CVS 12: Practical ECG methods

Question 1

What are electrodes?

Answer 1

The pads that are stuck onto the patients

Question 2

What are cable/ wires?

Answer 2

Connect electrodes to the device

Question 3

What are leads?

Answer 3

A digital representation of the changes in depolarisation in the heart

Question 4

What does an isoelectric line on a trace indicate?

Answer 4

No net change in voltage

• no electrical activity
• the impulse could be moving at a right angle to the electrodes

Question 5

What does an upward deflection indicate?

Answer 5

The impulse is moving towards the cathode (+ve electrode)

- generally depolarisation

Question 6

What does a downwards deflection indicate?

Answer 6

The impulse is moving towards the anode (-ve electrode)

- generally repolarisation

Question 7

How can you determine the velocity of an action potential from a trace?

Answer 7

The steepness of a line

Question 8

What does a sharp turn in a trace denote?

Answer 8

A rapid change in the direction of the action potential

Question 9

Which lead is mainly used an why?

Answer 9

Lead II between the Right arm and left leg
- the angle of this lead is roughy the same as the angle of the heart, so deflections will be large as they are along the same line as this lead

Question 10

You usually have one long recording which lead does this use and what is it used for?

Answer 10

• Lead II

- looks for anomalies that might not occur every heartbeat

Question 11

How many different leads are there? Why are there so many?

Answer 11

There are 12 leads
- each gives a different view of the heart which allows you to see which part of the heart is affected because the ECG will change

Question 12

Which three coronary arteries might be included in the ECG?

Answer 12

Left Circumflex artery
Right Coronary Artery
Left anterior descending artery

Question 13

Where are the three leads placed? What is formed by the placement of these leads and what is its significance?

Answer 13

Lead I: Right arm – > Left arm
Lead 2: Right arm –> Left Leg
Lead 3: Left arm–> Left Leg
Forms Einthoven’s triangle with the heart in the centre

Question 14

Explain where the 6 electrodes in the chest are placed

Answer 14

V1: Right sternal border in 4th IC space
V2: Left sternal border in 4th IC space
V4: Mid- Clavicular line in 5th IC space
V5: Anterior axillary line at the level of V4
V6: Mid-axillary line at the level of V4
V3: Halfway between V2 and V4

Question 15

What is a bipolar lead?

Answer 15

A lead which directly uses two physical electrodes to compare between each other

Question 16

What are unipolar leads?

Answer 16

Use one physical electrode and compare it to a virtual electrode

Question 17

What is a virtual electrode?

Answer 17

Made through a mathematical calculation of other lead values

Question 18

What sort of view do you get from the chest leads?

Answer 18

A Horizontal view

Question 19

Which lead acts as the reference point and why?

Answer 19

Lead I

- It is at 0 degrees

Question 20

Which leads are used to find out the QRS axis and why?

Answer 20

Lead II (60 degrees)
aVL. (-30 degrees)
To find out QRS axis you need two leads which are 90 degrees apart

Question 21

How do you find out the QRS axis?

Answer 21

• Find net deflection in Lead II and then net deflection in lead aVL
• Form a triangle with the two net deflections acting as vectors
• SOH CAH TOA it to find the missing angle by the heart = QRS axis

Question 22

What is the normal range for the cardiac axis?

Answer 22

-30 degrees to 90 degrees

Heart can be left or right axis deviated