User manual
Otherpossiblemodificationsoftheleads
Besides the already described 12 conventional leads, some other leads may be used in
certain situations and for certain specific purposes [2.6]:
Esophageal leads - The esophageal electrode is capable of sensing relatively high
atrium potentials thanks to its presence in the vicinity of the left atrium, thus accurately
determining the electrical activity of the atriums and its relation to the activity of the
ventricles. That is mostly significant in case of fibrillation and atrial flutter, AV block, etc.
Frank’s corrected orthogonal system - 7 electrodes are used.
Corrected orthogonal system of McFee-Parungao - a 9-lead system.
These systems are used namely in VCG (vectorcardiogram - imaging of the movement of the
electrical heart vector in a three-dimensional space).
SchematicdiagramofanECGapparatus
In practice, there are different technical solutions to electrocardiographs; the main
principle of the biosignal measurement and transmission has been settled into the form
presented in Fig. 2.11. The individual blocks of the measurement channel for one lead are
described in the text below.
Fig. 2.11: Fundamental scheme of an ECG measurement channel [2.8].
Input protective circuits of the amplifiers
These circuits are front-end to the input of the actual amplifier in order to protect the
amplifier’s input circuits from large electrostatic charges or from the defibrillation discharge.
At the same time, it is required that the protective circuit does not influence the qualities of
the actual amplifier.
The protection is realized via a voltage limiter, parallel-connected between the
amplifier’s inputs. As the voltage limiters, manufacturers of the medical devices use, for
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