EKG Flashcards
Describe the electrical status of a myocardial cell at rest?
The interior of the cell in negative while the exterior is positive with the membrane acting as an insulator.
When the myocardial cell is at rest, what is the resulting electrical status called?
Polarized, since the positive and negative charges are on opposite sides or ends.
What happens to the myocardial cell during depolarization?
Positive (Na+) ions move INTO the cell
What is a lead axis?
A straight line drawn between a positive and negative lead.
What type of lead measurement is involved in Einthoven’s Triangle?
Bipolar as the leads measure the potential between two limbs, not a single site
Which leads are bipolar?
I, II, III
What are the unipolar leads?
VR, VL, VF and precordial leads
Placement of leads V1, V2
Sternal border at 4th intercostal space
Placement of V3
Midpoint between V2 and V4
Placement of V4
Left MCL, 5th ICS
Placement of V5
“Anteroaxiallry line even with V4 (5th ICS)
Placement of V6
Midaxillary line at the 5th ICS
In what plane do the unipolar chest leads measure the cardiac vector?
Horizontal
In what plane do the Bipolar leads and augmented leads measure the cardiac vector?
Frontal
On an EKG tracing, what does the vertical axis measure?
Voltage
On an EKG tracing, what does the horizontal axis measure?
Time
What is the measurement of the “small” squares? (distance)
1mm
What is the measurement of the “big” squares? (distance)
5mm
In regards to time, what does one small square equal?
0.04 seconds OR 40 milliseconds (ms)
In regards to time, what does one big square equal?
0.2 seconds or 200ms
In regards to time, what does 5 large squares equal?
1 second or 1000ms
How long is the rhythm strip?
10 seconds
What does the T wave represent?
repolarization of the ventricles
What does the QRS wave represent?
depolarization of the ventricles
What does the P wave represent?
Depolarization of the atria
What determines the measurement of the cardiac axis?
The mean QRS vector
What 2 leads are used to determine axis?
I, and aVF
Normal PR interval in ms and boxes
0.12-.20 or 3-5 small boxes
Normal QRS in ms and boxes
0.06-0.12 ms or 1.5-3 small boxes
Normal QT interval in ms and boxes
0.36-.44 or 9-11 small boxes
Describe the “1500 Method” or determining rate?
In a REGULAR rythm, count the number of small boxes between R waves and divide that INTO 1500 to equal the rate per minute.
EX: 37.5 small boxes
1500/37.5= 40 bpm
If the QRS complex in Lead I and aVF are positive, what is the axis deviation?
Normal
If QRS complex in Lead I is positive and aVF is negative, what is the axis deviation?
Left
If QRS complex in Lead I is negative and aVF is positive, what is the axis deviation?
Right
If QRS complex in Lead I is negative and aVF is negative, what is the axis deviation?
Extreme axis leftward and upward (-90-180)
Causes of Left axis deviation (4)
- LVH
- LBB/LFB
- Inferior wall MI
- Raised Diaphragm (ascites, pregnancy, organomegaly)
Causes of Right axis deviation?
- RV overload
- RBB
- Lateral wall MI
- emphysema
- RV strain (PE, pulmonary stenosis, pulmonary HTN, chronic lung disease)
