Clinical Skills - ECG Interpretation

Question 1

Explain the process of basic electrical conductivity. (4)

Answer 1

1. Electrical impulses are sent to the atrium via internodal pathway to the AV node.
2. Impulse are delayed from AV node at approx. 0.1 sec allowing all the impulses from atrium to reach it. Hence, full contraction of both atrium chambers.
3. AV node depolarises and impulse will go the bundle of His to the Purkinje fibres.
4. Impulse disappears into the ventricles causing them to contract. So depolarisation occurs and heart returns to normal.

Question 2

How long does it take for a full electric conductivity cycle to take place? (1)

Answer 2

< 1 sec when at rest.

Question 3

What is does each box represent in the ECG paper? (horizontal) (2)

Answer 3

Small box = 0.04s
Large box = 0.20s

Question 4

What is does each box represent in the ECG paper? (vertical) (1)

Answer 4

0.5mV

Question 5

What does a vertical line in the ECG paper represent?

Answer 5

Every 3 sec (15 boxes) = heart rate.

Question 6

How many seconds do all rhythm strips have? (1)

Answer 6

6 seconds.

Question 7

Outline the steps of rhythm analysis. (5)

Answer 7

Calculate rate.
Determine regularity.
Assess P waves.
Determine PR interval.
Determine QRS duration.

Question 8

Explain the process of calculating the rate. (2)

Answer 8

Count no. of R waves (peak of QRS complex) in a 6 sec rhythm strip x 10.

Question 9

What is considered as a normal heart rate? (1)

Answer 9

60-100 bpm.

Question 10

Explain the process of determining regularity. (2)

Answer 10

Look at R-R distances (using caliper/markings on pen or paper)

Regular (are they equally distant apart)?, occasionally irregular? regularly irregular? irregularly regular?

Question 11

Explain the process of assessing P waves. (5)

Answer 11

Are there P waves?
Do the P waves all look alike?
Do the P waves occur at a regular rate?
Is there 1 P wave before each QRS?

(If any one of these Qs is answered yes, atrium is contracting + firing normally = sinus rhythm is present)

Question 12

What main features indicate that a sinus rhythm to be present? (2)

Answer 12

P waves are present in every QRS complex + equal spacing.

Question 13

What would be considered as a normal PR interval. (1)

Answer 13

Normal = 0.12-0.20 sec (3-5 boxes)

Question 14

What would we considered as a normal QRS duration? (1)

Answer 14

0.04-0.12 sec (1-3 boxes)