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ECG Flashcards

(60 cards)

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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
What demonstrates the time taken for depolarisation to spread from SA node to ventricular muscle?
PR interval
26
What is interference with the PR interval / SA-> V conduction time referred to as?
Heart block
27
What is first degree heart block?
Each wave of depolarisation from SA node conducted to ventricles BUT there is delay along conduction path ==> gives prolonged PR.
28
What is first degree heart block a sign of?
- CAD - Acute rheumatic carditis - Digoxin toxicity - Electrolyte disturbances
29
Is first degree heart block usually problematic?
No - not of itself. May be a sign of underlying pathology e.g. CAD, acute rheumatic carditis, digoxin toxicity, electrolyte distrubances.
30
What is second degree heart block?
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
What is Mobitz Type I?
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
What is Mobitz Type II?
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
What is 2/3/4:1 block?
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
Implications of second degree heart block?
Type I usually benign; Type II or 2/3/4:1 block may herald onset of complete (third degree) block
35
What is third degree heart block?
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
What may cause complete heart block?
- Acute: MI | - Chronic: fibrosis around bundle of his, block of both bundle branches
37
What are the ECG features of a third degree heart block?
- 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
What is indicated by a widened QRS?
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
What does block of both bundle branches cause?
Same as block of His; causes complete heart block
40
Is RBBB always pathological?
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
What occurs in RBBB?
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
Features of RBBB?
- 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
What occurs in LBBB?
-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
Where is RBBB best seen? What is seen?
V1; RSR1 pattern
45
Where is LBBB best seen? What is seen?
V6, broad QRS complex with notched top (resembles letter M); +/- W pattern in V1.
46
Explain distal conduction pathways?
AV node --> bundle of HIs --> RBBB: no major divisions LBBB: anterior and posterior fascicles
47
What is left anterior fascicular block?
LV has to be depolarised through the posterior fasicle so cardiac axis rotates upwards --> left anterior hemiblock. ECG will show left axis deviation.
48
What is bifasicular block?
RBBB and left anterior fasicular block. | ECG shows RBBB and LAD
49
What should be considered in LBBB?
AS and ischaemic disease. | If pt has CP, new LBBB may indicate AMI
50
What does left axis deviation and RBBB indicate?
Severe conducting tissue disease; no specific treatment needed. Pacemaker required is pt has symptoms of intermittent complete heart block
51
Where can abnormal cardiac rhythms begin?
- SA node - Atrial muscle - AV node - Ventricular muscle
52
What are the supra ventricular rhythms? Effect on QRS?
-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
Ventricular rhythms effect on QRS?
Depolarisation spreads through ventricles by abnormal slower pathways (Purkinjes). QRS complex is therefore wide.
54
What is the exception to the narrow/wide QRS complex rule for supraventrciular/ventrciular arrhythmias?
Wolff-Parkinson-White: supraventricular rhythm with R/LBBB. QRS will be wide
55
What are extrasystoles?
Occur as early single beats
56
Atrial muscle / AV node rate?
Spontaneous depolarisation frequencies about 50bpm
57
Ventricular focus rate?
30bpm
58
What is an atrial escape rhythm?
If SA node slows down and different focus in atrium assumes control
59
ECG features of atrial escape rhythm?
- 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
What is accelerated idioventricular rhythm?
-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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