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module 103 - theme 3 > introduction to the ECG > Flashcards

introduction to the ECG Flashcards

1
Q

what is syncytium?

A

one large cell having many nuclei that are not separated by cell membrane

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2
Q

what is a function syncytium?

A

many cells functioning as one

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3
Q

what are the 3 types of cardiac monocyte & their functions?

A
  • pacemaker cells = for setting heart rhythms
  • conducting cells = for transmitting rhythms throughout the body
  • contractile cells = for contracting to that rhythm (most numerous)
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4
Q

at what speed do the atrial and ventricular myocytes usually contract?

A

0.3-0.5 m/s

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5
Q

what speed do the Purkinje fibres contract at?

A

5m/s

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6
Q

what speed does the AV node contract at?

A

0.05m/s

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7
Q

how are cardiomyocytes linked together?

A

linked together by low resistance pathways associated with gap junctions at the intercalated disks

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8
Q

what ensures that the atria contract at the same time?

A

internodal bundles conduct the impulse from the SA node to the AV node

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9
Q

what do the 4 specialised bundles in the atria consist of?

A

contain Purkinje-like cells and the cardiomyocytes are modified to conduct

*these bundles are also in direct contact with the atrial muscle

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10
Q

what is the only point where the wave of depolarisation passes from atria to ventricles?

A

AV nodes

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11
Q

what are ventricles insulated by?

A

insulated by connective tissue from atria

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12
Q

how many seconds does the AV node delay the excitation from atria to ventricles by?

A

0.1-0.2s

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13
Q

why is there a delay in the electrical conduction from atria to ventricles?

A

to permit longer and more effective ventricular filling

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14
Q

what is the AV node composed of?

A

small modified myocytes

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15
Q

what order does the depolarisation occur?

A

first part of ventricular wall is depolarised in the septum, then the apex and then finally the atrioventricular groove

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16
Q

what is an ECG?

A

a gross electrical measurement of the heart

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17
Q

why is it possible to measure the ECG from the skin surface?

A

due to the heart being a functional syncytium which large groups of cells all make electrical changes simultaneously

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18
Q

what are 2 positives about ECGs?

A

they are very fast and affordable

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19
Q

what is a lead?

A

a configuration of electrodes

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20
Q

where is lead II placed?

A
  • positive electrode is on the left leg
  • negative electrode is on the right arm
  • ground electrode is on the right leg
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21
Q

what are the 12 standard leads?

A
  • 3 bipolar leads (I, II, III) frontal plane
  • 3 augmented leads
  • 6 precordial leads
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22
Q

what does the P-wave on an ECG show?

A

depolarisation of atria in response to SA node triggering

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23
Q

what does the PR segment show on an ECG?

A

the delay of the AV node allowing the ventricles to fill

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24
Q

what does the QRS complex show on an ECG?

A

depolarisation of the ventricles, triggering the main pumping contractions

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25
Q

what does the ST segment show on an ECG?

A

the beginning of the ventricle repolarisation

26
Q

what does the T wave show on an ECG?

A

ventricular repolarisation

27
Q

what is present on an ECG if the ventricular conduction is abnormal?

A

the QRS is wide

28
Q

what is a sign of dead tissue on an ECG?

A

large (deep) Q waves

29
Q

what generates the heart rhythm?

A

the SA node

30
Q

what is sinus tachycardia?

A

a tachycardia driven by the SA node beating too quickly: it has normal PR waves and each P is matched with QRS

31
Q

what is the normal duration of a PR interval on an ECG?

A

3-5 boxes (120-200ms)

32
Q

what is the normal duration of a QRS complex on an ECG?

A

2-3 boxes (80-120ms)

33
Q

what is the normal duration of a QT interval on an ECG?

A

9-11.5 boxes (360-460ms)

34
Q

what does the parasympathetic muscarinic stimulus lead to?

A

decreased heart rate, decrease in contractility and decrease in conduction velocity

35
Q

what does parasympathetic withdrawal lead to?

A

increased heart rate, increased contractility and increase in conduction velocity

36
Q

what is atropine?

A

a muscarinic antagonist

37
Q

what is not innervated by the parasympathetic system?

A

vasculature

38
Q

what does sympathetic stimulation lead to?

A

increased heart rate, increased contractility and increased conductance velocity

39
Q

what nerve is involved with parasympathetic input?

A

vagus nerve

40
Q

what nerve is involved with sympathetic input?

A

stellate nerve

41
Q

what effect do beta-agonists have on the heart rate?

A

increase rate

42
Q

what effect to beta-blockers have on the heart rate?

A

decreased rate

43
Q

what is heart block?

A

a type of dysrhythmia caused by any kind of impulse contraction block of the heart

44
Q

what causes a heart block?

A
  • ischaemia of AV node or AV bundle
  • compression of AV bundle by scar or calcified tissue
  • inflammation of the AV node or bundle
45
Q

what is an AV heart block?

A

a delay or failure of atrial signal stimulating ventricle

46
Q

what are the symptoms of heart block?

A
  • can be asymptomatic
  • palpitations
  • hypotension-like: dizziness, malaise, syncope
  • risk of sudden death
47
Q

what is first degree heart block?

A
  • when PR interval >5 little boxes
  • but all Ps followed by QRS
  • always almost asymptomatic
  • often young people
  • delayed AV node transmission
  • rarely treated
48
Q

what is mobitz type 1 second degree heart block?

A
  • PR interval gets longer until QRS wave fails to follow P wave
  • likely cause is AV node damage
  • usually no treatment given
49
Q

what is second degree heart block?

A

some P waves are blocked and are not followed by QRS so some QRS complexes are missing

50
Q

what is mobitz type II second degree heart block?

A
  • some P waves are blocked and are not followed by QRS
  • PR interval remains the same
  • likely problem in bundle of His
  • high risk: can progress to 3rd degree heart block
  • treatment: implant pacemaker
51
Q

what triggers premature (early) beats?

A

irritable tissue

52
Q

what triggers escape (late) beats?

A

natural rhythmicity of non-atrial tissue

53
Q

what are the characteristics of premature ventricular contractions?

A
  • usually wide and weird looking ventricular electrical activity
  • no S wave, instead wide negative dip where the T wave should be
  • often beat triggered in middle of myocardium
  • the 2 ventricles will be electorally unsynchronized
  • width is determined by slowed conduction velocity
54
Q

what is atrial fibrillation?

A
  • no P wave instead flat or wiggly line
  • ventricular rate is fast and irregular so many signals reach the AV node
  • it is very common in the elderly
55
Q

what can atrial fibrillation lead to?

A

thrombus formation in atrium due to slow flow of blood leads to stroke risk

56
Q

what is respiratory sinus arrhythmia?

A
  • heart beat is slightly faster during inspiration, slightly slower during expiration
  • sign of a healthy heart
  • usually only present in children and athletes
  • caused by respiratory centres in brains medulla
  • observe ventricular rate: opposite of RR interval
57
Q

what is an interval?

A

duration from start of one mark to the end of another mark

58
Q

what is a segment?

A

the wave form between 2 other waves

59
Q

what is the ST segment elevation a sign of?

A

an acute MI

60
Q

what is an iso-electric baseline?

A

from end of T to next P

module 103 - theme 3 (17 decks)

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