Electrocardiogram PQRS Flashcards
What happens at P wave?
Positive or negative deflection?
atrial depolarization - positive deflection
line goes up
What happens at Q wave?
Positive or negative deflection?
First negative/downward deflection before R wave
What happens at R wave?
Positive or negative deflection?
First positive deflection of QRS
start of ventricular depolarization
What happens at S?
Positive or negative deflection?
Negative/downward deflection after an R Wave
ventricle contracts after QRS
What happens at T wave? positive or negative deflection?
Ventricular repolarization
First major deflection/bump after QRS
Label the entire ECG of a heartbeat
- P
- R
- T
- PR interval
- PR segment
- Q
- S
- QRS interval
- ST segment
- QT interval
What is Ta wave? Positive or negative deflection? Why is it rarely seen?
It is atrial repolarization
not seen because low volt
down or opposite P wave
seen in 3rd degree AV block
What is the PR interval? What should it be called?
If this interval is prolonged what does it represent?
- start of P wave to first deflection of QRS complex
(should be called PQ interval) - prolonged = atrial enlargement or AV conduction problem
What is the qRs complex?
What does Q, R, and S represent individually?
ventricular depolarization
- Q = first negative deflection preceding R wave
- R = first positive deflection
- S = first negative deflection proceeding after R wave
Label the electrical prorogation compared to heart anatomy
1 = SA node
2 = atrial depolarization
3 = AV node
4 = His bundle
5 = left/right bundle branches
6 = Purkinje fibers
7 = ventricular depolarization
What is the ST segment?
What is its electrical voltage?
end of QRS to T wave
isoelectric – if increased/decreased
means myocardial ischemia
What is special about T wave?
ventricular repolarization
What is the QT interval? What does it measure?
start of QRS complex to end of T wave =
ventricular depolarization & repolarization
How can we calculate a heart rate independent index? (QTc)
Can we alter the duration of the QT interval?
YES - with sympathetic tone and prolonged or decreased Ca+2 entry into cell
When does the wave of depolarization reach the AV node on the ECG?
1/2 way through P wave
Describe priming the pump and its purpose
electrical activity of atria induces mechanical activity throwing about 10-15% of bld into right ventricle during depolarization
How does depolarization move through the myocardium in category A animals?
Where is the terminal wave?
endocardium to epicardium
- terminal wave = ventricular septum
What are Category A animals? Give example
- purkinje fibers on endocardial surface
- ex) dogs, cat, human, rat
What are category B animals?
How does this alter the depolarization movement?
give example
- purkinje fibers diffuse throughout the myocardium
- depolarization is simultaneous throughout ventricular myocardium
(bigger muscle takes longer to depolarize = needs to be simultaneous) - ex) horse, cow, sheep, goat, whale
When is the base-apex lead used?
What does it provide?
category B animals
provides greatest amplitude for P, QRS, and T wave
What can frontal bipolar/unipolar leads not detect in category B animals?
chamber enlargement
Where is the negative and positive terminal of the base-apex lead?
neg = right jugular vein furrow
pos = left thorax over apex beat
Label Category B ECG
- compare to lead II ECG
1 = PR interval 2 = PR segment
3 = QT interval 4 = ST segment
5 = TQ interval 6 = T wave
7 = rS complex 8 = r
9 = P wave 10 = S
How are small animals placed for ECG compared to LA?
Why?
small animals = right lateral recumbency
large animals = standing (less muscle tremor artifact on large animals)
What 4 features do we examine on an ECG?
- heart rate (atrial rate, ventricular rate)
- heart rhythm
- P-QRS-T complexes and intervals
- mean electrical axis in frontal plane (Category A only)
What is the R-R interval? What is it measuring?
What is the P-P interval? what is it measruing?
What can the mean electrical axis demonstrate?
What does a right shift indicate for the mean electrical axis?
Why?
