II. A "Method" of ECG Interpretation
Frank G. Yanowitz, MD
Professor of Medicine
University of Utah School of Medicine
This "method" is recommended when reading all 12-lead ECG's. Like the physical examination,
it is desirable to follow a standardized sequence of steps in order to avoid missing subtle
abnormalities in the ECG tracing, some of which may have clinical importance.
The 6 major sections in the "method" should be considered in the following order:
- Measurements
- Rhythm Analysis
- Conduction Analysis
- Waveform Description
- Ecg Interpretation
- Comparison with Previous ECG (if any)
1. Measurements (usually made in frontal plane leads):
Click to view
Heart rate (state atrial and ventricular, if different)
PR interval (from beginning of P to beginning of QRS)
QRS duration (width of most representative QRS)
QT interval (from beginning of QRS to end of T)
QRS axis in frontal plane (go to:
"How To Determine Axis")
Go to: ECG Measurement Abnormalities (Lesson IV) for description of normal
and abnormal measurements
2. Rhythm Analysis
State basic rhythm (e.g., "normal sinus rhythm", "atrial fibrillation", etc.)
Identify additional rhythm events if present (e.g., "PVC's", "PAC's", etc)
Consider all rhythm events from atria, AV junction, and ventricles
Go to: ECG Rhythm Abnormalities (Lesson V) for description of arrhythmias
3. Conduction Analysis
"Normal" conduction implies normal sino-atrial (SA), atrio-ventricular
(AV), and intraventricular (IV) conduction.
Click to view
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The diagram illustrates the normal cardiac conduction system.
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The following conduction
abnormalities are to be identified if present:
SA block (lesson VI): 2nd degree
(type I vs. type II)
AV block (lesson VI): 1st, 2nd
(type I vs. type II), and 3rd degree
IV blocks (lesson VI): bundle branch, fascicular, and nonspecific blocks
Exit
blocks: blocks just distal to ectopic pacemaker site
(Go to ECG Conduction
Abnormalities (Lesson VI) for a description of conduction abnormalities)
4. Waveform Description
Carefully analyze the 12-lead
ECG for abnormalities in each of the
waveforms in the order in which they appear: P-waves, QRS complexes, ST
segments, T waves, and... Don't forget the U waves.
P waves (lesson VII): are they too
wide, too tall, look funny (i.e., are they
ectopic), etc.?
QRS complexes: look for pathologic Q waves (lesson IX), abnormal voltage (lesson VIII),
etc.
ST segments (lesson X): look for abnormal
ST elevation and/or depression.
T waves (lesson XI): look for
abnormally inverted T waves.
U waves (lesson XII): look for prominent
or inverted U waves.
5. ECG Interpretation
This is the conclusion of
the above analyses. Interpret the ECG as
"Normal", or "Abnormal". Occasionally the term
"borderline" is used if
unsure about the significance of certain findings. List all abnormalities.
Examples of "abnormal" statements are:
Inferior MI, probably acute
Old anteroseptal MI
Left anterior fascicular block (LAFB)
Left ventricular hypertrophy (LVH)
Nonspecific ST-T wave abnormalities
Any rhythm abnormalities
Example:
Click to view
6. Comparison with previous ecg
If there is a previous ECG in the patient's file, the current ECG should be
compared with it to see if any significant changes have occurred. These
changes may have important implications for clinical management
decisions.
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