5 Drugs and the Heart Flashcards
How can drugs affect the heart?
directly (rate/rhythm, or contraction force)
Indirectly (vasculature or blood volume (renal))
Name 2 examples of Class I antiarrhythmic drugs
lidocaine
flecainide
How do class I antiarrhythmic drugs work?
block Na+ VGC’s (dirty tho)
slow the rate of depolarisation, increasing the refractory period
Name one example of a class II antiarrythmic drug
metoprolol (beta blocker)
How do Class II antiarrythmic drugs work?
decrease sympathetic effect
Name 2 examples of Class III antiarrythmic drugs
amiodarone
sotalol
How do Class III antiarrythmic drugs work?
block K+ channels, lengthening repolarisaiton prolonging AP
Name one side effect of amiodarone
it contains iodine so it impairs thyroid function
How does adenosine work?
binds to receptors in the SA/AV, opening K+ channels
more K+ efflux
hyperpolarisation, increases refractory period, as nodal conduction slows
How does caffeine increase HR?
antagonist to adenosine receptors in the SA/AV, therefore closing K+ channels, making cells more excitable
(opposite to adenosine)
in what 2 circumstances would we need drugs to affect the force of contraction?
anaphylaxis
heart failure
What are the 2 sorts of inotropic drugs?
+ inotropic drugs increase intracellular Ca2+
- inotropic drugs decrease intracellular Ca2+
Name one type of cardiac Glycosides
digoxin
How does digoxin increase contractility?
partial inhibition of Na+ / K+ ATPase
this reduces the Na gradient increasing Na intracellular concentration, reducing the amount of calcium that can be pumped out via the Na/Ca pump
What side effects are associated with cardiac glycosides?
ionic disturbance (can cause arrythmia if too much, or GI symptoms) gynaecomastia (iodine and thyroid)
What is Digoxin used for?
heart failure patients with arrhythmia
What drug interactions should we watch out for with Digoxin
diuretics reduce K+ levels, this promotes the digoxin effect as K+ isn’t competing with digoxin as much
How do PDE inhibitors work?
increases cAMP / cGMP levels and hence allows more Ca2+ in, increasing contraction force
Why are PDE inhibitors so useful?
PDEi type 3 are mainly expressed in the heart
What is a potential adverse effect of using PDE inhibitors?
arrhythmia
When are PDE inhibitors used?
Why?
acute heart failure - emergencies
they have a short half life
Name 3 types of drugs used for cardiac failure which don’t have a direct effect on heart cells
diuretics (decrease blood volume)
vasodilators (increase systemic volume)
ACE inhibitors
Name 2 other drugs used to decrease heart rate
beta blockers
ivabradine
How does ivabradine work?
blocks the IF channel in cardiac myocytes, which is important in determining pacemaker potential
this decreases HR
How does Digoxin increase HR?
decreases Vagal tone
