questions 13

Antiarrhythmics

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Topic updated on 06/05/17 11:44pm

Overview

Class I - Na+ Channel Blockers
  • General principles 
    • slow or block sodium conduction preferentially in depolarized cells
      • selective for abnormal cardiac tissue that is frequently depolarized
      • use and state dependent
    • phase 4 depolarization in SA node 
      • (automaticity current) is dependent on Na+ channel opening
        • blockage results in ↓ slope of phase 4 depolarization and ↓ SA node rate
    • hyperkalemia causes ↑ toxicity for all class I drugs
Class IA
  • iaExamples
    • quinidine, procainamide, and disopyramide
      • remember: quin + the amides
  • Effects
    • acts on atrial and ventricular arrhythmias
      • especially reentrant and ectopic supraventricular and ventricular tachycardia
    • ↓ rate of phase 0 depolarization resulting in
      • ↑ QT interval
      • ↑ AP duration
      • ↑ effective refractory period (ERP)
  • Toxicity
    • quinidine
      • cinchonism
        • headache, tinnitus, and vertigo
      • thrombocytopenia
      • ↑ QT interval
        • can result in torsades de pointes
      • can enhance digoxin toxicity
    • procainamide
      • reversible SLE-like syndrome
        • remember: procAiNAmide (antinuclear antibody in SLE)
Class IB
  • ibExamples
    • lidocaine, mexiletine, and tocainide ("Lido's Mexican Tacos")
      • phenytoin can also fall into class IB
  • Effects 
    • acts on ischemic or depolarized Purkinje and ventricular tissue
      • of Class I, have the lowest affinity for sodium channels
      • does not act on healthy or atrial tissue
      • effective in treating structurally abnormal tissue (especially post-MI)  
      • useful in acute ventricular arrhythmias and in digitalis-induced arrhythmias
    • ↓ duration of phase 3 repolarization resulting in
      • ↓ AP duration 
  • Toxicity
    • local anesthetic
    • CNS stimulation/depression   
Class IC
  • icExamples
    • flecainide, encainide, and propafenone
  • Effects
    • acts on His-Purkinje system in cardiac tissue WITHOUT structural abnormalities
      • useful in V-tachs progressing to VF and refractory SVT
      • drugs of last resort
    • no effect on AP duration
  • Toxicity
    • proarrhythmic
    • contraindicated with structural abnormalities
      • e.g., post-MI
    • significantly prolongs refractory period in AV node
Class II - β-blockers
  • Examples
    • propranolol, esmolol, metoprolol, atenolol, and timolol
      • esmolol very short acting
  • Mechanism
    • ↓ slope of phase 4 resulting in ↓ automaticity
      • due to ↓ cAMP and ↓ Ca2+ currents
      • results in ↑ PR interval and ↓ conduction in AV node
  • Clinical use
    • ventricular tachycardia and SVT
    • slowing ventricular rate during atrial fibrillation and atrial flutter
    • post-MI arrhythmia prophylaxis (cardioprotective)
  • Toxicity
    • cardiovascular effects
      • bradycardia, AV block, and CHF
    • CNS effects
      • sedation, sleep alterations, and depression
    • may mask the signs of hypoglycemia
    • impotence
    • exacerbation of asthma
      • only for non-selective (non-β1 specific)
    • metoprolol can cause dyslipidemia
    • treat overdose with glucagon 
      • ↑ cAMP via a mechanism independent of β receptors
Class III - K+ Channel Blockers
  • iiiExamples
    • sotalol, ibutilide, bretylium, dofetilide, and amiodarone  
  • Mechanism
    • ↑ phase 3
      • due to ↓ K+ current
      • results in ↑ AP duration, ↑ ERP, and ↑ QT interval
    • effective for atrial and ventricular arrhythmias
    • antiarrhythmics of last resort
    • amiodarone has class I, II, III, and IV effects
      • due to alterations in lipid membrane
  • Toxicity
    • torsades de pointes due to ↑ QT interval
      • amiodarone is the only example of a drug that lengthens QT but does not have risk of torsades de pointes 
    • sinus bradycardia
    • sotalol
      • excessive β blockade 
    • bretylium
      • new arrhythmias
      • ↓ BP
    • amiodarone
      • pulmonary fibrosis
      • hepatotoxicity
      • hypothyroidism/hyperthyroidism
        • amiodarone is 40% iodine by weight (amIODarone)
        • must watch LFTs, TFTs, and PFTs
      • corneal deposits
      • photosensitivity
      • skin color changes (blue/gray)
      • neurologic effects
      • constipation
      • cardiovascular effects
        • bradycardia, heart block, and CHF
Class IV - Ca2+ Channel Blockers
  • Examples
    • verapamil, diltiazem
      • note: other Ca2+ channel blockers (nifedipine and amlodipine) have little action on the heart
  • Mechanism  
    • ↓ L-type Ca2+ channels current primarily in AV nodal cells
      • L-type Ca2+ channels responsible for the plateau phase
    • results in ↓ conduction velocity, ↑ ERP, and ↑ PR interval
    • used in prevention of nodal arrhythmias and AV nodal reentry
  • Toxicity
    • antimuscarinic effects
      • constipation, dizziness, and flushing
    • edema
    • CV effects
      • negative inotropy, AV block, and sinus node depression 

 

 


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Qbank (8 Questions)

TAG
(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? Topic Review Topic

1. Sotalol
2. Digoxin
3. Esmolol
4. Amiodarone
5. Quinidine

PREFERRED RESPONSE ▶
TAG
(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? Topic Review Topic

1. Quinidine and insulin
2. Encainide and epinephrine
3. Propafenone and glucose
4. Esmolol and glucagon
5. Sotalol and norepinephrine

PREFERRED RESPONSE ▶
TAG
(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? Topic Review Topic
FIGURES: A   B   C   D    

1. Figure A
2. Figure B
3. Figure C
4. Figure D
5. No effect

PREFERRED RESPONSE ▶
TAG
(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? Topic Review Topic
FIGURES: A          

1. Central nervous system effects
2. Cinchonism
3. Torsades de pointes
4. Exacerbation of asthma
5. Flushing

PREFERRED RESPONSE ▶
TAG
(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)? Topic Review Topic
FIGURES: A   B        

1. 0
2. 1
3. 2
4. 3
5. 4

PREFERRED RESPONSE ▶
TAG
(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? Topic Review Topic
FIGURES: A          

1. Amlodipine
2. Ezetimibe
3. Adenosine
4. Nifedipine
5. Verapamil

PREFERRED RESPONSE ▶
TAG
(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? Topic Review Topic

1. Flecanide
2. Propafenone
3. Mexiletine
4. Diltiazem
5. Sotalol

PREFERRED RESPONSE ▶
TAG
(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? Topic Review Topic

1. Diarrhea
2. Shortening of action potential length at the AV node
3. Tachycardia
4. Hypotension
5. Torsades de pointes

PREFERRED RESPONSE ▶
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