Antiarrhythmic drugs II - Lee

Question 1

Vaughn Williams Classification of antiarrhythmics

Answer 1

Class I – Na+ Channel Blockers
Class II – b-blockers
Class III – K+ Channel Blockers
Class IV – Ca+2 Channel Blockers
Other

-looking at SA and AV node effects for class II and IV*

Question 2

class II anti arrhythmic drugs - beta blockers

Answer 2

• slower phase 4 depolarization in the SA, AV nodes –> slow conduction, lowers HR and contractility
• indications: tachyarrhythmias, AV nodal reentrant tachycardia, ventricular arrhythmias following MI
• action on beta 2 –> bronchoconstriction, peripheral vasoconstriction
• action on beta 1 –> decrease HR and CO
• propanolol has both beta 1 and 2 effects (bad)

all have same contraindications**:

• sinus bradycardia
• heart block greater than 1st degree
• cardiogenic shock or overt heart failure

Question 3

class IV anti arrhythmic drugs - Ca2+ channel blockers

Answer 3

• decrease rate of phase 4 spontaneous depolarization in AV and SA nodes –> lower HR, conduction velocity, and contractility
• non-dihydropyridine Ca2+ channel blockers
• work on heart and vascular smooth muscle
• better for atrial arrhythmias
• use dependent** –> bind better to open channels –> better effect with high HR
• similar contraindications like beta blockers –> hypotension, 2nd/3rd degree AV block, sick sinus rhythm
• similar adverse effects –> constipation, bradycardia, AV conduction block

Question 4

action of beta receptors

Answer 4

• NE or Epi binds to beta receptor –> signaling cascade –> increase in Ca2+ influx through L-type Ca2+ channels increasing HR, conduction, and contractility
• beta blockers prevent this signaling cascade by preventing binding of NE/Epi*

Question 5

metoprolol** - beta blocker

Answer 5

• most widely used
• less risk of bronchospasm and CNS penetration (only bind to beta2 at high [])
• beta1 antagonist*
• for Afib/flutter, PACs/PVCs, VT, post MI, Angina*
• risk of fatigue, dizziness, depression, bradycardia*
• metabolized by CYP2D6* –> toxic effect risk if there are inhibitors
• concern with discontinuation** with ischemic heart disease –> angina, MI, CAD –> get off slowly 1-2 weeks**
• additive effects with MAO inhibitors, digitalis glycoside, and Ca2+ channel blockers**
• avoid with antidepressants/psychotics/retroviral/malarial and other antiarrhythmics**

Question 6

esmolol - beta blocker

Answer 6

• for acute arrhythmias
• only used IV** (short half life, fast acting) –> used during surgery or emergency situations**
• metabolized by esterases in RBCs**
• risk of hypotension, dizziness, bronchospasm, nausea
• side effects go away quickly once drug is stopped

Question 7

acebutolol - beta blocker

Answer 7

• partial agonist*** (lower effect agonist by itself; antagonist in the presence of other agonist)
• for HTN*, ventricular arrhythmia
• risk of hypotension, dizzy, bronchospasm, nausa

Question 8

verapamil*** - Ca2+ channel blocker

Answer 8

• block L-type Ca2+ channels (different site than diltiazem)
• decrease cardiac contractility –> decrease BP
• for A-fib/flutter, HTN
• prophylaxis for PSVT***
• not used with CHF, LV dysfunction, or cardiogenic shock
• risk of asystole*

Question 9

diltiazem

Answer 9

• block L-type Ca2+ channel
• for A-fib/flutter, HTN
• prophylaxis for vasospastic and classic angina***
• not used acute MI, pulmonary congestion*
• don’t give with breast feeding moms*** –> excreted in milk

Question 10

digoxin** aka digitalis - other

Answer 10

• increase contractility, but SLOW AV node conduction**
• increased vagal tone (autonomic) –> decrease HR
• for rate control in Afib and improves systolic heart failure** (increase LV ejection fraction)**
• blocks Na+/K+ pump** –> build up of Na+ and Ca2+ in cell –> increase contractility**
• hyperkalemia by inhibiting pump** (also hypokalemia)
• dose dependent risks –> fatigue, muscle weakness, 2nd/3rd degree AV block, bigeminy, arrhythmias, anorexia, psychosis, yellow halos*

Question 11

adenosine - other

Answer 11

• bind to adenosine receptor in heart in AV node and atria –> slow conduction
• similar effects as ACh*
• block reentry pathways through AV node and restore sinus rhythm***
• antagonized by caffeine/theophylline
• for PSVT, Wolff-Parkinson-White syndrome, AVNRT, unknown SVTs**
• not used with 2nd/3rd degree AV block unless there is pacemaker
• rapid bolus IV injection** –> short half life (<10 sec) –> short term therapy in emergencies**
• higher doses –> risk of facial flushing**, light headed, dyspnea*
• warn patient before giving with SVT*

Question 12

atropine - other

Answer 12

• muscarinic receptor antagonist –> more sympathetic activity –> increase HR and conduction**
• used for bradycardia**
• risk of dry mouth, blurred vision, photophobia*

Question 13

Mg2+ sulfate - other

Answer 13

• block Ca2+ channel –> slower HR and conduction
• treatment for torsades de pointes if Mg2+ levels normal***
• also for digitalis-induced arrhythmias