Slide 1
An ECG records electrical activity at the skin
An electrocardiogram records voltage differences detected at the skin. It provides information about the heart’s electrical activity.
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Often abbreviated ECG, the test does not directly photograph the heart or measure the amount of blood pumped. Those questions may require imaging or other measurements alongside the electrical record.
Slide 2
Each lead gives a different electrical view
Electrodes placed at selected body locations allow several electrical views of the heart. A lead is one such measured viewpoint.
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A lead is not simply another name for a sticky electrode. The recording compares electrical potentials in defined ways, which is why electrode placement affects interpretation.
Slide 3
The upper heart chambers activate before the lower ones
The normal heartbeat activates the atria, the upper heart chambers, before the ventricles, the lower chambers.
The ECG trace contains features associated with this ordered electrical sequence.
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Electrical recovery also contributes to the trace. The waveform therefore records more than the instant of contraction, and its intervals help describe how activation travels.
Slide 4
An intermittent problem can escape a short recording
A resting ECG records a limited period. An intermittent rhythm disturbance may not occur while that particular recording is being made.
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Longer monitoring can sample activity during ordinary daily events. Extending the observation window answers a different question from repeating a brief record at one quiet moment.
Slide 5
The trace needs symptoms and other evidence
Clinicians interpret the ECG alongside symptoms, examination and other evidence. A waveform is useful information rather than a diagnosis by itself.
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Movement and poor electrode contact can introduce artifacts. Before interpreting an unusual pattern as cardiac activity, the quality and conditions of the recording must be considered.
Sources
- Electrocardiogram
MedlinePlus Medical Test
- Arrhythmias: Diagnosis
NHLBI, NIH
- How the Heart Beats
NHLBI, NIH