Test 7 Flashcards
(126 cards)
PR interval
TIme from beginning of P wave to beginning Q wave. Represents beginning and end of atrial depolarization.
QT interval
Entire time ventricles remain depolarized
PP interval
TIme between each atrial depolarization or contraction.
RR interval
Time between each ventricular depolarization or contraction.
What is the hexagonal lead system and why is it used?
Superimposed standard and augmented leads that midpoints of lead coincide with each other forming a circular field used to determine the direction and magnitude of the net electrical axis during a ventricular depolarization.
What is the triaxial lead system?
Transposing Lead I, II and III to form a triangle with a center point of zero potential.
What are the six steps taken when evaluating an ECG printout?
- Heart rate
- Measure complexes (mV) and intervals (sec)
- Is rhythm regular or irregular?
- P-wave for very QRS complex, QRS complex for every p-wave?
- Origin of QRS complex (supraventricular or ventricular)
- Mean electrical axis
If there is a long P-R interval, what are some problems associated?
First degree AV node block
If there is a discrepancy between the number of P waves and QRS waves, what are some problems associated?
Second and Third degree AV node blocks
If we see deep S waves, what may be occurring?
Ventricular hypertrophy
Bundle branch blocks
Delays depolarization in part of ventricle after the block which takes away dipole because electrical signal go through more slowly in the affected side.
What can an ECG give us information about?
- Heart rate
- Relative sizes of heart chambers
- Rhythm or conduction disturbances
- Origin of the pacemaker
- Effects of altered electrolytes like K+
- Effects of certain drugs
- Anatomical orientation of heart
What can an ECG not give us information about?
- Cardiac output
2. Mechanical performance
What is electrical mechanical dissociation? Can an ECG detect this?
When you see normal heart rhythm but no palpable pulse or measurable blood pressure…NO
T/F: Each cardiac cell has an electrical dipole and can be characterized as a vector with magnitude and direction and each can be summated to represent one single dipole of the heart.
True
In order for an ECG to detect an electrical signal, what must occur?
There must be a wave of electrical charges moving over the heart
Why would we see lower amplitude ECG recordings in larger, fatter, or deeper chested animals or animals with a small heart (cats)?
The heart is further away from the electrodes and the lung field is larger.
If a wave of electrical potential moves towards a positive electrode, what kind of deflection will occur?
Positive
If a wave of electrical potential moves towards a negative electrode, what kind of deflection will occur?
Negative
What occurs if there is no deflection in the electrical signal?
The electrical potential wave is perpendicular to the electrode axis
Why would there be high plasma K+ but not noticeable electrical problems on ECG?
Hypercalcemia
How can be protect an animal from hyperkalemia?
Give bicarbonate, calcium, insulin, or glucose to drive K+ back into cells out of the plasma
What do we see on an ECG from hyperkalemia and why?
- Bradycardia-due to the depressive effects K+ has on the rate of diastolic depolarization.
- P wave becomes broad and flattened-due to depressed excitability of atrial myocardium
- 1st and 2nd degree AV node block
- Duration of QRS complex increases
- Spiked T wave
* Imagine ECG is a string and you pull on it, what happens? -stretch it all out, except for T wave*
What must happen to the cardiac cell membrane in order for diastolic depolarization to occur? How does hyperkalemia mess with this process?
Cell membrane must become less permeable to K+. Increases permeability of cell membrane to K+ even though the concentration gradient favors K+ leaving the cells. This change in permeability slows down diastolic depolarization.