3. Heart produces currents
Electrodes sense electrical currents
transmit them to an ECG monitor.
transformed into waveforms
4.
5. • Marey, 1867, first electrical measurement
• Waller, 1887, first human ECG published.
• Einthoven, 1895,
names waves,
1912 invents triangle,
1924, wins Nobel Prize.
• Goldberger, 1924, adds precordial leads
6.
7.
8. provides a view of the heart’s electrical activity
one positive pole and one negative pole.
isoelectric waveform.
9. Einthoven Limb Leads (1895—1912)
Goldberger, 1924: augmented and precordial leads
Wilson Central Terminal (1944): the "indifferent” reference
EASI system
21. Risks
no chance of problems
No electricity passes
Editor's Notes
A plane refers to a cross-section view of the electrical
activity of the heart
Usually six standard chest leads are
recorded, one at a time, from the anterior chest wall,
the chest electrode being placed sequentially at the six
points shown in the diagram. The different recordings
are known as leads V1, V2, V3, V4, V5, and V6.
E lead: lower part of the sternum
A lead: left midaxillary line
S lead: upper part of the sternum
I lead: right midaxillary line
Ground: anywhere on the torso.
three-dimensional view of the electrical activity
Artifact, also called waveform interference, may be seen with
excessive movement (somatic tremor). The baseline of the ECG
appears wavy, bumpy, or tremulous. Dry electrodes may also
cause this problem due to poor contact.
Electrical interference, also called 60-cycle interference, is caused
by electrical power leakage. It may also occur due to interference
from other room equipment or improperly grounded equipment.
As a result, the lost current pulses at a rate of 60 cycles per second.
This interference appears on the ECG as a baseline that’s
thick and unreadable.
A wandering baseline undulates, meaning that all waveforms are
present but the baseline isn’t stationary. Movement of the chest
wall during respiration, poor electrode placement, or poor electrode
contact usually causes this problem.
Faulty equipment, such as broken leadwires and cables, can
also cause monitoring problems. Excessively worn equipment
can cause improper grounding, putting the patient at risk for
accidental shock.
After counting the number of boxes between the R waves, use the table shown at right to
find the rate.
For example, if you count 20 small blocks or 4 large blocks, the rate would be 75 beats/
minute. To calculate the atrial rate, use the same method with P waves instead of R waves.
