Download Cardiovascular System Block (CVS 311)

Al Maarefa College
Cardiovascular System Block
Physiology lab
ECG Analysis
Page 1
[M.S.A.QUADRI]
HOW TO READ THE ECG
 Rhythm
 Analyzing individual wave & segments
 Determine the mean electrical axis
RHYTHM ANALYSIS
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


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Step
Step
Step
Step
Step
1:
2:
3:
4:
5:
Determine regularity.
Calculate rate.
Assess the P waves.
Determine PR interval.
Determine QRS duration.
1-CALCULATING HEART RATE
H.R = 1500
÷
NO OF SMALL SQURES
BETWEEN R-R WAVES
OR
H.R = 300
÷
NO OF BIG SQURES
BETWEEN R-R WAVES
2-DETERMINE REGULARITY
 Look at the R-R distances (using a caliper
or markings on a pen or paper).
 Regular
(are
they
equidistant
apart)?
Occasionally irregular? Regularly irregular?
Irregularly irregular?
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3-ASSESS THE P WAVES




Are there P waves?
Do the P waves all look alike?
Do the P waves occur at a regular rate?
Is there one P wave before each QRS?
4-DETERMINE PR INTERVAL
Normal: 0.12 - 0.20 seconds.(3 - 5 boxes)
5-QRS DURATION
Normal: 0.04 - 0.12 seconds.(1 - 3 boxes)
ANALYSING INDIVIDUAL WAVES &
SEGMENTS
P WAVE :





Page 3
upright except in avR
Normal duration: 0.08 to 0.11 sec
do see p waves
are all p waves same
does all QRS complexes have p waves
[M.S.A.QUADRI]
P-R INTERVAL :
 Normal range 0.12 – 0.20 sec
 Is the PR interval constant ?
 If prolong indicates various blocks
QRS COMPLEXES:
 Are the p waves & QRS complexes are
associates with each other
 Are the QRS complexes narrow or wide
 The shape of the QRS complex change when
there is abnormal conduction of electrical
impulses within the ventricles.
ST SEGMENT
The isoelectric period (ST segment) following
the QRS is the time at which the entire
ventricle is depolarized and roughly corresponds
to the plateau phase of the ventricular action
potential.
The ST segment is important in the
diagnosis of ventricular ischemia or hypoxia
because under those conditions, the ST segment
can become either depressed or elevated.
T WAVE
The T wave represents ventricular repolarization
and is longer in duration than depolarization
(i.e., conduction of the repolarization wave is
slower
than
the
wave
of
depolarization).
Sometimes a small positive U wave may be seen
following the T wave . This wave represents the
last remnants of ventricular repolarization.
Inverted
or
prominent
U
waves
indicates
underlying pathology or conditions affecting
repolarization.
Page 4
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Q-T INTERVAL
 The Q-T interval represents the time for
both ventricular depolarization and
repolarization to occur, and therefore
roughly estimates the duration of an average
ventricular action potential.
 This interval can range from 0.2 to 0.4
seconds depending upon heart rate.
 At high heart rates, ventricular action
potentials shorten in duration, which
decreases the Q-T interval.
 Because prolonged Q-T intervals can be
diagnostic for susceptibility to certain
types of tachyarrhythmias, it is important
to determine if a given Q-T interval is
excessively long.
 In practice, the Q-T interval is expressed
as a "corrected Q-T (QTc)" by taking the Q-T
interval and dividing it by the square root
of the R-R interval (interval between
ventricular depolarizations). This allows
an assessment of the Q-T interval that is
independent of heart rate. Normal corrected
Q-Tc intervals are less than 0.44 seconds.
Page 5
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DETERMINATION OF MEAN LECTRICAL
AXIS
 When a vector is exactly horizontal and
directed toward the person’s left side,the
vector is said to extend in the direction of
0 degrees
 From this zero reference point, the scale of
vectors rotates clockwise
 when the vector extends from above and
straight downward, it has a direction
of +90 degrees

when it extends from the person’s left to
right, it has a direction of +180 degrees;
and when it extends straight upward, it has
a direction of -90 (or +270) degrees.
 In a normal heart, the average direction of
the vector during spread of the
depolarization wave through the ventricles,
called the mean QRS vector, is about +59
degrees
The QRS axis is determined by overlying a
circle, in the frontal plane. By convention,
the degrees of the circle are as shown.
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[M.S.A.QUADRI]
The normal QRS axis lies between -30o and
+110o.
A QRS axis that falls between -30o and -90o
is abnormal and called left axis deviation
A QRS axis that falls between +110o and
+180o is abnormal and called right axis
deviation.
A QRS axis that falls between +180o and -90o
is abnormal and called Indeterminant .
HOW TO CALCULATE THE QRS AXIS
Page 7
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OTHER METHOD TO CALCULATE THE
QRS AXIS
Lead I
+
+
-
Page 8
Lead aVF
+
+
-
AXIS
NORMAL
LEFT AXIS DEVIATION
RIGHT AXIS DEVIATION
RIGHT SUPERIOR
DEVIATION/INDETRMINANT
[M.S.A.QUADRI]