Flashcards in Drugs Acting on the CVS Deck (52)
What are cardiovascular drugs used to treat?
Risk of thrombus formation
What can cardiovascular drugs alter?
The rate and rhythm of the heart
The force of myocardial contraction
Peripheral resistance and blood flow
What can cause arrhythmias?
Ectopic pacemaker activity
How can ectopic pacemaker activity lead to arrhythmias?
Damaged area of myocardium becomes depolarised and spontaneously active. The latent pacemaker region is activated due to ischaemia, and dominates over the SA node
What are after-depolarisations?
Abnormal depolarisations following the action potential
What are after-depolarisations thought to be caused by?
High intracellular Ca
What does a longer action potential in after-depolarisation lead to?
A longer QT interval
What causes a re-entry loop?
Conduction delay, whereby normal spread of excitation is disrupted due to damaged area .
When will a re-entry loop occur?
When there is incomplete conduction damage leading to uni-directional block
What happens if you get several small re-entry loops in the atria?
What can cause several small reentry loop in the atria?
Being stretched over time
What are the basic classes of anti-arrythmic drugs?
I. Drugs that block voltage gated Na channels
II. Antagonists of ß-adrenoreceptors
III. Drugs that block K channels
IV. Drugs that block Ca channels
What is a typical example of a class I anti-arrythmic drug?
What channels does lidocaine block?
Voltage gated Na channels
Only those that are in an open or inactive state
How quickly does lidocaine dissociate?
Quickly- in time for next AP
What is the advantage of lidocaine?
Normal firing of APs is not stopped, but it prevents the firing of APs too close to one anoterh
Why can lidocaine be used as an anti-arrythmic?
Because Na channels are blocked, after-depolarisations cannot trigger another AP
Give two examples of class II anti-arrythmic drugs
How do class II anti-arrythmic drugs work?
They block sympathetic action by acting on ß1 receptors in the heart, decreasing the slope of the pacemaker potential in the SAN
Inhibits adenylyl cyclase, decreasing intropy
What are class II anti-arrythmic drugs also known as?
When are beta-blockers used?
After a MI
What are beta-blockers used after an MI?
To combat increases in sympathetic activity
To reduce oxygen demand of myocardium
How do class III anti-arrythmic drugs work?
Prolong the action potential, by blocking K channels (which are responsible for repolarisation). The absolute refractory period is lengthened, preventing another AP from occurring too soon
Why are class III drugs not generally used?
Because they can also be pro-arrythmic
Give an example of a class IV anti-arrythmic drug?
How do class IV drugs work?
Decreases slope of pacemaker potential at SA node
Decreases AV node condutction
Decreases force of contraction
Some coronary and peripheral vasodilation
Where is adenosine produced?
What does adenosine act on?
A1 receptors at AV node
What kind of receptor are A1 receptors?