Lecture 04: ECG: Fundamental Theory (Hayward)

Question 1

Electrocardiography

Answer 1

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

Question 2

ECG

Answer 2

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.

Question 3

How is dipole established for ECG?

Answer 3

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

Question 4

Negative wave approaching + pole is reflected on ECG as

Answer 4

upward (positive) deflection

Question 5

repolarization

Answer 5

process by which cell returns to the original resting sate after being depolarized.

Question 6

What are potential differences at rest?

Answer 6

none

Question 7

what does ECG read when whole cell is depolarized?

Answer 7

nothing

Question 8

negative wave moving towards negative pole is reflected on ECG as

Answer 8

downward (negative) deflection

Question 9

measurement on ECG if repolarization occurs from same place that depolarization started

Answer 9

negative deflection

Question 10

which is longer: depolarization repolarization?

Answer 10

repolarization

Question 11

measurement on ECG if repolarization occurs in opposite direction as depolar.

Answer 11

positive (positive T wave deflection)

Question 12

measurement on ECG if wave of depolarization moves at right angle to positive electrode

Answer 12

small or absent deflection

Question 13

P wave represents

Answer 13

atrial depolarization (from RA to LA)

Question 14

QRS complex represents

Answer 14

ventricular depolarization

Question 15

T wave represents

Answer 15

ventricular repolarization

Question 16

most common lead system

Answer 16

bipolar (leads on RA, LL)

Question 17

flat line b/w P and QRS represents

Answer 17

conduction delay as depolarization passes through the AV node, Bundle of His, Bundle branches

Question 18

LBB or RBB activates first?

Answer 18

LBB because it’s larger

Question 19

Q wave represents

Answer 19

depolarization across the ventricular septum from L to R side

Question 20

definition of R wave on ECG in lead II

Answer 20

first upward deflection, whether or not there’s a Q wave

Question 21

Why is R always positive in lead II?

Answer 21

ventricles depolarize outward toward epicardium, especially on L side towards + lead

Question 22

definition of S wave on ECG in lead II

Answer 22

downward deflection following the R wave. Reflects final depolarization of the base or back wall of the heart (neg. deflection)

Question 23

Flat line b/w QRS and T wave represents

Answer 23

time of total ventricular depolarization before repolarization

Question 24

T wave represents

Answer 24

ventricular repolarization. Occurs slowly and in variable directions

Question 25

ATRIAL repolarization on ECG

Answer 25

produces low amplitude wave that typically occurs during the QRS complex and typically NOT observed

Question 26

Normal sequence of activation in the heart and intervals on ECG

Answer 26

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)