2. A "Method" of ECG Interpretation
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:
Topics for study:
- Rhythm Analysis
- Conduction Analysis
- Waveform Description
- Ecg Interpretation
- Comparison with Previous ECG (if any)
Measurements (usually made in frontal plane leads):
- 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 ("How To Determine Axis")
Go to: ECG Measurement Abnormalities (Lesson 4) for description of normal and abnormal measurements.
- 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 5) for description of arrhythmias.
"Normal" conduction implies normal sino-atrial (SA), atrio-ventricular (AV), and intraventricular (IV) conduction.
The following conduction abnormalities are to be identified if present:
- SA block (lesson 6): 2nd degree (type I vs. type II)
- AV block (lesson 6): 1st, 2nd (type I vs. type II), and 3rd degree
- IV blocks (lesson 6): bundle branch, fascicular, and nonspecific blocks
- Exit blocks: blocks just distal to ectopic pacemaker site
Go to: ECG Conduction Abnormalities (Lesson 6) for a description of conduction abnormalities.
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 7): are they too wide, too tall, look funny (i.e., are they ectopic), etc.?
- QRS complexes: look for pathologic Q waves (lesson 9), abnormal voltage (lesson 8), etc.
- ST segments (lesson 10): look for abnormal ST elevation and/or depression.
- T waves (lesson 11): look for abnormally inverted T waves.
- U waves (lesson 12): look for prominent or inverted U waves.
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
Comparison with Previous ECG (if any)
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.
Continue reading: "How To Determine Axis"