CAL: ECG Interpretation

Question 1

How should you work out the HR from an ECG?

Answer 1

If you have time, count every single QRS during a minute

Question 2

T/F: P waves have their own T waves

Answer 2

True - often - but often you can’t see this

Question 3

Name 4 conditions associated with there not always being a P wave for every QRS

Answer 3

• Premature beats – ventricular or supraventricular
• Sinus arrest with escape complexes
• Atrial standstill
• Atrial fibrilliation

Question 4

Distinguish complexes of ventricular and supraventricular origin

Answer 4

• VENTRICULAR - wide and bizarre, AV dissociation or no associated P waves
• SUPRAVENTRICULAR - narrow upright QRS complexes in appropriate leads (unless concurrent hypertrophy or conduction disturbance), may be associated with P waves (may have AV dissociation if junctional), same QRS as sinus complexes where present.

Question 5

What happens in atrial standstill?

Answer 5

Bradycardia (<70 bpm) without any P waves

Question 6

What can cause a P wave without a QRS complex? 2

Answer 6

Failure of conduction through AVN – 2nd (intermittent) or 3rd degree (persistent)

Question 7

What are the different types of 2nd degree block?

Answer 7

• Mobitz type 1 = progression prolongation of PR interval, prior to failure of P wave conduction. This is almost always due to disease of the AVN.
• Mobitz type 2 = this is almost always a disease of the distal conduction system. The ECG has intermittently non-conducted P waves, not preceded by PR prolongation and not followed by PR shortening. There is usually a fixed number of non-conducted P waves for every successfully conducted QRS complex.

Question 8

Describe what happens in 1st degree AV block?

Answer 8

all the P-wave are conducted but some of them are conducted with delay leading to lengthy P-Q intervals.

Question 9

Typically what is meant by HR on an ECG trace?

Answer 9

the ventricular rate

Question 10

What implies the atria and ventricules are depolarising autonomously?

Answer 10

varied interval between atrial and vetricular depolarisations. . This is called “atrioventricular dissociation” = 3rd degree AV block.

Question 11

What are DDx for P wave absence 4

Answer 11

• Atrial fibrillation (this trace)
• Atrial standstill
• Ventricular tachycardia/fibrillation
• Asystole (flatline)

Question 12

Describe ventricular fibrillation

Answer 12

has an absence of any organized ventricular or atrial activity. You would not be able to recognize any QRS complexes.

Question 13

What are features of atrial standstill?

Answer 13

absence of P-waves and supraventricular QRS complexes, usually bradycardic (<70bpm)

Question 14

Define asystole

Answer 14

when there is a “flatline” or a complete absence of any electrical activity.

Question 15

What does the presence of P waves on any trace suggest?

Answer 15

The atria are depolarizing in an organized way and therefore they cannot be fibrillating.

Question 16

What does a VPC look like on an ECG?

Answer 16

relatively normal appearance but just appears early (i.e. premature)

Question 17

What pathology can ECGs indicate? 3

Answer 17

• changes in myocardial mass
• metabolic abnormalities affecting the myocardium
• alterations in conductivity between heart and skin

Question 18

Can you determine the mean electrical axis from an ECG?

Answer 18

yes

Question 19

DDx for not a P for every QRS - 3

Answer 19

• Premature complexes (VPC or
  Junctional premature)
• Sinus arrest with escape complexes
  (Ventricular escape and Junctional escape)
• No organised atrial depolarisation (Atrial standstill or Atrial fibrillation)

Question 20

Define AF

Answer 20

Enlarged atria
with multiple waves
of depolarisation
spreading in a 
disorganised fashion
simultaneously. No evidence of P-waves. Coarse oscillation of the baseline
demonstrates the presence of f-waves.

Question 21

DDx - No QRS following a P wave

Answer 21

FAILURE OF AV CONDUCTION:

• Second degree AV block (Intermittent failure of AV conduction, Mobitz type I - Prolongation of P-R interval, Mobitz type II - No prolongation of P-R interval)
• Third degree AV block (Complete failure of AV conduction, Complete AV dissociation)

Question 22

What do P wave variations indicate? 3

Answer 22

• May be normal - wandering pacemaker
• May indicate atrial ectopy
• P-wave should be positive in lead II

Question 23

What does variation in QRS complex indicate?

Answer 23

• Some variation may be normal
• May indicate variable conduction
• May indicate electrical alternans

Question 24

What is the main determinant of the significance of rhythm disturbance?

Answer 24

• where the rhythm disturbance is causing clinical signs
• why is the rhythm disturbance present
• always treat the patient and not the ECG

Question 25

Why might abnormalities of generation or conduction of the depolarisation arise? 7

Answer 25

• Intrinsic cardiac disease
• Hypoxia
• Autonomic influence
• Mechanical abnormalities
• Metabolic abnormalities
• Electrolyte disturbances
• Drugs