Updated: 10/21/2019

Antiarrhythmics

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Snapshot
  • A 56-year-old man recently had a myocardial infarction. While in the hospital, he reported being lightheaded. An electrocardiogram revealed a ventricular arrhythmia. His past medical history included hypertension, diabetes mellitus type 2, and chronic kidney disease. He was initially given amiodarone with no effect. He was then given a medication known to be effective in post-myocardial infarction arrhythmias. (Mexiletine)
Introduction
  • Anti-arrhythmic medications are divided into 4 classes
    • class I drugs are Na+ channel blockers
    • class II drugs are β-blockers
    • class III drugs are K+ channel blockers
    • class IV drugs are Ca2+ channel blockers
Antiarrhythmics
Class
Mneumonic Mechanism
Class IA Na+ channel blockers
  • Double Quarter Pounder
    • Disopyramide
    • Quinidine
    • Procainamide
  • ↑ Action potential (AP)
  • ↑ Effective refractory period (ERP)
  • ↑ QT interval
Class IB Na+ channel blockers
  • Lettuce and Mayo
    • Lidocaine
    • Mexiletine
  • ↓ AP
  • ↓ ERP
  • Affects ischemic or depolarized tissue 
    • hence, great for post-myocardial infarction arrhythmias 
Class IC Na+ channel blockers
  • Fries Please
    • Flecainide
    • Propafenone
  • ↑ ERP in atrioventricular node but not in ventricular tissue
Class II β-blockers
  • Drug name - lol
  • Selective β-blockers
    • metoprolol, esmolol, propranolol, atenolol, and timolol
    • esmolol is the most short-acting
  • Nonselective α- and β-blockers
    • carvedilol
    • labetalol 
  • ↓ Sinoatrial and atrioventricular nodal activity
    • ↓ cAMP and ↓ Ca2+ currents
    • ↓ slope of phase 4
  • ↑ PR interval
Class III K+ channel blockers
  • AIDS 
    • Amiodarone
    • Ibutilide
    • Dofetilide
    • Sotalol
  • ↑ AP
  • ↑ ERP
  • ↑ QT interval
Class IV Ca2+ channel blockers
  • Class IV Drugs
    • Verapamil
    • Diltiazem
  • ↑ ERP
  • ↑ PR interval
  • ↓ Conduction velocity
 
Class I - Na+ Channel Blockers
  • Double Quarter Pounder, with Lettuce and Mayo, and Fries Please for classes IA, IB, and IC respectively
    • these drugs slow down conduction and ↓ slope of phase 0 depolarization
  • Class IA (disopyramide, quinidine, and procainamide)
    • clinical use
      • atrial and ventricular arrhythmias
        • re-entrant and ectopic supraventricular tachycardias (SVTs) and ventricular tachycardias (VTs)
    • toxicity
      • thrombocytopenia
      • torsades de pointes
        • from ↑ QT interval
      • heart failure (disopyramide)
      • headache (quinidine)
      • tinnitus (quinidine) 
      • reversible systemic lupus erythematosus-like syndrome (procainamide)
  • Class IB (lidocaine and mexiletine)
    • clinical use
      • post-myocardial infarction and other ventricular arrhythmias
      • digitalis-induced arrhythmias
    • toxicity
      • cardiovascular depression 
      • central nervous system effects 
  • Class IC (flecainide and propafenone)
    • clinical use
      • SVTs, including atrial fibrillation
    • toxicity
      • proarrhythmic
      • contraindicated in structural and ischemic heart disease, especially post-myocardial infarction
Class II - β-Blockers
  • Clinical use
    • SVTs, including atrial fibrillation and atrial flutter
  • Toxicity
    • impotence
    • exacerbation of lung disease (chronic obstructive pulmonary disease and asthma)
    • cardiovascular effects
      • bradycardia
      • atrioventricular block
      • heart failure
    • central nervous system effects
      • sedation
      • sleep disturbance
    • dyslipidemia (metoprolol)
    • exacerbate Prinzmetal angina (propranolol)
  • Treatment for overdose of β-blockers
    • saline
    • atropine
    • glucagon 
Class III - K+ Channel Blockers
  • Clinical use
    • atrial fibrillation
    • atrial flutter
    • VTs
      • especially amiodarone and sotalol
  • Toxicity
    • torsades de pointes (sotalol and ibutilide)
    • excessive β-blockade (sotalol) 
    • amiodarone
      • no risk of torsades de pointes 
      • check pulmonary function tests (PFTs), liver function tests (LFTs), and thyroid function tests (TFTs)
        • pulmonary fibrosis and interstitial pneumonitis 
        • hepatotoxicity
        • thyrotoxicity
      • blue/gray skin deposits and photodermatitis
      • corneal deposits
      • neurologic effects
      • gastrointestinal effects
      • cardiovascular depression
        • bradycardia
        • heart block
        • heart failure
Class IV - Ca2+ Channel Blockers
  • Clinical use
    • atrial fibrillation
    • prevention of SVT
  • Toxicity
    • constipation
    • flushing
    • edema
    • cardiovascular depression 
      • heart failure
      • atrioventricular block
      • sinus node depression
Other Anti-Arrhythmics
  • Adenosine
    • mechanism
      • ↑ K+ out of cells causes hyperpolarization of the cell and decreased atrioventricular node conduction
      • very short-acting (approximately 15 seconds)
    • clinical use
      • diagnosing and/or terminating SVT
    • toxicity
      • flushing
      • hypotension
      • chest pain
      • sense of impending doom
      • bronchospasm
  • Mg2+
    • clinical use
      • torsades de pointes
      • digoxin toxicity
    • toxicity
      • lethargy
      • bradycardia
 

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Questions (4)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M2.CV.4698) A 65-year-old man with hypertension and paroxysmal atrial fibrillation presents to his cardiologist for follow-up after recently starting metoprolol for rate control. His EKG shows an atrial rate of 260/min with ventricular rate of 50/min on an irregular baseline. An echocardiogram from his previous visit revealed no evidence of hypokinesis or hypertrophy with functionally intact valves. The patient does not drink alcohol and had no evidence of liver dysfunction in prior studies. What is the best medication for rhythm control in this patient? Review Topic

QID: 108178
1

Verapamil

27%

(7/26)

2

Flecainide

31%

(8/26)

3

Procainamide

12%

(3/26)

4

Mexiletine

0%

(0/26)

5

Amiodarone

31%

(8/26)

M2

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