Session 7 - Cardiac Arrhythmias And CVS Drugs Flashcards
What is ectopic pacemaker activity?
Damaged area of myocardium becomes depolarized and spontaneously active and dominates over SA node
What are afterdepolarisations?
Abnormal depolarisations following the action potential
What is sick sinus syndrome?
Intrinsic SA node dysfunction
When are early after depolarisations more likely to happen?
If AP is prolonged // if longer QT interval
When are delayed after depolarisations more like to happen?
High intracellular Ca2+
What is the re entrant mechanism for generating arrythmias?
When there is incomplete conduction damage, excitation can take a long route to spread the wrong way through damaged area, setting up a circus of excitation
How does re entrant circuits lead to atrial fibrillation?
Multiple re entrant circuits in atria causes many atrial fibrillation impulses and chaotic signals passes through AV node, causing rapid ventricular impulses
How does AV nodal re entry occur?
Fast and slow pathways in AV node creates a re entry loop
What is ventricular pre excitation?
Accessory pathway between atria and ventricles creates re entry loop
What are 4 basic classes of anti arrhythmic drugs?
Na+ channel blockers
Beta adrenoceptor antagonist
K+ channel blockers
Ca2+ channel blockers
What is an example of a voltage dependent-Na+ channel blocker?
Lidocaine
How does Na+ channel blocker work?
Only blocks in open or inactive state, hence preferentially blocks damaged depolarized tissue and not normal tissue as it dissociates rapidly
What is the effect of lidocaine?
Blocks Na+ channels, slows upstroke, shortens action potential and slows conduction velocity
What are 2 examples of beta blockers?
Propranolol
Atenolol
How do beta blockers work?
Block sympathetic action at beta 1 adrenoceptors in heart, decreases slope of pace,alter potential in sinoatrial node and slows conduction at AV anode
What can beta blockers used to prevent?
Supraventricular tachycardia as it slows conduction in AVnode and can slow ventricular rate in patients with atria fibrillation
What can beta blockers be used following?
MI as it often causes increased sympathetic activity, so beta blockers can prevent ventricular arrythmias
What can K+ channel blockers do?
Prolong action potential and lengthen absolute refractory period
What is an example of K+ channel blocker?
Amiodarone
What can amiodarone be used for?
Treat tachycardia associated with Wolff-Parkinson-White syndrome
What are 2 examples of non dihydropyridine Ca2+ channel blockers?
Verapamil
Diltiazem
What do non-dihydropyridine Ca2+ channel blockers do?
Decrease slope of action potential at SA node, decrease AV nodal conduction, hence slowing heart rate and decrease force of contraction
What does adenosine do?
Act on A1 receptors at AV node but has very short half-life, enhances K+ conductance hence hyper Polaris into cells of conducting tissue
What can adenosine be used for?
Termination re entrant supraventricular tachycardia
What are 2 conditions that ACE inhibitors can be used to treat?
Hypertension
Heart failure
What is an example of ACE inhibitors?
Perindopril
What is the mechanism of action of ACEi?
Angiotensin converting enzyme inhibitor, prevents conversion of angiotensin I to angiotensin II
What does angiotensin II do?
Acts on kidney to increase Na+ and water reabsorption and causes vasoconstriction
What is a side effect of ACEi?
Dry cough
How does ACEi reduce blood pressure?
It is a vasoconstrictor so it decreases vasomotor tone, hence decreasing after load
How does ACEi reduce blood volume?
Reduce fluid retention and preload
When are angiotensin II receptor blockers used?
If patients cannot tolerate ACEi
What is an example of a ARB?
Losartan
What are 2 conditions that diuretics treat?
Heart failure
Hypertension
What are loop diuretics used for?
Congestive heart failure
What are 2 examples of diuretics?
Furosemide
Thiazide diuretics
What do dihydropyridine Ca2+ channel blockers do?
Act on vascular smooth muscle, decreases peripheral resistance, decreases arterial BP and reduces afterload
What are 3 examples of dihydropyridine Ca2+ channel blockers?
Amlodipine
Nicardipine
Nifedipine
What do positive inotropes do?
Increase contractility and thus cardiac output
What are 2 types of positive inotropes?
Cardiac glycosides
Beta-adrenergic agonists
What is an example of cardiac glycosides?
Digoxin
What is an example of a beta-adrenergic agonist?
Dobutamine
What is cardiac glycosides primary mode of action?
Block Na K ATPase, leads to rise in intracellular Na+, so NCX doesn’t work as well so intracellular Ca2+ increases and more is stored in SR, hence increasing force of contraction
How does cardiac glycosides affect heart rate?
Increased vagal activity, slowing AV conduction, slowing heart rate
What is an example of beta adrenoceptor agonist?
Dobutamine
What do beat adrenoceptor agonists do?
Stimulate beta 1 receptors on SA AV node and ventricular myocytes
What are 2 uses of beta adrenoceptor agonists?
Cardiogenic shock
Acute but reversible heart failure
Are cardiac glycosides good treatment of heart failure?
It will relieve symptoms by making heart contract harder but no long term benefit, it’s better to reduce workload
How does angina occur?
When O2 supply doesn’t meet its demand, causing ischaemia and hence chest pain
How does nitrates work to treat angina?
Reaction of organic nitrates with thiols in vascular smooth muscle causes NO2- to be released and reduced to NO which is a powerful vasodilator particularly effective on veins
What are 2 examples of organic nitrates and the difference between them?
GTN spray short acting
Isosorbide dinitrate longer acting
How does NO cause vasodilation?
Activates guanylate cyclase, increase cGMP, lowers intracellular Ca2+ and hence relaxation of vascular smooth muscle
Why do organic nitrates preferentially act on veins?
Less endogenous nitric oxide in veins
What is the primary action of nitrates that help alleviate symptoms?
Venodilation reduces venous pressure, return of blood to heart, lowers preload, reducing workload of heart, heart fills less, reducing force of contraction, reducing O2 demand
What is the secondary action of organic nitrates that help alleviate symptoms?
Dilate coronary collateral arteries improved O2 delivery to ischaemic myocardium
What are 2 types of anti thrombotic drugs?
Anticoagulants
Antiplatelet
What are 4 types of anticoagulants?
Heparin
Fractionated heparin
Warfarin
Direct acting oral thrombin inhibitors
How does heparin work as a anticoagulant?
Inhibits thrombin, used acutely for short term action
What do antiplatelet drugs do?
Prevent platelet rich arterial thrombus formation
What are 2 examples of antiplatelet drugs?
Aspirin
Clopidogrel
