ECG

Question 1

Intro

Answer 1

PID
ECG date + time
Calibration

Question 2

Calibration
- speed
- voltage

Answer 2

speed : 25mm/s
voltage: 1mm/mV (i.e. 1mV deflection should be 2 large squares in height)

Question 3

Rate

Answer 3

Calculate by dividing 300 by number of large squares between R peaks OR (if irregular) - total R waves on ECG multiplied by 6

Question 4

Causes of bradycardia (HR<60bpm)

Answer 4

physical fitness, hypothermia, hypothyroidism, SA node disease, beta blockers/digoxin

Question 5

Causes of tachycardia (HR>100bpm)

Answer 5

exercise, pain, anxiety, pregnancy, anaemia, PE, hyovolaemia, fever/sepsis, thyrotoxicosis

Question 6

Rhythm

Answer 6

1. Regularity: mark 4 R waves on piece of paper
   (if irregular - AF, ectopic, 2nd degree HB, sinus arrhythmia, atrial flutter with variable block)
2. Sinus rhythm
   - look for AF or flutter (saw-tooth baseline)
   - narrow complex tachy with no p waves - SVT
   - broad “ “ = VF, VT or rarely SVT/AF with BBB
   - brady with no p wave - SA arrest with junctional escape rhythm
   - p waves present but inconstant PR - HB

Question 7

Axis

Answer 7

Leads I and II
- QRS predominantly +ve in I and II

If (predominantly) +ve in I and -ve in II –> LAD (leaving each other = left axis)

If (predominantly) -ve in I and +ve in II –> RAD (Reaching towards each other = R axis)

Question 8

Causes of LAD

Answer 8

More electricity to L due to
- LV hypertrophy
- LA hemiblock
- LBBB
- inferior MI
- WPW
- VT

Question 9

Causes of RAD

Answer 9

More electricity to R
- tall and thin
- RV hypertrophy (e.g. PE, lung disease)
- left posterior hemiblock
- lateral MI
- WPW

Question 10

P wave

Answer 10

Use rhythm strip
- Height: <2 squares (increased in atrial enlargement e.g. pulmonary hypertension
- Morphology
1. Bifid (look like m) -P mitrale (L atrial enlargement - mitral stenosis
2. Peaked = p pulmonale (R atrial enlargement in pulmonary disease)

Question 11

PR interval

Answer 11

Use rhythm strip
- Length: 3-5 small squares (120-200ms)
- Decreased: accessory pathway conduction (look for delta wave in WPW)
- Increased: AV node block (‘heart block’)
1st degree - PR>200ms (5 squares) and regular
2nd degree -
* Mobitz 1 - PR extends until QRS skips (failure of conduction of atrial beat)
* Mobitz 2 - constant PR in conducted beats but some P waves not conducted
* 2nd degree with 2:1/3:1/4:1 block: alternate conducted and non-conducted atrial beats (P:QRS)
3rd degree / complete heart block - complete dissociation between P waves and QRS complexes

Question 12

What happens in complete heart block

Answer 12

Normal atrial beats not conducted to ventricles, which results in ventricles self-depolarising at much slower rate (ventricular escape rhythm)

Question 13

QRS complex: all leads

Answer 13

Check in all leads
- Q wave <1 square wide and 2 squares deep is normal in I, aVL and V6 due to SPETAL DEPOLARISATION
- pathological Q waves

Question 14

QRS complex: chest leads

Answer 14

Chest leads
- R wave progression: from dominant S to dominant T through V1-V6 (from mostly -ve to mostly +ve): transition point at V3/4
* Clockwise rotation e.g. TP after V4 - RV dilatation 2ndary to lung disease
* Dominant R wave in V1/2 - RVH, posterior MI

Question 15

QRS complex: rhythm strip

Answer 15

Rhythm strip
- Lenght <3 small squares (120ms). Increased = BBB
* RBBB - QRS in V1 has M (RSR) pattern and QRS in V6 has W - MaRRoW
* LBBB - QRS in V1 has W pattern and V6 has RSR M pattern - WiLLiaM

nb: W pattern usually not fully developed;
- RSR may be seen with normal QRS length - incomplete BBB and is of no clinical significance

Question 16

Causes of LBBB

Answer 16

Aortic stenosis
Ischaemia
HTN
Anterior MI
Cardiomyopathy
Conduction system fibrosis
Hyperkalaemia

Question 17

Causes of RBBB

Answer 17

RVH
Cor pulmonale
PE
ASD
ischaemia
cardiomyopathy

Question 18

QRS complex: V1 and V5/6

Answer 18

Height - ventricular hypertrophy
- S wave depth in V1 + tallest R wave in V5/6 = > 7 big squares = LVH eg HTN, AS, AR, MR, coarctation of aorta, HOC
- R wave dominant in V1 + S wave dominant in V5/6 - RVH e.g. pulmonary HTN, MS, PE = other signs present too e.g T wave inversion in R chest leads (V1-3) and RAD

Question 19

ST segment: elevation/depression

Answer 19

Check in all leads - measure from J point (start of ST segment)
- Elevation 1 or more small squares - infarction (or pericarditis or tamponade if in EVERY LEAD)
- Depression 0.5 or more small squares - ischaemia (or reciprocal change in POSTERIOR MI)

Question 20

ST segment: morphology

Answer 20

• Normally upwardly concave