Anti-arrhythmic drugs Flashcards
what is an arrhythmia?
abnormality in heart rate, regularity, site of pulse origin or disruption of conduction
what is the increased automaticity mechanism for arr?
area of faster depolarisation so extra beats
what is the triggered activity mechanism?
early/ late depolarisation elicited by previous AP and usually associated with Ca abnormality
Reentry mechanism?
area of blocked conduction so slower to depolarise
what is the 1st step in treating arr?
investigate primary problem - underlying disease
what is the main problem with incorrect use of anti-arr drugs?
they can be pro-arr
what is a supraventricular (atrial) arr?
slows conduction through AVN so reduce ventricular response rate.
what is a ventricular arr?
affects AP and conduction
what are class 1 drugs?
Na channel blockers
what are class 2 drugs?
beta blockers
what are class 3 drugs?
K channel blockers
what are class 4 drugs?
ca channel blockers
class 1a - quinidine properties
(Na channel blocker) slows depolarisation so therefore conduction. used in horses with atrial fibrillation but can cause arr and hypotension (slower beat) used for SV and V
procainamide (class 1a)
similar to Quinidine but rarely used
class 1b - lidocaine properties?
also a local anaesthetic. IV bolus followed by CRI as therapeutic effect short acting. used in life-threatening circumstances. can cause bradyarr and death (cats - lower dose) adverse effects = nausea and seizures. used for ventricular arr
class 2 - beta blockers. how do they work?
decrease sympathetic tone so reduce HR and - inotrope, prolong refractory period. do not use in CHF patients. careful use in resp disease due to bronchoconstriction (blocked)
give 3 examples of beta blockers
atenolol, propanolol, esmolol
describe the properties of atenolol
most widely used as selective for B1 (heart) cf propanolol. never used in CHF and care in patients with resp disease
describe the properties of esmolol
short acting B1 antagonist (selective) given IV in emergency situations
describe the properties of propanolol
non-selective B1 and B2 (bronchoconstriction)
name 2 class 3 drugs
K channel blockers - sotalol and amiodarone
how does sotalol work?
blocks K channels so prolongs refractory period, thus prolonging diastole. also B blocker effects (name) given PO. don’t abruptly stop. -ve inotrope
how does amiodarone work?
same as sotalol. inhibits repolarisation, prolonging refractory period. also class 1 and 2 effects so used when arr can’t be controlled by other drugs. given PO. does is not a -ve inotrope cf sotalol
what are the SE of amiodarone?
anorexia, GI disturbances, thyroid dysfunction, hepatopathy, neutropenia. therefore used as a last resort.
problems resolve when stop using.
name 2 class 4 drugs (ca channel blockers)
diltiazem and Verapamil
how do class 4 drugs work?
inhibit ca influx and conduction at AVN. used only for SV arr. also -ve inotropic and cause vasodilation
How does diltiazem work?
given PO/ IV fast acting so used for tachycardia (atrial fibrillation) also different formulations so altered duration of action.
what are the main differences with verapamil?
more pronounced - inortrope than diltiazem. rarely used
name 1 unclassified drug
digoxin
how does digoxin work?
parasympathomimetic, slows conduction through AVN. also not a - inotrope. used for SV arr mainly atrial fibrillation. main problems = slow onset of action and digitalis intoxication, poss fatal affecting GI, heart function etc, use low doses. often combined with diltiazem
