from epicardium toward the endocardium.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

electrophysiology of the heart the different waveforms for each of the specialized cells
Electrophysiology of the heartThe different waveforms for each of the specialized cells

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

isochronic surfaces of the ventricular activation
Isochronic surfaces of the ventricular activation

(From Durrer et al., 1970.)

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

the genesis of the electro cardiogram
The genesis of the electro-cardiogram

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

slide21

A and B show a segment of cardiac tissue through which propagating

depolarization (A) and repolarization (B) wavefront planes are passing.

In this illustration the wavefronts move from right to left, which

means that the time axis points to the right.

There are two important properties of cardiac tissue that we shall

make use of to analyze the potential and current distribution

associated with these propagating waves.

First, cells are interconnected by low-resistance pathways

(gap junctions), as a result of which currents flowing in the

intracellular space of one cell pass freely into the following cell.

Second, the space between cells is very restrictive (accounting for

less than 25% of the total volume). As a result, both intracellular

and extracellular currents are confined to the direction parallel to

the propagation of the plane wavefront.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

electric field of the heart on the surface of the thorax recorded by augustus waller 1887
Electric field of the heart on the surface of the thorax, recorded by Augustus Waller (1887).

The curves (a) and (b) represent

the recorded positive and negative isopotential lines, respectively.

These indicate that the heart is a dipolar source having the positive and negative poles at (A) and (B), respectively.

The curves (c) represent the

assumed current flow lines..

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

slide23

(A) The 10 ECG leads of Waller.(B) Einthoven limb leads and Einthoven triangle. The Einthoven triangle is an approximate description of the lead vectors associated with the limb leads.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

einthoven triangle
Einthoven Triangle

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

the signal produced by the propagating activation front between a pair of extracellular electrodes
The signal produced by the propagating activation front between a pair of extracellular electrodes.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

the generation of the ecg signal in the einthoven limb leads i
The generation of the ECG signal in the Einthoven limb leads - I

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

the generation of the ecg signal in the einthoven limb leads ii
The generation of the ECG signal in the Einthoven limb leads - II

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

the normal electrocardiogram
The normal electrocardiogram

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

slide29

The Wilson central terminal (CT) is formed by connecting a 5 k resistance to each limb electrode and interconnecting the free wires; the CT is the common point. The Wilson central terminal represents the average of the limb potentials. Because no current flows through a high-impedance voltmeter, Kirchhoff\'s law requires that IR + IL + IF = 0.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

slide30

(A) The circuit of the Wilson central terminal (CT).(B) The location of the Wilson central terminal in the image space (CT\'). It is located in the center of the Einthoven triangle.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

slide31
(A) The circuit of the Goldberger augmented leads. (B) The location of the Goldberger augmented lead vectors in the image space.

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

precordial leads
Precordial leads

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

slide33

The projections of the lead vectors of the 12-lead ECG system in three orthogonal planes(when one assumes the volume conductor to be spherical homogeneous and the cardiac source centrally located).

EE-515 Bioelectricity & Biomagnetism 2002 Fall - Murat Eyüboğlu

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