Erwinanto Div. Of Cardiology, Dept. of Internal Medicine Padjadjaran University School of Medicine Hasan Sadikin Hospital Bandung
Jan 17, 2016
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+
–
– ––
+ +
++
– ––
+ +
++
+ ++
– ––
– ––
+
–
Systole Diastole
Activation Recovery
Electrical Excitation Recovery
Depolarization Repolarization
Shortening Lengthening
Mechanical Contraction Relaxation
Emptying Filling
Terms describing cardiac cycle
(SAN)
(AVN)
(BB)
(BB)
(HB)RA
LA
V
V
SAN
RALA
AVN
HB
BB
V
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
AUGMENTED UNIPOLAR LIMBS LEADS
aVR Right arm
aVL Left arm
aVF Left leg
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
Positive
input
Positive
input
R R R
SQ
R
Q S QS
R
S
R’
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): between –30
degrees and –120 degrees
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