ECG

Question 1

What is an electrocardiogram

Answer 1

• a graph of voltage against time
• visual representation of electrical potentials in the heart
• electrical signals stimulate and coordinate contraction of heart

Question 2

What causes dipoles in the heart

Answer 2

The depolarising and repolarising of cardiac cells (myocytes)

Question 3

Einthoven triangle

Answer 3

Electrical potential generated from heart form an equilateral triangle when measured from 3 positions in body (wrists and left ankle)

Question 4

6 limb leads

Answer 4

3 bipolar leads (I, II, III)

3 unipolar leads (aVR, aVL, aVF)

Question 5

V1 chest lead

Answer 5

4th IC

right sternal edge

Question 6

V2 chest lead

Answer 6

4th IC

Left sternal edge

Question 7

V4 chest lead

Answer 7

5th IC

Midclavical line

(Bottom right of left sternum)

Question 8

V5 chest lead

Answer 8

Left anterior axillary

Edge of left ribcage, in line with v4

Question 9

V6

Answer 9

Mid axillary line

Under armpit, in line with v4 and v5

Question 10

Draw P wave

Answer 10

Atrial contraction

Both atria are depolarising

Road bump before QRS

Question 11

PR interval

Answer 11

Time taken for signal to travel from AVN to Ventricle

AVN conduction time

Question 12

Draw QRS interval

Answer 12

Ventricular contraction

Ventricles depolarising

Traverse Bundle of His and Purkinje fibres

Question 13

Negative deflection vs Positive deflection

Answer 13

Negative deflection = become positive electrode
E.g. Q and S

Positive deflection = become negative again
E.g. R

Question 14

Draw ST segment

Answer 14

Repolarisation of ventricles (T wave)

Isoelectric flat segment

Question 15

P wave QRS complex T wave are collectively known as…

Answer 15

Sinus rhythm

Question 16

Buckmans bundle

Answer 16

Transfers electrical impulses from SAN in the right atrium to the left atrium

Question 17

Normal resting heart rate for adult

Answer 17

50 to 90 bpm

Bradycardia= below range

Tachycardia= above range

Question 18

Abnormal cardiac rhythm is called…

Answer 18

Arrhythmia

Question 19

2 types of arrhythmia

Answer 19

1) Conduction abnormalities in SAN and AVN, unable to initiate impulses so no P wave and QRS. Valve fibrosis.
2) Abnormal impulse initiation where ventricles beat abnormally, impairs cardiac output, hypotension and collapse

Question 20

3 causes of tachyarrhythmia

Answer 20

1) altered automaticity
2) Another depolarisation occurs abnormally

E.g. atria fibrillation and atrial flutter

3) re-entry

Question 21

Ischaemia

Answer 21

Shortage of oxygen supply to muscle

Ischaemic myocytes have reduced membrane potentials compared to healthy myocytes which displace the ST segment

Injury current

Question 22

Angina

Answer 22

Chest pain on exercising

Due to chronic arterial narrowing

Question 23

Myocardial infarction

Answer 23

Heart attack