Pharmacology-Antiarrhythmic Drugs

Question 1

What channel is responsible for the spontaneous depolarization in nodal cells?

Answer 1

If (funny) sodium channels. They open upon cellular repolarization.

Question 2

What channels and pumps are responsible for the transmembrane potential in cardiac cells?

Answer 2

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Question 3

A patient comes in to see you with a heart rate of 140. He has a previous history of heart attack so you do an EKG and find that he has a ventricular arrhythmia. You prescribe hims sodium channel blockers. Where do these blockers work on his cells? How will this help his arrhythmia?

Answer 3

They bind to the open and inactivated state of the sodium channels. These will help with his arrhythmia because it will make it harder for the cells to depolarize during the relative refractory period.

Question 4

Why do sodium channel blockers have no effect on the SA or AV node?

Answer 4

Those cells are not voltage dependent. They are only time dependent.

Question 5

How do beta-1 receptor stimulation, hypokalemia and mechanical stretch affect sinus rhythm by altering the action potential? What about Na+ channel blockers? What about ACh, Adenosine and Digoxin?

Answer 5

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Question 6

What is the difference between triggered and ectopic automaticity?

Answer 6

Triggered automaticity = delayed or early afterdepolarization. Ectopic automaticity = ventricular or atrial origin of automaticity.

Question 7

What are the two mechanisms for triggered automaticity?

Answer 7

Delayed afterdepolarization and early after depolarization.

Question 8

Why does vomiting induce arrhythmias?

Answer 8

Vagal stimulation causes a change in action potential slope and baseline. This changes the rate at which the heart contracts.

Question 9

What is responsible for the majority of tachyarrhythmias?

Answer 9

Reentry caused by a functional or anatomical barrier.

Question 10

What are the different mechanisms for atrial arrhythmias?

Answer 10

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Question 11

You find a man who died two days ago. He was in his late 40s with no history of health problems. Postmortem examination only revealed puncture in his right forearm. Autopsy showed the heart was in a state of asystole (no cardiac electrical activity). What combination of electrolytes injected could have caused this?

Answer 11

KCl. K+ goes through K+ channels, hyper polarizing the cells and stopping contraction.

Question 12

What are the four classes of drugs used to treat arrhythmias?

Answer 12

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Question 13

Why would you consider use of class I antiarrhythmatic drugs for someone with an ectopic arrhythmia?

Answer 13

They are sodium channel blockers. Ectopic arrhythmias originate in tissue that utilizes sodium channels to generate action potentials.

Question 14

A patient comes in with ventricular tachycardia. You prescribe him a drug with a very long half life? What drug did you prescribe him?

Answer 14

A class III K+ channel blocker: Amiodarone. This will increase the QT interval and prevent early depolarization by the ventricle.

Question 15

What drugs should you not us if you have a patient with a prolonged QT interval?

Answer 15

Drugs that further prolong the QT interval: Sodium channel blockers that also block K+ channels (IA: procainamide and quinidine) and all class III drugs (K+ channel blockers).

Question 16

A patient with heart failure comes to see you with ventricular arrhythmia. What drugs should you NOT use?

Answer 16

Class IV calcium channel blockers (Verapamil and Diltiazem) and beta blockers. They will decrease contractility of the heart.

Question 17

You see a patient with WPW syndrome. What drugs do you not want to prescribe to this patient?

Answer 17

Those that block the AV node. (Digitalis, verapamil and diliazem (class IVs).

Question 18

What drugs should you not prescribe if someone has asthma or diabetes?

Answer 18

Beta blockers.

Question 19

What drugs do you use to treat atrial fibrillation and atrial flutter?

Answer 19

You need to control ventricular response if you cannot control sinus rhythm. This can be done with digoxin (slows AV conduction and slows HR).

Question 20

What drugs do you use to treat supra ventricular tachycardia?

Answer 20

Adenosine or verapamil (IV injection).

Question 21

What drugs do you use to treat a patient with ventricular tachycardia with MI?

Answer 21

Amiodarone or lidocaine.

Question 22

What drugs do you use to treat ventricular fibrillation?

Answer 22

Amiodarone or lidocaine.

Question 23

What do you do to treat digitalis toxicity?

Answer 23

Correct Mg++ and stop digoxin.

Question 24

When can you use procainamide/ quinidine?

Answer 24

Life-threatening ventricular tachycardia. This is because adverse effects include Lupus and increasing QT interval.

Question 25

When do you use lidocaine and mexiletine?

Answer 25

To treat and prevent ventricular arrhythmias.

Question 26

When can you use flecainide?

Answer 26

Life threatening ventricular tachyarrhythmias without ischemic heart disease. They are almost exclusively used for supra ventricular tachycardias.

Question 27

What are the different generations of beta-blockers?

Answer 27

1: propranolol (blocks beta-1 and beta-2). 2: atenolol, metoprolol (selectively block beta-1). 3: labetalol and carvedilol (blocks beta-1, alpha-1 and agonist for beta-2)