Datasheet

Thursday, 17 July 2003 MiniProject: Design Aspects Colin K McCord
EEE512J2 – Electronic Product Design Page 3 Chapter 2: Fundamentals
body, only a dipole changing in both space and time. According to cardiac theory, in order to detect the
strongest difference in potential (the peak signal); the optimum electrode placement is to have one on the
right shoulder, and one on the left hip. This is what is usually referred to as “Lead II”, a convention that arises
from the work of Willem Einthoven, a pioneer in ECG development, who observed the differences in signal
strength as he took measurements between two electrodes with placement on the left shoulder, the right
shoulder and the left hip (Einthoven’s Triangle). See reference [W3] for an overview of the different standard
electrode placements.
Figure 2.1c.
Limb leads (Bipolar) [W3]
Figure 2.1d. Einthoven's triangle / axial reference system [W3]
Figure 2.1e. Augmented limb leads (Unipolar) [W3]
Figure 2.1f. Chest leads (unipolar) [W3]
The electrocardiogram (ECG) is a simple, non-invasive technique for detecting abnormalities and diagnosing
heart defects, merely by noting the presence of irregularities in the PQRST waveform. For example an
electrocardiogram may show: -
• Signs of insufficient blood flow to the heart.
• Signs of a new or previous injury to the heart (heart attack).
• Evidence of heart enlargement.
• Heart rhythm problems (arrhythmias).
• Signs of inflammation of the sac surrounding the heart.
• Changes in the electrical activity of the heart caused by a chemical (electrolyte) imbalance in the
body.
Note: Electrocardiography cannot predict whether a person will have a heart attack.
2.2. Electrodes
The role of the electrodes is to act as bio-electric transducers at the interface between the body and the
ECG. Inside the body, electricity exists in the form of ions. Thus, the purpose of the electrodes is to convert
electricity from its ionic form in the body into an electric current in the wires.