Anti-arrhythmic drugs

Question 1

what is an arrhythmia?

Answer 1

abnormality in heart rate, regularity, site of pulse origin or disruption of conduction

Question 2

what is the increased automaticity mechanism for arr?

Answer 2

area of faster depolarisation so extra beats

Question 3

what is the triggered activity mechanism?

Answer 3

early/ late depolarisation elicited by previous AP and usually associated with Ca abnormality

Question 4

Reentry mechanism?

Answer 4

area of blocked conduction so slower to depolarise

Question 5

what is the 1st step in treating arr?

Answer 5

investigate primary problem - underlying disease

Question 6

what is the main problem with incorrect use of anti-arr drugs?

Answer 6

they can be pro-arr

Question 7

what is a supraventricular (atrial) arr?

Answer 7

slows conduction through AVN so reduce ventricular response rate.

Question 8

what is a ventricular arr?

Answer 8

affects AP and conduction

Question 9

what are class 1 drugs?

Answer 9

Na channel blockers

Question 10

what are class 2 drugs?

Answer 10

beta blockers

Question 11

what are class 3 drugs?

Answer 11

K channel blockers

Question 12

what are class 4 drugs?

Answer 12

ca channel blockers

Question 13

class 1a - quinidine properties

Answer 13

(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

Question 14

procainamide (class 1a)

Answer 14

similar to Quinidine but rarely used

Question 15

class 1b - lidocaine properties?

Answer 15

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

Question 16

class 2 - beta blockers. how do they work?

Answer 16

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)

Question 17

give 3 examples of beta blockers

Answer 17

atenolol, propanolol, esmolol

Question 17

describe the properties of atenolol

Answer 17

most widely used as selective for B1 (heart) cf propanolol. never used in CHF and care in patients with resp disease

Question 18

describe the properties of esmolol

Answer 18

short acting B1 antagonist (selective) given IV in emergency situations

Question 19

describe the properties of propanolol

Answer 19

non-selective B1 and B2 (bronchoconstriction)

Question 20

name 2 class 3 drugs

Answer 20

K channel blockers - sotalol and amiodarone

Question 21

how does sotalol work?

Answer 21

blocks K channels so prolongs refractory period, thus prolonging diastole. also B blocker effects (name) given PO. don’t abruptly stop. -ve inotrope

Question 22

how does amiodarone work?

Answer 22

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

Question 23

what are the SE of amiodarone?

Answer 23

anorexia, GI disturbances, thyroid dysfunction, hepatopathy, neutropenia. therefore used as a last resort.
problems resolve when stop using.

Question 24

name 2 class 4 drugs (ca channel blockers)

Answer 24

diltiazem and Verapamil

Question 25

how do class 4 drugs work?

Answer 25

inhibit ca influx and conduction at AVN. used only for SV arr. also -ve inotropic and cause vasodilation

Question 26

How does diltiazem work?

Answer 26

given PO/ IV fast acting so used for tachycardia (atrial fibrillation) also different formulations so altered duration of action.

Question 27

what are the main differences with verapamil?

Answer 27

more pronounced - inortrope than diltiazem. rarely used

Question 28

name 1 unclassified drug

Answer 28

digoxin

Question 29

how does digoxin work?

Answer 29

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