EKG Basics Flashcards
The vertical axis of an EKG strip measures?
measure voltage in millimeters (mm) or Millivolts (mV)
The horizontal axis of an EKG strip measures?
measures units of time in milliseconds
Each vertical small box of an EKG represents how many mm/mV?
1 mm or 0.1 mV
Each horizontal small box of an EKG represents how much time?
40 milliseconds (msec) or .04 sec
What is the lead marker on an EKG strip?
straight vertical line that indicates every 3 seconds
What is the standardization bar on an EKG strip?
Found on the fore most left of the strip and indicates the EKG machine is properly calibrated
Specifications of the standardization bar indicating the EKG machine is properly calibrated?
- 10 mm tall or 2 large squares high
- 0.20 sec or 1 large square wide
Each vertical large box of an EKG represents how many mm/mV?
5 mm/0.5 mV or 5 small boxes
Each horizontal large box of an EKG represents how many msecs?
0.20 secs or 200 milliseconds
The limb leads of an EKG shows the activity of which part of the heart?
the frontal plane, from top to bottom
Which EKG leads are limb leads?
- I, II, III
- aVR, aVL, aVF
- are bipolar leads
The precordial or chest leads of an EKG show which the activity of which part of the heart?
activity of the horizontal plane from front to back
Which EKG leads are precordial or chest leads?
V-leads (V1 - V6)
What is the Isoelectric line on an EKG?
Baseline of an EKG and is the straight line before the the p-wave
What is the J-Point of an EKG?
The point marking the end of the QRS complex and the beginning of the ST segment at the isoelectric line
Sections of the heart that are depolarized by slow calcium channels?
SA and AV nodes
Sections of the heart that are depolarized by fast sodium channels?
- Bundle of His/Purkinje fibers
- atrial muscle
- ventricular muscle
What happens during Phase 0 of a fast channel (Na+) depolarization cycle?
initiates the action potential through rapid depolarization with Na+ influx into cell
What happens during Phase 1 of a fast channel (Na+) depolarization cycle?
Partial repolarization due to K+ leaving cell through iK1 channels
What happens during Phase 2 of a fast channel (Na+) depolarization cycle?
Membrane potential plateau – calcium enters cell and promotes contraction of muscle (K+ efflux continues)
What happens during Phase 3 of a fast channel (Na+) depolarization cycle?
- Rapid repolarization
- Na+ out and K+ in
What happens during Phase 4 of a fast channel (Na+) depolarization cycle?
- Membrane potential stable
- cell is in a polarized state and ready for depolarization
What happens to cardiac cells if no stimulus is received?
They will depolarize by themselves due to the eventual influx of Na+
Where are the cardiace pacer cells located?
SA and AV node
What happens during Phase 0 of a slow channel (Ca++) depolarization cycle?
slow depolarization due to slow influx of Ca++
What action do epi and NE have on cardiac Ca++ channels?
Epi and NE stimulate B1 receptors, opening Ca++ channels; sympathetic response that increase the HR
What action does acetylcholine have on cardiac Ca++ channels?
acetylcholine stimulates the vagus nerve, preventing the opening of the Ca++ channels; parasympathetic response that slows the HR
What happens during Phase 1 of a slow channel (Ca++) depolarization cycle?
there is no phase 1 or rapid depolarization of the Ca++ channels
What happens during Phases 2 & 3 of a slow channel (Ca++) depolarization cycle?
Slow repolarization as Ca++ is pumped out of the cell
What is the normal vector/direction for Lead I?
RA to LA
What is the normal vector/direction for Lead II?
RA to RL
What is the normal vector/direction for Lead III?
LA to LL
Which leads are known as the limb leads?
aVR, aVF, aVL
Which leads are known as the precordial leads?
V1-V6
What is a normal QRS duration?
80-100 ms
What is a normal P-R interval?
120-200 ms
What is a normal QT interval?
400-440 ms
What is a normal QTc for males?
< 420 ms
What is a normal QTc for females?
< 440 ms
