Lecture 6: Intro to the ECG Flashcards

1
Q

what is a syncytium

A

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

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2
Q

what is a functional syncytium

A
  • many cells functioning as one

- large groups of cells make electrical changes simultaneously

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3
Q

in which order are parts of the ventricular wall depolarised

A

1) septum
2) apex
3) atrioventricular groove

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4
Q

what is the ECG good for measuring

A
  • heart rate, with Holter moniter

- especially when atrial rate is not equal to ventricular rate

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5
Q

where are the electrodes in lead II

A

pos: left leg
neg: right arm
ground: right leg (but could be almost anywhere)

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6
Q

how many leads are in a standard ECG

A
  • 3 bipolar leads: leads I,II and III let us see in frontal plane
  • 3 augmented leads in frontalplane
  • 6 precordial in transverse plane
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7
Q

what does a wide or misshapen QRS wave suggest

A
  • ectopic pacemaker

- bundle branch block

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8
Q

what does a large Q wave suggest

A

dead tissue, eg from an old myocardial infarction

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9
Q

what is sinus rhythm

A

when the heart rhythm is generated from the SAN

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10
Q

what are indicators that the heart is in sinus rhythm

A
  • each P wave matched with QRS complex

- PR interval always normal, 4-5 little boxes

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11
Q

what is sinus tachycardia

A

tachycardia driven by SAN beating too quickly

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12
Q

what are the sizes of the boxes in an ECG

A

small box 40 ms
big box is 200 ms
5 big boxes is 1 sec

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13
Q

what is the height of each little box in an ECG

A

0.1 mV

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14
Q

where is the PR interval

A

start of P wave to start of QRS complex

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15
Q

where is the PR segment

A

end of P wave to start of QRS complex

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16
Q

where is the ST segment

A

end of QRS complex to start of T wave

17
Q

where is the QT interval

A

start of QRS complex to end of T wave

18
Q

PR interval duration

A

3 - 5 boxes

120 - 200 ms

19
Q

QRS complex duration

A

2 - 3 boxes

80 - 120 ms

20
Q

QT interval duration

A

9 - 11.5 boxes

360 - 460 ms

21
Q

how do you calculate ventricular rate from an ECG

A

count between R waves

22
Q

how do you calculate atrial rate from an ECG

A

count between P waves

23
Q

how to calculate heart rate from ECG

A

300 divided by number of big boxes

24
Q

what is the parasympathetic pathway of the heart

A

vagus nerve stimulates muscarinic receptors

25
what does atropine do
- muscarinic antagonist | - causes parasympathetic withdrawal
26
what is the sympathetic pathway to the heart
- stellate nerves - beta agonists increase rate - beta blockers decrease rate
27
what is a heart block
- type of dysrhythmia | - any blocking of impulse conduction of the heart
28
what are causes of AV heart blocks
- ischaemia of AV node or bundle - compression of AV bundle by scar or calcified tissue - inflammation of AV node or bundle
29
symptoms of AV heart blocks
- can be asymptomatic - palpitations - hypotension-like: - dizziness - malaise - syncope - if serious, risk of sudden cardiac death
30
what is 1st degree heart block
- PR interval > 5 little boxes | - caused by delayed AV node transmission
31
what is Mobitz Type I
- type of second degree heart block - aka Wenckebach - PR interval gets longer until QRS wave fails to follow P wave - caused by AV node damage
32
what is Mobitz Type II
- type of second degree heart block - aka Hay - PR interval stays the same, some not followed by QRS wave - caused by problem in bundle of his
33
what is third degree heart block
- atrial signals fail to reach ventricles - PR intervals vary radically, sometimes >12 boxes - very dangerous
34
what are premature beats
individual early beats triggered by irritable tissue
35
what are escape beats
individual late beats triggered by lack of stimulation from atria
36
what are premature ventricular contractions
- unusually wide ventricular activity | - no S wave and negative dip where T wave should be
37
what is atrial fibrillation
- very common in elderly - disorganised electrical activity in atria - no P wave, but flat or wiggly line - ventricular rate is fast and irregular - AVN only lets some signals from atria to ventricles
38
what is respiratory sinus arrhythmia
- sign of healthy heart, seen in children and athletes | - heart beat slightly faster during inspiration, slower during expiration