Updated: 8/23/2019

Antiarrhythmics

Topic
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Questions
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Evidence
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Snapshot
  • A 65-year-old man with atrial fibrillation presents to his primary care physician for a rash. He reports that he recently switched antiarrhythmic medications as instructed by his cardiologist. He reports to having discoloration of his skin and a burning sensation after sun exposure. On physical exam, there are blue and gray discolorations of his skin. An eye exam also reveals yellow-brown granules in the cornea. He was discontinued from the new anti-arrhythmic medication. (Amiodarone photosensitivity)
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
Anti-arrhythmics
Class
Drugs 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
  • 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 an overdose of β-blockers
    • saline
    • atropine
    • glucagon
Class III - K+ Channel Blockers
  • Clinical use
    • atrial fibrillation
    • atrial flutter
    • VT
      • 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 
        • 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 (15)
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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(M1.CV.75) A 65-year-old female with a history of HTN, type 2 diabetes, and asthma presents to the emergency department with severe nausea, sweating, and shortness of breath. The emergency room physician obtains an EKG which is demonstrated in Figure A. She immediately receives treatment for her condition and is subsequently admitted to the cardiac intensive care unit (CICU). In the CICU, the patient has episodes of recurrent sustained ventricular tachycardia. The hospital is in short supply of amiodarone, so the attending physician starts lidocaine IV to prevent the development of an arrhythmia. Which of the following toxicities is associated with this medication? Review Topic

QID: 106835
FIGURES:
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1

Central nervous system effects

67%

(133/199)

2

Cinchonism

11%

(21/199)

3

Torsades de pointes

13%

(26/199)

4

Exacerbation of asthma

3%

(6/199)

5

Flushing

6%

(11/199)

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(M1.CV.29) A 62-year-old man presents to the emergency department complaining of chest tightness. An electrocardiogram reveals ST segment elevation in the infero-lateral leads. He is treated for an acute myocardial infarction. His hospitalization is complicated by ectopy and several runs of non-sustained ventricular tachycardia. In an effort to reduce the risk of further arrhythmia in the post-myocardial infarction period, he is started on a Class 1 antiarrhythmic medication with very low affinity for its target channel. Which of the following images best represents the effect of the likely medication on the patient's action potential? Review Topic

QID: 100545
FIGURES:
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1

Figure A

16%

(11/68)

2

Figure B

66%

(45/68)

3

Figure C

6%

(4/68)

4

Figure D

12%

(8/68)

5

No effect

0%

(0/68)

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(M1.CV.75) A 50-year-old male is being treated for ventricular arrhythmias and presents to the cardiologist, as he is concerned about the recent skin changes he has seen in his face (Figure A). Which of the following phases of the action potential is affected by this patient's medication (See Figure B)? Review Topic

QID: 106840
FIGURES:
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1

0

16%

(11/69)

2

1

1%

(1/69)

3

2

12%

(8/69)

4

3

68%

(47/69)

5

4

3%

(2/69)

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(M1.CV.106) A 57-year-old Caucasian male presents to your office with heart palpitations and shortness of breath. On exam, he is tachycardic and his rhythm is irregularly irregular. He fails standard pharmacologic therapy and you refer to cardiology, where he is started on an antiarrhythmic medication. The action of this agent results in a longer action potential duration, an increased effective refractory period, and a longer QT interval. Which drug has been prescribed? Review Topic

QID: 100622
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1

Flecanide

7%

(5/69)

2

Propafenone

1%

(1/69)

3

Mexiletine

3%

(2/69)

4

Diltiazem

12%

(8/69)

5

Sotalol

75%

(52/69)

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(M1.CV.110) A 58-year-old Caucasian male is being treated for atrial fibrillation and angina complains of dyspnea on exertion. On exam, his heart rate 104-115/min and irregularly irregular at rest. He has no chest pain. You believe his rate control for atrial fibrillation is suboptimal and the likely cause of his dyspnea. You are considering adding verapamil to his current metoprolol for additional rate control of his atrial fibrillation. Which of the following side effects should you be most concerned about with this additional medication? Review Topic

QID: 100626
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1

Diarrhea

9%

(6/68)

2

Shortening of action potential length at the AV node

15%

(10/68)

3

Tachycardia

7%

(5/68)

4

Hypotension

60%

(41/68)

5

Torsades de pointes

9%

(6/68)

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(M1.CV.99) A 50-year-old male is seen in your clinic. Physical examination reveals a resting heart rate of 120. You perform an ECG (the reading from the V5 lead is shown in Figure A). After reviewing the ECG, you decide to start the man on a medication that primarily reduces the rate of depolarization during phase 0 and the latter part of phase 4 in cardiac slow-response tissue. What is the medication? Review Topic

QID: 100615
FIGURES:
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1

Amlodipine

10%

(26/248)

2

Ezetimibe

4%

(11/248)

3

Adenosine

17%

(43/248)

4

Nifedipine

5%

(12/248)

5

Verapamil

62%

(155/248)

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(M1.CV.9) A 63-year-old man with a history of hypertension and atrial fibrillation is brought into the emergency room and found to have a ventricular tachyarrhythmia. Ibutilide is discontinued and the patient is switched to another drug that also prolongs the QT interval but is associated with a decreased risk of torsades de pointes. Which drug was most likely administered in this patient? Review Topic

QID: 100525
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1

Sotalol

7%

(5/76)

2

Digoxin

4%

(3/76)

3

Esmolol

3%

(2/76)

4

Amiodarone

80%

(61/76)

5

Quinidine

7%

(5/76)

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(M1.CV.16) A 57-year-old woman with a history of diabetes and hypertension accidentally overdoses on antiarrhythmic medication. Upon arrival in the ER, she is administered a drug to counteract the effects of the overdose. Which of the following matches an antiarrhythmic with its correct treatment in overdose? Review Topic

QID: 100532
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1

Quinidine and insulin

3%

(6/237)

2

Encainide and epinephrine

9%

(21/237)

3

Propafenone and glucose

2%

(5/237)

4

Esmolol and glucagon

74%

(175/237)

5

Sotalol and norepinephrine

11%

(27/237)

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