L06-Drugs affecting the heart Flashcards
What are the two main ways that drugs can affect the heart?
Directly-rate, force of contraction
Indirectly-vasculature, blood volume/composition
How are arrhythmias described?
Through site and rate e.g. ventricular tachycardia
How are antiarrhythmic drugs classified?
classes I-IV and others (drugs that dont fall into a class)
What are class I drugs, how do they work and give examples?
They are Na+ channel blockers so target the voltage gated sodium channels. This affects the phase 0 by reducing the slope of the action potential so lengthens the overall action potential. This increases time for conduction in non nodal tissue e.g. for treating tachycardias. Examples of these include lidocaine and flecainide.
What are class II drugs, how do they work and give examples?
They are B-adrenoceptor blockers which blocks sympathetic innervation. This affects nodal tissue. This decreases sodium and calcium permeability which means that it takes longer to reach threshold potential. This slows down the heart rate and decreases contractility. An example is propanolol.
What are class III drugs, how do they work and give examples?
They act as K+ channel blockers which prevents repolarisation. This increases the effective refactory period. Examples include amiodarone and sotalol
What are class IV drugs, how do they work and give examples?
They are Ca2+ channel blockers which are specific to L-type receptors so are cardio selective. These cause a decreased rate of depolarisation in phase 4 so slows HR and decreased rate of plateau in phase 2. Act on nodal and non-nodal tissue. Example is verapamil.
What effect does adenosine have and how?
It acts as a neurotransmitter at the AVN which causes opening of K+ channels. This causes an increase in hyperpolerisation, This causes the heart rate to slow down as it takes longer for the voltage to reach the threshold potential again.
How do cardiac glycosides work? give an example
They get past the BBB and cause an increase in vagal activity. this causes a decrease in AVN conduction so it effectively disconnects the atria and the ventricles. This is useful for superventricular tachycardia. An example is digoxin.
What are the three classes of drugs that increase the contractility of the heart?
Sympathomimetics
Cardiac glycosides
Phosphodiesterase inhibitors
How do cardiac glycosides cause increased contractility?
They affect the Na/k ATPase which in turns affects the Na-Ca transporter that transports calcium out of the cells. This means the intracellular calcium levels increase which causes increased contractility.
What are the side effects of cardiac glycosides?
They cause ionic disturbance that can lead to neurological disturbances.
Gynaecomastia (male developing breasts) as the drug is shapes like a steroid ring
How do phosphodiesterase inhibitors cause increased contractility? Give an example and when it is used?
Inhibiting PDE then there is less cAMP broken down, this means that Ca2+ channels remain open longer so intracellular calcium increases. An example is milrinone and it is only used in emergencies as it has such a short half life that it needs to be regularly administered.
What other three drug types are used for cardiac failure?
Diuretics: Decrease in blood volume - Vasodilators : Increase in systemic volume - ACE inhibitors
