eLFH - The Electrocardiogram Part 1

Question 1

Standard ECG paper speed

Answer 1

25 mm/s

= 5 large squares per second

Question 2

Usual representation of one small square on ECG

Answer 2

0.04 s on x axis

0.1 mV on y axis

Question 3

X and Y axis on ECG

Answer 3

X axis = time (s)

Y axis = Amplitude (mV)

Question 4

Implication of negative deflection vs positive deflections on ECG

Answer 4

Negative deflection means electrical impulse is moving away from electrode

Positive deflection means electrical impulse is moving towards electrode

Each lead looks at electrical activity in different plane to the others

Question 5

Directions of limb lead planes

Answer 5

Coronal plane

Question 6

Direction of chest lead planes

Answer 6

Horizontal plane

Question 7

Bipolar leads

Answer 7

Leads I, II and III

Form triangle called Einthoven’s triangle

Question 8

Unipolar leads

Answer 8

Augmented limb leads (aVR, aVF and aVL) and chest leads (V1-V6)

Measured from imaginary reference point of zero potential called the ‘indifferent electrode’ (centre of limb lead electrodes)

Lower amplitude than bipolar leads and therefore need to be augmented

Question 9

Normal cardiac axis

Answer 9

Between - 30 degrees and + 90 degrees

Question 10

Left axis deviation

Answer 10

Between - 30 degrees and - 90 degrees

Question 11

Causes of left axis deviation

Answer 11

Inferior MI

Left anterior hemiblock

LBBB

Pregnancy - mechanical displacement of the heart

Cardiomyopathy

Question 12

Right axis deviation

Answer 12

Between + 90 degrees and + 180 degrees

Question 13

Causes of right axis deviation

Answer 13

RBBB

Right ventricular hypertrophy

Normal variant in young

Question 14

Causes of right ventricular hypertrophy

Answer 14

COPD

PE

ASD

Pulmonary stenosis

Question 15

Net electrical potential calculation

Answer 15

For a particular lead:
Number of small squares positive - number of small squares negative = net electrical potential

Question 16

Leads commonly used in anaesthesia and why

Answer 16

Usually lead II

Gives best visualisation of P wave and QRS to determine rhythm

Question 17

CM5 configuration of leads use

Answer 17

More sensitive to identify ischaemia

Allows detection of 80% of LV ischaemia as it is exploring largest mass of LV muscle

Question 18

CM5 electrode positions

Answer 18

Right Arm electrode placed on manubrium

Left Arm electrode placed on at V5

Left Leg electrode placed on Left Clavicle

Select lead I for monitoring (between Manubrium and V5)

Question 19

Electrode positioning in cardiac anaesthesia

Answer 19

5 electrode ECG monitoring - allows monitoring of a limb lead and chest lead

Usual 3 lead electrodes placed + right leg electrode + choose one from any of V1 to V6

Question 20

Elements of the ECG

Answer 20

P wave
Q wave
QRS complex
PR interval
ST segment
T wave
QT interval

Question 21

P wave - represents

Answer 21

Atrial depolarisation

Question 22

P wave - size

Answer 22

< 0.2 s
< 2.5 mm

Question 23

P wave abnormalities

Answer 23

Absence - AF

Flutter waves (saw tooth) - atrial flutter

Hypertrophy:
- Right atrial (P pulmonale)
- Left atrial (P mitrale)

Question 24

Q wave - represents

Answer 24

1st downward deflection after P wave

Abnormal in chest leads

Question 25

Q wave - abnormalities

Answer 25

Q waves in any lead are abnormal - previous MI with full thickness myocardial loss

Question 26

QRS complex - represents

Answer 26

Ventricular depolarisation

Question 27

QRS complex - size

Answer 27

< 0.12 s

Question 28

QRS complex - abnormalities

Answer 28

Widened QRS - Bundle branch block (right, left and hemiblocks) Increased height QRS - ventricular hypertrophy Small QRS - pericardial effusion

Question 29

PR interval - represents

Answer 29

Normal delay at AV node

Question 30

PR interval - duration

Answer 30

< 0.2 s

Question 31

PR interval - abnormalities

Answer 31

Long PR - 1st degree heart block (AV conduction delay) Short PR - Wolff-Parkinson-White (extra nodal conduction)

Question 32

ST segment - abnormalities

Answer 32

ST depression - Reversible ischaemia ST elevation (>1mm limb leads or >2mm chest leads) - Irreversible ischaemia Saddle ST elevation - Pericarditis

Question 33

T wave - represents

Answer 33

Ventricular repolarisation

Question 34

T wave - size

Answer 34

< 5 mm in limb leads < 10 mm in chest leads

Question 35

T wave - abnormalities

Answer 35

T wave inversion (except aVR and V1) - non specific e.g. ichaemia, infection, LVH Tented T waves - hyperkalaemia

Question 36

QT interval - represents

Answer 36

Ventricular refractory period

Question 37

QT interval - duration

Answer 37

350 to 430 ms

Question 38

QT interval - correction

Answer 38

Bazett's formula - corrects for HR QTc = QT / square root RR (s)

Question 39

QT interval - abnormalities (prolonged QT causes)

Answer 39

Congenital Electrolyte disturbance - low K+, low Mg2+, low Ca2+ Drugs

Question 40

Congenital causes of prolonged QT

Answer 40

Romano Ward syndrome Lervell Lange Nielson syndrome

Question 41

Drug causes of prolonged QT

Answer 41

Antiarrhythmics class III - amiodarone Antibiotics - macrolides Antihistamines Antipsychotics - phenothiazines Antidepressants - tricyclic antidepressants

Question 42

Potential additional ECG waves

Answer 42

Delta waves J waves U waves

Question 43

Delta waves

Answer 43

Up-stroking between P wave and QRS complex Seen in WPW - pre excitatory syndrome

Question 44

J waves

Answer 44

Extra deflection at end of QRS complex Seen in hypothermia < 25 degrees Celsius

Question 45

J waves alternative name

Answer 45

Osborne waves

Question 46

U waves

Answer 46

Small deflection following T wave Represents repolarisation of papillary muscles Seen in hypokalaemia most commonly

Question 47

Causes of U wave

Answer 47

Hypokalaemia Hypercalcaemia Hyperthyroidism Digoxin therapy