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Physiology- CP > ECG > Flashcards

ECG Flashcards

1
Q

What does ECG stand for?

A
  • Elctrocardiogram
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2
Q

What does an ECG show?

A
  • Representation of cardiac cycle
  • Volume rise in systole
  • Ejection as pressure exceeds systolic pressure
  • Volumes drop at same time
  • Muscle depolarisation and contraction, volume decreases as blood leaves chamber
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3
Q

What is ECG a measure of?

A
  • Not a measure of contraction
  • The measure of electrical activity
  • Which then precedes the muscle contraction
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4
Q

What are the components of the ECG?

A
  • SA node (pacemaker) depolarises first
  • Atrial muscle and AV node depolarise at the same time, during P wave
  • Purkinje fibres depolarise at QRS complex
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5
Q

What is the P wave?

A
  • First event of cycle is SA node depolarisation
  • Triggers adjacent cells in atria to depolarise
  • Spreads through L and R atria
  • Generates P wave- reflection of SAN
  • P wave shows atrial function
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6
Q

What is the PR interval?

A
  • Depolarisation spread though AVN towards ventricle
  • Delay at AVN to allow ventricular filling
  • Gap between top of P wave and R wave- usually flat
  • Normally 0.12-0.2 secs, 3-5 small ECG squares
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7
Q

What is the QRS complex?

A
  • Ventricular depolarisation
  • Spread though AVN, down Bundle of His, though Purkinje fibres and up through epicardium
  • 3D spread
  • Produces different waveforms that make up QRS complex
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8
Q

Describe Q wave in QRS complex

A
  • Negative wave preceding R, depolarisation of ventricular septum
  • Only seen in left pointing leads (I, II, AvL, V5, V6)
  • by def QRS does not need Q because only present in certain leads
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9
Q

Describe R wave in QRS complex

A
  • Upwards deflection
  • Wave always R, irrespective of whether Q is present
  • Always R wave, unlike Q
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10
Q

Describe S wave in QRS complex

A
  • Not a downward reflection of R
  • Follows R but deflection below isoelectric line
  • Once R wave back to baseline, S wave starts
  • Occurs regardless of Q
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11
Q

What is the T wave?

A
  • Repolarisation of ventricle- appears positive
  • Same deflection of QRS
  • I.e. if QRS negative, T is also
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12
Q

Why does repolarisation appear positive?

A
  • Depolarisation flows from endo to epicardium
  • Repolarisation flows opposite
  • Epicardium to endocardium double negative- so appears positive
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13
Q

What are U waves?

A
  • Small deflections in the same direction as T wave

- Unknown origin (possibly papillary muscles)

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14
Q

Where in the ECG does atrial repolarisation occur?

A
  • Within QRS complex

- Tends not to show due to larger events occurring in ventricle at the same time

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15
Q

How many leads in the ECG?

A

12

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16
Q

What are the bipolar limb leads?

A
  • Lead 1
  • Lead 2
  • Lead 3
  • Make up Eindhoven’s triangle
17
Q

Describe lead 1 of ECG

A
  • Runs from negative electrode in right arm to positive electrode in left arm
  • Records from right to left across the body
18
Q

Describe lead 2 of ECG

A
  • Right arm (negative) to left leg (positive), down and across the body
19
Q

Describe lead 3 of ECG

A
  • Negative electrode from the left arm to the positive electrode in left leg down across body
20
Q

What is Eindhoven’s triangle?

A
  • Equilateral triangle with equal angles of 60 degrees, recording vertically through the body
21
Q

What are the unipolar limb leads?

A
  • Augmented leads:
  • Lead AvF
  • Lead AvL
  • Lead AvR
22
Q

Describe lead AvF

A
  • Lead 1 to left leg
  • Joining the electrodes from left arm and right arm- collapse lead 1 into a midpoint
  • Record to remaining electrode (left leg)
23
Q

Describe lead AvL

A
  • Lead 2 to left arm

- Collapse lead 2 into a midpoint and record to left arm

24
Q

Describe lead AvR

A
  • Lead 3 to right arm

- Collapse left arm and left leg lead 3 and record up to right arm

25
Q

Describe the 2 axes of the ECG

A
  • Limb and augmented leads look at heart in vertical plane (from sides and feet)
  • Remaining 6 leads are in horizontal plane
  • Chest leads look at horizontal
  • Collapsing electrodes in RA, LA, LL and recording out to electrodes placed chest
26
Q

Describe the chest leads

A
  • Particular places- V1, 2, 3, 4, 5 & 6
  • Specific orientation of chest leads
  • They give a horizontal view of chest
27
Q

Which leads give view of anterior surface?

A
  • V1, 2, 3 and 4
28
Q

Which leads give view of lateral surface?

A
  • I, AvL, V5 and 6
29
Q

Which leads give view of the inferior surface?

A
  • Pointing downwards

- II, III and AvF

30
Q

Which leads give view of right side of heart?

A
  • Point from left to right

- AvR and V1

31
Q

How do you report an ECG?

A
  • Rhythm
  • Conduction intervals
  • Cardiac axis
  • Description of QRS complexes
  • Description of ST segment
  • Are they normal?
32
Q

How do you assess rhythm in an ECG?

A
  • Rhythm, strip at bottom of ECG with numerous QRS complexes
  • 60-100? tachy
  • Is the pattern regular?
  • Does every P wave produce a QRS complex?
  • Are QRS complexes driven by P wave (SA node)?
33
Q

How do you assess conduction intervals?

A
  • ECG based on cardiac cycle, should reflect those timings
  • PR interval 0.12-0.2s
  • Shorter? Depolarisation near AVN
  • Longer? heart block
  • Is the timing of each event normal?
  • QRS should be <3 squares
  • Depolarisation of ventricles is rapid and spreads equally
34
Q

How do you assess cardiac axis?

A
  • Represents general depolarisation with heart
  • Starts top right (SAN) and spreads to bottom left and apex
  • Axis of 0 consistent with depolarisation that moved R to L across body
  • Calculated by looking at heights of ECG leads
  • If not in this axis, may be problematic
  • Not migrating round to right- bigger ventricles and pulling more depolarisation (hypertrophy)
35
Q

10 rules for normal ECG

A

1) PR interval 3-5 squares
2) QRS <3 squares
3) QRS mainly upward in I and II
4) QRS + T same direction
5) AvR waves downward (against depolarisation)
6) R wave should increase in size from V1-4
7) ST segment isoelectric (except V1 + V2- may be raised)
8) P wave upward in I, II, V2-6
9) No or only small wave in I, II, V2-6
10) T wave upward in I, II, V2-6

Physiology- CP (19 decks)

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