Lecture 23: ECG 1 and 2

Question 1

What do recording electrodes detect?

Answer 1

A small portion of the electrical activity that has reached the body surface

Question 2

ECG

Answer 2

The graphic record of the electrical activity that reaches the surface of the body as a result of cardiac depolarization and repolarization

Question 3

Where can electrodes be placed to record the electrical activity of the heart

Answer 3

Anywhere on the surface of the body, however waves will look differently on left vs right

Question 4

Why do waves look different on left versus right?

Answer 4

1. There is a positive deflection on the ECG when a wave of depolarization moves towards a positive electrode
2. A negative deflection when a wave of depolarization moves away from a positive electrode

Question 5

What waves do electrodes record?

Answer 5

Depolarization and repolarization

Question 6

What are used to monitor electrical forces in the heart?

Answer 6

ECG leads (sets of reference electrodes)

Question 7

What depend on how the electrical forces align to the leads of the ECG recording

Answer 7

direction, magnitude, and deflections

Question 8

Lead

Answer 8

When an ECG machine is connected between recording electrodes at two points on the body, the specific arrangement of each pair of connections

Question 9

What is the right leg electrode used for?

Answer 9

An electrical ground, NOT for measurement

Question 10

The standard ECG consists of how many leads?

Answer 10

12

Question 11

Each lead views the heart at a

Answer 11

Unique Angle (Angle of Orientation)

Question 12

What are the locations of the 12 leads?

Answer 12

6 are limb, 6 are precordial (chest)

Question 13

In vet med, what leads are used most frequently

Answer 13

The three limb standard leads

Question 14

How is an electrode designated as positive or negative?

Answer 14

Automatically by the ECG machine

Question 15

The angle of each lead can be determined by

Answer 15

Drawing a line from the negative to the positive electrode

Question 16

Bipolar limb leads

Answer 16

One limb electrode is the (+) pole and another is the (-) pole

Question 17

Augmented (unipolar) limb leads

Answer 17

• Single electrode is chosen as the (+) pole
• There is no single (-). Rather, all the other electrodes are averaged together to create a composite (-) reference
• When the active electrode is the RA, LA, or LF, the lead is designated aVR, aVL, or aVF respectively.

Question 18

What does aV stand for?

Answer 18

Augmented voltage

Question 19

Axial Reference System

Answer 19

Angles of orientation of limb leads

Question 20

Each ECG electrode records only the ____ _____ ____ at any given moment

Answer 20

average current flow

Question 21

Although tiny swirls of current may be going off in every direction, each lead only records

Answer 21

the instantaneous average of these forces

Question 22

The average movement of forces is represented by

Answer 22

a single arrow or vector

Question 23

Describe ECG paper

Answer 23

A long, continuous roll of graph paper, with light and dark lines running vertically and horizontally

Question 24

What do light lines of ecg circumscribe

Answer 24

1mm x 1mm

Question 25

What do dark lines of ecg circumscribe

Answer 25

5mm x 5mm

Question 26

Horizontal axis of ecg paper measures

Answer 26

time (duration)

Question 27

The width of each square represents

Answer 27

0.04 seconds

Question 28

The vertical lines measure

Answer 28

voltage and amplitude

Question 29

Voltage calibration

Answer 29

A 1mV electrical signal will produce a deflection measuring 10 mm

Question 30

Waves that appear on an ECG reflect

Answer 30

the electrical activity of myocardial cells which comprise the vast bulk of the heart

Question 31

What generally aren’t seen by the ECG

Answer 31

pacemaker activity and transmission by the conducting system

Question 32

Three main characteristics of waves

Answer 32

1. Duration
2. Amplitude
3. Configuration

Question 33

Duration

Answer 33

measured in fractions of a second

Question 34

Amplitude

Answer 34

measured in mV

Question 35

Configuration

Answer 35

The shape and appearance of a wave

Question 36

Three things happen to a wave on the ECG when a chamber hypertrophies (enlarges):

Answer 36

1. The chamber may take longer to depolarize, therefore the ecg wave may therefore increase in duration
2. The chamber may generate more current and thus a larger voltage, therefore the ecg wave may increase in amplitude
3. A larger percentage of the total electrical current may move through the expanded chamber, therefore the main electrical vector of the ECG wave may shift

Question 37

The first step in determining the rhythm of the heart is to determine the

Answer 37

heart rate

Question 38

First vector represents

Answer 38

septal depolarization

Question 39

Each successive vector represents

Answer 39

progressive depolarization of the ventricles

Question 40

The vectors swing progressively leftward because

Answer 40

the electrical activity of the much larger ventricle increasingly dominates the ECG

Question 41

Mean vector

Answer 41

The average vector of all instantaneous vectors

Question 42

Mean electrical axis

Answer 42

• The direction of the mean vector

- The average of all the instantaneous vectors that are generated as the ventricles depolarize

Question 43

Each species has a normal range for its mean electrical axis. Therefore values outside this range suggest

Answer 43

a myocardial abnormality