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Electrocardiograms
Cindy Chan, MD
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Electrocardiograms (EKGs or ECGs)display the electrical activity of the heart
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One electrode is placed on each arm
One electrode is placed on a leg(sometimes, one on each leg)
Six electrodes are placed across the chestwall (from right sternal border to left mid-
axillary line)
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Each lead has its own an axis (or direction) Each lead then reads the electrical current
relative to its axis Imagine that youre standing at the receiving
end of the axis, watching the current
If the current is coming toward you, the EKGdeflection is upward (ie. positive)
If the current is going away from you, the EKGdeflection is downward (ie. negative)
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So, if there is no deflection on the EKG,there are two explanations:
No currentThe current is perpendicular to the lead axis
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L R
Precordium
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1
23
Right Lef
arm ar
Up
Down
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1
23 avF
avR avL
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1
23 avF
avR avL
I nfer ior leads
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23 avF
avR
1
avL
Lateral leads
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Rate
0.04 sec (or 40 msec) = small box
0.2 sec = (small box) X 5 = large box
0.2 sec = 1/300thof minute So, if QRSs are 1 large box apart, rate is 300
If QRSs are 2 large boxes apart, rate is 150 (300/2)
If QRSs are 3 large boxes apart, rate is 100 (300/3), etc.
MEMORIZE: 300, 150, 100, 75, 60, 50
Bradycardia: (cycles/10 sec strip) X 6
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Rhythm
P before QRS
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RhythmTachyarrhythmias:
1. Sinus Tach
2. Supraventricular tachycardia (SVT) (paroxysmal atrial,junctional, or ventricular tachycardia; with or withoutblock) - rate 150-250
3. Atrial flutter - "saw-tooth", from single atrial focus, rate250-350
4. Ventricular flutter - "sine waves", rate 250-350
5. Atrial fibrillation with rapid ventricular rate (RVR) - frommultiple atrial foci, no P waves + irregular ventricularrhythm, rate 350-450
6. Ventricular Fibrillation - from multiple ventricular foci,erratic rhythm, rate 350-450
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Rhythm
Bradyarrhythmias:
1. Sick sinus syndrome - with pauses
2. 1 AVB - prolonged PR interval3. 2 AVB - ie. Wenckeback, Mobitz Type I,
gradual lengthening of PR until dropped QRS
4. 2 AVB - ie. Mobitz Type II, sporadic dropped
QRS5. 3 AVB - ie. Complete HB, complete
disassociation of P and QRS
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Axis
Normal axis is -30 to +105 degrees
Normal axis if upright in leads I and aVF
I downwards, aVF upright: RAD I downwards, aVF downwards: extreme RAD
I upright, aVF downards: LAD
LAD: left axis deviation
RAD: right axis deviation
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1
23avF
avR
avL
0
90
Normal axis
Extreme RAD
RAD
LAD
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Normal
QRS
ST
TP
P wave
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Normal
QRS
ST
TP
PR interval
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Normal
QRS
ST
TP
QRS complex
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Normal
QRS
ST
TP
QT interval
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Intervals
P wave:
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Intervalsquick method
P wave: less than 2.5 small boxes
PR interval: 3-5 small boxes
QRS: 1-2.5 small boxes
QT interval:
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Hypertrophy
1. R atrial hypertrophy: P height > 2.5 mm (right high)
2. L atrial hypertrophy: P length >0.12 sec (left long)
3. R Ventricular Hypertrophy (RVH) criteria:
RAD with widened QRS Persistent S wave in V5, V6 R > S in V1, but progressively smaller from V1-V6
4. L Ventricular Hypertrophy (LVH) criteria:
LAD with widened QRS S in V1 + R in V5 = >35 mm R in aVL > 11 mm
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Infarction
Q waves: 1 mm wide, 1/3 amplitude of QRS
Inverted T waves: ischemia
ST segment elevation: infarct
Anterior leads: V1, V2, V3, V4, V5
Lateral: 1, aVL, V6
Inferior: II, III, aVF
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Normal
QRS
ST
TP
ST segment
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Anterior
Posterior
Right Lef
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RV
LV
Anterioseptum
Inferioseptum
Inferio-Posterior
Lateral
Anterior
Anterioseptum
AnterioseptumAnterior
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LAD RCA LCx
Inferoseptum
RVRV
LVLV
AnterioseptumAnterioseptum
Inferio-PosteriorInferio-Posterior
Lateral
Inferioseptum
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LATERAL
WALL
Circumflex
LAD
ANTERIOR
WALL
RCA
POSTERIOR
WALL
Frontal plane
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LATERALWALL
Circumflex
LAD
ANTERIO
WALL
RCA
POSTERIOR
WALL
2 avF 3
1
avLavR
Leads 2, 3 and avFST
and then Q waves
inferior
Dead tissue
Frontal plane
Inferior MI
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Inferior MI
Occlusion of RCA
Significant Q waves
in 2,3 and avF
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INFERIOR
= RCA Anterior
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LAD RCA LCx
RVRV
LVLV
AnterioseptumAnterioseptum
Inferioseptum
Inferio-PosteriorInferio-Posterior
Lateral
Anterior
EKG: V1-V5 2,3,avF 1,avL,V6
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Lets look at a few
EKGs..