Chapter 4 : Vectors and the Basic Beat

Question 1

What is the sum of all ventricular vectors?

Answer 1

Electrical Axis

Question 2

What do vectors represent?

Answer 2

Energy and direction

Question 3

What are electrodes?

Answer 3

Sensing devices that pick up the electrical activity occurring beneath them

Question 4

When a positive electrical impulse is moving away from the electrode the ECG machine converts it into a what?

Answer 4

Negative Wave

Question 5

When a positive electrical impulse is towards from the electrode the ECG machine converts it into a what?

Answer 5

Positive Wave

Question 6

What is the position for leads V1 and V2?

Answer 6

Each side of the sternum at fourth intercostal space

Question 7

What is the position for lead V4?

Answer 7

Fifth intercostal space in the midclavicular line

Question 8

What is the six limb leads? (Hexaxial system)

Answer 8

I, II, III, aVR, aVF, aVL

Question 9

What is the lead aVR?

Answer 9

The augmented unipolar right arm lead faces the heart from the right side and is usually orientated to the cavity of the heart. Therefore, all the deflections P, QRS and T are normally negative in this lead

Question 10

What is the lead aVF?

Answer 10

The augmented unipolar left leg lead, orientated to the inferior surface of the heart Precordial Chest Leads

Question 11

What is the lead aVL?

Answer 11

The augmented unipolar left arm lead faces the heart from the left side and is orientated to the anterolateral surface of the left ventricle

Question 12

How many degrees apart are all the leads using the haxaxial system?

Answer 12

30 degrees

Question 13

The six limb leads view the heart at what angle?

Answer 13

Coronal

Question 14

The six precordial leads view the heart at what angle?

Answer 14

Transverse

Question 15

The Hexaxial System

Answer 15

Question 16

What is the normal duration of the P wave?

Answer 16

0.08 to 0.11 seconds

Question 17

What does the P wave represent?

Answer 17

Electrical depolarization of the atria

Question 18

The axis of the P wave is usually directed in what direction?

Answer 18

Downward and to the left

Question 19

What does the TP wave represent?

Answer 19

Repolarization of the atria

It deflects in the opposite direction of the P wave but is usually not seen because it occurs at the same time as the QRS wave.

Question 20

If the PR segment is depressed more than 0.8mm it could be a sign of what?

Answer 20

Pericarditis or atrial infarct

Question 21

What happens in the PR segment?

Answer 21

The initiation of electrical impulse in the SA node up to the moment of ventricular depolarization

Question 22

What is the normal duration of the PR segment?

Answer 22

0.12 - 0.20 seconds (3 to 5 little boxes)

Question 23

What does the QRS complex represent?

Answer 23

Ventricular depolarization

Question 24

The Q wave can be present or absent

Question 25

Q wave significance

Answer 25

Can be benign, or it can be a sign of dead myocardial tissue. The Q wave is considered significant if it is 0.03 seconds or wider, or its height is equal or greater than 1/3 the height of the R wave. If it meets that criteria it indicates a Myocardial Infarction (MI)

Question 26

What happens during the R wave peak time?

Answer 26

The amount of time it takes the electrical impulse to travel from the purkinje system in the endocardium to the surface of the epicardium immediately under an electrode.

Question 27

How long is the R wave peak time?

Answer 27

Up to 0.035 seconds in the right precordial leads (v1 and v2) because the right ventricle is thin compared to the left. 0.045 seconds in the left precordial leads (v5 and v6) because of the left ventricles thickness

Question 28

ST elevations?

Answer 28

It can vary up to 1mm from baseline in limb leads and 3mm in precordials. Any ST elevation in a symptomatic patient should be considered significant and representative of myocardial injury or infarction.

Question 29

What does the T wave represent?

Answer 29

Ventricular repolarization

Question 30

Should the T wave be asymmetric or symmetric?

Answer 30

Asymmetric

Question 31

Why is the T wave in the same direction as the QRS if it represents repolarization?

Answer 31

The increased pressure on the endocardium during contraction, the repolarization wave travels in the opposite direction from the epicardium back to the endocardium.

Question 32

What does QTc stand for? And what is its purpose?

Answer 32

QT corrected interval It is corrected for heart rate. As the heart rate decreases, the QT interval lengthens. And as the heart rate increases the QT interval shortens. The QTc is less than 0.45 in males and 0.46 in females. Anything above this is considered prolonged. Considered at risk of lethal arrhythmias.