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Module 103: Theme 3: Physiology of the cardiovascular system. Principles of pathology, diagnosis and treatment of cardiovascular disease > Introduction to the ECG > Flashcards

Introduction to the ECG Flashcards

1
Q

What is a functional syncytium?

A

One large cell having many nuclei that are not separated by cell membranes. Many cells acting as one. (Cardiomyocytes)

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2
Q

List and describe the 3 types of cardiac myocyte

A

Pacemaker cells- For setting hearts rhythm
Conducting cells- For transmitting rhythm throughout the heart.
Contractile cells- For contracting to that rhythm throughout the heart

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3
Q

How does speed of transmission vary throughout the heart?

A

Contractile- atrial and ventricular monocytes (0.3-0.5 m/s)

Conducting system- purkinje fibres (5m/s) and AV node (0.05m/s)

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4
Q

Cardiomyocytes are linked by low resistance pathways in close association with what?

A

Gap junctions

Intercalated discs

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5
Q

Explain how a signal is moved between cells

A

Action potential arrives at a cell and causes depolarisation which then initiates an action potential in the adjacent cell.

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6
Q

What is the purpose of internodal bundles?

A

Conduction between SAN and AVN. Ensure synchronous contraction of both atria.

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7
Q

Why are bundles used to conduct the impulses instead of through the atria?

A

Atria conduction is 0.3m/s-0.5m/s
Bundles conduction is 1.0m/s
Bundles conduct much faster leading to quicker transmission

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8
Q

How many specialised bundles are in the atria?

A

4

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9
Q

What happens to the impulse at the AVN?

A

Waves of depolarisation travel at 0.05m/s across the small modified cardiomyocytes to the AVN. The AVN delays the wave of excitation to allow the ventricles to be sufficiently filled by the atria.

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10
Q

How many ms delay is there in the transmission of SAN to AVN?

A

160ms

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11
Q

What causes the delay between transmission of signal from SAN to AVN?

A

Mostly due to increased RESISTANCE
Smaller fibres which lead to:
More resistance along length of fibre (smaller diameter)
More intercellular junctions (shorter length)
With diminished numbers of gap junctions per surface area

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12
Q

What does the AV node connect to?

A

Bundle of his followed by the purkinje fibres

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13
Q

Why do the purkinje cells conduct impulses faster than other cells?

A

Larger diameter

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14
Q

Which parts of the ventricle are depolarised in order?

A

Septum, apex, atrioventricular groove

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15
Q

How does an ECG manage to measure the electrical activity of the heart?

A

The heart is a functional syncytium and although the electrical charge of one individual cardiac myocyte is too small, a group of them together is large and changes occur simultaneously.

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16
Q

What is the purpose of leads in an ECG?

A

A lead is a configuration of the electrodes. Looks at the heart at different angles depending on where the leads have been placed

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17
Q

What is the most common lead analysed?

A

Lead 2

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18
Q

How is lead 2 organised on the body?

A

Positive electrode on left leg, negative electrode on right arm and ground electrode on the right leg

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19
Q

List the different types of standard leads

A

3 Bipolar leads (1,2,3)
3 Augmented leads
6 Precordial leads

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20
Q

In which plane do the bipolar leads look?

A

Frontal plane

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21
Q

What is the lower lead called on the bottom of the trace?

A

Rhythm strip- shows the beats/heart rate from lead 2

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22
Q

Give the axes for an ECG

A

Voltage (y) and time (x)

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23
Q

List the different sections of the ECG wave in order

A 
P wave
PR segment
QRS complex
ST segment
T wave
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24
Q

What does the P wave represent?

A

The depolarization of the atria in response to the SSN triggering

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25
Q

What does the PR segment represent?

A

Delay in the AV node to allow filling of the ventricles

26
Q

What does the QRS complex represent?

A

Transmission of depolarisation through the ventricular myocardium

27
Q

What does the ST segment represent?

A

Beginning of the ventricular repolarization- should be flat

28
Q

What does the T wave represent?

A

Ventricular repolarization

29
Q

When is the QRS complex abnormal?

A

Wide/misshapen complex is abnormal

Large Q waves are a sign of an old MI

30
Q

What are the conditions for sinus rhythm?

A

Each P wave is followed by a QRS complex
Each QRS complex is preceded by a P wave
When PR interval is always normal (3-5 little boxes)

31
Q

What is sinus tachycardia?

A

A tachycardia driven by the SA node beating too quickly. It has normal PR intervals, and each P matched with a QRS

32
Q

How many seconds is 1 small box on an ECG trace?

A

0.04 seconds

33
Q

How many seconds is 1 big box on an ECG trace?

A

0.2 seconds (200 ms)

34
Q

Define PR interval and state its normal length

A

From start of P wave to start of QRS complex

3-5 boxes (120-200ms)

35
Q

Define QT interval and state its normal length

A

From start of QRS complex to end of T wave

9-11.5 boxes (360-460ms)

36
Q

Define ST segment

A

From end of QRS complex to start of T wave

37
Q

How long is a normal QRS complex?

A

2-3 boxes (80-120 ms)

38
Q

What is the box equivalent of 1 second?

A

5 Big boxes

39
Q

How is rate calculated?

A

The number of big boxes between two P waves

40
Q

How is ventricular rate calculated?

A

The number of boxes between two R waves

41
Q

Give the formula for calculating rate

A

300/no. big boxes

42
Q

Give the rate of 1 box

A

300 bpm

43
Q

Give the rate of 2 boxes

A

150 bpm

44
Q

Give the rate of 3 boxes

A

100 bpm

45
Q

Give the rate of 4 boxes

A

75 bpm

46
Q

Give the rate of 5 boxes

A

60 bpm

47
Q

Give the rate of 6 boxes

A

50 bpm

48
Q

Give the rate of 10 boxes

A

30 bpm

49
Q

What is heart block?

A

A type of dysrhythmia

Any type of impulse conduction block of the heart

50
Q

What is AV heart block?

A

A delay of failure of atrial signal stimulating the ventricle

51
Q

What are the causes of AV heart block?

A

Ischemia of AVN or AV bundle
Calcified or scar causing compression on AVN
Inflammation of the AVN or AV bundle

52
Q

List the symptoms of AV heart block

A 
Can be asymptomatic
Palpitations
Syncope
Malaise
Sudden death (3rd degree) 
Hypotension
53
Q

Describe first degree heart block

A 
When the PR interval is greater than 5 little boxes (200 ms) 
Almost always asymptomatic
Usually in adolescents
Delayed AVN transmission 
Rarely treated
54
Q

What is second degree heart block?

A

Some QRS complexes are missing since some P waves are blocked and therefore are not followed by QRS complex

55
Q

Name the two types of second degree heart block

A

Mobitz type 1 (wenckebach)

Mobitz type 2 (Hay)

56
Q

Describe mobitz type 1 (wenckebach)

A

When the PR interval gets longer until the QRS wave fails to follow the P wave
Likely caused by AVN damage
Usually no treatment is given

57
Q

Describe mobitz type 2 (Hay)

A

Some P waves are blocked out and are not followed by QRS. The PR interval remains the same.
Likely problem in the bundle of his
High risk- can progress to 2nd degree
Treatment: Implant a pacemaker

58
Q

Describe third degree heart block

A

Atrial signals consistently fail to arrive at ventricles. Ventricular rate is consistent. Time between atrial beats and ventricular beats is variable. PR interval varies. Sometimes > 12 boxes. Intrinsic ventricular rate is quite slow ( < 60 bpm). Atrial beats are consistent

59
Q

Describe atrial fibrillation

A

Disorganised electrical activity in atria
No P wave. Instead:
Flat line OR Wiggly line instead of P
Ventricular rate is fast & irregular
Many signals reach AV node
AF is very common in the elderly
Can lead to thrombus formation in atrium
Due to slow flow of blood which increases stroke risk
Patient given anticoagulants as prophylaxis

60
Q

Describe respiratory sinus arrythmia

A

Heart beat is slightly faster during inspiration, slightly slower during expiration
Normal: sign of a healthy heart
Usually only present in children & athletes
Caused by respiratory centres in brain’s medulla
Observe ventricular rate: inverse of RR interval

61
Q

What is an RR interval

A

Duration in time between two QRS complexes

62
Q

What does an ST segment elevation suggest?

A

Myocardial infarction

Module 103: Theme 3: Physiology of the cardiovascular system. Principles of pathology, diagnosis and treatment of cardiovascular disease (19 decks)

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