ECG review

Question 1

How is heart rate on an ECG determined?

Answer 1

Look at the RR intervals

Question 2

How long should a p wave last?

Answer 2

no more than 0.08 seconds

Question 3

What is the normal duration of a PR interval? What could a prolonged interval indicate?

Answer 3

0.12-0.2 seconds

Prolonged = heart block

Question 4

What is the normal duration of a QRS complex?

Answer 4

0. 06-0.1 seconds

- usually <0.12 seconds

Question 5

What is the normal duration of a QT interval? What could a prolonged interval indicate?

Answer 5

=0.4 seconds (for a HR ~70bpm)

Prolonged = ventricular arrhythmia

Question 6

What are the different classes for anti-arrhythmic drugs?

Answer 6

Class I: Na+ channel blockers
Class II: Beta blockers
Class III: K+ channel blockers
Class IV: Ca2+ channel blockers

Question 7

Give examples of Na+ channel blockers/Class I anti-arrhythmics?

Answer 7

• Quinidine
• Procainamide
• Lidocaine
• Phenytoin
• Flecainide
• Propafenone

Question 8

Give examples of beta blockers/Class II anti-arrhythmics?

Answer 8

Metoprolol

Propanolol

Question 9

Give examples of K+ channel blockers/Class III anti-arrhythmics?

Answer 9

Amiodarone

Sotalol

Question 10

Give examples of Ca2+ channel blockers/Class IV anti-arrhythmics?

Answer 10

Verapamil

Diltiazem

Question 11

Describe a normal sinus rhythm.

Answer 11

4-5 R waves (in 15 squares)
Regular RR intervals
Everything of normal duration

Question 12

Describe how sinus bradycardia would appear on ECG. When does sinus bradycardia usually occur?

Answer 12

Less than 60 bpm - ~3 R waves in 15 squares
Occurs:
- in athletic people 
- drug abusers
- hypoglycaemia
- brain injury

Question 13

Describe how sinus tachycardia would appear on ECG. When does sinus tachycardia usually occur?

Answer 13

More than 100 bpm - ~6 R waves in 15 squares
Occurs:
- stress 
- fright
- illness
- exercise

Question 14

Describe how ventricular tachycardia would appear on ECG. When does ventricular tachycardia usually occur?

Answer 14

Rate is high (180-190bpm)
QRS is prolonged
No P wave
Occurs:
- abnormal tissues in ventricles
- poor CO = cardiac arrest 

(looks like little fishing sticking their heads out of water)

Question 15

Describe how ventricular fibrillation would appear on ECG. When does ventricular fibrillation usually occur?

Answer 15

Irregular rhythm
rate ~300 bpm
Occurs:
- previous heart attacks 
- myocardial damage

Question 16

How does first degree heart block appear on an ECG? When does this usually occur?

Answer 16

PR interval has fixed duration of >200 ms
Rate is regular
Occurs:
- trained athletes

Question 17

What is the difference between type 1 and type 2 second degree heart block? When does this usually occur?

Answer 17

Type 1: PR interval progressively longer
- resets once QRS complex doesn’t follow P

Type 2: ECG irregularly irregular
An expected QRS complex is missed

Occurs:
- underlying heart condition (CHD)

Question 18

How does third degree heart block appear on an ECG?

Answer 18

P waves before or after QRS

Bradycardia is present

Question 19

How does atrial fibrillation appear on an ECG?

Answer 19

Rate: 100-160 bpm
Rhythm: irregularly irregular
P waves: not visible
PR: immeasurable

Question 20

How does atrial flutter appear on an ECG?

Answer 20

Rate: ~110 bpm
Rhythm: regular
P wave: replaced by multiple flutter (F) waves –> rate is ~300 bpm

Question 21

How does junctional rhythm appear on an ECG? What is junctional rhythm?

Answer 21

Bradycardia
Rate: 40-60 bpm
P wave: Normally absent, but if visible in 1:1 ratio with QRS complex
PR: variable

Junctional rhythm = block in conduction pathway to atria (damage to SA node)

Question 22

How does supra ventricular tachycardia appear on an ECG? What is the most common type of supra ventricular tachycardia?

Answer 22

Rate: 140-220 bpm
P wave: absent/obscured by T wave

Most common type = AV node re-entrant tachycardia

• QRS is regular but narrow (<0.12s)
• no distinct P wave or retrograde P wave

Question 23

How does bundle branch block appear on an ECG?

Answer 23

Widening of QRS complex
May see notched/double R wave
Everything else is normal

Question 24

What can cause ST segment depression

Answer 24

Coronary ischaemia or hypokalaemia

Question 25

How does depressed ST segment appear on an ECG?

Answer 25

must have new ST elevation in 2 or more adjacent ECG leads
Rate: ~80 bpm
Everything else normal

Question 26

Is a significantly visible Q wave pathological or physiological?

Answer 26

Pathological
Q wave is usually not seen or is not usually significant
If it is enlarged this is a sign of damage to inter ventricular septum
–> may be due to previous AMI/combined with STEMI

Question 27

Apart form heart block, what else can a prolonged PR interval be associated with?

Answer 27

• hypokalaemia
• acute rheumatic fever
• carditis

Question 28

What is indicated by a long QRS duration?

Answer 28

ventricular muscle not contracting normally –> taking longer to depolarise

(normal = synchronisation of the contraction of the ventricular muscle)

Question 29

In terms of QRS complex and T wave, when is an ECG signal seen?

Answer 29

When there is a difference in the depolarisation of the endocardial and epicardial layers of ventricular muscle

• endocardial depolarises first
• epicardial depolarises slightly later - action potential is also shorter
• -> when it repolarises the T wave appears

Question 30

Which layer of ventricular muscle is more susceptible to the effects of ischaemia - endocardial or epicardial? What is the impact of this?

Answer 30

Endocardial

–> reduces the duration of the endocardial action potential (shorter than epicardial) giving an inverted T wave