Lecture 04: ECG: Fundamental Theory (Hayward) Flashcards
Electrocardiography
study and interpretation of the electrical activity in the heart, as evidenced by differences in the electrical potential measured on the surface of the body
ECG
measurement of voltage changes on body over time. Displays deflections through thorax. A record of the electrical activity of the heart with respect to time.
How is dipole established for ECG?
Current flows from depolarized cells to those that are at rest, causing a difference in membrane potential, which creates electrical field/dipole on the surface. Electrical difference is recorded by electrodes
Negative wave approaching + pole is reflected on ECG as
upward (positive) deflection
repolarization
process by which cell returns to the original resting sate after being depolarized.
What are potential differences at rest?
none
what does ECG read when whole cell is depolarized?
nothing
negative wave moving towards negative pole is reflected on ECG as
downward (negative) deflection
measurement on ECG if repolarization occurs from same place that depolarization started
negative deflection
which is longer: depolarization repolarization?
repolarization
measurement on ECG if repolarization occurs in opposite direction as depolar.
positive (positive T wave deflection)
measurement on ECG if wave of depolarization moves at right angle to positive electrode
small or absent deflection
P wave represents
atrial depolarization (from RA to LA)
QRS complex represents
ventricular depolarization
T wave represents
ventricular repolarization
most common lead system
bipolar (leads on RA, LL)
flat line b/w P and QRS represents
conduction delay as depolarization passes through the AV node, Bundle of His, Bundle branches
LBB or RBB activates first?
LBB because it’s larger
Q wave represents
depolarization across the ventricular septum from L to R side
definition of R wave on ECG in lead II
first upward deflection, whether or not there’s a Q wave
Why is R always positive in lead II?
ventricles depolarize outward toward epicardium, especially on L side towards + lead
definition of S wave on ECG in lead II
downward deflection following the R wave. Reflects final depolarization of the base or back wall of the heart (neg. deflection)
Flat line b/w QRS and T wave represents
time of total ventricular depolarization before repolarization
T wave represents
ventricular repolarization. Occurs slowly and in variable directions
ATRIAL repolarization on ECG
produces low amplitude wave that typically occurs during the QRS complex and typically NOT observed
Normal sequence of activation in the heart and intervals on ECG
1) SA node
2) SA node through atrial myocardium (150 msec)
3) AV node (80-100 ms)
4) AV bundle, bundle branches, purkinje network (80 ms)
5) ventriculr myocardium (80 ms)
