ECG

Question 1

What does the P wave represent?

Answer 1

Atrial depolarisation
Duration: <0.12 secs (3 small squares)
Amplitude: <0.25 mV (2.5 small squares)
Direction: Upright in leads I, AvF, V3-V6

Question 2

What does the PR segment represent?

Answer 2

Delay at AV node
Amplitude: 0.0mV (Isoelectric)
i.e. this should always be on the baseline

Question 3

What does the PR interval represent?

Answer 3

Atrial depolarisation and delay at AV node

Duration: 0.12-0.20 secs (3-5 small squares)

Question 4

What does the QRS complex represent?

Answer 4

Ventricular depolarisation 
 Duration: <0.12 secs (3 small squares)
Amplitude: >0.5 mV (in ≥1 limb lead) >1mV (in ≥1 chest lead)
Upper Limit: 3.0mV (6 big squares)
Direction: Positive in I, II, V4-V6
Negative in aVR, V1 and V2

Question 5

What does the QT interval represent?

Answer 5

Whole ventricular action potential 
Duration:
Males: <0.40 secs (2 big squares)
Females: <0.44 secs (11 small, or 2 big 1 small)
This needs rate-correcting (QTc)

Question 6

What does the ST segment represent?

Answer 6

Plateau phase of ventricular action potential
Amplitude: Isoelectric, slanting up to the T-wave
Direction:
Elevation of up to 2mm normal in chest leads
Not normally depressed >0.5mm

Question 7

What does the T wave represent?

Answer 7

Ventricular depolarisation
Normally rounded and asymmetrical (gradual upslant)
Amplitude: >0.2 mV (2 small squares) in leads V3 and V4
Direction: Same as QRS in at least 5 of 6 limb leads

Question 8

How can you assess heart rate on an ECG?

Answer 8

Count the number of large squares between 2 R waves and divide by 300
Count the number of QRS complexes on the entire strip and multiply by 6

Question 9

How do you assess axis on an ECG?

Answer 9

Normal- QRS complexes point up in lead 1 and AVF
Left deviation- QRS up in lead 1 and down in AVF
Right deviation- QRS down in lead 1 and up in AVF
Extreme- QRS down in lead 1 and AVF

Question 10

What are common abnormalities seen on ECG?

Answer 10

Absent P wave- AF
Prolonged PR- 1st degree and Mobitz type 1
Broad QRS- BBB, ventricular ectopic beats, accessory pathways
ST elevation- STEMI
ST depression- ischameia
Tall tented T wave- hyperkalaemia
T wave inversion- ischaemia, BBB, PE, HCM
Flattened T wave- hypokalaemia
Prolonged QT- life-threatening arrhythmias/drugs

Question 11

What is seen on an ECG in a STEMI?

Answer 11

ST elevation >1mm (limb leads)

>2mm in chest leads

Question 12

What are the rates within the heart?

Answer 12

SA node- 60-100bpm
Atrial foci- 60-80bpm
Junctional (AVN and bundle of His)- 40-60bpm
Ventricular foci- 20-40bpm

Question 13

What is seen on an ECG in Wolff Parkinson White?

Answer 13

PR interval shortened
Right axis deviation
QRS complex broad with delta wave (V1-V2)
Abnormal QT interval

Question 14

How can you determine the territory of the heart that is affected by ischaemia?

Answer 14

Anterior- V1-V4 (left anterior descending)
Lateral- 1, AVL, V5, V6 (left circumflex)
Inferior- II, III, AVF (right coronary artery)
Anterolateral- I, AVL, V2-V6

Question 15

How does the wave morphology of STEMIs develop over time?

Answer 15

Onset of pain- normal ECG
Within 1 hour- ST segment elevation
Following treatment- T wave inversion
24 hours- ST segment to baseline, T wave inversion persists
Days/months- deep Q wave indicating tissue death

Question 16

What is seen in left ventricular hypertrophy?

Answer 16

QRS- narrow, large amplitude, normal direction
Left axis deviation
ST elevation in V1-3, depression in V5-V6, 1, AVL
T wave inverted in I, AVL, V5-6