What are three common solutions to prevent baseline offset of ECG caused by the halfcell potential created between an electrode and skin?
1. Use a differential input dc amplifier so that the effects of two halfcell potentials (one from each electrode) are canceled out.
2. Use an ac coupled amplifier so that the DC voltage is blocked.
With an ECG, what is the most common cause of artifact signal? How can this be prevented?
electrode slippage
use a rough surface electrode (like BIS)
Differential amplifier
diff amp- AC COUPLED
Explain this graph
Transmembrane potential occurs slightly before muscle contraction
The INTERFERENCE THEORY states that the ECG is the result of _________ and _________ summation of electrical activity of the _____ as seen by the electrode placed external to the _________ cells of the ______________.
temporal
spatial
heart
depolarizing
myocardium
Explain the dipole theory (ECG)
separation of charge creates moving current? depolarization can be seen as a dipole
Equipotential lines: True or false: current and potential lines do not exist the limbs?
The limbs act as a ___________.
TRUE
Resistor
Myocardial electrical activity:
1) Vector length is the ________ of the gradient.
2) Vector __________ indicates anatomic pathway.
magnitude
direction
ID structure (all names) and charges
triaxial reference system (einthoven's triangle rearranged)
ID part of contraction including wave and area for all 3 leads
Atrial Depol
I- P
II- P
III- P
ID part of contraction including wave and area for all 3 leads
Septal Depol
I- Q
II- Q
III- R
ID part of contraction including wave and area for all 3 leads
Apical Depolarization
I- R
II- R
II- R
ID part of contraction including wave and area for all 3 leads
L Ventricular Depolarization
I- R
II- R
III- S
ID part of contraction including wave and area for all 3 leads
Late L ventricular depolarization
I- R
II - R
III- S
ID part of contraction including wave and area for all 3 leads
Complete depol or repol (looks same for both)
ID part of contraction including wave and area for all 3 leads
Ventricular repolarization
I- T
II- T
III- T
What is the acquisition axis?
leads 1,2,3
When making a diagnosis, ECG leads should ______ the heart, to get a proper reading.
Encase
Define Einthoven's Law, explain reasoning.
II = I + III
potential of any wave in lead II equals sum of I and III.
This comes from Kirchhoff's law, voltages around loop must equal zero.
Augmented vector leads are also called ___________ leads. They show a ___% increase in voltage (over vector leads). This is accomplished but using the sum of the vector leads, and another electrode.
UNIPOLAR
50%
This is accomplished but using the sum of the vector leads, and another electrode.