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ECG Changes, Each lead "views" the heart from the angle of its…
ECG Changes
Leads
Bipolar Limb Leads
2
3
(+) Inferior wall of the heart
1
(+) high lateral wall of LV
same ECG readings
1 positive electrode & 1 negative electrode
Augmented Unipolar Limb Leads
1 positive electrode & 2 negative electrodes with mean (-)
aVR
(+) on the RA
tells us abt IVS:basal septum and a bit of right ventricle
Inverted ECG
aVF
same as lead 2
(+) on LL
inferior wall of the heart
aVL
(+) on LA
high lateral wall of LV
Same as lead 2
Unipolar Chest Leads
V1-V6
R wave increases from 1-6
S waves decreases from 1-6
Reading ECG
Heartrate Calculation
1 small box x-axis: 0.04 secs
1 big box x-axis: 0.2 secs
Small box measurements: 1 by 1 mm
Big box measurements: 5 by 5 mm
calculate the number of boxes from R-R wave
300/big boxes
1500/small boxes
Common Pathologies
PR-Interval
less than 0.2 secs (one large box) = normal
QRS
less than 0.12 secs (3 small boxes) = normal
QT-Interval
less than 0.43 secs = normal for male
Less than 0.46 secs = normal for female
ST segment
depression indicates myocardial ischaemia or digoxin use
elevation indicates myocardial injury
PT-segment
prolonged indicates heart block
0.12 - 0.20 sec = normal
Triangle
RA, LA, LL
QRST
Each lead "views" the heart from the angle of its positive electrode
"Narrow" is another term for normal
