ECG Interpretation
Chapter 22
ECG Interpretation
1. Rate
3. Axis
a. Atrial rate: PP interval
4. Hypertrophy
b. Ventricular rate: RR interval
5. Blocks
2. Rhythm
a. P wave
b. PR interval
c. QRS
i. voltage (height)
ii. width
6. Infarct
7. Ischemia
Standardization
Standardization mark
10 mm vertical deflection = 1 mVolt
Rate
Ventricular rate (heart rate)
RR interval
Atrial rate
PP interval
3rd degree AV block
Heart Rate Calculation
1500 divided by the
number of small boxes
between two R waves
•most accurate
•take time to calculate
•only use with regular
rhythms
•quick
300 divided by the number
•
not too accurate
of large boxes between
•
only use with regular
two R waves
rhythm
10 multiplied by the
number of R waves in 6
seconds
•less precise
•use with irregular rhythms
•very quick
1 lg sq = 300 bpm
2 lg sq = 150 bpm
3 lg sq = 100 bpm
4 lg sq = 75bpm
5 lg sq = 60 bpm
6 lg sq = 50 bpm
Rhythm
Sinus rhythm - consistent P waves
Atrial rhythm - irregular P waves
Junctional/Nodal rhythm - no P waves, late
P waves, or inverted P waves
Ventricular rhythm - no P waves, wide QRS
AV Junctional Rhythms
Retrograde P waves immediately preceding
the QRS complexes in aVR and II.
Retrograde P waves immediately following
the QRS complexes
Absent P waves
ECG Waves
P wave
atrial depolarization
≤ 2.5 mm in amplitude
< 0.12 sec in width
PR interval (0.12 - 0.20 sec.)
time of stimulus through atria and
AV node
prolonged interval = first-degree heart
block
P wave
Tall = RAE
Wide = LAE
PR Interval
Long PR interval = first degree AV block
Short PR interval = WPW
Short PR interval with inverted P waves =
ectopic atrial or junctional pacemaker
Classification of AV Heart Blocks
Degree
Degree Block
Uniformly prolonged PR
interval
Degree, Mobitz Type I
Progressive PR interval
prolongation
1St
2nd
AV Conduction Pattern
2nd Degree, Mobitz Type II
Sudden conduction failure
3rd Degree Block
No AV conduction
Wolff-White-Parkinson
Wide QRS
due to early depolarization
not due to a delay in depolarization
Shortened PR interval
Upstroke QRS complex is slurred; delta
wave
ECG Waves
QRS
width 0.12 second or less
Normal QRS
V6?
V1?
Fig. 4-6
V1?
V6?
Normal Q waves
• Septal r wave
• Septal q wave
Q Waves
Abnormal if wider than 0.04 sec
Leads I, II, III, aVf or leads V3 - V6.
Greater than 25% of the R wave
Note: Not all Q waves are abnormal, Not all Q waves
are the result of MI.
QRS Width
Wide
RBBB or LBBB
Premature ventricular beats
WPW
QRS Voltage
RVH
LVH
Mean QRS Axis
Axis Deviation
LEAD aVF
LEAD I
(or Lead II or
III)
Normal
Positive
Positive
LAD
Positive
Negative
RAD
Negative
Positive
Intermediate
axis
Negative
Negative
LEAD aVR
Positive
(or Negative)
R Wave Progression
Transmural MI
Ischemia
Tall T waves
(and/or reciprocal T wave inversion)
ST segment elevation.
Injury
T wave inversion of the previously tall
T waves
Pathalogical Q waves
Infarct
(at least one small box wide or 11/3 the entire
QRS height)
Overview
LEAD
AREA OF THE HEART
V1-V2
Anterior/Septum
V3-V4
Anterior Wall
V5-V6
Anterior/Lateral
II, III, aVF
Inferior
I and aVL
Lateral
V1-V2
Posterior (reciprocal)
ST Segments
J point:
end of QRS wave
beginning of ST segment
ST segment
beginning of ventricular repolarization
normally isoelectric (flat)
changes, elevation or depression, may indicate
pathological condition
Subendocardial Ischemia
ST segment depression criteria
1 mm or more
horizontal or downward
lasts 0.08 seconds
depression of only the J point with rapid
upward sloping are considered normal.