PHARM: Anti-Arrhythmic Drugs

Question 1

examples of atrial tachyarrhythmias and what can they lead to?

Answer 1

• atrial fibrillation: persistent irregular
• atrial flutter
• supraventricular tachycardia: rapid, regular heart beat
• paroxysmal SVT: intermittent
• CAN LEAD TO HEART FAILURE AND STROKE

Question 2

examples of ventricular tachyarrhythmias and what can they lead to?

Answer 2

• ventricular fibrillation: irregular
• ventricular tachycardia: rapid, regular
• ventricular ectopics: premature contractions
• CAN LEAD TO AMI

Question 3

how do arrhythmias occur?

Answer 3

• abnormal impulse generation: ectopic automaticity (when another part of the CCS takes over)
• abnormal impulse conduction e.g. AV block, re-entry circuits, after-depolarisations

Question 4

re-entry circuits

Answer 4

• obstacle present, causes conduction block
• conduction has to go back around it via a diff route and then come back to that area

Question 5

early and delayed after-depolarisation causes

Answer 5

• early (phase 2/3): K+ overload due to decreased efflux = increased QT interval (e.g. K+ channel blocker, hypokalaemia)
• delayed (phase 4): Ca2+ overload due to increased influx = (e.g. digoxin and catecholamines - dopamine, NA)

Question 6

4 classes of anti-arrhythmics (general)

Answer 6

• class I: Na+ channel blockers
• class II: B-blockers
• class III: K+ channel blockers
• class IV: non-DHP Ca2+ channel blockers

Question 7

class I anti-arrhythmics MOA

Answer 7

• Na+ channel blockers - PARTIALLY selective to non-resting (open/inactive) channels
• MOA: prevent Na+ influx and therefore depolarisation (phase 0 of CARDIAC AP) to slow conduction

Question 8

subclasses of class I anti-arrhythmics + indications

Answer 8

• IA: prolongs action potential duration b/c also blocks K+ channels (AF, atrial flutter, VT, SVT)
• IB: shortens action potential duration by only partially blocking Na+ channels (post-AMI and ventricular arrythmias)
• IC: decreases AP INITIATION but doesn’t change actual AP duration b/c only blocking Na+ channels - slows down conduction (ventricular ectopics, AF, VT, SVT)

Question 9

side effects and contraindications of class I anti-arrhythmics

Answer 9

• (Na+ channel blockers)
• lupus-like Sx: fatigue, muscle ache, redness
• contraindicated in heart failure and AV block

Question 10

class II anti-arrhythmics MOA + indications

Answer 10

• B-blockers (-olol)
• blocks B1 receptors = reduce pro-arrhythmic sympathetic effects of adrenaline and NA (catecholamine toxicity) - phase 4 of cardiac AP
• indications: HTN, HFrEF, angina, tachyarrhythmias

Question 11

adverse effects and contraindications of B blockers

Answer 11

• A/Es: cold extremities, bradycardia, bronchoconstriction
• contraindicated in asthma, UNSTABLE heart failure and with class IV anti-arrhythmics (non-DHP Ca2+ channel blockers)

Question 12

class III anti-arrhythmics MOA + indications

Answer 12

• e.g. sotalol, amiodarone (v. quick, 20-30 secs)
• K+ channel blockers - prevent K+ efflux (phase 3) to prolong repol
• indications: prevent VF, atrial flutter, VT

Question 13

class III adverse effects + contraindications

Answer 13

• A/Es: hypokalaemia, pulmonary toxicity, pro-arrhythmic, Torsades de pointes (twisting QRS complexes)
• contraindicated in heart failure

Question 14

class IV anti-arrhythmics MOA + indications

Answer 14

• verapamil
• non-DHP Ca2+ channel blockers: block L-type Ca2+ channels to slow depol in PACEMAKER action potentials = decreased rate and force of contraction
• indications: AF, atrial flutter, PSVT

Question 15

class IV anti-arrhythmics adverse effects + contraindications

Answer 15

• adverse effects: bradycardia, hypotension, AV block
• contraindicated in heart failure and w/ B blockers

Question 16

other/unclassified anti-arrhythmics

Answer 16

• digoxin: treat Afib by blocking AV node conduction (can cause ventricular arrhythmia in high doses)
• adenosine: treat SVT by rapidly inhibiting AV nodal conduction