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Glossary of EKG Basics

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What are leads V1 - V6 called?
V1, V2, V3, V4
What are 4 left lateral leads?
I, aVL, V5, V6
II, III, aVF
What is the sequence of cardiac depolarization? (5 places)
1) Sinoatrial (SA) node - pacemaker
2) Atrioventricular node
3) Bundle of His
4) Bundle braches
5) Purkinje fibers
What does P wave, QRS complex, & T wave represent?
P wave - atrial depolarization
QRS - ventricular depolarization
T wave - ventricular repolarization
What is Q?
What is R?
What is S?
Q = 1st negative portion
R = 1st postitive portion
S = 2nd negative portion or a negative portion after an R
On ECG graph paper (x axis), how many seconds is 1 small box? how many sec is 1 large box?
Sm box = 0.04 sec
Lg box = 5 sm boxes = 0.2 sec
On ECG graph paper (y axis) how many small boxes makes up 1 mV?
1mV is 10 small boxes or 2 large boxes
What is the sequence of boxes to find the heart rate (ex. 1 lg box over is ?, 2 lg boxes over is ?, etc)
300,150,100,75,60,50,43,37
1 box = 300
2 boxes = 150
3 boxes = 100
4 boxes = 75
5 boxes = 60
6 boxes = 50
7 boxes = 43
8 boxes = 37
Where is PR interval? What is normal time of this interval? What does it measure
PR interval is start of P wave to start of QRS;
120 - 200 ms (.12 - .2 s)
(< 1 big box or < 5 sm boxes)
measures atrial depolarization & delay in AV node
What prolongs PR interval (>200ms)?
What makes PR interval short (<120ms)?
PR interval prolonged if problem w/ AV node - eventually atrial rate will differ from ventricular rate;
PR interval short if impulse not being delayed - bad - extra pathway that bipasses AV node
What is QT interval a measure of? How many ms (sec) long should QT interval be?
QT interval is a measure of ventricular depolarization & repolarization
QT should be <450ms (.45sec)(just over 2 big boxes) QT should be < 1/2 of R-R interval
Which 3 leads always have a + or upright P wave in Normal sinus rhythm?
What are 3 causes of P wave varients (abnormal P waves)?
1) ectopic origin &/or sequence of atrial depolarization
2) Right atrial enlargement
3) Left atrial enlargement
What will the P wave look like if there is Rt atrial enlargement?
> 2.5mm in II, III, & aVF
What will the P wave look like if there is Left atrial enlargement?
1.
2.
1. Notched in II, III, aVF,
2. Biphasic in V1 & V2
In what direction is initial depolarization & why?
Initial depolarization (septal depolarization) is from left to right because electrical current from the bundle of His goes through left bundle branch faster (summary: 1st impule from left to right)
What will the first impulse (septal depolarization) look like in Lead I?
Inital depolarization will be negative in Lead I (Q wave)
After initial depolarization, what direction is depolarization? What deflection is seen in Lead I & what is it called?
After initial septal depolarization, direction of ventricular depolarization is from right to left (somewhat downward too). This shows a positive deflection in Lead I, called an R wave
What do these septal then complete depolarization look like on V1? on V6?
V1 is an anterior precordial lead: 1st impulse towards, 2nd away so small R wave, large S wave

V6 is a left lateral lead so 1st impulse is away & 2nd is towards so small Q wave & large R wave
V5 & V6 will look similar to Lead I
Which precordial leads will be mirror images of each other?
V1 & V6 will be mirror images
Q waves
Can be normal esp in V1
Patholgical if:
1. Width of .04 sec or >
2. Amplitude 1/3 of QRS
ST segment
Not necessarily pathological if <0.1mV elevation
U wave
May be normal
Usually associated with Hyperkalemia