13: Arrhythmias

Question 1

Identify the three strategies of antiarrhythmia drugs.

Answer 1

1. Decrease automaticity (↓phase 4 slope)
   
   • Beta or calcium blockers
2. Change conduction velocity (↓phase 0/4 slope)
3. Change refractory period (↑phase 2/3)
   
   • Potassium (2/3) or sodium (0/4) blockers

Question 2

Outline the Vaughn Williams Classification of Antiarrhythmics.

Answer 2

• **Class I: **Sodium channel blockers
  
  • Decrease slope of 0, 4
• Class II: Beta blockers
• Class III: Potassium channel blockers
• Class IV: Calcium channel blockers

Question 3

Class Ib Antiarrhythmics

1. Drugs
2. Net effect
3. Indication
4. SFx

Answer 3

1. Lidocaine, mexiletine, phenytoin
2. ↓AP duration –> block persistent Na channels
3. VT
4. L&M: CNS stim/depr; P: gingival hyperplasia

Question 4

Class Ia Antiarrhythmics

1. Drugs
2. Net effect
3. Indication
4. SFx
5. Other

Answer 4

1. Quinidine, procainamide, disopyramide
2. ↑AP duration, ↑effective refractory period
3. SVT, AF, VT
4. Q: diarrhea, vagolytic, low platelets, torsades; P: SLE-like syndrome, torsades; D: anticholinergic, negative inotrope (use w/ HTCM + AF)

Question 5

Class II Antiarrhythmics (Beta-Blockers)

1. Drugs
2. Net effect
3. Indication
4. SFx
5. Other

Answer 5

1. Ending in -olol
2. Block cardiac beta-1 adrenergic receptors –> ↓sinus rate, prolong AV node conduction/refractoriness, inhibit automaticity, block effect of catecholamines
3. SVT, VT (esp. exercise/emotionally-induced), control ventricular rate in AFib/AFlu, mortality benefit in MI, CHF pts.
4. Brady, fatigue, dizziness, HoTN, depression

Question 6

Class II Antiarrhythmics (Beta-Blockers)

1. Drugs
2. Net effect
3. Indication
4. SFx
5. Other

Answer 6

1. Ending in -olol
2. Block cardiac beta-1 adrenergic receptors –> ↓sinus rate, prolong AV node conduction/refractoriness, inhibit automaticity, block effect of catecholamines
3. SVT, VT (esp. exercise/emotionally-induced), control ventricular rate in AFib/AFlu, mortality benefit in MI, CHF pts.
4. Brady, fatigue, dizziness, HoTN, depression

Question 7

Class III Antiarrhythmics (Potassium Channel Blockers)

1. Drugs
2. Net effect
3. Indication
4. SFx
5. Other

Answer 7

1. Sotalol, Dofetilide, Amiodarone, Ibutilide, Dronedarone
2. Prolong refractoriness; amiodarone also decreases conduction velocity (phase 0) and automaticity (phase 4)
3. AFib, VT
4. Long QT/torsades, reverse-use dependence (greater FX at slower HR), S&Dof contraindicated with renal dysfunction

Question 8

Class IV Antiarrhythmics (Calcium Channel Blockers)

1. Drugs
2. Net effect
3. Indication
4. SFx

Answer 8

1. Verapamil, diltiazem
2. ↓conduction velocity, ↑ERP, ↑PR interval
3. Rate control for AF/AFL, tx of SVT
4. Brady, CHF, fatigue, dizziness, constipation, HoTN, gingival hyperplasia, edema

Question 9

Digoxin

1. Net effect
2. Indication
3. SFx

Answer 9

1. ↓SNS, ↑PsNS (vagal tone); ↑inotropy
2. AF w/ RVR, esp. in CHF
3. Narrow therapeutic window (particularly with low K+), AV block, brady, arrhy, N/V, color changes, SVT/VT w/ overdose

Question 10

Adenosine

1. Net effect
2. Indication
3. SFx

Answer 10

1. ↓AV node conduction, ↓automaticity
2. Re-entry SVT
3. Propensity for AF (2/2 shortened atrial refractoriness), AV block/asystole, flushing, H/A, chest pain, bronchospasm (contraindicated in asthmatics)