Basic Cardiac Rhythm Interpretation
P Wave - Atrial Depolarization stimulated by the firing of the SA node.
Evaluate: consistent appearance and 1:1 relationship with QRS complex.
If not identical some, or all, may be atrial, but not SA node, in origin.
IF >1 P-wave precedes QRS a heart block may be present.
PR Interval - Impulse traveling time from the atrium to the ventricles.
Measure from the beginning of the P-wave to the beginning of the QRS complex.
Evaluate: Duration & regularity of interval.
If > 0.20 seconds a conduction delay called an AV heart block is present.
QRS complex - Ventricular Depolarization
Measure from beginning of Q-wave to end of S-wave where it returns to baseline.
Evaluate: all complexes should look alike in the same lead. Normal Duration < 0.12 seconds.
Widening QRS complex suggests bundle branch block or other conduction delay.
ST segment - Represents the completion of ventricular depolarization and the beginning of ventricular
repolarization.
, Along isoelectric line between the end of the QRS complex and the beginning of the T-wave.
Depressed with myocardial ischemia. Elevated with myocardial infarction.
T-wave - Ventricular Repolarization
Upstroke = absolute refractory period
Downstroke = relative refractory period
QT Interval - Length of time it takes for ventricles to depolarize and depolarize.
Measure from beginning of Q-wave to end of T-wave. Should be less than half of the R-R interval.
Length > 0.50 seconds is considered dangerously prolonged.
R-R Interval - Represents rate of ventricular depolarization (therefore heart rate).
Evaluate: regularity
Eight Steps of ECG Interpretation - 1. Measure HR
2. Examine R-R Interval (regular or irregular)
3. Examine the P-wave (same configuration)
4. Measure the PR interval (constant <0.20 sec)
5. Determine if each P-wave is followed by a QRS complex
6. Examine and measure the QRS complex (< 0.12 sec)
7. Examine and measure the QT interval (<1/2 R-R)
8. Diagnose the rhythm
hypokalemia - Causes resting membrane potential to become more negative - requiring a greater
stimulus to reach threshold for excitation and opening of sodium channels.
P Wave - Atrial Depolarization stimulated by the firing of the SA node.
Evaluate: consistent appearance and 1:1 relationship with QRS complex.
If not identical some, or all, may be atrial, but not SA node, in origin.
IF >1 P-wave precedes QRS a heart block may be present.
PR Interval - Impulse traveling time from the atrium to the ventricles.
Measure from the beginning of the P-wave to the beginning of the QRS complex.
Evaluate: Duration & regularity of interval.
If > 0.20 seconds a conduction delay called an AV heart block is present.
QRS complex - Ventricular Depolarization
Measure from beginning of Q-wave to end of S-wave where it returns to baseline.
Evaluate: all complexes should look alike in the same lead. Normal Duration < 0.12 seconds.
Widening QRS complex suggests bundle branch block or other conduction delay.
ST segment - Represents the completion of ventricular depolarization and the beginning of ventricular
repolarization.
, Along isoelectric line between the end of the QRS complex and the beginning of the T-wave.
Depressed with myocardial ischemia. Elevated with myocardial infarction.
T-wave - Ventricular Repolarization
Upstroke = absolute refractory period
Downstroke = relative refractory period
QT Interval - Length of time it takes for ventricles to depolarize and depolarize.
Measure from beginning of Q-wave to end of T-wave. Should be less than half of the R-R interval.
Length > 0.50 seconds is considered dangerously prolonged.
R-R Interval - Represents rate of ventricular depolarization (therefore heart rate).
Evaluate: regularity
Eight Steps of ECG Interpretation - 1. Measure HR
2. Examine R-R Interval (regular or irregular)
3. Examine the P-wave (same configuration)
4. Measure the PR interval (constant <0.20 sec)
5. Determine if each P-wave is followed by a QRS complex
6. Examine and measure the QRS complex (< 0.12 sec)
7. Examine and measure the QT interval (<1/2 R-R)
8. Diagnose the rhythm
hypokalemia - Causes resting membrane potential to become more negative - requiring a greater
stimulus to reach threshold for excitation and opening of sodium channels.
