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CVS > ECG > Flashcards

ECG Flashcards

1
Q

Outline the 9 steps of how an AP travels in the heart

A
  1. SA Node depolarises
  2. Atrial depolarization
  3. Delayed by 120-200ms at AV node
  4. Spreads to ventricle via Bundle of His
  5. Spreads through ventricle via LBB, RBB and Purkyne system
  6. Inter-ventricular septum is first depolarised
  7. Apex and free ventricular walls depolarised
  8. Base of ventricles depolarised
  9. Repolarisation in opposite direction to depolarisation
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2
Q

What are 2 meanings of ‘leads’

A
  1. Cable used to connect electrode to ECG recorder

2. Electrical view of heart obtained from a combo of electrodes

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3
Q

How many electrodes are placed and where
How many views/ leads are produced

What is the right leg electrode used for

A

4 on limbs
6 on chest

12 leads

Used as a grounding electrode, not for any leads

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4
Q

How do limb leads differ to Augmented Limb leads

Which electrodes are involved in, and identify the +ve electrode in;

  1. Limb lead I
  2. Limb lead II
  3. Limb lead III
A

Limb leads are Bipolar- 1+ve, 1-ve electrode
Augmented Limb Leads are Unipolar- 1 +ve electrode

  1. RA and LA- LA is +ve
  2. RA and LL- LL is +ve
  3. LA and LL- LL is +ve
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5
Q

Where are the positive electrodes on the leads;

  1. aVR
  2. aVF
  3. aVL

When using Augmented limb leads, what represents the negative electrode

A
  1. aVR: Right Arm
  2. aVF: Left Leg
    3 aVL: Left Arm

The mid-point of the other 2 remaining electrodes

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6
Q

In regards to positive electrode and direction of depolarisation/ repolarisation, state 4 rules that determine the sign of deflection on an ECG

A
  1. Depolarisation towards +ve electrode= Upwards deflection
  2. Depolarisation away from +ve electrode= Downwards deflection
  3. Repolarisation towards +ve electrode= Downwards deflection
  4. Repolarisation away from +ve electrode= Upwards deflection
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7
Q

Of the limb and augmented limb leads ,

  1. Which leads look at left surface of heart
  2. Which leads look at inferior surface
  3. Which leads look at right atrium
A
  1. I, aVL
  2. II, III and aVF
  3. aVR
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8
Q

What represents the negative electrode in the Chest/ Precordial Leads

In what directions do the chest electrodes view the heart? In what plane?

A

Mid-point of electrodes on RA, LA and LL

Front to back + right to left, in horizontal plane

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9
Q

What 2 things do the amplitude of deflection depend on

A
  1. How directly the depolarisation wave is coming towards +ve electrode
  2. Amount of muscle mass conducting activity
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10
Q

How does the QRS complex appear if;

  1. Depolarisation directly towards +ve electrode
  2. Wave obliquely towards electrode
  3. Wave at right angle to electrode
  4. Wave directly away from electrode
A
  1. Tall upright complex
  2. Small upright complex
  3. No complex OR biphasic
  4. Tall downwards complex
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11
Q

When viewing from the apex, explain the ECG appearance of;

  1. SA node depolarisation
  2. Atrial depolarisation
  3. AV node delay + Spread through Bundle of His
  4. Depolarisation of IV Septum
  5. Depolarisation of apex and free ventricular walls
  6. Depolarisation spreading to base of ventricles
  7. Ventricular Repolarisation
A
  1. No deflection, as insufficient signal to be detected
  2. Small upright deflect, as low muscle mass and towards +ve electrode
  3. Flat line (Isoelectric segment)
  4. Small downward, as moving obliquely away
  5. Large upright, as directly towards and large muscle mass
  6. Small downward, as moving obliquely away
  7. Medium upwards, as moving away from heart
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12
Q

On an ECG scan,

  1. How much time is shown by 1 small square
  2. How much time is shown by 1 large square
  3. How much time is shown by 30 large squares
A
  1. 40ms
  2. 0.2s (200ms)
  3. 6s
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13
Q

How to calculate heart rate from ECG if irregular

Can this be used for regular Heart rates too?

A

Count number of QRS complexes in 6 seconds, then multiply by 10
Yes

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14
Q

On an ECG, a PR interval is measured from where to where?
How long is the normal range?

What do longer PR intervals indicate

A

From start of P wave to start of Q wave
0.12-0.2 seconds (3-5 small squares)

Delayed conduction through AV Node and Bundle of His

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15
Q

On an ECG, a QRS interval is measured from where to where?
How long is the normal range?

What do longer QRS intervals indicate

A

Start of Q wave to end of S wave
<0.12s (3 small squares)

Indicates that depolarisation arises in the ventricle, not from the Bundle of His. (Hence it is slower)

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16
Q

On an ECG, a QT interval is measured from where to where?
How long is the normal range?

What do longer QT intervals indicate
What can this lead to

A

Start of Q wave to end of T wave
If corrected, <0.44-0.45s (11 small squares)

Indicates prolonged ventricular repolarisation
Can lead to arrhythmia

17
Q

What 4 questions do you ask to determine if Heart Rhythm is normal Sinus Rhythm

A
  • Is the Rythm regular
  • Is the heart rate normal (60-100)
  • Are there P waves, and are they followed by QRS waves
  • Are the intervals normal
18
Q

What is Atrioventricular conduction block/ Heart block

What are the types

A

Delay/ failure of conduction of impulses from atria to ventricles via AV node and Bundle of His

  • First degree
  • Second degree (Mobitz type 1 and 2)
  • Third degree
19
Q

Identify 4 causes of an AV conduction block

A
  • Degeneration of conduction system with age (Sclerosis and fibrosis)
  • Acute myocardial ischaemia
  • Drugs
  • Valvular disease
20
Q

What happens in First Degree AV Block

Which interval is affected and how

A

When conduction is slowed without skipped beats

PR Interval is longer than normal (>0.2s)

21
Q

What happens in Second Degree AV Block- Mobitz Type 1 (AKA Wenkebach 2nd degree heart block)

A

PR intervals get longer until one QRS is skipped, then cycle starts again

22
Q

What happens in Second Degree AV Block- Mobitz Type 2

A

PR intervals do not get longer, but QRS is suddenly skipped

23
Q

What happens in Third Degree AV Block
What sets the new rhythm and at what BPM
Why is the Heart block the most dangerous

A

Atria and ventricles depolarise independently
(Complete failure of AV conduction)

Ventricular pacemaker sets rhythm at 20-40bpm
Too slow to maintain BP

24
Q

How does a Bundle Branch Block appear and why

A

Normal P wave, PR Interval, Longer QRS complex

Because only bundle branches have delayed conduction

25
Q

Where can an arrhythmia arise from

A

Atria; (Supraventricular)

  • SA node
  • AV Node
  • Atrium

Ventricles

26
Q

In an Atrial Fibrillation ECG describe the P waves, RR intervals and QRS complexes

A

No P waves-> Wavy baseline
Irregular impulses-> Irregular RR intervals
Normal QRS complexes (as ventricles depolarise normally)

27
Q

Is Afib slow or fast? (<60 or >100?)

Compare coarse and fine fibrillation

A

Can be Slow OR fast

Coarse- Amplitude> 0.5mm
Fine- Amplitude< 0.5mm

28
Q
  • What is an Ventricular Ectopic Beat/ Contraction

- How do the QRS complexes appear

A
  • An extra ventricular beat/ depolarisation that doesn’t spread via His-Purkyne system.
  • Wider QRS complexes (Slower ventricular depolarisation)
29
Q

What can a series of Ventricular Ectopic Beats (Contractions) cause?
Why’s this dangerous

A

Can cause Ventricular Tachycardia

VTACH can reduce Cardiac Output and cause Vfib
In Vfib, there is no co-ordinated contraction so no cardiac output leading to death.

30
Q

Compare the 2 types of Myocardial Infarction, in reference to the ST segment

A

STEMI/ ST Segment Elevation: Full thickness of ventricular wall is affected

Non-STEMI/ ST Segment Depression: Not affected full thickness of ventricular wall

31
Q

Describe the changes in an ECG after a STEMI at the following stages;

Acute
Hours
Day 1-2
Few days later 
Weeks later
A

Acute: ST elevation

Hours: ST Elevation, Smaller R wave, Q wave begins

Day 1-2: T wave inversion, Deeper Q wave

Few days later: Normal ST, T wave inverted to normal

Weeks later: Normal T and ST, Q wave persists

32
Q

How does a pathological Q wave appear

A

1 small square wide

2 small squares deep

33
Q

What are 2 ECG changes in Ischaemia AND a Non-STEMI

A

ST depression

T wave inversion

34
Q

Identify 3 ECG features during Hypokalemia

A

Peaked p waves
T wave flattens and inverts
U waves formed (Between S and T)

35
Q

Identify 4 ECG features during Hyperkalemia in order of increasing Serum [K]

A

<6.5: Tall tented T waves
6.5-7.5: P wave lost
7.5-8.5: QRS Widens
>8.5: QRS Widens further

CVS (15 decks)

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