Anti-arrhythmic Drugs Flashcards
What are the different classifications for anti-arrythmic drugs?
1 = Na antagonists2 = B-blockers3 = K antagonists4 = Ca antagonists
Describe class 1
Voltage gated Na+ blockers- decrease conduction velocity- decrease automaticity- increase depolarisation threshold
Why are there different sub-classes of class 1 drugs?
Different effects on AP duration, effective refractory period and phase 0 slopeA = increase APD and ERP, moderate decrease in phase 0 slopeB = decrease APD and ERP, small reduction in phase 0 slopeC = no change in APD and ERP, large reduction in phase 0 slope
Give a 1a drug
quinidine
Give a 1b drug
Lidocaine
Give a 1c drug
Flecainide
Describe flecainide
Use for SVTsDon’t give in heart failure or with MI historyADRs = dizziness, vision disturbances and arrythmiasDDIs = CYP metabolism and renally excreted
Describe lidocaine
Use for ventricular arrhythmias after MIDon’t give in AV block or heart failureADRs = hypotension, bradycardia, nystagmus and seizures
Describe class 2
Beta-adrenoceptor blockers- block sympathetic action, decrease slope of pacemaker potential and decrease chronotropy- decreased automaticity- decrease phase 4 slope- increased threshold for activation in SAN and AVN- increase AVN conduction time and refractory period
When would you give a bete blockers?
Post MIAnginaHypertension Arrythmias
When would you not give a beta blocker?
AV blockHypotensionBradycardiaCongestive Heart Failure
ADRs of beta blockers
BronchospasmFatigue and insomniaCold extremitiesBradycardiaHypotensionDecrease glucose tolerance in diabetic patients
DDIs for beta blockers
Prevents salbutamol from working - antagonist overrides agonist actionsVerapamil - both are negative inotropes
Describe class 3 drugs
Block K+ channels- increases the absolute refractory period and the AP duration- suppresses re-entry circuits by closing excitable gap
Why are class 3 drugs not generally used?
Can be arrhythmic and increase the risk of torsades des points.
Give some examples of class 3 drugs
AmiodaroneSotalol - high dose (low dose gives a class 2 action)
Why would you give class 3?
SVT and other ventricular arrythmias
When would you not give a class 3 drug?
AV block
DDIs of class 3 drugs
Amiodarone inhibits CYP enzymes and P-glycoprotein- need to reduce other drugs (warfarin, flecainide and digoxin)
Describe class 4 drugs
Block Ca2+ channels- decrease slope of pacemaker AP at SAN and AVN- increases refractory period and decreases chronotropy and inotropy
Examples of class 4 drugs
Verapamil Diltiazem
When would you give class 4 drugs?
SVTProphylaxis for angina and hypertension
When would you not give class 4 drugs?
Heart failureBradycardiaAVN block
ADRS of class 4 drugs
HypotensionBradycardiaHeart failureHeart block
Describe adenosine
AVN blocker- decrease automaticity- increases AVN refractory period- short t1/2- diagnoses and treats SVT
Describe the mechanism for digoxin
Inhibits Na/K/ATPase which also inhibits Na/Ca exchanger. - increased intracellular Ca2+ causing an increase in inotropy Increases AVN refractory period and decreases conduction velocity of AVN
ADRs of digoxin
Narrow therapeutic index, can easily lead to digoxin toxicity- cardiac toxicity (bradycardia, AVN block, atrial tachycardia)- toxicity is enhance with hypokalaemia
What are the main ways to improve ventricular stroke volume and therefore the cardiac output?
- Increase pre-load- Decrease after-load- Increase inotropy
Why is increasing pre-load not a good option for someone in heart failure?
- Heart is on flat region of frank-starling curve- Can exacerbate pulmonary and systemic congestion or oedema
Describe how decreasing afterload helps to increase ventricular stoke volume
An increased afterload will reduced ejection velocity. Treating this will hale to increase stroke volume and decrease the pre-load which will help in improving the ejection-fraction.
How does increasing inotropy help to improve ventricular stroke volume?
Increases stroke volume and ejection fraction. - Should only be used for acute systolic failure/ end stage failure as prolonged use can worsen outcomes and increase mortality. - Increase oxygen demand in the long term which is bad in the long term- Good acutely, as they increase stroke volume and ejection fraction but also decrease preload.
