EKG Flashcards
what information do limb leads provide
provide information in the frontal plane of the body
what are the limb leads
- bipolar limb leads (I,II,II)
- augmented unipolar limb leads (aVR, aVL, aVF)
what are the bipolar limb leads
I, II, III
What are the augmented unipolar limb leads
aVR, aVL, aVF
what information does the chest leads provide
provide information in the transverse plane of body
what are the chest leads
precordial leads V1-V6
what information can be obtained from an EKG
- pattern and frequency of events
- conduction time
- direction of depolarization and repolarization of cardiac structures
- size of chamber
list the sequence of electrical events in the heart
- SA node
- AV node
- Bundle of His
- Bundle branches (left and right)
- Purkinje fibers
impulse passes from atria into ventricles through which node
AV node
what happens with conduction to ensure atrial contraction precedes ventricular contraction to allow complete ventricular filling
Action Potential briefly delayed at AV node
impulse travels rapidly down interventricular septum via
bundle of His
impulse rapidly disperses throughout myocardium by means of
purkinje fibers
interval
a period of time that includes waves
segments
a period of time between waveforms
- normally isoelectric
what is the P wave? how many seconds is it in duration normally
- depolarization of both atria
- first wave in cardiac cycle
- 0.08-0.10 seconds
what is the QRS complex
depolarization of both ventricles
how many seconds is the QRS in duration normally
0.05-0.10 sec
what is the T wave
repolarization of the ventricles
what does T wave inversion indicate
may indicate coronary ischemia or left ventricular hypertrophy
tall and narrow (“peaked” or “tented”) symmetrical T waves may indicate what condition
hyperkalemia
flat T waves may indicate what condition
coronary ischemia or hypokalemia
why is the T wave an upward deflection
repolarization of the ventricle is a negative current and it happens in the opposite direction of depolarization
- this double negative (charge and direction) causes T wave to be positive
why is the depolarization of the SA and AV nodes not reflected by any wave in the EKG
mass of tissue is too small
what is the U wave
- not always seen
- repolarization of papillary muscles
prominant U waves are seen with what conditions
- hypokalemia
- hypercalcemia
- thyrotoxicosis
what is the P-R interval
- measured from beginning of P wave to the beginning of the QRS complex
- represents time for atrial depolarization and the delay through the AV node
what is the normal value for the P-R interval
0.12-0.20 seconds
what is the P-R segment
- isoelectric period between end of P wave and beginning of QRS complex
- period between atrial and ventricular depolarization
what is the P-R segment used as a baseline for
to evaluate the EKG for QRS complex or S-T segment displacement
what is the Q-T interval
- measured from onset of QRS complex to end of T wave
- time for ventricular depolarization and repolarization
- approximates the time for a ventricular action potential
what is the Q-T interval dependent on
heart rate
what is the S-T segment
- period of time between end of QRS complex and beginning of T wave
- corresponds to period between completion of ventricular depolarization and beginning of ventricular repolarization
- corresponds to plateau of ventricular action potential
- isoelectric
what is the P-P interval
- time between consecutive atrial depolarizations
- measured from beginning of one P to beginning of next P
- can be used to determine atrial rate
What is R-R interval
- measured from beginning of one QRS to beginning of next QRS
- can be used to determine ventricular rate
what is the normal length of ST segment
0.36 seconds
what is average time for normal T wave
0.16 seconds
what is the TP interval
ventricles are relaxing and filling
x axis on EKG reads paper speed. paper speed = what mm/sec
25 mm/sec
y axis on ekg measures voltage gain. voltage gain = what mV/cm
1 mV/cm
identify voltage polarities
- up = positive
- down = negative
- baseline (0mV) is the isoelectric line
big boxes on EKG represent how much time
0.2 seconds
a small box within a big EKG box correlates to how many seconds
0.04 seconds
a big box on EKG correlates to what volgate gain
0.5 mV
a small box on EKG represents what voltage gain
0.1 mV
how do you determine heart rate in an EKG: (not quick estimation)
- rate (bpm) = beats per 6 seconds x 10
- determine how many QRS complexes are in a 6 second interval: first QRS complex is time zero
6 seconds = how many large boxes
30 large boxes
what is the quick estimation to determine HR on a EKG
HR = 300/# large squares per cycle
what are A-V nodal conduction blocks
- partial or complete failure of the AV node to spread the action potential from atria to ventricles
