CV V - Antiarrhythmic Drugs Flashcards
Which β blocker would most likely be used to treat CHF?
Carvedilol
It is nonselective (β1 and β2) and α1 receptors).
What are the classes and specific drugs for treating arrhythmia? (3 for bradycardia, 6 for tachycardia)
Bradycardia (slow HR)
- Adrenaline (β agonist)
- Atropine (muscarinic antagonist)
- Implantable pacemaker
Tachycardia
- Class I (Na channel blocker)
- Class II (beta blocker)
- Class III (increase in action potential duration/refractory period)
- Class IV (Ca channel blocker)
- Digoxin
- Adenosine
What is the average HR and how is it generated?
Each heartbeat initiated by action potential that originates at the SA-node pacemaker
70 bpm
What is arrhythmia?
Disruption in the rate, rhythm, origin or conduction of the heartbeat.
Causes include myocardial infarction (MI), ischemia, drug toxicity (eg. digoxin, anesthetics) or electrolyte imbalances.
In essence, it reduces the ability of the heart to pump blood.
Cardiac arrhythmias arising from the atria or AV node are called ____. From the ventricles: ____
AV node: supraventricular arrhythmia
Ventricles: ventricular arrhythmia (most serious)
What are bradycardias?
Slow heart rates
- Low CO
- <40 bpm
- Brain undersupplied
What are tachycardias?
Fast heart rates
- Regular or irregular
- Heart beats too quickly to fill properly, reduced CO can lead to CHF
True or false, some arrhythmia are benign and don’t need intervention.
True
Additionally, non-pharmacological means can be used sometimes (such as removing abnormal tissue or implanting a defibrillator (particularly in the case of bradycardia.
Also, all anti-arrhythmic drugs can cause arrhythmia.
How are bradycardias treated? (3)
- Adrenaline (β agonist) stimulate β1 receptors and increase HR
- Muscarinic antagonist (blocking PNS)
- Implantable pacemaker
How are tachycardias treated? (6)
Which are most dangerous?
- Class I (Na channel blocker)
- Class II (beta blocker)
- Class III (increase in action potential duration/refractory period)
- Class IV (Ca channel blocker)
- Digoxin
- Adenosine
Class I and III are most dangerous
How can an ectopic pacemaker cause tachycardia?
Abnormal impusle formation
When an abnormal pacemaker located anywhere in the heart is faster than the SA node, it can take over and cause a tachycardia. This tachycardia will depend on Na or Ca influx (which class I and class IV drugs can help with, respectively).
Cells in the SA and AV nodes use Ca to initiate action potentials. Other cells use Na to initiate APs.
What are the two basic mechanisms of cardiac tachycardia?
- Abnormal impulse formation (eg. ectopic pacemaker)
- Abnormal impulse conduction (reentry of impulse, where an AP activates the heart more than once). This can be treated with class I antiarrhythic drugs, which prevent Na mediated conduction.
How can pain and stress (such as from myocardial infarction) cause tachycardia?
How can this be treated?
Activation of the SNS can cause normally quiescent areas in the heart to develop ectopic pacemakers.
Blocking the SNS with beta blockers (class II) can suppress tachycardia
Beta blockers also slow conduction velocity through the AV node and increase AV node refractory period, which allows the ventricles to fill properly by lowering HR.
How do class III antiarrhythmic drugs treat arrhythmia?
Block potassium channels and prolong the action potential and its refractory period.
Rapid conduction is slowed because activity cannot reenter normal tissue!
How do class IV antiarrhythmic drugs treat arrhythmia?
What type of arrythmia is this used to treat (eg. ventricular or supraventricular/AV-node)
Ca channel blockers can act on cardiac tissue (eg. verapamil and diltiazem, but not nifedipine).
- Can stop reentry in SA and AV nodes
- Slows conduction through AV node and increases AV node refractory period
Used in supraventricular (AV-node) arrhythmia to decrease the number of beats that get from the atria to the ventricles via the AV node and therefore decreases ventricular beating rate.
