Antiarrhythmic Class IV, Digoxin, adenosine, magnesium and A-fib

Question 1

Class IV drugs include Diltiazem and Verapamil. This class of drugs are the cardiac selective Ca channel blockers. What is their MOA?

Answer 1

Decrease Ca dependent action potentials in slow response tissues (Decrease rate of phase 4)

• -this decreases the rate of automaticity, slow conduction velocity, and prolong the effective refractory period.
• -heart rate is slowed and PR interval lengthened
• -prolonged repolarization at the AV node

Question 2

What are the clinical applications for Class IV drugs?

Answer 2

Supraventricular tachycardia
Reduction of ventricular rate in atrial fibrillation and flutter
–2nd line to adenosine for conversion of PSVT to normal sinus rhythm

Question 3

What are the adverse effects of Class IV calcium channel blockers?

Answer 3

Excessive bradycardia 
Impaired electrical conduction 
Depressed Contractility 
Constipation 
Flushing/Dizziness

Question 4

What are the contraindications for Class IV calcium channel blockers?

Answer 4

Negative inotropes

–contraindicated in patients with preexisting depressed cardiac function

Question 5

The next drug to speak about is a cardiac glycoside called Digoxin. What is the main clinical application of this drug?

Answer 5

Control of ventricular response rate in atrial fibrillation and flutter with impaired left ventricular function or heart failure

Question 6

What is the MOA for digoxin?

Answer 6

Actives vagal efferent nerves to the heart —- reduction in the conduction of electrical impulses within the AV node.
–therefore fewer impulses reach the ventricles and ventricular rate falls

Question 7

What are the major side effects of digoxin?

Answer 7

Cardiac arrhythmia

–esp atrial tachycardias and AV block

Question 8

Next drug to discuss is Adenosine. What is the clinical application?

Answer 8

Drug of choice for abolishing acute supraventricular tachycardia

Question 9

What is the MOA for adenosine?

Answer 9

Opens K channel
–inhibits SA nodal, atrial, and AV nodal conduction
Inhibits cAMP mediated Ca influx therefore depresses action potentials
–AV node much more sensitive

Question 10

What are the pharmacokinetics and adverse effects of adenosine?

Answer 10

Pharmaco:
–lasts about 15 seconds, use IV
Adverse Effects;
–effects blunted by theophylline and caffeine
–flushing, hypotension, chest pain, sense of impeding doom and bronchospasm

Question 11

The next drug is Magnesium, what are the clinical applications of this drug?

Answer 11

Tx:
torsades de pointes
digitalis induced arrhythmias
prophylaxis of arrhythmia in acute MI

Question 12

What is the mechanism of action of Magnesium?

Answer 12

Ca2+ antagonist

–prevents the influx of Ca2+ into the cell

Question 13

The next drug is Atropine, what is the clinical use?

Answer 13

Bradyarrhythmias

–decrease vagal tone

Question 14

What is the mechanism for Atropine?

Answer 14

Muscarinic receptor antagonist

–inhibits the effects of excessive vagal activation on the heart

Question 15

Finally the last topic will be drug therapy for Atrial Fibrillation. What are the three objectives when managing a patient with a-fib?

Answer 15

1) Slowing the ventricular rate
2) prevention of thromboembolism
3) correction of the rhythm disturbance

Question 16

First lets discuss rate control in a-fib. What is the goal?

Answer 16

Slow the ventricular rate

–allows more time for the ventricles to fill with blood and increased cardiac output

Question 17

Drugs that are used to control ventricular rate are drugs that are able to slow down conduction at the AV node. Which include?

Answer 17

First-line rate control:

–B-blockers, verapamil or diltiazem (used for tx of atrial fibrillation with rapid ventricular response)

Question 18

How are beta blockers used for rate control in a-fib?

Answer 18

Acute and chronic control of ventricular rate
–particularly if excess catecholamines are suspected
Should not be used to acutely control the ventricular response in patients with HF or patients with COPD

Question 19

Digoxin are the least effective in controlling rate of A-fib, when is digoxin indicated?

Answer 19

Reduced EF or CHF

Question 20

How is amiodarone used as a rate control in A-fib?

Answer 20

Patients who are refractory or have contraindications to beta-blockers, Ca channel blockers or digoxin
–use for critically ill patients with CHF

Question 21

Now after treatment with AV nodal blocking drugs and successful response, the patient needs their rhythm restored to sinus rhythm, if a-fib persists

Answer 21

:)

Question 22

In patients with heart failure of other hemodynamic compromise attributable to new onset a-fib, restoration of normal sinus rhythm is indicated

Answer 22

:)

Question 23

If sinus rhythm is to be restored, anticoagulation therapy should be initiated prior to what?

Answer 23

Cardioversion

–because return of atrial contraction increases the risk of thromboembolism

Question 24

Patients with a-fib for longer than 48 hours or an unknown duration should receive what?

Answer 24

Warfarin for at least 3 weeks prior to cardioversion and return of normal sinus rhythm

Question 25

There are two methods for restoring sinus rhythm in a-fib. The first is direct current cardioversion (DCC). What is this?

Answer 25

Sedation

—small risk of complications

Question 26

What drug therapy restores sinus rhythm in a-fib ?

Answer 26

Flecainide
Propafenone
Dofetilide
Amiodarone