How To Read An ECG
The electrocardiogram or ECG is a medical
device that measures the electrical activities of the heart using electrodes placed in certain positions on the
body. Physicians use the information gathered from the device to record the heart rate, myocardial infarctions,
arrhythmias, ventricular hypertrophies, atrial enlargements, and bundle branch blocks.
The ECG gives out ten basic
pieces of information about the heart. They are the following:
1. Rate. To determine the
rate, consider two durations of identical points in a consecutive ECG waveform (R-R interval). Take this duration
and divide it into 60. The equation should be: Rate = 60/(R-R interval)
2. Rhythm. This includes
normal sinus rhythm (NSR), regular, and irregular rhythm.
3. Axis. The basic principle
in finding the axis is searching for the lead whose QRS complex is closest zero.
4. P Wave Morphology.
Generally, the P wave should neither measure more than one box wide nor one box tall. If it exceeds these, it means
that either or both atria is enlarged and the patient is hypertrophied. V1 is the best lead to look for the P
5. PR Interval. The PR
interval defines AV conduction time which is usually between 0.12 - 0.20 milliseconds (or three to five boxes
wide). An AV block is present if the PR interval is more than 0.2 seconds.
6. QRS Complex Morphology.
This is not so easy to interpret. However, stepwise evaluation can be helpful. The following are the things to
- Duration should be between
0.08 - 0.10 seconds (or 2 - 2.5 boxes) only.
- Presence of Q waves (a Q
wave should be greater than one box wide).
7. ST Segment Morphology.
This can determine whether ischemia or infarction is present. In general, ischemia is indicated with a depressed ST
segment while an elevated ST segment confirms that there is infarction.
8. T Wave Morphology. T
waves generally point to the same direction as the QRS's largest deflection. Changes in the T waves can be usually
associated with ischemia, hyperkalemia, and hypokalemia.
9. U Wave Morphology. The
presence of U waves may indicate hypokalemia.
10. QTc Interval. With
quinidine toxicity, Qtc interval is lengthened. It is shortened with hypocalcemia.
ECG provides detailed information on ECG, ECG Course, ECG Cross Reference, ECG
Semiconductors and more. ECG is affiliated with EKG Interpretation.
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