Drugs and the CVS Flashcards
Describe the types of drugs used to treat patients with common cardiovascular disorders and their mechanisms of action
Cardiovascular drugs are used to treat: arrythmias, heart failure, angina, hypertension or risk of thrombus formation. They achieve this through altering the rate and rhythm of the heart, force of myocardial contraction, peripheral resistance and blood flow as well as blood volume.
Define the term inotropic drug and the circumstances under which these drugs can be used
An inotropic drug is one which affect the force of contraction. Cardiac glycosides such as digoxin increase the force of contraction and can increase cardiac output in heart failure. They work by inhibiting Na/K ATPase pump leading to a smaller Na gradient. This prevents the Ca pump from working so well, increasing intracellular calcium. This causes an increase in the contraction.
Describe how drugs can be used in the treatment of heart failure
Inotropic drugs may be used to increase cardiac output, such as dioxin which inhibits Na/K ATPase, preventing the Ca pump from working so well due to reduced Na gradient thus higher cytosolic Ca and better contraction.
Angiotensin Converting Enzymes inhibitors and diuretics may also be used. ACE inhibitors prevent the synthesis of angiotensin II, a vasoconstrictor, thus promoting veno and vaso dilatation, reducing both pre and afterload.
Explain the mechanisms by which organic nitrates alleviate angina
Organic nitrates release nitric oxide which is a powerful dilator produced naturally by endothelial cells lining blood vessels. It acts mainly by venodilatation, thereby reducing central venous pressure (preload) and therefore the work of the heart. They DO NOT alleviate angina by dilating arterioles.
Name some cardiovascular conditions which have an increased risk of thrombus formation and describe the pharmacological agents used to minimise this risk.
Atrial fibrillation, valve diseases. Antithrombotic drugs are used to prevent clot formation, such as warfarin or aspirin. Warfarin is a vitamin K antagonist whilst aspirin is an antiplatelet.
Describe the classes of anti-arrhythmic drugs and the principles of their therapeutic use
They can be divided into four main classes depending on their primary target. They include (1) Na channel blockers such as local anaesthetics (2) beta adrenoreceptor antagonists, (3) Potassium channel blockers and (4) calcium channel blockers.
Amiodarone is an important drug which acts on calcium potassium and beta adrenoreceptors.
Explain class II antiarrhythmic drugs
Class II. (beta-adrenoceptor antagonists)
E.g. Propranolol, Atenolol (Beta Blockers)
Block sympathetic action by acting on beta 1 receptors in the heart, decreasing the slope of the pacemaker potential in the SAN. Inhibits adenyl cyclase, decreasing inotropy.
Used after an MI, to combat increased sympathetic activity and to reduce the O2 demand of the myocardium.
Explain how arrhythmias can arise
Arrhythmias can arise from ectopic pacemaker activity; after- depolarisations (?high Ca2+); re-entry loops because of conduction delay or block. It is possible to get multiple atria re-entry loops from being stretched over time, leading to AF. Arrhythmias can also arise from antiarrhythmic medication.
Describe the classes of anti-arrhythmic drugs and the principles of their therapeutic use
There are 4 basic classes of anti-arrhythmic drugs:
I. Drugs that block voltage gated Na+ channels
II. Antagonists of beta adrenoceptors
III. Drugs that block K+ channels
IV. Drugs that block Ca2+channels
Amiodarone is an important drug which acts on calcium potassium and beta adrenoreceptors.
Explain class I antiarrhythmic drugs
Class I. (Voltage Gated Na+ Channel Blockers)
A typical example is the local anaesthetic lidocaine. Only channels that are in an open or inactive state are blocked, and it dissociates rapidly in time for the next AP.
Normal firing of AP’s is not stopped, but it prevents the firing of AP’s too close to one another. As Na+ channels are blocked, after-depolarisations cannot trigger another AP.
Explain class IV antiarrhythmic drugs
Class IV (Drugs that block Ca2+ channels) E.g. Verapamil Decreases slope of pacemaker action potential at SA node. Also decreases AV nodal conduction and decreases the force of contraction. Some coronary and peripheral vasodilation. It also dilates coronary vessels, improving subendocardial perfusion.
Explain class II antiarrhythmic drugs
Class II. (beta-adrenoceptor antagonists)
E.g. Propranolol, Atenolol (Beta Blockers)
Block sympathetic action by acting on 1 receptors in the heart, decreasing the slope of the pacemaker potential in the SAN. Inhibits adenyl cyclase, decreasing inotropy.
Used after an MI, to combat increases sympathetic activity and to reduce the O2 demand of the myocardium.
Explain class III antiarrhythmic drugs
Class III. (Drugs that block K+ channels)
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.
They are not generally used because they can also be pro-arrhythmic.
Explain class IV antiarrhythmic drugs
Class IV (Drugs that block Ca2+ channels)
E.g. Verapamil
Decreases slope of pacemaker action potential at SA node. Also decreases AV nodal conduction and decreases the force of contraction. Some coronary and peripheral vasodilation.
