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Electrocardiograph
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History
• 1842- Italian scientist Carlo Matteucci
realizes that electricity is associated with
the heart beat
• 1876- Irish scientist Marey analyzes the
electric pattern of frog’s heart
• 1895 - William Einthoven , credited for the
invention of EKG
• 1906 - using the string electrometer EKG,
William Einthoven diagnoses some heart
problems.
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Contd..
• 1924 - the noble prize for physiology or
medicine is given to William Einthoven for
his work on EKG
• 1938 -AHA and Cardiac society of great
Britan defined and position of chest leads
• 1942- Goldberger increased Wilson’s
Unipolar lead voltage by 50% and made
Augmented leads
• 2005- successful reduction in time of onset
of chest pain and PTCA by wireless
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transmission of ECG on his PDA.
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Modern ECG Instrument
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Heart Functions
• Heart has three functions:
• Pumps oxygenated blood to all parts of the
body
• Has its’ own blood supply – called the
coronary arteries
• Has an electrical conduction system because
cells are electrically charged and produce a
wave form
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Bioelectricity in Tissues
• Polarized =
• high concentration of potassium inside the
cell
• high concentration of sodium outside the cell
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Contd…
• Stimulation of cell/Depolarization = sodium
rushes in and potassium rushes out
• When depolarization is completed, sodium
and potassium return to their normal
places, bringing the cell back to rest called
repolarization.
• This process of depolarization and
repolarization produces wave forms on the
EKG
• ECG shows repolarization → polarization 10
with ECG complex.
Impulse Conduction of Heart
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
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Biopotential In Heart
• SA node = Pacemaker of the heart (initiates the
electricity that causes the heart to beat)
• Rate=60-100 beats per minute (NSR)
• Stimulates the right and left atrium to contract
after depolarization of the cells
Impulse travels to the:
• AV Node= Functions as a delay, keeping the atria
and ventricles from contracting at the same time.
• Rate is 40-60 beats/minute
• Bundle of His= Distal portion of the AV node
• Splits into the Right and Left Bundle Branch,
stimulating the right and left ventricle
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Contd…
• Purkinje Fibers= Receives the electrical impulse
from the Bundle of His
• Fibers transmit through the walls of the ventricles
• Rate is 20-40/min
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Definition of ECG
• The ECG is a graphical representation of
the electrical impulses that the heart
generates during the cardiac cycle.
• These electrical impulses are conducted to
the body's surface, where they are
detected by electrodes placed on the
patient's limbs and chest.
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A NORMAL ECG WAVE
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Standard Lead System
• The Standard ECG have 12 Leads
• 6 Limbs Leads
Limbs lead divided into Bipolar and Unipolar
Leads
 3 Bipolar Limb Leads
 3 Unipolar Limb Leads
• 6 Precordial Leads
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Bipolar Limb Leads
• They are formed by
voltage tracings between
the limb electrodes (RA,
LA, RLand LL). These
are the only bipolar
leads. Or
• THE EINTHOVEN’S
TRIANGLE
– LEAD I
– LEAD II
– LEAD III
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13-61
LEAD I
• LA is connected to
amplifier’s
noninverting input,
while RA is
connected to
inverting input.
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LEAD II
• The LL is connected
to amplifier’s
noninverting input,
while RA is
connected to
inverting input.
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LEAD III
• The LL is connected
to amplifier’s
noninverting input,
while LA is
connected to
inverting input.
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Unipolar Limb Leads
• They are also derived
from the limb
electrodes, they
measure the electric
potential at one point
with respect to a null
point. They are the
AUGMENTED LIMB
LEADS.
– aVR
– aVL
– aVF
aVR
aVL
aVF
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aVR
• RA is connected to
noninverting input,
while LA and LL are
summed at inverting
input.
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aVL
• LA is connected to
noninverting input,
while RA and LL are
summed at inverting
input.
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aVF
• LL is connected to
noninverting input,
while RA and LA are
summed at inverting
input.
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PRECORDIAL LEADS
They are placed directly on the
chest. Because of their close
proximity of the heart,
• V1 is recorded with the electrode in
the 4th intercostals space just to the
right of sternum.
• V2 is recorded in the 4th
intercostals space just to left of
sternum.
• V3 is recorded on a line midway
between V2 and V4.
• V4 is recorded in the midclavicular
line in the fifth interspace.
• V5 is recorded in the anterior
axillary line at the same level as lead
V4.
• V6 is recorded in midaxillary line at
the same level as V4
LA
RA
V1
RL
V2
V3
V4V5 V6
LL
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ECG Waveform
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ECG
• Three distinct wave are produced during
cardiac cycle
• P wave caused by atrial depolarization
• QRS complex caused by ventricular
depolarization
• T wave results from ventricular
repolarization
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P Wave
• P wave represent the atrial depolarization.
• P duration: < 3 small squares or 0.08 to
0.1 sec.
• P amplitude : < 2.5 small squares
or < 2.5 mm
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PR Interval
• Represents the time between the onset of
atrial depolarization (P wave) and the
onset of ventricular depolarization (QRS
Complex).
• Normal duration = 0.12-2.0 sec (120-200
ms) (3-5 small squares of ECG paper)
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QRS Complex
• Represent the Ventricular depolarization
• Normal duration = 0.08-0.12 seconds
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ST Segment
• Connects the QRS complex and T wave
• Duration of 0.08-0.12 sec (80-120 msec)
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T Wave
• It represents the ventricular depolarization
and longer in duration than depolarization.
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QT interval
•
It represent the time for both ventricular
depolarization and repolarization
• Measured from beginning of QRS to the end of
the T wave
• Normal QT is usually about 0.40 sec
• QT interval varies based on
heart rate.
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Fig. 13.24b
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Fig. 13.24c
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Fig. 13.24d
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Fig. 13.24g
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Calibration
• Check that your ECG is calibrated correctly
• Height
– 10mm = 1mV
– Look for a reference pulse which should be
the rectangular looking wave somewhere
near the left of the paper. It should be 10mm
(10 small squares) tall.
• Paper speed
– 25mm/ s
– 25 mm (25 small squares / 5 large squares)
equals one second
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ECG Paper
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