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)
Where is the P wave here?
2 sharp waves before the QRS
Where is the P wave here?
Inverted and superimposed on the ST-segment
Normal:
- P wave length
- QRS length
- PR interval: 3-5 small squares (120-200 ms)
- P wave : < 3 squares (<120 ms)
- QRS 1.5-2.5 small squares (<120 ms)
If you have a QRS, you must have _____
A T wave
How to name the waves in QRS when:
- the first deflection is up
- the first deflection is down
first deflection up: R wave
first deflection down: Q wave
Characteristics of a sinus pacemaker
- max rate 220 -age
- always has a P wave preceding QRS
- normal PR interval from delay in AV node
- regular rhythm
What are is the bpm for the following pacemakers:
SA node
atria
AV node
His bundle
Purkinje cells
myocardial cells
SA: 60-100
Atrial: 55-60
AV node: 45-50
His bundle: 40-45
Purkinje cells: 35-40
Myocardial: 30-35
The AV node is always supplied by what?
The right coronary artery
What plane are the precordial leads in? Which end is positive?
The horizontal plane of the AV node. The end with the electrode is always positive, and the line from each goes through the AV node.
Which part of the heart does each precordial lead “see”?
V1, V2: septal wall
V3, V4: anterior wall
V5, V6: lateral wall
Which leads are anterior, inferior, lateral and septal?
- Anterior – V1-V6
- Inferior – II, III, AVF
- Lateral – V4-V6, I, AVL
- Septal – V1-V2
What part of an ECG varies with respiration?
only the T-P interval (e.g. PR, QRS and ST all stay the same)
What are the 2 broad processes that arrhythmias result from?
- impaired/altered conduction
- impaired/altered automaticity
Define tachyarrythmia and bradyarrhythmia
Tachyarrhythmia: an inappropriately fast heart rate (>100 bpm)
Bradyarrhythmia: an inappropriately slow heart rate (<60 bpm)
What can alter the automaticity of the pacemaker cells to make them fire more slowly?
- more negative RMP
- increased PNS
- decreased phase 4 slope (slower funny current)
- making the threshold potential more positive
What are 1st, 2nd and 3rd degree conduction blocks?
1st degree:
- delay in AV node conduction
- PR is uniformly prolonged, but P:QRS is 1:1
2nd degree (AKA Mobitz 1 or Wenckebach)
- PR interval lengthens with each beat until a beat is dropped, then the cycle starts again.
2nd degree (AKA Mobitz 2)
- PR interval constant
- dropped QRSs, but the P:QRS ratio is usually constant
3rd degree
- complete dissociation between atrial and ventricular contraction
- P wave rate and QRS rate are different
- QRS may be normal or wide depending on where the escpe beat comes from
*** these are all in the AV node and can result in bradyarrythmia***
What is a re-entry circuit? What kinds are there?
Re-entry requires two things:
- a fast pathway with long refractory period
- a slow pathway with a short refractory period
If the fast pathway is blocked (e.g. it is still in its refractory period), the impulse will travel slowly down the slow pathway. If by this point the fast pathway is ready-to-go again, the impuls travels retrograde up the fast pathway and depolarizes the slow pathway again.
Can by micro re-entry or macro (as in Wolfe-Parkinson-White syndrome)
What are afterdepolarizations?
An abnormal depolarization (it happens in the middle of the AP, or just after repolarization)
Can result in tachyarrhytmias…
What is this and why?
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What is this? Is this normal? Who might not have this?
Sinus arrhythmia. The Hr normally increases with inspiration and slows with expiration.
People with autonomic dysfunction may not have this (e.g. diabetics
What is this and why?
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Atrial flutter with atrial rate 300, 4:1 AV block, and ventricular rate of 75
What is this and why?
Atrial flutter with 2:1 block. Difficult to see P waves
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What is SVT? What can be called SVT?
SVT is a blanket statement for any narrow QRS complex tachycardia in which the P waves are not obvious. The most important learning point regarding SVT is that it is not one rhythm, but rather a classification that encompasses many rhythms. The term is used to differentiate these tachycardias from VT (ventricular tachycardia) which is a wide QRS tachycardia, is usually more dangerous and is treated with different drugs.
E.g: sinus tachycardia, atrial tachycardia, atrial flutter, atrial fibrillation and re-entry tachycardias
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