17& 18 EKG Flashcards
Which EKG leads provide information in the frontal plane of the body?
Bipolar limb leads - I, II, and III
Augmented unipolar limb leads- aVR, aVL, and aVF
Which EKG leads provide information in the transverse plane of the body?
Precordial leads V1-V6
What information can be obtained from an EKG?
1) Pattern and frequency of events
2) Conduction time
3) Direction of depolarization and repolarization
3) size of chamber
What are the things an EKG cannot tell you?
1) Not a lot about mechanical activity (contraction and relaxation) except during ventricular fibrillation
2) It does not make an diagnosis
What does the P wave correspond to?
Atrial depolarization
What does the PR segment correspond to?
AV nodal delay
What does the QRS complex correspond to?
Ventricular depolarization
What does the ST segment correspond to?
The time during which the ventricles are contracting and emptying ( completion of ventricular depolarization and beginning of ventricular repolarization)
-Also corresponds to the plateau of the ventricular action potential
What dos the T wave correspond to?
Ventricular repolarization
What does the TP interval correspond to?
Time during which the ventricles are relaxing and filling
Where does the PR segment start and stop?
Starts at the end of the P wave and stops at the beginning of the Q wave
Where does the PR interval begin and end?
Begins at the start of the P wave and ends at the start of the Q wave
What is the difference between a segment and interval?
A segment is a period of time BETWEEN waveforms that is normally isoelectric. And interval is a period of time that INCLUDES wave
Are the Q, R, and S waves present in all QRS complexes?
They do not have to be
What can T wave inversion indication?
Coronary ischemia or left ventricular hypertrophy
What can tall and narrow T waves indicate?
Hyperkalemia
What can flat T waves represent?
Coronary ischemia or hypokalemia
Why is the T wave an upper deflection?
Repolarization of the membrane. Repolarization of the ventricle happens in the opposite direction of depolarization and is a negative current. This double negative of direction and charge is why the T wave is positive.
The cell becomes more negatively charged, but the net effect is positive, so the EKG reports it as positive
Where is the wave for atrial repolarization?
Masked behind the QRS segment
Where is the depolarization of the SA and AV node seen on an EKG? Why?
They are not reflected by a wave in the EKG because the mass of the tissue is too small
What is used as a baseline to evaluate for ST segment displacement?
The PR segment
What does the PR interval represent?
Time for atrial depolarization and the delay through the AV node
What is the normal value for a PR interval?
0.12-0.20 seconds- ONE LARGE BOX
What is the QT interval?
Measured from the onset of the QRS complex to the end of the T wave
What does the QT interval correspond to?
The time for ventricular depolarization and repolarization (time for ventricular action potential)
-Very dependent on heart rate
What is the P-P interval?
The time between consecutive atrial depolarizations, measured from beginning of one P to the beginning of the next P
What can the P-P interval be used to determine?
Atrial rate
What is the R-R interval?
Time between consecutive ventricular depolarizations, measured between beginning of one QRS to the beginning of the next QRS
What can the R-R interval be used to determine?
Ventricular rate
This will not always be identical to the P-P interval
HR is typically determined using what?
The R-R interval
How much time is one large box on EKG?
0.20 seconds
How much time is one small box on EKG?
0.04 seconds
What is the calculation to get heart rate from an EKG?
HR= 300/ #large squares per cycle
What is LAD?
When the mean QRS axis is more negative than 0 degrees
What is RAD?
When the mean QRS axis is more positive than 90 degrees
What are common causes for LAD?
LV hypertrophy, obesity, and pregnancy
What are the common causes for RAD?
RV hypertrophy, LV infarct, and a tall, thin body type
What is a prolonged PR interval?
A PR interval greater than 200 ms
What is a 1st degree AV block?
Prolonged P-R interval greater than 200ms due to slowed conduction through the AV node or bundle of his.
-There is a P wave for every QRS complex
What is a second degree AV block?
- Partial dissociation of atria and ventricles
- Not every P wave is followed by a QRS complex
What is a 3rd degree AV block?
- Complete heart block
- No conduction though the AV node
- Complete dissociation of atria and ventricles
- P and QRS are completely independent of one another
