Transcript 1. Normal ECG - Akademik Ciamik 2010

Erwinanto
Div. Of Cardiology, Dept. of Internal Medicine
Padjadjaran University School of Medicine
Hasan Sadikin Hospital
Bandung
What medical problems can be
diagnosed with an ECG?
• Enlargement of cardiac chambers
• Hypertrophy of cardiac muscle
• Cardiac arrhythmias
• Insufficient coronary blood flow
• Death of heart muscle and its location
• Electrolyte abnormality
What is an Electrocardiogram?
An ECG is the recording (“gram”) of the
electrical activity (“electro”) of the cells of the
heart (“cardio”) that reaches the body surface
Initiates the heart muscle to contract, to
pump blood to the tissues
What does an ECG actually measure?
An ECG records voltage on its vertical axis
against time on its horizontal axis
• Measurement along the vertical axis indicates
“summation” of the electrical activation of all of the
cardiac cells
• Measurement along the horizontal axis indicates
heart rate, regularity, and the time intervals
required for electrical activity to move from one
part of the heart to another
+
+ +
+ +
+ +
+
– – – – – – – – – – – –
+
+ +
+ +
+ +
+
+
+ – – –
– – – + + +
+
+ – – –
+
+ +
+
– – – – – –
+
+ +
+
– – – – – – – – – – – –
+ + + + + + + + + + + +
– – – – – – – – – – – –
– – – – – – – – – – – –
+ + + + + + + + + + + +
– – – – – – – – – – – –
– – –
+ + +
– – –
+
+ – – – – – –
– – – + + + + + +
+
+ – – – – – –
+
+ +
+ +
+ +
+
– – – – – – – – – – – –
+
+ +
+ +
+ +
+
+
0
+
– – –
+
– – –
+ + +
– – –
+
– – –
+
+
–
+
–
+
+
+
Terms describing cardiac cycle
Systole
Electrical
Mechanical
Diastole
Activation
Recovery
Excitation
Recovery
Depolarization
Repolarization
Shortening
Lengthening
Contraction
Relaxation
Emptying
Filling
LA
RA
(SAN)
(HB)
V
V
(AVN)
(BB)
HB
SAN
RA
AVN
LA
BB
V
(BB)
RECORDING ELECTRODES AND LEADS
1. Bipolar limb leads:
record the potential differences between two limbs
2. Unipolar precordial leads:
record the absolute electrical potential at each of
designated torso sites
3. Augmented unipolar limb leads:
is designed to increase the amplitude of the output
of limb leads
BIPOLAR LIMBS LEADS
Lead I
Left arm
Lead II
Left leg
Lead III
Left leg
Positive
input
AUGMENTED UNIPOLAR LIMBS LEADS
aVR
Right arm
aVL
Left arm
aVF
Left leg
Positive
input
PRECORDIAL LEADS
V1
Right sternal margin, 4th intercostal space
V2
Left sternal margin, 4th intercostal space
V3
Midway between V2 and V4
V4
Left midclavicular line, 5th intercostal space
V5
Left anterior axillary line
V6
Left midaxillary line
R
R
R
Q
R
S
R
R’
Q
S
QS
S
Systematic evaluation of the ECG
1. Rate and regularity
2. P-wave morphology
3. PR interval
4. QRS-complex morphology
5. ST-segment morphology
6. T-wave morphology
7. U-wave morphology
8. QTc interval
9. Rythm
Rate and regularity
 P waves and QRS complexes are used to determine
cardiac rate and regularity
 Over a particular interval of time, normally, there
are same numbers of P waves and QRS complexes
 Heart rate:

* 1500 divided by number of small squares
between successive P waves or QRS
complexes
* 300 divided by number of large squares
between successive P waves or QRS
complexes
 Normal heart rate: 60-100 beats per minute (bpm)
P-wave morphology
1. The contour: is normally smooth and monophasic
(entirely positive or negative) in all leads except V1
or occasionally V2
2. Upright or positive P waves are normally seen in
leads I, aVL, aVF, V4-V6 and downward in lead aVR.
P wave in lead III may be either upright or downward.
3. P-wave duration is normally less than 0.12 seconds
4. The maximal amplitude is normally no more than 0.2
mv
Abnormal P waves
The PR interval
1. The PR interval measures the time required for an
electrical
impulse
to
travel
from
the
atrial
myocardium adjacent to the SA node to the
ventricular myocardium adjacent to the fibers of
the Purkinye network
2. The duration is normally from 0.11 to 0.20 seconds
3. PR interval varies with the heart rate. The faster
the heart rate, the shorter the PR interval
Abnormal PR interval
Morphology of the QRS
complex
1. Q waves.
• The presence of Q waves in leads V1, V2, and
V3 should be consider abnormal.
• The absence of small Q waves in leads V5 and
V6 should be consider abnormal
• A Q wave of any size is normal in leads III and
avR
• In all other leads, a “normal” Q wave would be
very small (less than 0.04 second and its
voltage is less than 25% of the R-wave)
Anbormal Q waves
2. R waves
The positive R wave normally increases in
amplitude and duration from lead V1 to V4 or V5.
Loss of normal R-wave progression is considered
abnormal
3. S wave
S
wave
should
be
large
in
V1
and
then
progressively smaller to V6
4. Ratio of R/S amplitude in V1 and V2 is normally
less than 1
Abnormal R wave in V1
5. Duration of the QRS complex (QRS interval)
It normally ranges from 0.07 second to 0.11
second (less than 0.12 second). The QRS interval
has no lower limit that indicates abnormality
6. Amplitude of QRS complex
There is no arbitrary upper limit for normal
voltage of the QRS complex. An abnormally low
QRS complex when the amplitude is no more than
0.5 mV in any limb leads and no more than 1.0 mV
in any of the precordial leads
Abnormal QRS interval
0.19 s
7. The axis of QRS complex
• Normal axis: between –30 degrees and +90
degrees
• Right axis deviation (RAD): between +90
degrees and ± 180 degrees
• Left
axis
deviation
(LAD):
degrees and –120 degrees
between
–30
Right axis deviation (RAD)
Left axis deviation (LAD)
Morphology of the ST
segment
1. The ST segment represents the period during
which the ventricular myocardium remains in an
activated or depolarized state
2. ST
segment
normally
located
at
the
same
horizontal level with the PR segment
3. Normal variations:
• Slight upsloping, downsloping, or horizontal
depresion
• Early
repolarization:
displacement
of
ST
segment by as much as 0.1 mV in the direction
of the ensuing T wave
4. ST segment may be altered when there is
prolonged QRS complex
Normal ST segment
Normal ST-segment deviation
Morphology of the T and
U waves
The T wave
•
The T waves are positively directed in all leads
except aVR (negative) and V1 (biphasic)
•
T waves do not normally exceed 0.5 mV in any limb
lead or 1.5 mV in any precordial lead
The U wave
U wave is either absent or present as a small wave
following the T wave and is usually most prominent in
leads V1 and V2. Increased prominence of the U wave
indicates the possibility of hypokalemia
The QTc interval
1. The QT interval measures the duration of electrical
activation and recovery of the ventricular
myocardium
2. The QT interval decreases as the heart rate
increases and therefore should be corrected for
cardiac rate (QTc interval)
3. QTc= QT/RR interval (in seconds)
The upper limit of QTc is 0.46 second (slightly
longer in in females)
4. QT interval varies among different leads. The
longest QT interval measured in multiple leads
should therefore be considered the true QT interval