Lecture 8 - Basis of ECG Flashcards
what is the resting membrane potential of a cardiac myocyte
-90mV
what cations are in high concentrations extracellularly
sodium and calcium
what cations are in high concentrations intracellularly
potassium
what has the longest repolarization period
a. motor neuron
b. skeletal muscle
c. cardiac ventricle
c. cardiac ventricle
the size of the wave on an ECG is dependent on what
area and cos function
describe the 5 steps of normal depolarization
- SA node spontaneously depolarizes
- wave spreads across atria R-L,Cr-caud, d-v
- conduction slowed in AV node
- rapid conduction through his bundle
- myocardium completely depolarized
P-wave
atrial depolarization
P-Q interval
delayed conduction through AV node
QRS complex
ventricular depolarization
S-T segment
ventricular myocardium is completely depolarized
T wave
ventricular repolarization
what information is gained from the ECG
heart rate, rhythm, nature of depolarization and repolarization
what can an ECG provide clues about
hypertrophy and metabolic disturbances
in what position is it ideal to have a patient in for an ECG
right lateral recumbency
what angle is associated with aVR
-150
what angle is associated with aVL
-30
what angle is associated with I
0
what angle is associated with II
60
what angle is associated with aVF
90
what angle is associated with III
120
what will create artifacts on an ECG
movement, tremor, breathing
how is heart rate measured from the ECG
R-R intervals in 6sec x 10
how is instantaneous heart rate measured from the ECG
60,000/R-R interval in msec
1500/R-R @25mm/sec
3000/R-R @ 50mm/sec
P-R interval
speed of conduction from SA node and atria to the ventricles
P wave duration
larger = left atrial enlargement
QRS duration
time taken to depolarize ventricles
Q-T interval
time takes for ventricles to depolarize and repolarize
what is the Q-T interval affected by
electrolyte disturbances (hypocalcemia)
drugs (potassium current disruptors)
alterations in amplitudes can reflect what
changes in myocardial mass and chamber volumes
and increased P wave indicates
R atrial enlargement
increased R wave indicates
L ventricular enlargement
increased T wave amplitude indicates
drug, electrolyte, acid-base disturbances
T/F: increased T wave amplitude can be normal in dogs
TRUE
