ECG

Question 1

Outline the 9 steps of how an AP travels in the heart

Answer 1

1. SA Node depolarises
2. Atrial depolarization
3. Delayed by 120-200ms at AV node
4. Spreads to ventricle via Bundle of His
5. Spreads through ventricle via LBB, RBB and Purkyne system
6. Inter-ventricular septum is first depolarised
7. Apex and free ventricular walls depolarised
8. Base of ventricles depolarised
9. Repolarisation in opposite direction to depolarisation

Question 2

What are 2 meanings of ‘leads’

Answer 2

1. Cable used to connect electrode to ECG recorder

2. Electrical view of heart obtained from a combo of electrodes

Question 3

How many electrodes are placed and where
How many views/ leads are produced

What is the right leg electrode used for

Answer 3

4 on limbs
6 on chest

12 leads

Used as a grounding electrode, not for any leads

Question 4

How do limb leads differ to Augmented Limb leads

Which electrodes are involved in, and identify the +ve electrode in;

1. Limb lead I
2. Limb lead II
3. Limb lead III

Answer 4

Limb leads are Bipolar- 1+ve, 1-ve electrode
Augmented Limb Leads are Unipolar- 1 +ve electrode

1. RA and LA- LA is +ve
2. RA and LL- LL is +ve
3. LA and LL- LL is +ve

Question 5

Where are the positive electrodes on the leads;

1. aVR
2. aVF
3. aVL

When using Augmented limb leads, what represents the negative electrode

Answer 5

1. aVR: Right Arm
2. aVF: Left Leg
   3 aVL: Left Arm

The mid-point of the other 2 remaining electrodes

Question 6

In regards to positive electrode and direction of depolarisation/ repolarisation, state 4 rules that determine the sign of deflection on an ECG

Answer 6

1. Depolarisation towards +ve electrode= Upwards deflection
2. Depolarisation away from +ve electrode= Downwards deflection
3. Repolarisation towards +ve electrode= Downwards deflection
4. Repolarisation away from +ve electrode= Upwards deflection

Question 7

Of the limb and augmented limb leads ,

1. Which leads look at left surface of heart
2. Which leads look at inferior surface
3. Which leads look at right atrium

Answer 7

1. I, aVL
2. II, III and aVF
3. aVR

Question 8

What represents the negative electrode in the Chest/ Precordial Leads

In what directions do the chest electrodes view the heart? In what plane?

Answer 8

Mid-point of electrodes on RA, LA and LL

Front to back + right to left, in horizontal plane

Question 9

What 2 things do the amplitude of deflection depend on

Answer 9

1. How directly the depolarisation wave is coming towards +ve electrode
2. Amount of muscle mass conducting activity

Question 10

How does the QRS complex appear if;

1. Depolarisation directly towards +ve electrode
2. Wave obliquely towards electrode
3. Wave at right angle to electrode
4. Wave directly away from electrode

Answer 10

1. Tall upright complex
2. Small upright complex
3. No complex OR biphasic
4. Tall downwards complex

Question 11

When viewing from the apex, explain the ECG appearance of;

1. SA node depolarisation
2. Atrial depolarisation
3. AV node delay + Spread through Bundle of His
4. Depolarisation of IV Septum
5. Depolarisation of apex and free ventricular walls
6. Depolarisation spreading to base of ventricles
7. Ventricular Repolarisation

Answer 11

1. No deflection, as insufficient signal to be detected
2. Small upright deflect, as low muscle mass and towards +ve electrode
3. Flat line (Isoelectric segment)
4. Small downward, as moving obliquely away
5. Large upright, as directly towards and large muscle mass
6. Small downward, as moving obliquely away
7. Medium upwards, as moving away from heart

Question 12

On an ECG scan,

1. How much time is shown by 1 small square
2. How much time is shown by 1 large square
3. How much time is shown by 30 large squares

Answer 12

1. 40ms
2. 0.2s (200ms)
3. 6s

Question 13

How to calculate heart rate from ECG if irregular

Can this be used for regular Heart rates too?

Answer 13

Count number of QRS complexes in 6 seconds, then multiply by 10
Yes

Question 14

On an ECG, a PR interval is measured from where to where?
How long is the normal range?

What do longer PR intervals indicate

Answer 14

From start of P wave to start of Q wave
0.12-0.2 seconds (3-5 small squares)

Delayed conduction through AV Node and Bundle of His

Question 15

On an ECG, a QRS interval is measured from where to where?
How long is the normal range?

What do longer QRS intervals indicate

Answer 15

Start of Q wave to end of S wave
<0.12s (3 small squares)

Indicates that depolarisation arises in the ventricle, not from the Bundle of His. (Hence it is slower)

Question 16

On an ECG, a QT interval is measured from where to where?
How long is the normal range?

What do longer QT intervals indicate
What can this lead to

Answer 16

Start of Q wave to end of T wave
If corrected, <0.44-0.45s (11 small squares)

Indicates prolonged ventricular repolarisation
Can lead to arrhythmia

Question 17

What 4 questions do you ask to determine if Heart Rhythm is normal Sinus Rhythm

Answer 17

• Is the Rythm regular
• Is the heart rate normal (60-100)
• Are there P waves, and are they followed by QRS waves
• Are the intervals normal

Question 18

What is Atrioventricular conduction block/ Heart block

What are the types

Answer 18

Delay/ failure of conduction of impulses from atria to ventricles via AV node and Bundle of His

• First degree
• Second degree (Mobitz type 1 and 2)
• Third degree

Question 19

Identify 4 causes of an AV conduction block

Answer 19

• Degeneration of conduction system with age (Sclerosis and fibrosis)
• Acute myocardial ischaemia
• Drugs
• Valvular disease

Question 20

What happens in First Degree AV Block

Which interval is affected and how

Answer 20

When conduction is slowed without skipped beats

PR Interval is longer than normal (>0.2s)

Question 21

What happens in Second Degree AV Block- Mobitz Type 1 (AKA Wenkebach 2nd degree heart block)

Answer 21

PR intervals get longer until one QRS is skipped, then cycle starts again

Question 22

What happens in Second Degree AV Block- Mobitz Type 2

Answer 22

PR intervals do not get longer, but QRS is suddenly skipped

Question 23

What happens in Third Degree AV Block
What sets the new rhythm and at what BPM
Why is the Heart block the most dangerous

Answer 23

Atria and ventricles depolarise independently
(Complete failure of AV conduction)

Ventricular pacemaker sets rhythm at 20-40bpm
Too slow to maintain BP

Question 24

How does a Bundle Branch Block appear and why

Answer 24

Normal P wave, PR Interval, Longer QRS complex

Because only bundle branches have delayed conduction

Question 25

Where can an arrhythmia arise from

Answer 25

Atria; (Supraventricular) - SA node - AV Node - Atrium Ventricles

Question 26

In an Atrial Fibrillation ECG describe the P waves, RR intervals and QRS complexes

Answer 26

No P waves-> Wavy baseline Irregular impulses-> Irregular RR intervals Normal QRS complexes (as ventricles depolarise normally)

Question 27

Is Afib slow or fast? (<60 or >100?) | Compare coarse and fine fibrillation

Answer 27

Can be Slow OR fast Coarse- Amplitude> 0.5mm Fine- Amplitude< 0.5mm

Question 28

- What is an Ventricular Ectopic Beat/ Contraction | - How do the QRS complexes appear

Answer 28

- An extra ventricular beat/ depolarisation that doesn’t spread via His-Purkyne system. - Wider QRS complexes (Slower ventricular depolarisation)

Question 29

What can a series of Ventricular Ectopic Beats (Contractions) cause? Why’s this dangerous

Answer 29

Can cause Ventricular Tachycardia VTACH can reduce Cardiac Output and cause Vfib In Vfib, there is no co-ordinated contraction so no cardiac output leading to death.

Question 30

Compare the 2 types of Myocardial Infarction, in reference to the ST segment

Answer 30

STEMI/ ST Segment Elevation: Full thickness of ventricular wall is affected Non-STEMI/ ST Segment Depression: Not affected full thickness of ventricular wall

Question 31

Describe the changes in an ECG after a STEMI at the following stages; ``` Acute Hours Day 1-2 Few days later Weeks later ```

Answer 31

Acute: ST elevation Hours: ST Elevation, Smaller R wave, Q wave begins Day 1-2: T wave inversion, Deeper Q wave Few days later: Normal ST, T wave inverted to normal Weeks later: Normal T and ST, Q wave persists

Question 32

How does a pathological Q wave appear

Answer 32

1 small square wide | 2 small squares deep

Question 33

What are 2 ECG changes in Ischaemia AND a Non-STEMI

Answer 33

ST depression | T wave inversion

Question 34

Identify 3 ECG features during Hypokalemia

Answer 34

Peaked p waves T wave flattens and inverts U waves formed (Between S and T)

Question 35

Identify 4 ECG features during Hyperkalemia in order of increasing Serum [K]

Answer 35

<6.5: Tall tented T waves 6.5-7.5: P wave lost 7.5-8.5: QRS Widens >8.5: QRS Widens further