ECG Flashcards
What are the bipolar limb leads?
What are the unipolar limb leads?
What is the hexaxial system?
All the frontal leads superimposed on each other. 0 degrees is the positive end of lead I, and then negatives are on the top and positives are on the bottom. Each lead is 30 degrees apart.
What is the ventricular mean electrical axis? What are the bounds (on the hexaxial system)?
It is the AVERAGE of all the depolarization vectors. Normally points down and to the left.
How to determine the MEA?
- You need two perpendicular lead (e.g. I and aVF or III and aVL
- For each lead decide whether the QRS complex is mostly up or mostly down
- If it is mostly up, shade in the half of the circle by the positive end of the lead and vice versa for mostly down.
- Repeat with the second lead
- The overlapping area is the MEA
Quick MEA tricks for aVF/I:
- normal axis
- right axis deviation
- LAD
- Normal: upwards in both
- RAD: downward in 1
- LAD: positive in lead I, negative in aVF and II
When do you need to use a “tiebreaker” lead to determine the MEA? Which lead do you use?
If there is LAD… that’s because the normal MEA goes all the way up to -30
Lead 2 tiebreaks ?LAD in aVF/I pairs. This is because it is perpendicular to the -30 line.
What does an isoelectric lead signify? What does it not tell you?
If a lead is isoelectric it means that the depolarization moves towards it and then away from it equally. This can only happen if teh depolarization is perpendicular to the lead. So an isolectric lead (upward deflection=downward deflection) means the MEA is perpendicular to that lead.
It DOES NOT tell you which direction the vector is facing.
Why does the rhythm strip use lead I or II?
- they show the P waves well.
Upward deflection means ____ downward deflection means___
Upward: charge (depolarization) is moving towards lead
Downward: charge is moving away from lead
What is a lead?
It is the potential difference between to electrode recorder (i.e. it is not the wire itself, but the comparison between 2 electrodes)
What is happening during each phase of an ECG (P wave, PR segement, QRS, ST segment, T wave)?
What is the difference between a segment and an interval?
Intervals contain waves, segments are isoelectric
What is the max sinus rhythm?
220-age
What is a junctional pacemaker?
The AV node (it is at the junction of the atria and ventricles)
Escape beats vs. premature beats
A premature beat occurs early than expected, and escape beat occurs later than expected (e.g. the expected beat doesn’t happen)
** both are “ectopic beats”
Electrical conduction moves _______ through muscle and ________ through the conducting system
- slowly
- quickly
How to measure rate
5 large squares= 1 second
1 large square= 0.2 seconds (200 ms)
1 little square= 0.04 seconds (40 ms)
So,
- divide 300 by the number big squares between each beat.
- count the number of beats in 3 seconds (15 large squares) and multiply by 20
- Start at the peak of QRS and count down for each big square: 300, 150, 100, 75, 60, 50
What are the 3 kinds of rhythm?
- regular (including regular with an early beat)
- irregular with a pattern
- iregular without a pattern
What is the rate and rhythm?
~75 bpm, regular
What is the rhythm?
Irregular with a pattern
What is the rhythm?
Irregularly irregular
What are the 4 questions to ask for P waves?
1) Are they present?
2) What is their shape and size? (e.g. inversion? constant?)
3) Are there more or fewer than QRS?
4) What is their relationship to the QRS? (e.g.some P’s have no QRS)