How to Read an EKG
Jason Ryan, MD
Intern Report
How to read an EKG
1. Rate and Rhythm



how fast/slow
regular/irregular
wide/narrow
2. Axis and Intervals

PR, QRS, QT
3. Hypertrophy


LAE/RAE
LVH/RVH
4. ST Changes and Q waves
How to read an EKG
Rate
40
300 100 60
150 75
50
(-)
How to read an EKG
-90o
Lead aVF (+)
Axis QRS
LAD
Lead I (-)
-180o
(+)
0o
RAD
Normal Axis
90o
How to read an EKG
Intervals
Correct QT
1. QTc=QT/(RR)1/2 (Bazett)
2. QTC=QT + 0.00175(HR60) (Hodges)
PR
0.14-0.21
QRS
0.7-011
QTc
<0.46
How to Read and EKG
Atrial
Enlargement
How to Read and EKG
Ventricular
Enlargement
Sinus Rhythm
Rate between 60 to 100
P wave before every QRS
– Smooth contour
– Either all positive or all negative except V1
– <0.12s and <0.2mv
Upright P waves in I, II, aVF
Negative P wave in aVR
Limb Lead Reversal
Right and Left arm reversed
– P wave positive aVR
– P wave negative aVL and I
– Limb leads look normal
Right arm and Right leg reversed
– P wave positive aVR
– P wave negative I, L
– Lead II isoelectric (almost no QRS)
Left Bundle Branch Block
Criteria:
– QRS > 120ms (3 small boxes)
– Broad, notched, or slurred R waves in I, aVL, and V5V6
– Secondary ST-T changes in I, aVL, and V5-V6
– Absence of Q waves in I, V5-V6
– R-wave peak time >60ms (1.5 small boxes) V5-V6
Separate criteria for STE AMI
Right Bundle Branch Block
Criteria:
– QRS >120ms (3 small boxes)
– R’ in the right precordial leads with R’>R
– Secondary ST-T changes in R precordial
leads
Supporting findings:
– Slurred S wave in I, aVL, left precordial leads
Usual criteria for STE AMI apply
Left Ventricular Hypertrophy
SV1orV2+ RV5orV6>35mm
– >40 if 30-40yrs old
– >60 if 16-30yrs old
RaVL>11mm
RI + SIII >25mm
RaVL + SV3 >28mm(men) or 20mm(wmn)
Left Ventricular Hypertrophy
Associated ST-T wave abnormalities
– STD and TWI in V5-V6
Leads where QRS is mainly positive
– Slight STE with upright T in V1-V2
Leas where QRS is mainly negative
Sinus Tachycardia
All sinus rhythm criteria
– P before every QRS
– Upright P in I, II, aVF
– Inverted P aVR
Rate >100
T Wave Inversions
Indicative of subendocardial or evolving ischemia
Can be a normal variant in several leads or in the presence of
BBB
Can be caused by several other conditions
– Hypertrophic obstructive cardiomyopathy
– Intracranial processes (hemorrhage)
– Medications or electrolyte abnormalities
– Myocarditis/pericarditis or pulmonary embolism
ST depressions
Horizontal ST depressions
are strongly suggestive of
ischemia in the appropriate
clinical setting
Don’t necessarily localize
– Stress testing
– Reciprocal changes
Several other conditions
can provoke ST
depressions:
– LVH
– Medications or
electrolytes
– Bundle Branch Block
– Pulmonary embolism
ST Elevations
Localizes best of all
ischemic EKG changes
Usually indication of acute
myocardial injury (occluded
artery)
Several conditions can also
cause ST elevations:
–
–
–
–
Pericarditis
Early repolarization
LBBB
LVH
ST Elevation MI
Evolution of EKG changes
Normal
Acute
Hours
1-2 Days
3-7 Days
> 7 Days
Leads go together
Anterior
Leads go together
Lateral
Leads go together
Inferior