Flashcards in Actions Of Drugs On CVS Deck (35):
Name some things that cardiovascular drugs are used to treat
Risk of thrombus
What parts of the CVS can drugs alter?
Rate and rhythm
Force of contraction
Peripheral resistance and blood flow
Describe the re-entrant mechanism
Incomplete conduction damage to an areas of tissue
Depolarisation keeps going round in a loop
What are the 4 basic classes of anti-arrhythmic drugs?
Class I: block VG Na+ channels
Class II: beta adrenoceptor antagonists
Class III: block K+ channels
Class IV: block Ca2+ channels
How does lidocaine work?
Local anaesthetic that blocks VG Na+ channels when they are open or inactive
(Use dependent block)
Dissociates rapidly in time for the next AP
Little effect in normal cardiac tissue
When might lidocaine be given?
Following an MI if patient show signs of ventricular tachycardia (given via IV)
Name 2 beta adrenoceptor antagonists
Why might beta blockers be given after a MI?
MIs cause an increase in sympathetic activity and beta blockers block sympathetic activity
Reduce oxygen demand
Slow conduction in AVN - slows ventricular rate and prevents supra ventricular tachycardias
Describe the theory of K+ channel blockers as anti-arrhythmics
Prolong the AP therefore lengthen the absolute refractory period
Supposed to prevent another AP occurring too soon
(In reality they are likely to cause after depolarisations)
What is the useful exception to K+ channel blockers and why?
Has other actions, not just a K+ channel blocker
Used to treat tachycardia associated with Wolff-Parkinson-White syndrome
How do Ca2+ channel blockers work as anti-arrhythmics?
Decrease slop of AP at SAN
Decrease AVN conduction
Decrease force of contraction
What happens if we given adenosine pharmacologically?
Acts of alpha 1 receptors at AVN
Enhances K+ conductance so causes hyperpolarisation
Briefly blocks conduction so the heart can start again in a proper rhythm
Define heart failure
The chronic failure of the heart to provide sufficient output to meet the body's requirements
What are some features of heart failure?
Reduced force of contraction
Reduced cardiac output
Reduced tissue perfusion
Name 2 types of positive inotropes
Beta adrenoceptor agonists
Why don't we tend to use positive inotropes to treat heart failure?
They work to increase the output by increasing force of contractions
This may relieve symptoms however will cause the heart to stop working sooner as we are pushing it harder
How do cardiac glycosides (eg. Digoxin) increase the contractility of the heart?
Blocks Na+/K+ - ATPase
Increase intracellular Na+, decreased activity of NCX
Increased intracellular Ca2+
Increase force of contraction
What is the effect of cardiac glycosides on heart rate?
Increased vagal activity
Slows AVN conduction
Slows heart rate
Which class of drugs are often used to reduce the workload of the heart?
How do ACE inhibitors work?
Inhibit the action of angiotensin converting enzyme
Prevents the conversion of angiotensin I to angiotensin II
What are the effects of angiotensin II?
Increase water and Na+ reabsorption via aldosterone
What are the effects of ACE inhibitors?
Decrease vasomotor tone
Decrease fluid retention
Name 2 other classes of drugs (other than ACE inhibitors) which reduce the workload of the heart?
Beta adrenoceptor antagonists
What types of drugs improve the blood supply to the heart?
Ca2+ channel antagonists
How do organic nitrates work?
In vascular smooth muscle cells nitric oxide is released
Activates guanylate cyclase, increase cGMP, decrease intracellular calcium
What is the primary action of organic nitrates?
Venodilation to lower preload
What is the secondary action of organic nitrates?
Dilation of collateral arteries around the coronary arteries
(Doesn't work well as there aren't many collateral arteries around there)
Name 3 heart conditions that carry an increased risk of thrombus
Mechanical prosthetic heart valves
What is the action of heparin?
Inhibits thrombin formation
How is fractionated heparin given?
How is warfarin given?
What is the action of warfarin?
Antagonises the action of vitamin K
Less clotting factors are formed
Name an anti platelet drug
Finish the equation: pressure =
Flow x resistance