EKGs Flashcards
Is depolarization a process or a state?
Process
What is an EKG electrode detecting?
The flow of current
True or false: an EKG electrode will not show anything, unless there is a change in the membrane potential/ a flow of current
True
Positive charges moving toward an electrode produces what change on the EKG (rise above isoelectric line or drop below)?
Rises above
What is the P wave a result of?
Atrial myocyte depolarization
Where does depolarization begin for each heart beat?
In the SA node
Which wave on an EKG recording represents the SA node depolarizing?
There is none–too small to detect
What does the Q wave represent (if present)?
Septal depolarization
What is the first downward deflection of an EKG recording after the P wave? Is it alway present?
Q wave, not always there
What is the first upward deflection of an EKG recording after the P wave? Is it alway present?
R wave, should always be there
What is the first downward deflection of an EKG recording after the R wave? Is it alway present?
S wave, may be present
What does the R wave represent?
Ventricular muscle depolarization
What does the T wave represent?
Repolarization of the Ventricles
Which part of the EKG recording represents atrial repolarization?
There is none–hidden in the R wave
What is occurring in the atrial muscles between the P wave and the Q wave?
Ca influx into the atrial myocytes, maintaining the depolarization
What is happening to the AP between the P wave and the Q wave?
Going through the Purkinje fibers
What does the S wave represent?
Ventricular muscle depolarization away from the electrode
What does the ST segment represent relative to the ventricular myocytes?
Plateau of the AP d/t Ca influx
What is the chart speed of EKG paper?
25 mm/min
10 mm on the EKG paper corresponds to what mV?
1 mV
5 small boxes on EKG paper represent how many seconds?
0.2 seconds
5 large boxes (25 small boxes) on EKG paper represents what amount of time?
1 second
What is the interval between the beginning of the P wave, and the Q/R wave (whichever is present)?
PR interval
What is the interval between the end of the S (or R) wave, and the beginning of the T wave?
ST segment
What is the QRS interval?
Time between onset of the Q wave, to the end of the S wave
What is the QT interval?
Time between the onset of the Q wave, and the end of the T wave
What is the normal duration for the P wave?
1-2 small boxes
What is the normal duration of the PR interval?
3-5 small boxes
What is the normal duration of the QRS complex?
<1 to 3 small boxes
What is the normal duration of the ST segment?
Roughly half of R-R interval
What is the normal duration of the QT interval?
Variable (with HR)
What are the precordial leads?
V1, V2, V3, V4, V5, V6
What are the limb leads?
I, II, & III
What are the three augmented lead?
aVR, aVL, aVF
Lead I begins and ends where?
Right arm to left arm
Lead II begins and ends where?
Right arm to left leg
Lead III begins and ends where?
Left leg to left arm
Where is the positive electrode for aVR?
Right arm
Where is the positive electrode for aVL?
Left arm
Where is the positive electrode for aVF?
Foot
Where is V1 placed on the chest?
4th intercostal space, along the right sternal border
Where is V2 placed on the chest?
4h intercostal space along the left sternal border
Where is V4 placed on the chest?
5th left intercostal space in the midclavicular line
Where is V3 placed on the chest?
Between V2 and V4
Where is V5 placed on the chest?
In line with V4, on the anterior axillary line
Where is V6 placed on the chest?
In line with V4 and V5, on the midaxillary line
What are the three features you look at in an EKG?
Rate/regularity
Mean QRS axis
Rhythm
What are the two components that you assess for, for an EKG rhythm?
Intervals
Waveform morphologies
What is the best way to determine the HR on an EKG?
R to R interval
300 / (# of large boxes) = rough HR
Why is the T wave (ventricular repolarization) in the same direction as the R waveform (ventricular depolarization)?
The + electric potential spreads from endocardial to epicardial, then repolarization spreads from epicardial to endocardial
What does the U wave represent?
Repolarization of papillary, septum, or purkinje fibers
What is the cause of the EKG findings of a STEMI?
Current is flowing between injured and normal
areas of the heart
What is characteristic of a first degree AV block?
PR interval >200 ms (5 small boxes), but all P wave followed by a QRS complex
What is characteristic of a second degree AV block?
More P wave than QRS complexes, but majority normal
What is characteristic of a third degree AV block?
None of the P waves are generating a QRS
complex
Thus Heart is being paced from below the
AV node
The magnitude of the vector/the EKG depolarization is reflecting what physiologically?
More muscle undergoing depolarization
Which lead is the 0 degree line?
Lead I
The voltage of a depolarization will be greatest when its vector is (parallel/perpendicular) to the EKG lead, and least when?
greatest = parallel Least = perpendicular
True or false: it is physiological to have a heart that is not exactly at 60 degrees relative to Lead I, and it is normal if this change within an individual
False– it is normal to not have 60 degrees, but it should be constant.
Changing axis = pathological finding
What is the angle between lead I and lead II?
60 degrees
What is the angle between lead I and lead III?
120 degrees
What is the angle between lead I and lead aVL?
-30 degrees
What is the angle between lead I and lead aVF?
90 degrees
What is the angle between lead I and lead aVR?
210 degrees
What is the axis of rotation if you see a positive deflection in lead I and aVF?
Normal axis
What is the axis of rotation if you see a negative deflection in lead I and a positive deflection in aVF?
RAD
What is the axis of rotation if you see a negative deflection in lead I and aVF?
“no man’s land”
What is the axis of rotation if you see a positive deflection in lead I and a negative deflection in aVF?
LAD
What type of deviation will obesity cause?
LAD
What type of deviation will LVH cause?
LAD
What type of deviation will RVH cause?
RAD
What type of deviation will a LBB cause?
LAD
What type of deviation will a RBB cause?
RAD
What type of deviation will a tall stature cause?
RAD
What type of deviation will a supine position cause?
RAD
Why is the Q wave negative?
Septum depolarizes from the left to the right
Why is the R wave positive?
Depolarization straight down septum
What is the cause of the S wave?
Left ventricle depolarizes from left to right
What are the two major causes of increased voltage of the QRS?
Hypertrophy
Thin chest
What are the three major causes of decreased voltage of the QRS?
Previous MI
Fluid
Large chest (COPD)
What is the cause of ST depression?
Subendocardial injury
What is the cause of ST elevation?
Epicardial injury
Charges flow toward or away from the direction of injury
Toward
A PR interval greater than 0.2 seconds is indicative of what?
AV block
A PR interval of less than .12 is indicative of what?
Pre-excitation
A QRS complex than lasts longer than .12 seconds is indicative of what?
RBB or LBB
What is the rule for determining if the QT interval is normal?
less than half of the R-R interval
