Lecture 23: ECG 1 and 2 Flashcards

1
Q

What do recording electrodes detect?

A

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

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2
Q

ECG

A

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

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3
Q

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

A

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

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4
Q

Why do waves look different on left versus right?

A
  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
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5
Q

What waves do electrodes record?

A

Depolarization and repolarization

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6
Q

What are used to monitor electrical forces in the heart?

A

ECG leads (sets of reference electrodes)

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7
Q

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

A

direction, magnitude, and deflections

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8
Q

Lead

A

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

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9
Q

What is the right leg electrode used for?

A

An electrical ground, NOT for measurement

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10
Q

The standard ECG consists of how many leads?

A

12

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11
Q

Each lead views the heart at a

A

Unique Angle (Angle of Orientation)

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12
Q

What are the locations of the 12 leads?

A

6 are limb, 6 are precordial (chest)

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13
Q

In vet med, what leads are used most frequently

A

The three limb standard leads

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14
Q

How is an electrode designated as positive or negative?

A

Automatically by the ECG machine

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15
Q

The angle of each lead can be determined by

A

Drawing a line from the negative to the positive electrode

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16
Q

Bipolar limb leads

A

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

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17
Q

Augmented (unipolar) limb leads

A
  • 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.
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18
Q

What does aV stand for?

A

Augmented voltage

19
Q

Axial Reference System

A

Angles of orientation of limb leads

20
Q

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

A

average current flow

21
Q

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

A

the instantaneous average of these forces

22
Q

The average movement of forces is represented by

A

a single arrow or vector

23
Q

Describe ECG paper

A

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

24
Q

What do light lines of ecg circumscribe

25
What do dark lines of ecg circumscribe
5mm x 5mm
26
Horizontal axis of ecg paper measures
time (duration)
27
The width of each square represents
0.04 seconds
28
The vertical lines measure
voltage and amplitude
29
Voltage calibration
A 1mV electrical signal will produce a deflection measuring 10 mm
30
Waves that appear on an ECG reflect
the electrical activity of myocardial cells which comprise the vast bulk of the heart
31
What generally aren't seen by the ECG
pacemaker activity and transmission by the conducting system
32
Three main characteristics of waves
1. Duration 2. Amplitude 3. Configuration
33
Duration
measured in fractions of a second
34
Amplitude
measured in mV
35
Configuration
The shape and appearance of a wave
36
Three things happen to a wave on the ECG when a chamber hypertrophies (enlarges):
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
37
The first step in determining the rhythm of the heart is to determine the
heart rate
38
First vector represents
septal depolarization
39
Each successive vector represents
progressive depolarization of the ventricles
40
The vectors swing progressively leftward because
the electrical activity of the much larger ventricle increasingly dominates the ECG
41
Mean vector
The average vector of all instantaneous vectors
42
Mean electrical axis
- The direction of the mean vector | - The average of all the instantaneous vectors that are generated as the ventricles depolarize
43
Each species has a normal range for its mean electrical axis. Therefore values outside this range suggest
a myocardial abnormality