L13 - Antiarrythmics Flashcards
Early after depolarisations occur more often in extended action potentials, which disease are they particularly associated with
Long QT syndromes
What are the four basic classes of antiarrythmic drugs, give an example of each
Nav channel blockers - lidocaine
Beta blockers - propanolol
K+ channel blockers - amiodarone
Calcium channel blockers (non-dihydropyridine)- diltiazem
Afterdepolarisations are associated with damaged depolarised tissue that can cause re-entrant loops. Lidocaine preferentially blocks damaged depolarised tissue during depolarisation but dissociates in time for next AP thus preventing arrythmias - T/F?
T
When would lidocaine be used?
Following MI only if patient shows signs of ventricular tachycardia
How do B blockers work to prevent arrythmias?
Block B1 receptors thus slowing conduction through av node and thus slows HR
Beta blockers are useful in preventing supraventricular tachycardia. They are useful for patients with AF to slow HR and following MI as MI’s are associated with increased SYM activity. What is a bonus of them too?
They reduce the myocardiums oxygen demand by slowing hr
K+ channel blockers work by lengthening the refractory period through blocking k channels, why in theory are they actually often pro-arrythmic?
Extended QT interval is associated with early after depolarisations -> arrythmias
Why is amiodarone not pro-arrhythmic?
Because it blocks other channels than just k ones
What is first line treatment for suppressing ventricular arrythmias post MI and wolf-Parkinson white syndrome?
Amiodarone
CCb’s have a three pronged effect, name each
1) decrease slope of action potential at sa node
2) decrease AV nodal conduction
3) decrease force of contraction
Adenosine is produced endogenously but can also be administered IV as an anti-arrhythmic agent. What is it used for specifically?
Terminating supraventricular tachycardia
Give an example of something which ACEi’s would be used for
Hypertension
Heart failure
How do ACEi’s treat heart failure?
Decrease blood pressure and thus the afterload on the heart
Decrease fluid retention and thus the preload on the heart
Ace inhibitors can cause a dry cough in users, why is this?
Also enhances production of bradykinin which causes a dry cough
Angiotensin receptor blockers are used for heart failure and hypertension in patients who can’t tolerate ace inhibitors, give an example of one
Losartan
What drugs are useful in treating hypertension and heart failure?
Diuretics
ARB’s
ACEI’s
Are dihydropiridine calcium channel blockers effective in preventing arrythmias?
No but they act on smooth muscle and are useful in:
Hypertension/angina/superventricular tachycardias they work by reducing afterload on heart
Digoxin is a cardiac glycoside (positive inotrope), they are useful in treating symptoms of heart failure but not affecting outcome, what is their primary mode of action?
Block Na/k atpase -> rise in IC Na -> loss of gradient to extrude ca -> accumulation -> increases in contractility
When are cardiac glycosides useful and why?
Heart failure with AF - they also slow the HR
Dobutamine is a B1 selective agonist, it stimulates receptors and sa and av node and ventricular myocytes, suggest a use
Cardiogenic shock
Acute heart failure (if reversible)
Nitrates are useful in treating Angina, how do they work?
They are reduced endogenously to nitric oxide which is a vasodilator (mainly a venodilator)
Specifically how does nitric oxide cause vasodilation?
Converts GTP to cGMP which activates PKG, which decreases IC calcium -> relaxation of smooth muscle
NO from nitrates acts preferentially on the venous system and thus reduces preload on the heart (lowers oxygen demand), it also acts on coronary collateral arteries to improve o2 delivery to the myocardium, what does it not work on?
arterioles
Give three drugs used for treatment of angina
Organic nitrates
B blockers
Ca channel blockers (non-dihydropyridine)
Give two of the theee heart conditions that carry an increased risk of thrombus formation
AF
acute MI
Mechanical prosthetic valves
What preventative drugs are used to prevent thrombosis - antithrombotics
Anticoagulants e.g. heparin or warfarin
Antiplatelets e.g. aspirin/clopidogrel
