CVS 7 (ECG)

Question 1

Name the tissue which electrically connects the atria, allowing an action potential to travel from the SAN to the left atria:

Answer 1

Bachmann’s Bundle

Question 2

Which surface of the heart tissue repolarises first?

Answer 2

Epicardial surface

Question 3

How many electrodes are attached for a standard 12-lead ECG?

Answer 3

10 electrodes

Question 4

How many leads are used for a standard ECG?

Answer 4

12 leads

Question 5

Which limb lead looks from the apex of the heart to the right atria? Where are the electrodes placed?

Answer 5

Lead II
Right arm
Left leg

Question 6

Why does depolarisation appear as a positive deflection from the baseline of an ECG?

Answer 6

Depolarisation moves towards positive electrode = positive deflection

Question 7

Depolarisation moving away from an electrode would appear as what kind of deflection in an ECG?

Answer 7

Negative deflection

Question 8

Repolarisation moving away from an electrode would appear as what kind of deflection in an ECG?

Answer 8

Positive deflection

Question 9

What are the chest leads used in an ECG?

Answer 9

V1-6 (medial to lateral)

Question 10

What does the P wave show?

Answer 10

Atrial depolarisation

Question 11

What does the QRS complex show?

Answer 11

Ventricular depolarisation

Question 12

What point of the ECG shows atrial repolarisation?

Answer 12

Lost in QRS complex

Question 13

What does the T wave show?

Answer 13

Ventricular repolarisation

Question 14

List some possible confounders for an incorrect ECG:

Answer 14

• Lead misplacement
• Sweat
• Hair
• Muscle contraction
• Interference

Question 15

What is the name given to the normal rhythm of the heart?

Answer 15

Sinus rhythm

Question 16

What is meant by ‘sinus rhythm’?

Answer 16

The normal rhythm of the heart

Question 17

Why does atrial depolaristaion produce a much smaller deflection in an ECG compared to ventricular depolarisation?

Answer 17

Atria have much less muscle compared to the ventricles, so less electrical activity needed to depolarise the muscle.

Question 18

If electrical activity started at the AVN instead of the SAN, how would the P wave appear in an ECG?

Answer 18

Negative deflection (rather than positive deflection), as depolarisation moving away from electrode.

Question 19

The muscle in the interventricular septum depolarises in which direction?

Answer 19

From left to right

Question 20

What part of an ECG should be used to assess heart rhythm?

Answer 20

Rhythm strip

Question 21

Which lead is used for the rhythm strip of an ECG?

Answer 21

Lead II

Question 22

What is the constant speed an ECG runs at?

Answer 22

25 mm/s

Question 23

How many large squares of an ECG corresponds to 1 sec?

Answer 23

5 large squares = 1 sec

Question 24

How many large squares of an ECG corresponds to 1 min?

Answer 24

300 large squares = 1 min

Question 25

How can you calculate heart rate from an ECG with a regular rhythm?

Answer 25

HR = 300 / number of large squares between 2 QRS complexes

Question 26

How can you calculate heart rate from an ECG with an irregular rhythm?

Answer 26

Count number of QRS complexes in 6 sec (30 large squares) and x 10

Question 27

How do you measure the RR interval? | What is the normal range of an RR interval?

Answer 27

Measure between peaks of R waves | 0.6-1.2 secs

Question 28

If the RR interval is decreased below the normal range, what can you tell about the heart rate?

Answer 28

Heart rate is increased above normal - tachycardic

Question 29

How do you measure the QRS interval? | What is the normal length?

Answer 29

From start of Q wave to end of S wave | < 3 small boxes, or 0.12 secs

Question 30

Wide QRS waves indicate that the ventricular depolarisations are not going through the normal purkinje system. List some causes of this:

Answer 30

- Left or Right bundle branch block - Hyperkalaemia - Na+-channel blockade - Pacemaker

Question 31

How do you measure the PR interval? | What is the normal length?

Answer 31

From start of P wave to start to Q wave | Between 3-5 small boxes, or 0.12 - 0.2 secs

Question 32

What is indicated by a short PR interval?

Answer 32

Either: - Atria have been depolarised from area close to AV node - Abnormally fast conduction from atria to ventricles

Question 33

What is the diagnosis if PR interval > 5 small squares, but normal P wave and QRS complex?

Answer 33

1st degree heart block

Question 34

How do you measure the ST segment?

Answer 34

From the end of S wave to start of T wave

Question 35

Elevated ST segment indicates:

Answer 35

- Acute MI | - Pericarditis

Question 36

Depressed ST segment indicates:

Answer 36

- Ischaemia

Question 37

How do you measure the QT interval?

Answer 37

From start of Q wave to end of T wave

Question 38

List some causes of Long QT syndrome:

Answer 38

Medication - diuretics, anti-arrhythmics, cholesterol-lowerers etc Hypokalaemia - excessive vomiting/diarrhoea, EDs, thyroid dysfunction

Question 39

Torsades de pointes is a complication of which heart syndrome?

Answer 39

Long QT syndrome

Question 40

How does Torsades de pointes lead to sudden syncope?

Answer 40

- Ventricular tachycardia - Decreased CO - Decreased blood to brain - Sudden syncope

Question 41

How can you diagnose atrial fibrillation from an ECG trace?

Answer 41

- Absent P waves | - Irregularly irregular QRS complexes

Question 42

Name the 4 types of heart block:

Answer 42

- 1st degree - Mobitz type 1 2nd degree - Mobitz type 2 2nd degree - Complete AV 3rd degree

Question 43

Which type of heart block is characterised by progressive lengthening of the PR interval (leading to loss of a QRS complex)?

Answer 43

Mobitz type 1 2nd degree

Question 44

Which type of heart block is characterised by a sudden dropped QRS complex (normal PR interval)?

Answer 44

Mobitz type 2 2nd degree

Question 45

What type of heart block is characterised by the lack of relationship between the P waves and QRS complexes?

Answer 45

Complete AV 3rd degree