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Common Investigations > ECG > Flashcards

ECG Flashcards

1
Q

How much time does each large square on ECG represent?

A

0.2s ie. 200ms

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2
Q

How many large squares per second? per minute?

A

5 large squares per second

300 per minute.

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3
Q

What is the HR if R-R interval is 1? 3? 6?

A

HR for R-R =

1: 300 bpm
3: 100 bpm
6: 50 bpm

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4
Q

What does the PR interval represent?

A

The time for depolarisation to spread from SA node, through atria, to AV node, down bundle of His and into ventricular muscle.

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5
Q

What is the normal PR interval?

A

120-220ms or 3-5 small squares.

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6
Q

What is the normal QRS duration?

A

120ms (3 small squares)

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7
Q

What causes a widened QRS?

A

Any conduction abnormality causes widened QRS.

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8
Q

What causes prolonged QT interval?

A

QT interval varies with HR.

It is prolonged in patients with some electrolyte abnormalities; and by some drugs!

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9
Q

What can a prolonged QT interval predispose to?

A

Ventricular tachycardia.

If QT >450ms.

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10
Q

What do leads I, II and VL observe?

A

The left lateral surface of the heart.

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11
Q

What do leads III and VF observe?

A

The inferior surface of the heart.

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12
Q

What does lead VR observe?

A

The right atrium.

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13
Q

What do leads V1 and V2 observe?

A

Right ventricle

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14
Q

What do leads V3 and V4 observe?

A

Interventricular septum and the anterior wall of the left ventricle.

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15
Q

What do leads V5 and V6 observe?

A

Anterior and lateral walls of the left ventricle.

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16
Q

Which lead should the cardiac rhythm be identified from?

A

Whichever shows the P wave most clearly. Usually II.

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17
Q

What is the shape of the QRS complex if the depolarisation is spreading toward the lead?

A

Predominantly upward/positive (R wave is greater than S wave).

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18
Q

What is the shape of the QRS complex if the depolarisation is spreading away from the lead?

A

Predominately downward / negative (S wave greater than R wave).

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19
Q

When would R and S waves be of equal size?

A

When the depolarisation is at right angles to the lead.

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20
Q

Features of normal cardiac axis on ECG?

A

Normal 11-5 o’clock axis:
-depolarisations spreads predominately towards I/II/III
therefore:
-upwared deflection in I-III, most positive in II.

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21
Q

Right axis deviation on ECG?

A

RV hypertrophied therefore more RV effect on QRS
Average depolarisation swings towards the right.
-Lead I becomes -ve
-Lead III more +ve

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22
Q

Left axis deviation on ECG?

A

-QRS mostly negative in III
-Most positive in I.
AND
-not significant until II also mostly negative

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23
Q

What determines the shape of QRS in the chest leads?

A
  • septum b/w ventricles is depolarised before the walls of the ventricles, and the depolarising wave spreads across septum from left to right
  • more muscle in wall of LV so LV has more influence on pattern
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24
Q

ECG description / report sequence?

A
  1. Pt name / time /date
  2. Rhythm
  3. Conduction intervals
  4. Cardiac axis
  5. Description of QRS
  6. Description of ST and T waves
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25
Q

What demonstrates the time taken for depolarisation to spread from SA node to ventricular muscle?

A

PR interval

26
Q

What is interference with the PR interval / SA-> V conduction time referred to as?

A

Heart block

27
Q

What is first degree heart block?

A

Each wave of depolarisation from SA node conducted to ventricles BUT there is delay along conduction path ==> gives prolonged PR.

28
Q

What is first degree heart block a sign of?

A
  • CAD
  • Acute rheumatic carditis
  • Digoxin toxicity
  • Electrolyte disturbances
29
Q

Is first degree heart block usually problematic?

A

No - not of itself. May be a sign of underlying pathology e.g. CAD, acute rheumatic carditis, digoxin toxicity, electrolyte distrubances.

30
Q

What is second degree heart block?

A

Excitation fails to pass through AV node or bundle of His - if intermittent = 2nd degree HB. 3 types:

i) Mobitz 1 / Wenckbach
ii) Mobitz 2
iii) 2:1/3:1/4:1 conduction

31
Q

What is Mobitz Type I?

A

Progressive lengthening of PR interval, then failure of conduction of an atrial beat, followed by conducted beat with shorter PR interval. Repetition of this cycle.

32
Q

What is Mobitz Type II?

A

Most beats conducted with consistent PR interval but occasionally there is atrial depolarisation without subsequent ventricular depolarisation (i.e. one P wave not followed by QRS)

33
Q

What is 2/3/4:1 block?

A

Alternate conducted and non-conducted beats (or one conducted atrial beat and then 2/3 non-conducted beats), giving twice (or 3x, 4x) as many P waves as QRS complexes. Gives name 2:1, 3:1 etc.

34
Q

Implications of second degree heart block?

A

Type I usually benign; Type II or 2/3/4:1 block may herald onset of complete (third degree) block

35
Q

What is third degree heart block?

A

Atrial contraction normal but no beats are conducted to the ventricles. Ventricles thus excited by slow escape mechanism from a depolarising focus within V muscle.

36
Q

What may cause complete heart block?

A
  • Acute: MI

- Chronic: fibrosis around bundle of his, block of both bundle branches

37
Q

What are the ECG features of a third degree heart block?

A
  • P wave rate at atrial rate (~90bpm)
  • No relationship between P waves and QRS
  • QRS complex rate slow (~36bpm)
  • Abnormal QRS shape due to abnormal spread of depolarsiation from ventricular focus
38
Q

What is indicated by a widened QRS?

A

i.e. larger than 120ms
Indicates conduction within the ventricles must have occurred by an abnormal and therefore slower pathway.
-Bundle branch block
-Depolarisation from within ventricles

39
Q

What does block of both bundle branches cause?

A

Same as block of His; causes complete heart block

40
Q

Is RBBB always pathological?

A

No - often indicates problem with right side of heart but RBBB patterns with a QRS complex of normal duration are common in healthy people.
Think about atrial septal defect.

41
Q

What occurs in RBBB?

A

No conduction down right bundle branch but septum is depolarised from left side as usual.

  • Causes R wave in RV lead (V1) and Q wave in LV lead (V6);
  • excitation spreads to LV causing S in V1, R in V6
  • longer for depolarisation to reach RV so depolarises after LV; causes second (R1) in V1, wide deep S in V6 (therefore widened QRS)
42
Q

Features of RBBB?

A
  • Sinus rhythm
  • Normal PR
  • Normal axis
  • Wide QRS (>160ms)
  • RSR1 pattern in V1; deep wide S waves in V6
  • Normal ST and T waves
43
Q

What occurs in LBBB?

A

-Septum depolarises from R–> L causing small Q wave in V1 and an R wave in V6
-RV depoloarises before LV: so V1 R, V6 S (even just a notch)
-Depolarisation of LV causes V1 S wave and V6 R wave
Associated with T wave inversion in lateral leads (I, vL, V5,V6) although not necessarily all

44
Q

Where is RBBB best seen? What is seen?

A

V1; RSR1 pattern

45
Q

Where is LBBB best seen? What is seen?

A

V6, broad QRS complex with notched top (resembles letter M); +/- W pattern in V1.

46
Q

Explain distal conduction pathways?

A

AV node –> bundle of HIs –>
RBBB: no major divisions
LBBB: anterior and posterior fascicles

47
Q

What is left anterior fascicular block?

A

LV has to be depolarised through the posterior fasicle so cardiac axis rotates upwards –> left anterior hemiblock. ECG will show left axis deviation.

48
Q

What is bifasicular block?

A

RBBB and left anterior fasicular block.

ECG shows RBBB and LAD

49
Q

What should be considered in LBBB?

A

AS and ischaemic disease.

If pt has CP, new LBBB may indicate AMI

50
Q

What does left axis deviation and RBBB indicate?

A

Severe conducting tissue disease; no specific treatment needed.
Pacemaker required is pt has symptoms of intermittent complete heart block

51
Q

Where can abnormal cardiac rhythms begin?

A
  • SA node
  • Atrial muscle
  • AV node
  • Ventricular muscle
52
Q

What are the supra ventricular rhythms? Effect on QRS?

A

-Sinus rhythm
-Atrial rhythm
-Junctional rhythms (around AV node)
Depolarisation spreads to ventricles in the normal way (along His) therefore QRS is normal/narrow.

53
Q

Ventricular rhythms effect on QRS?

A

Depolarisation spreads through ventricles by abnormal slower pathways (Purkinjes). QRS complex is therefore wide.

54
Q

What is the exception to the narrow/wide QRS complex rule for supraventrciular/ventrciular arrhythmias?

A

Wolff-Parkinson-White: supraventricular rhythm with R/LBBB. QRS will be wide

55
Q

What are extrasystoles?

A

Occur as early single beats

56
Q

Atrial muscle / AV node rate?

A

Spontaneous depolarisation frequencies about 50bpm

57
Q

Ventricular focus rate?

A

30bpm

58
Q

What is an atrial escape rhythm?

A

If SA node slows down and different focus in atrium assumes control

59
Q

ECG features of atrial escape rhythm?

A
  • SA node fails to depolarise (after previously sinus beats)
  • after delay, abnormal P wave is seen (excitation began in atrium somewhere other than SA node)
  • abnormal P wave followed by normal QRS
60
Q

What is accelerated idioventricular rhythm?

A

-Ventricular focus takes over with rate faster than that seen in complete heart block (appears similar to VTac but is benign and VT must be 120bpm+)

Common Investigations (4 decks)

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