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CVS > Session 6 - ECG > Flashcards

Session 6 - ECG Flashcards

1
Q

What is the electrical axis of the heart and where is it?

A

Net direction of depolarisation

Left of the interventricular septum and towards the apex

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2
Q

Which cells repolarise first?

Why?

A

Ventricular myocytes because repolarisation is in the opposite direction to depolarisation
(apex depolarises first)

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3
Q

What is the fibrous skeleton of the heart?

What does it do?

A

4 rings of dense connective tissue in the plane between atria and ventricles

Insulates electrical signals in the atrium so that they contract independantly to the ventricles and conduction is limited to the His-Purkinje system
(also anchors myocardium and valves)

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4
Q

What is a Sinus rhythm?

A

Any cardiac rhythm established by the SAN with a p-wave preceding a QRS complex on an ECG

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5
Q

Why is the region between the p-wave and QRS flat?

A

Electrodes detect the changes in membrane potential of myocytes (an electrical current).
This is the AVN delay and conduction through His-purkinje system so there is no change in myocyte potential (no current).

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6
Q

Why does the ECG look different when taken from different positions?

A

The signal changes bc the spread of current relative to the electrode position has changed

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7
Q

Depolarisation coming towards an electrode looks like what on an ECG?

When would depolarisation not be recorded?

A

upwards deflection

If the direction of depolarisation is at 90 degrees to the electrode position

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8
Q

Repolarisation moving towards an electrode appears as what on the ECG trace?

A

negative deflection

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9
Q

Which ECG interval encompasses the whole electrical activity of the ventricles?
(Depolarisation and repolarisation)

If the interval is prolonged what does it indicate?

A

QT interval
Beginning of Q until end of T

Delayed repolarisation which can cause arrythmias due to EAD’s (early after depolarisations).

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10
Q

Why does the ECG include a corrected QT interval?

Normal duration of the QT interval?

A

Because an increased heart rate shortens the QT interval which could mask underlying problems; long QT syndrome

below 0.45 s

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11
Q

Which ECG interval indicates heart rate?

A

R-R interval

between peaks of R waves; shorter interval means faster rate

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12
Q

Why is the S-T segment flat?

When is it raised?
When is it depressed?

A

Isoelectric; nothing is changing, there is no spread of depolarisation
Period between depolarisation and repolarisation

Myocardial infarction
Myocardial ischaemia

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13
Q

What does the P-R interval measure and what is a normal value?

A prolonged interval indicates what?

Where is it measured from?

A

Conduction from the atria to the ventricles
between 0.12-0.2 s

Slow conduction; first degree heart block

Beginning of p-wave to start of QRS complex

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14
Q

Wide QRS complexes occur when?

Normal QRS duration?

A

ventricular depolarisation initiated in the ventricles (not by the normal conductance mechanism) so slower

< 0.12 s

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15
Q

In a 12 view/ 10 lead ECG, how many leads are limb leads?

How do you position them?

A

4

RYGB
Ride your green bike starting at the right upper limb and finishing at the right lower limb

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16
Q

How many chest leads are on the right side of the body?

A

1 (out of 6)

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17
Q

How do you place the chest leads?

A

V1 - 4th intercostal space immediately right of sternum

V2- 4th intercostal space immediately left of sternum

V3- midway between V2 and

V4- 5th intercostal space at the mid clavicular line (left side)

V5- same horizontal level as V4 at the anterior axillary line

V6 - same h. level as V5, mid axillary line

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18
Q

What is the 4th intercostal space?

A

Space between ribs 4 and 5

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19
Q

Th chest and limb leads generate how many views each of the 12 view ECG?

A

limb leads- 6 in vertical plane

chest leads - 6 in horizontal plane

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20
Q

Which is the neutral limb electrode?

A

right lower limb

21
Q

What do unipolar views in the vertical plane measure?

Which are the unipolar views?

What type of lead is used?

A

potential difference between one limb and the neutral electrode

aVF
aVR
aVL

augmented lead because the signal from a unipolar view is small

22
Q

Which are the bipolar views in the vertical plane?

Which limbs do they measure between?

A

I - L and R upper limbs
II - R upper, L lower
III- L upper, L lower

23
Q

Which views in the horizontal plane face the septum?

Which face the apex?

Which face the left ventricle?

A

V1 and V2

V3 and V4 (inferiolateral)

The lateral leads- V5 & V6

24
Q

What makes up the inferior border of the heart?

A

The right ventricle mostly, with some left ventricle at the apex

25
Q

How many squares make up

  • 1 second
  • 1 minute

A prolonged P-R interval measures how long? How many squares is this?

A

1 second = 5 large squares
1 minute = 300 large squares

Prolonged = > 0.2 s
More than 1 large square as this equals 0.2 seconds

26
Q

How can you calculate a regular heart rate in bpm from the ECG trace?

A

Divide 300 (large squares in 1 minute) by the number of boxes in the R-R interval

300/ boxes in R-R interval

27
Q

How can you calculate heart rate from an irregular rhythm?

A

Count QRS complexes in 6 seconds, multiply by 10

28
Q

What is heart block?

How can you see it on an ECG?

A

Delayed or blocked conduction between the atria and ventricles

Prolonged P-R interval

29
Q

Second degree heart block;
Type 1 vs Type 2

Which one is more serious?

A

Both result in a dropped beat (missing QRS)

Type 1

  • delayed conduction at AVN
  • progressively longer P-R intervals until a dropped QRS

Type 2

  • delayed conduction at His-Purkinje system
  • usually a fixed ratio (2:1)

Type 2 is more serious bc its unstable and has a high chance of progression to third degree heart block

30
Q

What can cause 1st degree heart block?

A

inappropriate vagal stimulation (parasympathetic) which delays conduction at AVN

31
Q

What happens in 3rd degree heart block?

What does this look like on the ECG?

A

Complete block between atria and ventricles, ventricles depolarise at their own intrinsic rate - the ventricular escape rhythm.

Wide QRS complexes

32
Q

How many bpm is the ventricular escape rhythm?

Why is this dangerous? What action must be taken?

A

30-40 bpm

The heart rate is too slow to maintain blood pressure and organ perfusion
so a pacemaker must be fitted immediately

33
Q

What happens in bundle branch block?

What does the ECG look like?

A

Conduction to the ventricles is delayed in one bundle branch so this ventricle depolarises via the ventricular escape rhythm/ intrinsic depolarisation rate of the myocytes

Broad QRS
(any ventricular depolarisation which originates outside of the normal SAN)

34
Q

What is a ventricular ectopic beat?
How does it affect the time for the ventricle to depolarise?

What does it look like on the ECG?

A

An extra depolarisation arising in the ventricle.
It takes longer for the full ventricle to depolarise (His-Purkinje system is most efficient).

Broad, abnormally shaped QRS

35
Q

A run of ventricular ectopic beats can become what?

A

More than 3 = ventricular tachycardia

which has a high risk of progression to VF

36
Q

What happens in VF?

Describe the ECG trace

A

Multiple ectopic sites in the ventricles; their impulses cause quivering rather than a coordinated contraction. There is no cardiac output

The ECG is irregularly irregular. It has a wavy baseline due to rapid ventricular depolarisations

37
Q

Explain how you treat ventricular fibrillation

A

Defibrillation
- Apply a controlled shock to restore SAN sinus rhythm; depolarises all ventricular myocytes simultaneously so that coordinated depolarisations and contractions can restart

38
Q

What happens in an NSTEMI? (Non STEMI)

Appearance on an ECG?

A

Ischaemia or infarction affecting part of the ventricular wall

Depressed ST segment

39
Q

What happens in a STEMI?

Appearance on an ECG?

A

Infarction affecting the full thickness of the ventricular wall

Elevated ST segment in leads facing the damaged area
Afterwards, pathological Q waves (deflect downwards)

40
Q

Explain pathological Q waves

A
  • Occur after a STEMI
  • The infarcted tissue is now electrically silent so the electrode records electrical activity in the region opposite the dead tissue
  • Deflect downwards because depolarisation in the opposite region is directed away from the electrode (due to endocardial to epicardal spread).
41
Q

Which artery is causing the N/STEMI if these leads are abnormal;
- II, III & vAF

A

(Inferior border of heart)

RCA, right coronary artery

42
Q

Which artery is causing the N/STEMI if these leads are abnormal;
- V5, V6, aVL

A

Circumflex artery

43
Q

If the leads facing the posterior border are abnormal, which artery is involved?
Which are the leads?

A

RCA, right coronary artery

V1, V2,

44
Q

What does the left coronary artery branch into?

A

circumflex artery and the left anterior descending artery

45
Q

What happens in atrial fibrillation?

What does it look like on an ECG?

A

Multiple atrial foci fire rapid and chaotic impulses causing the atria to quiver rather than contract. Heart rate is abnormal (irregularly irregular)

wavy baseline
no p-waves
normal QRS

46
Q

Why are the QRS complexes normal in atrial fibrillation?

How is conduction at the AVN affected by atrial fibrillation?

A

Ventricles depolarise normally, just at an irregular rate

Not all impulses are conducted at the node due to the AVN refractory period

47
Q

Why is urgent re-perfusion therapy given to patients who’ve suffered a STEMI?

A

To restore blood flow and limit muscle necrosis

48
Q

ECG changes for acute NSTEMI and for weeks after?

Which other condition has the same ECG changes as an NSTEMI?

How do you decide which has occurred?

A

Acute; ST depression and/or T wave inversion
After; normal ECG

Unstable angina (severe ischaemia)

Test for myocyte necrosis (Troponin)

CVS (7 decks)

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