Antidysrhythmics

Question 1

What are class I cardiac antidysrhythmic drugs? Identify class IA drugs, class IB drugs, and class IC drugs, and specify how each of these groups (IA, IB, and IC) act.

Answer 1

Class I antidysrhythmic drugs are membrane stabilizers. Class I antidysrhythmic drugs stabilize membranes by blocking sodium channels. Class IA drugs include quinidine and procainamide. Class IB drugs include lidocaine and phenytoin. Class IC drugs include flecainide and encainide.

Question 2

**What is your concern with giving phenytoin (Dilantin) to the hyperglycemic patient?

Answer 2

Phenytoin (Dilantin) partially inhibits (blunts) insulin release and may lead to increased blood glucose levels in patients who are hyperglycemic.

Question 3

Class I antidysrhythmic drugs are used to treat what three conditions?

Answer 3

Class I drugs are used to treat supraventricular tachydysrhythmias, to treat premature ventricular contractions, and to slow atrial rate in atrial fibrillation.

Question 4

What drugs are class II cardiac antidysrhythmic drugs, and what do they do?

Answer 4

Class II antidysrhythmic drugs are beta-adrenergic antagonists. Class II drugs depress automaticity (decrease heart rate) and conduction speed of cardiac impulses.

Question 5

What drugs are class III cardiac antidysrhythmic drugs, and what do they do?

Answer 5

Class III antidysrhythmic drugs prolong repolarization. Bretyllium, amiodarone, and ibutilide are class III antidysrhythmics. These drugs increase the duration of action potentials in atria, ventricles and Purkinje fibers.

Question 6

What drugs are class IV cardiac antidysrhythmic drugs, and what are they used to treat?

Answer 6

Class IV antidysrhythmic drugs are the calcium entry blockers, including verapamil and diltiazem. These calcium entry blockers are used to treat reentrant supraventricular tachydysrhythmias.

Question 7

Lidocaine works on what two areas of the heart? Which area is affected first by lidocaine?

Answer 7

Lidocaine works on Purkinje fibers and ischemic ventricular myocardial tissue. Ventricular fibers are affected first.

Question 8

What four antidysrhythmics are appropriate for treating premature ventricular contractions? What is the drug of choice in the treatment of ventricular dysrhythmias?

Answer 8

Lidocaine, procainamide, phenytoin, and quinidine are appropriate for treating premature ventricular contractions. Lidocaine is the drug of choice for treating ventricular dysrhythmias.

Question 9

In what phase of the ventricular cell action potential does lidocaine work to suppress premature ventricular contractions?

Answer 9

Lidocaine depresses automaticity by reducing the rate of spontaneous phase 4 depolarization in Purkinje fibers or ventricular cells.

Question 10

How does lidocaine slow phase 4 depolarization in Purkinje fibers or ventricular cells?

Answer 10

Depolarization during phase 4 occurs in ventricular cells because of a progressive decrease in potassium ion permeability during phase 4. Lidocaine delays the rate of spontaneous phase 4 depolarization by preventing or diminishing the gradual decrease in potassium ion permeability that normally occurs during this phase.

Question 11

How does procainamide (Pronestyl) work?

Answer 11

Procainamide, like lidocaine, slows phase 4 depolarization, which reduces automaticity.

Question 12

Verapamil and diltiazem slow heart rate by working on what phase of the sino-atrial node action potential?

Answer 12

Verapamil and diltiazem slow heart rate by slowing phase 4 depolarization of the sinoatrial node action potential.

Question 13

Calcium channel blockers such as verapamil act on what phase of the ventricular action potential?

Answer 13

Verapamil and other calcium channel blockers decrease myocardial (ventricular) contractility by blocking the entry of calcium during phase 2 (plateau) of the ventricular action potential. (This action of the calcium channel blockers is a side-effect, not a therapeutic effect).

Question 14

Verapamil acts where in the cardiac myocyte?

Answer 14

The key to answering this question is to appreciate what the myocyte is. A myocyte is a muscle cell. The myocytes of the heart are the ventricular cells. Verapamil works on phase 2 (plateau phase) of the ventricular action potential. Specifically, verapamil blocks calcium ion influx during phase 2 of the ventricular action potential. Recall also that verapamil slows heart rate by slowing phase 4 of the action potential of the sino-atrial node.

Question 15

On what tissue of the heart does verapamil work: atrial

muscle, ventricular muscle, nodal tissue, Purkinje network?

Answer 15

For therapeutic effect, verapamil works on nodal tissue where it slows phase 4 depolarization. Verapamil secondarily works on phase 2 (plateau) of the ventricular muscle action potential.

Question 16

You would use verapamil to treat what dysrhythmias?

Answer 16

Verapamil is used in anesthesia most commonly to terminate supraventricular tachycardia. It also slows heart rate in patients with atrial fibrillation and flutter.

Question 17

What three medications may be used to treat sinus tachycardia?

Answer 17

Verapamil, or a beta-blocker, or digitalis may be used to treat supraventricular tachycardia.

Question 18

Identify 5 drugs or treatments for cardiac dysrhythmias due to digoxin toxicity.

Answer 18

Digoxin-induced cardiac dysrhythmias are best treated with: (1) lidocaine, (2) procainamide, (3) phenytoin, (4) propranolol, or (5) DC countershock.

Question 19

A patient showing signs and symptoms of digitalis toxicity begins having premature ventricular contractions. What drugs could be given to treat this? Which of these drugs is particularly useful in suppressing cardiac ventricular dysrhythmias associated with digitalis toxicity?

Answer 19

Phenytoin (0.5 to 1.5 mg/kg IV over 5 minutes) or lidocaine (0.5 mg/kg to 1 mg/kg IV) is useful in the initial treatment of digitalis-induced ventricular irritability. Small doses of propranolol have also been effective in treating such dysrhythmias. Phenytoin is particularly useful in suppressing ventricular dysrhythmias associated with digitalis toxicity.

Question 20

What antidysrhythmic drugs are not local anesthetics but have local anesthetic activity?

Answer 20

Class I antidysrhythmic drugs produce sodium channel blockade. All class I antidysrhythmic drugs have local anesthetic activity. Only lidocaine is used both as a local anesthetic and also a class I antidysrhythmic.

Question 21

Why should verapamil, quinidine, or amiodarone be avoided in the digitalized patient?

Answer 21

Verapamil, quinidine, and amiodarone can increase digitalis concentration and promote digitalis intoxication.

Question 22

What two drugs are appropriately used to treat

dysrhythmias resulting from mitral valve prolapse?

Answer 22

Lidocaine and esmolol should be immediately available to treat these dysrhythmias.

Question 23

What two drugs may be used to treat heart block?

Answer 23

Atropine or isoproterenol.

Question 24

Adenosine is used to treat what two dysrhythmias? How does it work?

Answer 24

Adenosine is used to treat paroxysmal supraventricular tachycardia and Wolff-Parkinson-White syndrome. Adenosine blocks conduction of impulses through the atrioventricular (AV) node by hyperpolarizing AV nodal cells. Hyperpolarization occurs because adenosine opens potassium channels in these cells and increases the flux of potassium out of nodal cells. As you know, hyperpolarization decreases excitability.

Question 25

**Describe the metabolism and elimination of adenosine (Adenocard).

Answer 25

Adenosine is rapidly eliminated by enzymatic clearance (less than one minute). Specifically, adenosine is deaminated in the plasma forming inosine, or is taken up in erythrocytes (RBCs) and vascular endothelial cells where it is metabolized to inosine (by deamination) or adenosine monophosphate (by phosphorylation).

Question 26

How is adenosine administered? Why?

Answer 26

Adenosine is administered (6-12 mg for adults or 0.05-0.25 mg/kg for children) rapidly through an intravenous (central) line or into the right atrium. Adenosine must reach the heart before it is metabolized.

Question 27

Would administration of adenosine via an endotracheal tube (ETT) be effective?

Answer 27

No. Adenosine is rapidly metabolized in the plasma by adenosine deaminase. To be effective, adenosine must be administered rapidly into a central line or the right atrium.

Question 28

Is treatment of atrial fibrillation during the case generally required? How can the anesthetist treat atrial fibrillation if pharmacological treatment is required?

Answer 28

Unless the atrial fibrillation adversely affects cardiovascular function (i.e., development of ventricular tachycardia with hypotension) during anesthesia, treatment is usually not required. If treatment of supraventricular tachydysrhythmias is required, verapamil, a calcium entry blocker, is a first line drug. Verapamil slows conduction through the atrioventricular node. Esmolol could also be used to treat ventricular tachycardia associated with atrial fibrillation. Other drugs mentioned for cardioversion and/or controlling ventricular rate include ibutiliden and amiodorone (class III antidysrhythmics), digitalis, and propranolol.

Question 29

During a bilateral hernia repair under spinal anesthesia your patient develops atrial fibrillation. His vital signs are stable. What is your treatment?

Answer 29

With stable vital signs, pharmacological treatment of atrial fibrillation usually is not required.

Question 30

Your digitalized patient develops atrial fibrillation and heart rate increases to 160bpm. How would you treat this?

Answer 30

You could give esmolol. Recall that you want to AVOID verapamil in the digitalized patient.