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:

1. Measurements
2. Rhythm Analysis
3. Conduction Analysis
4. Waveform Description
5. Ecg Interpretation
6. Comparison with Previous ECG (if any)

1. Measurements (usually made in frontal plane leads):

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 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.


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The diagram illustrates the normal cardiac conduction system.


 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:

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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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