What is an electrocardioGRAPH
- an instrument that measures electrical potentials on body surface
- generates record of electrical currents generated by heart
What is an electrocardiogram? (ECG)
recording of time dependent electrical activity changes of heart detected on the surface of the body
What is a cardiac electrogram?
- recording of time dependent electrical activity changes of heart detected with electrocardiograph within or directly on heart
Why is an ECG useful?
- detects arrhythmias and conduction disturbances
- visualize effects of altered plasma electrolyte concentrations (too much K+ = hyperkalemia)
- influence of drugs on heart
- anatomical orientation of heart- relative size changes of chambers
- extent, location, and progress of heart injury
Which ECG uses are for Category A animals only?
- anatomical orientation of heart
- relative size of chambers
- extent, location, and progress of heart injury
What is dipole theory?
The ECG is a basic bio electric phenomenon
What is a dipole?
What is a vector?
How can a dipole be represented as a vector?
The dipole can be displayed as a quantitative vector
As the action potential moves through the heart, what does it produce?
“wave” like dipole - action potential to resting cell through gap junction (nexus)
Where can voltage be detected on the body surface relative to main vector of depolarization? Where can voltage not be detected?
- in line with main vector
- 90 degree angle to lead
How can a dipole be measured on the body’s surface if the heart is the thing producing electrical activity?
- body tissues/fluids are homogeneous conductors of electrical potential
- 60-70% of body is water with charged ions carrying electrical current
What are Einthoven’s standards for dipole theory? (4)
- vector oriented with arrowhead toward positive electrode = positive deflection upward
- vector oriented with arrowhead toward negative electrode = negative deflection downward
- vector parallel to the recording electrodes = maximum deflection
- vector perpendicular to recording electrodes = no potential detected (isoelectric)
Where does the overall (net) depolarization of the heart start and end?
Depolarization waves normally spread from right to left and from cranial to caudal
How are Einthoven’s standard 12 lead ECG split?
- six frontal plane leads
- six transverse place leads
What are the 6 frontal plane leads?
3 bipolar limb leads I,II,III
3 unipolar limb leads aVR, AVL, aVF
Which bipolar limb lead is the most important and why?
Lead II - because depolarization moves right to left, cranial to caudal, the voltages picked up by RA to LL are the largest
T or F: the unipolar limb leads are true measurements
F: they are averages comparing the electrical activity of reference limb to other two limbs
- bipolar leads are true measurements
What are the 6 transverse plane leads?
V1 , V2, V3, V4, V5, V6
What is the main use for unipolar chest leads in animals?
The unipolar limb lead compares the electrical activity of the reference limb to an average of the electrical activities at the other two limbs
How do depolarization waves spread?
What do unipolar limb leads compare?
How is positive deflection present on the ECG?
- placing bipolar positive limb leads left and caudal
Unipolar limb leads: ____ limbs are connected to the _______ terminal and the third limb is connected to the ________ terminal
2
negative
positive
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