Lecture 7 Starting at Vectors

Question 1

A ________ is an arrow that points in the directionof the electrical potential generated by the _______ flow, with the arrowhead in the _______ direction

Answer 1

Vector
Current
Positive

Question 2

Axis for lead I (both arms), what do the following equal?
R-arm = ?
L-arm = ?
Direction of Lead = ?

Answer 2

R = negative
L = positive
Direction of lead = 0 degrees

Question 3

Axis for lead II (r-arm and l-leg), what do the following equal?
Arm = ?
Leg = ?
Direction of Lead = ?

Answer 3

Arm = negative
Leg = positive
Direction of Lead = 60 degrees

Question 4

Axis for lead III (l-arm and l-leg), what do the following equal?
Arm = ?
Leg = ?
Direction of Lead = ?

Answer 4

Arm = negative
Leg = positive
Direction of Lead = 120 degrees

Question 5

When is the voltage recorded in the ECG very low?

Answer 5

when the vector in the heart is in a direction almost perpendicular to the axis of the lead

Question 6

What happens when the heart vector has almost the same axis as the axis of the lead?

Answer 6

The entire voltage of the vector will be recorded

Question 7

What do we call the summated vector of the generated potential at a particular instant?

Answer 7

Instantaneous mean vector

Question 8

With respect to the base of the heart, the apex of the heart remains ______ as a result of the depolarization wave through the ventricles

Answer 8

Positive

Question 9

What is the mean electrical axis of the heart?

Answer 9

59 degrees

The direction of the electrical potential (- to +) from the base of the ventricles toward the apex

Question 10

In T-waves, what is the greatest portion of ventricular mass to repolarize first?

Answer 10

The entire ouster surface, especially near the apex

Question 11

In T-waves, what areas normally repolarize last?

Answer 11

Endocardial

Question 12

In T-waves, where is the ventricular vector during repolarization?

Answer 12

Towards the apex of the heart

Question 13

Is the normal T-wave in all three bipolar leads positive or negative?

Answer 13

Positive

Question 14

In the P-wave, where does atrial depolarization begin?

Answer 14

Sinus node

Question 15

In the P-wave, what direction is the atrial vector generally in?

Answer 15

In the direction of the axes of the three standard bipolar limb leads

Question 16

P-wave ECG is normally _____ in all three leads

Answer 16

positive

Question 17

In atrial T-wave, is the spread of depolarization through the atrial muscle faster or slower than in the ventricles?

Answer 17

Slower

Question 18

In the atrial T-wave, what is the first part to become repolarized?

Answer 18

Sinus node

Question 19

What is different about each lead?

Answer 19

Each lead provides a different perspective on the voltage differences between areas of the heart

Question 20

Name abnormal ventricular conditions that cause axis deviation (5):

Answer 20

Change in position of heart in the chest
Hypertrophy of one ventricle
Bundle branch block 
Fluid in pericardium 
Pulmonary emphysema

Question 21

High-voltage ECG is said to occur when the sum of the voltages of all the QRS complexes of the three standard leads is greater than ____

Answer 21

4 mV

Question 22

What is the most common cause of High-Voltage ECG?

Answer 22

Hypertrophy of the ventricle

Question 23

What causes decreased voltage in the standard bipolar leads?

Answer 23

Cardiac myopathies

Conditions surrounding the heart

Question 24

How long does a normal QRS last?

Answer 24

0.06 to 0.08 seconds

Question 25

How long may a QRS be prolonged in hypertrophy or dilation of the left or right ventricle?

Answer 25

0.09 to 0.12 seconds

Question 26

What conditions cause bizarre complexes?

Answer 26

Destruction of cardiac muscle and replacement by scar tissue

Multiple small local blacks in the conduction impulses at many points in the Purkinje system

Question 27

Define Currents of Injury

Answer 27

Different cardiac abnormalities cause part of the heart to remain partially or totally depolarized all the time

Question 28

What abnormalities cause current of injury?

Answer 28

Mechanical trauma
Infectious processes
Ischemia (most common cause)

Question 29

What is the effect of current of injury on QRS complex?

Answer 29

Abnormal negative current flows from infarcted area and spreads toward the rest of the ventricles

Question 30

What is the name of the reference point for analyzing current of injury?

Answer 30

J point

Question 31

Where does the J point occur and what does it represent?

Answer 31

It occurs at the very end of the QRS wave and is the point at which all parts of the ventricle, including the injured areas, have become depolarized