anti-arrhythmic drugs

Question 1

arrhythmia

Answer 1

Irregular heart beat
* Classification based on EKG
o Abnormalities in rate
o Abnormalities in rhythm
o Cardiac myopathies

Question 2

common cardiac arrhythmia

Answer 2

Tachycardia (fast rate); Bradycardia (slow rate)
o Premature Atrial and Ventricular contractions
o Atrial Flutter
o Atrial and Ventricular Fibrillation
o Conduction defects (AV block; Bundle Branch
block)

Question 3

Symptoms

Answer 3

• No symptoms
• Palpitation
• Lightheadedness, dizziness, fainting due to low cardiac
  output and low blood pressure
• Stroke (after atrial fibrillation)
• Cardiac arrest (stop beating)
• Sudden death

Question 4

Pacemaker cells

Answer 4

Sinoatrial node (SA node):
70~80 /min
* Atrioventricular node (AV
node): 40~60 /min
* Bundle of His
(atrioventricular bundle):
20~40 /min
* Purkinjie fibers: 20~40 /min

Question 5

pacemaker cell and nonpacemaker cell

Answer 5

Ion movements:
* Na+ influx
* Ca2+ influx
* K+ efflux

Question 6

EKG

Answer 6

EKG records the electrical activity that reaches the body surface
* EKG represents the overall spread of activity
* EKG: comparisons in voltage detected at two points on the body
surface, not the actual potential

Question 7

normal EKG

Answer 7

1. Atrial depolarization, initiated by the SA node, causes the P wave
2. With atrial depolarization complete, the impulse is delayed at the AV node (PR
   segment)
3. Ventricular depolarization begins at apex, causing the QRS complex. Atrial
   repolarization occurs
4. Ventricular depolarization is complete. Ventricles are contracting and emptying
   during ST segment
5. Ventricular repolarization begins at apex, causing the T wave
6. Ventricular repolarization is complete. Ventricles are relaxing and filling during TP
   interval

Question 8

ventricular tachycardia

Answer 8

repetitive stimuli originating from an abnormal location in a ventricle

Question 9

atrial flutter

Answer 9

1) flutter shows very frequent, rather large P waves
2) atrial fibrillation does not show any good P waves
3) AV conduction defect
4) shows P waves occurring at a higher frequency than the QRS complex

Question 10

ventricular fibrillation is not compatible with life

Answer 10

1) due to lack of efficient pumping

Question 11

classes of antiarrhythmic drugs

Answer 11

1) Na+ channel blockade
2) beta adrenergic receptor blockade
3) prolong action potentials and repolarization
4) ca++ channel blockade
5) other

Question 12

case; paroxysmal atrial fibrillation, hypertension and carotid endarterectomy, moderate left ventricular hypertrophy

Answer 12

1) most dangerous complication outcome
- cardiac arrest and stroke after afib
2) what is metoprolol and why is she taking it
- anti hypertension
- beta 1 selective blocker, adrenergic receptor blocker
3) other medications could not remember and may be important?

Question 13

Na channel blockers

Answer 13

Class I: Block Na+ channels
IA: slow the rate of rise of phase 0 of the action potential,
slow conduction, prolong the ventricular refractory period
Quinidine(IA)
o Frequency dependent manner (more efficient block at
higher HR)
o Slows the rate of rise of phase 0 (reduces Vmax)
o Slows pacemaker activity by reducing slope of phase
4 depolarization in SA node and also in ectopic foci
o Decreases heart rate and AV conduction
o Prolongs duration of action potential and refractory
period (inhibits the delayed rectifier K+ channel)
o Anticholinergic effect may produce initial increase in
heart rate

Question 14

quinidine

Answer 14

Used clinically in Atrial Fibrillation, Premature
ventricular contractions (PVC), and Ventricular
Tachycardia. The use has been diminished.
* Oral administration
* Side effects
o Negative inotropic effect (reduce force of contraction)
o Cinchonism (quinism): flush, sweating, blurred vision,
tinnitus (ringing in the ear), confusion, headache etc.
o Thrombocytopenia (low platelet count, mediated by
the immune system, and may lead to thrombocytic
purpura)
o Granulomatous hepatitis, myasthenia gravis (muscle
weakness)
o Torsades de pointes (twisting of the spikes
polymorphic ventricular tachycardia)
* Procainamide: similar to Quinidine

Question 15

Lidocaine (IB)

Answer 15

Block Na+ channel
* Interact with both inactivated and
activated states and slow conduction
* Less frequency dependence
* Used clinically for ventricular
arrhythmias and in digitalis induced
arrhythmias, significant effect on
damaged cardiac cells
* Give i.v. due to first pass inactivation
* Phenytoin: similar to Lidocaine, but it
can be given orally

Flecainide and Propafenone (IC): strong Na+ channel block and Ca2+ channel block
as well. Probably b sympathetic block as well.

Question 16

b adrenergic receptor blockers

Answer 16

Class II
o Block b sympathetic receptors (myocardial b1
receptors)
o Direct membrane stabilizing effects at higher
concentrations related to blockade of Na+ channels
* Propranolol
o Nonselective beta blocker
o Slow SA and nodal automaticity as well as AV
conduction
o More active in atrial than in ventricular muscle
o Used for treatment of supraventricular arrhythmias
o Contraindicated in patients with severe AV node
block, uncompensated heart failure, and bronchial
asthma
* Metoprolol and Acebutolol are b1 selective

Question 17

K channel blockers

Answer 17

*Class III: Block K+ channel (action potential prolonging
agents)
* Amiodarone
o Prolongs action potential by blocking K+ channel
o Slows down rhythm
o Prolong refractory period
o Depresses automaticity of SA node, AV node and ectopic
pace makers
o Also blocks Na+, Ca2+ and noncompetitive b adrenergic
receptor blocker
o Sometimes effective in suppressing ventricular and super ventricular arrhythmias that are
refractory to other agents.
o May be given orally, one of the most effective drugs for maintenance of sinus rhythm in
patients with atrial fibrillation and for decreasing risk of ventricular tachyarrhythmia

• Sotalol: blocking delayed rectifier K+ channel , non –selective b adrenergic receptor blocker
• Dofetilide: selectively block of the delayed rectifier outward potassium current

Question 18

Ca channel blockers

Answer 18

**Class IV: L type Ca2+ channel blockers
Verapamil (phenyalkylamine) and Diltiazem
(Benzothiazepines) from the class are most
often used to treat arrhythmias

• *Depresses atrial automaticity, negative
  chronotropic effect (reduces heart rate)
  Depresses AV conduction
  *Used clinically in supraventricular
  tachycardia, flutter and fibrillation
  *Many other uses. e.g. lower blood pressure,
  release angina pectoris

Question 19

other medication

Answer 19

Digitalis: used to reduce AV conduction and ventricular response in
atria flutter or fibrillation
* Adenosine: used to terminate paroxysmal ventricular tachycardia
by activating K+ channel (hyperpolarization)
* Anticoagulants

Question 20

other treatment

Answer 20

Artificial pacemaker
Very frequently used in cases of reduced or abnormal automaticity.
Implantable Cardioverter Defiribillator (ICD) of modern technology, not only
have the ability to defibrillate, but also to pace, terminate ventricular
tachycardia and provide back up pacing for bradycardia.
* Cardioversion
Counter shock to depolarize simultaneously the entire myocardium, so that
hopefully synchronous repolarizations and regular rhythm will follow.
Usually set to be triggered by QRS complex. However, in ventricular
fibrillation there are no QRS complexes; therefore, manual firing
* Ablation
A procedure performed either during an electrophysiology study or in the
surgical suite, in which the source of a patient’s heart arrhythmia is
mapped, localized, and then destroyed (i.e., ablated.) Generally, ablation is
accomplished by applying radiofrequency (RF) energy, applying electrical
energy, or freezing the offending area (usually through a catheter) thus
creating a small scar that is electrically inactive and thus incapable of
generating heart arrhythmias

Question 21

Dentists and Antiarrhythmic drugs

Answer 21

Cardiac arrhythmias are relatively common. Atrial fibrillation is rather
common and is treated with anticoagulants to prevent embolisms
Dentists and Antiarrhythmic drugs
* Well controlled arrhythmias pose little
concern for the dentist. Elective dental care
is contraindicated for high risk and
symptomatic arrhythmias
* Minimize epinephrine usage
* Generally pacemakers do not require
antibiotic prophylaxis