17 The Electrocardiogram Flashcards
EKG’s provide info about what 5 things?
- Anatomical orientation of heart
- Size of chambers
- Rhythm/Conduction disturbances
- Ischemic damage
- Effects of altered electrolytes and drugs
In an EKG, the convention size for small mV boxes and small time boxes is what?
- 0.1 mVolt
* 0.04 sec
What does the S-T segment of an EKG signify?
-Ventricular myocytes are almost all resting/depolarized (not repolarized yet)
What does the P-R segment of an EKG signify?
-Start atrial depolarization to start ventricular depolarization (due to AV node)
What does QRS segment of an EKG signify?
-Time to depolarize the whole ventricle (due to His-Purkinje)
What does QT segment of an EKG signify?
-AP duration of ventricular myocytes
What is a dumb way to calculate heart rate, by using an EKG? (What is the equation?)
-60 divided by R-R interval
EKG’s record intra or extracellular voltage?
-Extracellular
A repolarization vector moving away from you would look like what on an EKG?
Thus, extracellular voltage in front of a DEpolarization wave is pos. or neg?
- Positive wave
- Positive
A depolarization vector moving toward you would look like what on an EKG?
-Positive wave (if you can do these 2 you can figure out the rest)
In a ventricle, does the endo or epicardium depolarize first?
-The endocardium
As time passes through one beat, the VENTRICLE depolarizes in what direction?
-Left to right across septum, then toward apex, then toward base, then toward posterior base
After depolarization of ventricle, which tissue repolarizes first?
The LAST tissue to depolarize
Where are leads 1, 2, 3 placed on the body to get an EKG?
- Right to left arm
- Right arm to left foot
- Left arm to left foot
As time passes through one ventricular contraction, describe what happens to the OVERALL direction of vectors the heart creates?
-Looking at a person face on, the first vector points toward 8:00 (down and to THEIR right) and successive vectors move counterclockwise, with the last pointing toward 2:00. (See pic, this is responsible for the shape of QRS complex)
How can you remember what aVR, aVL, and aVF are measuring?
Mneumonic:
- avR: Right arm versus sum
- avL: Left arm versus sum
- avF: Foot versus sum
What direction do leads 1,2,3 point on Einthoven’s triangle?
-Horizontal to the right
-Down and to the right
-Down and to the left
(these correspond to the positions of the leads on the person’s body, but are “backwards” because we are looking AT the person)
What is the # range for the normal QRS axis?
-30 to 90
Where are the 6 Precordial (V) leads located?
1-right 4th intercostal
2-left 4th intercostal
3,4,5,6- left 5th intercostal w/ 4th at midclavicular line
