5.1.2 Arrhythmia Generation and Class 1 Drugs

Question 1

How can arrhythmias arise?

Answer 1

Abnormal impulse generation

or

Abnormal conduction

Question 2

What are the different types of abnormal impulse generation?

Answer 2

Automatic rhythms
- Enhanced normal automaticity
- Ectopic focus (AP arises from sites other than SAN)

Triggered rhythms
- Delayed afterdepolarisation
- Early afterdepolarisation

Question 3

What are the different types of abnormal conduction?

Answer 3

Conduction block
- Impulse not conducted from atria to ventricles
- 1st, 2nd or 3rd degree block

Re-entry
- Circus movement
- Reflection

Question 4

What condition has an acessory pathway in the heart?

Answer 4

Wolf-Parkinson-White Syndrome

Leads to re-entry rhythm causing arrhythmias

Question 5

What causes re-entry loops?

Answer 5

Impulse does not spread through damaged myocardium

Impulses spreads via longer route, this leads to slow and fast pathways

When these pathways meet it can cause a cancellation of the impulses

Question 6

What drugs are given for treating abnormal generation?

Answer 6

Drugs which:
Decrease slope of phase 4 in pacemaker cells

Raise threshold for AP

Question 7

What drugs are given for treating abnormal conduction?

Answer 7

Drugs which:
Decrease conduction velocity

Increase refractory period so the cell won’t be re-excited again

Question 8

Complete the table

Answer 8

Question 9

Give examples of 1B agents and how they are taken

Answer 9

Lidocaine IV
Mexiletine Oral

Question 10

What is the effect of Class 1B on cardiac activity?

Answer 10

No change in phase 0 in normal tissue

Action potential duration slightly decreased in normal tissue

Increased threshold

Decreased phase 0 conduction in fast beating or ischaemic tissue

Question 11

What are the effects on ECG of Class 1B

Answer 11

None in normal

Increased QRS duration in fast beating or ischaemic

Question 12

When do you use Class 1B drugs?

Answer 12

Acute ventricular tachycardia, especially during ischaemia

Not used in atrial arrhythmias or AV junctional arrythmias

Question 13

What are the side effects of 1B drugs?

Answer 13

CNS effects: dizziness, drowsiness

Abdominal upset

Question 14

Give an example of a Class 1C agent and how it’s taken

Answer 14

Flecainide, oral or IV

Question 15

What are the effects of Class 1C drugs on cardiac activity?

Answer 15

Substantially decreased phase 0 in normal tissue

Decreased automaticity by increasing the threshold

Increases AP duration and refractory period especially in rapidly depolarising atrial tissue

Question 16

What are the effects on an ECG with class 1C?

Answer 16

Increased PR interval
Increased QRS duration
Increased QT

Question 17

When are class 1C drugs used?

Answer 17

Wide spectrum

Used for supraventricular arrhythmias (fibrillation and flutter)

Premature ventricular contractions

Wolf-Parkinson-White syndrome

Question 18

What are the side effects of class 1C drugs?

Answer 18

Pro-arrhythmia and sudden death especially with chronic use and in structural heart disease

Increased ventricular response to supraventricular arrhythmias (felcainide flutter)

CNS and GI effects

Question 19

What is felcainide flutter?

Answer 19

Atrial flutter as there is transmission of APs through the AVN which would normally be stopped