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CI1 > ECG Interpretation > Flashcards

ECG Interpretation Flashcards

1
Q

What is the physiological basis of ECGs?

A
  • Contraction of muscles associated with electrical changes (depolarisation)
  • Changes detected by electrodes
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2
Q

Why must the patient be fully relaxed when an ECG recording is made?

A

Otherwise skeletal muscle activity may obscure the heart muscle activity

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3
Q

How is the heart viewed from an electrical point of view?

A

As only having two sections/chambers, i.e. the two atria contract together & the two ventricles contract together

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4
Q

Why is the electrical activity of the atria smaller than the ventricles?

A

The muscle mass of the atria is relatively smaller

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5
Q

What produces a P ECG wave?

A

Contraction of the atria

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6
Q

Where does the P wave arise from?

A

The sino atrial node (SA node) of the right atrium, spreads across the atria

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7
Q

What does the QRS complex represent?

A

Ventricular contraction

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8
Q

What is the line between the ECG waves called and what does it represent?

A

Isoelectric line - where there is no depolarisation or repolarisation occurring

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9
Q

What does the T wave represent?

A

Repolarisation: Return of ventricular mass to its resting electrical state

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10
Q

Where does the repolarisation of the atria lie on an ECG?

A

Hidden by the QRS

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11
Q

What is the pathway of the electrical current to the ventricles?

A
  • Starts in SA node
  • Depolarisation spreads across atrial muscle fibres & internal pathways
  • Spreads to ventricles via AV node
  • Delayed in the AV node
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12
Q

Why is the electrical current delayed in the AV node?

A

To allow time for the blood to move into the ventricles so it can be pumped out

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13
Q

What happens to the electrical current once it reaches the ventricles?

A
  • Passed by specialised conducting tissue
  • Bundle of His (single pathway)
  • Then divides into L & R bundle branches in inter ventricular septum
  • L bundle branch divides in 2
  • Current spreads across mass of the ventricle via Purkinje fibres
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14
Q

What is the intrinsic rhythm of the heart usually set by?

A
  • SA node, normally has the highest frequency of discharge of all possible sites
  • But any other conducting part can also have its own intrinsic rhythm
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15
Q

Under normal conditions, what keeps the heart working as an effective pump?

A

Intrinsic firing rates of pacemaker cells in 3 critical areas of the heart

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16
Q

What is the intrinsic firing rate of the SA node?

A

60-100 depolarisations/min

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17
Q

What happens if there is a failure of the SA node to depolarise?

A

The AV node acts as a backup

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18
Q

What is the intrinsic firing rate of the AV node?

A

40-60/minute (only happens if SA node fails)

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19
Q

What happens if there is a failure of both the SA & AV nodes?

A

Purkinje fibres act as a backup for depolarisation

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20
Q

What is the intrinsic firing rate of the Purkinje fibres?

A

20-40/minute

21
Q

What does it mean when the waves on an ECG are upside down?

A

The wave is moving away from the electrode, i.e. the electrode is in a different position

22
Q

On ECG paper, what does each large & small square represent?

A

Large: 0.2 seconds
Small: 0.04 seconds

23
Q

What does the duration of the QRS complex represent?

A
  • How long it takes for excitation to spread through the ventricle
  • Normal QRS < 0.12 seconds (3 small squares)
24
Q

What does the PR interval represent?

A
  • How long it takes for excitation to spread from SA node through atrial muscle & AV node, down Bundle of His & into ventricular muscle
  • Normal PR interval 0.12-0.2 seconds (3-5 small squares)
25
Q

What are the characteristics of a normal sinus rhythm?

A
  • HR 60-100bpm
  • Rhythm regular
  • P wave before each QRS, identical
  • PR interval 0.12-0.2 seconds
  • QRS < 0.12 seconds
26
Q

What are some of the conduction abnormalities?

A
  • Ventricular ectopic beats
  • First, second, third (complete) degree heart block
  • Bundle branch block
27
Q

What is an example of ventricular ectopic beats?

A

Ventricular extrasystoles

  • Extra beat not arising from SA node
  • Looks abnormal & wide
  • Depolarisation & repolarisation mixing together
28
Q

What is first degree heart block?

A
  • Slowing of electrical current moving through conducting system
  • Prolongation of PR interval
29
Q

What is second degree heart block?

A
  • Excitation fails to pass through AV node or bundle of His
  • I.e. P waves not being conducted through to ventricles
  • No QRS complex
  • 3 variations
30
Q

What are the 3 variations of second degree heart block?

A
  1. Mobitz type 2 phenomena: Normal PR intervals, then sudden atrial contraction without subsequent ventricular contraction
  2. Wenkebach phenomena: Progressive lengthening of PR interval then failure to conduct atrial beat, followed by shorter PR interval (cyclic)
  3. Alternate conducted/non-conducted atrial beats
31
Q

What is third degree (complete) heart block?

A
  • Atrial contraction is normal
  • No beats conducted to ventricles
  • Atria & ventricles contracting independently
32
Q

What is a bundle branch block?

A
  • Depolarisation wave doesn’t spread via bundle branches
  • QRS complex wider due to delayed conduction in ventricles
  • Can be right or left
33
Q

How are heart rhythms classified?

A

According to their point of origin

34
Q

What is the difference between supraventricular rhythms & ventricular rhythms?

A
  • Supraventricular: Narrow (normal) QRS complex, arise from AV node or above
  • Ventricular: Wide complex
    (Exception: SV rhythm with R/L bundle branch block)
35
Q

What are the 4 ways abnormal rhythms are classified?

A
  1. Cardiac slowing (escape beats/rhythms, bradycardia)
  2. Early single beats (extrasystoles)
  3. Sustained & fast rhythm (tachycardias)
  4. Total disorganisation of atrial or ventricular firing (fibrillation)
36
Q

What is a type of cardiac slowing?

A

Sinus bradycardia

  • May be normal (e.g. in fit people)
  • Normal sinus pattern of conduction
  • Slow rate <60
37
Q

What are examples of early single beats?

A
  • Ventricular ectopic beats (VEBs)

- Premature ventricular contraction (PVCs)

38
Q

What is the R-on-T phenomenon?

A
  • VEB that occurs on top of preceding T wave

- Can cause ventricular tachycardia

39
Q

What are paired VEBs?

A
  • 2 VEBs occurring in a row
  • Can cause ventricular tachycardia
  • Can be normal in patients with heart conditions (i.e. check if it’s normal for them)
40
Q

What are multifocal VEBs?

A
  • VEBs look different from each other

- I.e. arising from different areas of the heart (more than one abnormal focus)

41
Q

What is bigeminy and trigeminy?

A
  • Bigeminy: Continuous rhythm of 1 normal beat, then 1 VEB

- Trigeminy: 2 normal beats, 1 VEB

42
Q

What are types of tachycardia?

A
  • Supraventricular (e.g. atrial flutter or fibrillation)

- Ventricular

43
Q

What is atrial flutter?

A

Atrial tachycardia with supra ventricular rhythm, e.g. multiple P waves for every QRS complex

44
Q

What are the risks of atrial flutter?

A
  • Stroke
  • Clotting
  • Blood pooling
  • Can degenerate into atrial fibrillation
45
Q

What is atrial fibrillation?

A
  • Multifocal tachycardia

- Disorganised baseline

46
Q

What is ventricular tachycardia?

A
  • Rapid QRS complex
  • All wide
  • Over 100bpm
  • Can degenerate into ventricular fibrillation
47
Q

What clinical features can be correlated with abnormal ECGs?

A
  • Total clinical picture (disease, meds, electrolytes, refer to prior tracings)
  • LOC
  • Hypotension
  • Palpitations
  • Abnormal pulse
  • Chest pain
  • Shortness of breath
48
Q

Where should the ST segment lie?

A

Isoelectric, i.e. should be at the same level as the line between T and the next P

49
Q

What are examples of ST segment abnormalities?

A
  • Horizontal depression with upright T wave: Sign of ischaemia
  • Elevation: Sign of acute myocardial injury (pericarditis or recent infarction)

CI1 (21 decks)

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