Arrhythmias

Question 1

What are the 2 types of ventricular arrhythmias?

Answer 1

Ventricular premature beat (VPB) - mild, normally not treated

Ventricular fibrillation (VF) - most severe, rapidly lethal, must be prevented

Question 2

What are the 2 causes if a heartbeat originates somewhere?

Answer 2

Abnormal pacemaking or the failure of conduction to stop at the end of the heartbeat (re-entry)

Question 3

How can re-entry happen?

Answer 3

Re-entry is caused by localised slow conduction due to ischaemia induced depolarisation = causes the wave front to be ragged and splitting into 2 = circles around and re-enters the original pathway

Question 4

What are the 2 (out of 4) main classes of anti-arrhythmic drugs that were discussed?

Answer 4

Class 1 (Na+ channel blockers) and Class 3 (b1 antagonists)

Question 5

What are the 2 main ways of blocking conduction of the re-entry wave? How do they work?

Answer 5

Direct - by targeting the ischaemic conduction region

Indirect - by delaying repolarisation in the pathway to prolong the refractory period

Question 6

What is the problem with direct targeting of re-entry?

Answer 6

Drugs must selectively target channels in the damaged region to block local condution. However, most aren’t selective enough and can slow the conduction in surrounding healthy tissue.

Question 7

What is the mechanism of action of lidocaine? Why is not widely used anymore?

Answer 7

Lidocaine is a Class 1 anti-arrhythmic drug that selectively blocks Na+ channels in ischaemic tissue. However, it can cause nerve effects such as paraesthesia and convulsions.

Question 8

How do Class 3 anti-arrhythmics indirectly block the re-entry? What should this effect be selective for and why?

Answer 8

Block the K+ channels delayed repolarisation = prolonged refractory period = indirect block of Na channels and conduction

This should be selective for abnormal or fast rhythms to block re-entry during tachyarrhythmia

Question 9

What is amiodarone? What are its problems?

Answer 9

Class 3 anti-arrhythmic used for VF prophylaxis

You can only take amiodarone for 3 years, it can cause thyroid dysfunction and corneal opacities

Question 10

What is D-sotalol? What are its problems?

Answer 10

Second generation of Class 3 anti-arrhythmics, high potency and selectivity for K+ channels

Increased mortality in patients