ECG Interpretation

Question 1

How do you calculate rate?

Answer 1

300 divided by the number of big squares between each QRS complexes

Question 2

What are the four criteria’s for sinus rhythem?

Answer 2

• Are normal P waves present (shorter than 0.25mm and upright in 1/2/3)
• Are the QRS complex narrow (less than 0.12s) or wide (more than 120ms)
• P wave ALWAYS come before a QRS complex
• Is the rhythm regular or irregular

Question 3

How can you physically tell if the rhythm is regular

Answer 3

Mark positions of 3 successive R waves then slide marker along to check intervals are equal

Question 4

Describe what is seen on an EGC for atrial fibrillation

Answer 4

There are no visable P wave and irregular QRS complexes

Question 5

How does atrial flutter appear on ECGs?

Answer 5

Where P waves are seen at a rate of 300BMP giving saw tooth appearance.

Question 6

What does a normal P wave look like?

Answer 6

Less than o.25mV in height and it deflects upwards in leads 1, 3 and AVF

Question 7

In what defects are the P waves absent?

Answer 7

Atrial fibrillation and Nodal rhythm

Question 8

Name and describe an abnormal P wave

Answer 8

P-mitrale - Bifid P waves that indicate left atrial hypertrophy.
P-Pulmonale - Peaked P wave which indicates right atrial hypertrophy.

Question 9

How to you measure the P-R interval?

Answer 9

From beginning of P wave to beginning of Q wave. Normal range is 0.12-0.2s.

Question 10

A prolonged P-R imples?

Answer 10

Delayed AV conduction

Question 11

How do you measure the QRS complex and what does a normal QRS complex look like?

Answer 11

From beginning of Q wave to end of S wave. Normal duration - 0.12s and the normal Q wave is 0.04s and less than 2mm depth.

Question 12

If the QRS wave lasts for longer than 0.12s what does this indicate?

Answer 12

Ventricular conduction defects such are left and right bundle branch defects

Question 13

If the voltage of the QRS complex is below 5mm then what does this indicate?

Answer 13

Hypothyroidism, COAD (chronic obstructive airway disease), myocarditis, pericarditis and pericardial effusion.

Question 14

How does left ventricular hypertrophy appear on an ECG and is the most common cause?

Answer 14

R wave in V5 is bigger than 25mm. This is most often due to high blood pressure

Question 15

How does right ventricular hypertrophy appear on an ECG?

Answer 15

Dominant R wave in V1, T wave inversion in V1-V3 or V4, and Deep S wave in V6

Question 16

What is a significant Q wave defined as and when might you see this

Answer 16

• Longer than 0.04s and deeper than 2mm. It can be present a couples hours/days after acute MI and if its present in lead 3 then consider PE.

Question 17

How calculate the correct QTc intercal?

Answer 17

QT/Square root of RR interval.

Question 18

What can cause a prolonged QT interval?

Answer 18

• Acute myocardial ischaemia,
• Myocarditis,
• Bradycardia,
• Hypothermia,
• U&E imbalance,
• Congenital
• Drugs

Question 19

What is the ST segment?

Answer 19

Time from end of ventricular depolarisation to the start of ventricular repolarisation. Usually isoelectric (sits at baseline)

Question 20

Describe when you have an abnormal ST segment and why this might occur

Answer 20

• If there is elevation in two adjacent limb or chest leads then indicates infarction.
• If the st segment is depressed then it indicates ischaemia

Question 21

Describe the normal and abnormal inverted T wave

Answer 21

Normal - aVR, V1 and (V2 in young folk)

Abnormal - Inversion all other leads (ischaemia/infarction)

Question 22

What are the effects of digoxin

Answer 22

T wave inversion and ST segment sloping depression

Question 23

What is the cardiac axis?

Answer 23

Average direction of spread of the depolarisation wave through the ventricles. Normal axis means all QRS complexes in leads 1-3 deflect up with lead 2 having the highest peak.

Question 24

Describe what occurs when there is deflections in the cardiac axis

Answer 24

If there is left axis deviation - there will be negative deflections in lead 2 and 3. Indicates LV hypertrophy or MI.
If there is right axis deviation then there will be negative QRS deflections in lead one. Indicates RV hypertrophy, PE or MI

Question 25

Describe the MI ECG changes

Answer 25

• T wave peaked followed by T wave inversion.
• ST elevation.
• Appearance of new Q waves

Question 26

Describe how you can use the ECG to localise the infarct causing the Infarct

Answer 26

Anterior infarction - Any precordial (chest) leads
Lateral infarction - Leads 1, AVL, V5 and V6.
Inferior - Leads 2, 3,and AVF
Posterior - Reciprocal changes in lead V1

Question 27

Describe how pulmonary embolism presents on ECG

Answer 27

Large S wave in lead 1,

Deep Q wave in lead 3 and inverted T wave in lead 3

Question 28

How do hyperkalaemia and hypokalaemia show on ECG?

Answer 28

Hyper - Tall, tented T waves and widened QRS.

Hypo - Small T waves and prominent U wave

Question 29

How does hyper/hypocalcaemia present on ECGs

Answer 29

Hyper - Short QT interval,

Hypo - Long QT interval and small T waves