Session 3: Class III and Class IV Drugs: Calcium Channel Blockers Flashcards
What is the effect of antiarrhythmic drugs on cardiac cell properties?
Alteration of the action potential affects the cardiac cells properties
Key properties include contractility, automaticity, excitability, and conductivity.
Define contractility in the context of cardiac cells.
Ability of cardiac cells to shorten and return to their original length in response to an electrical impulse.
What does automaticity refer to in cardiac cells?
The ability to spontaneously generate an electrical impulse.
What is excitability in cardiac cells?
The ability of resting, polarized cardiac cells to depolarize in response to an electrical impulse.
What is conductivity in cardiac cells?
The ability of cardiac pacemaker cells to depolarize and conduct electrical impulses to adjacent cardiac cells.
What are Class III antiarrhythmic drugs?
Potassium channel blockers or antagonists.
Name two effects of Class III antiarrhythmic agents.
- Markedly widens myocyte (Purkinje) action potential
- Lengthens action potential duration.
List four drugs classified as Class III antiarrhythmic agents.
- Sotalol
- Amiodarone
- Ibutilide
- Dofetilide.
What is torsades de pointes (TDP)?
A polymorphic ventricular tachycardia characterized by a varying QRS shape.
How do Class III antiarrhythmic drugs affect the QT interval?
They lengthen action potential duration by prolonging repolarization, which prolongs the QT interval.
What is a common adverse effect of Sotalol?
Torsades de pointes may be precipitated when used with potassium-wasting diuretics.
What is the primary indication for Amiodarone?
Refractory life-threatening arrhythmias.
What is the mechanism of action for Ibutilide?
Prolongs repolarization by activation of a slow inward sodium current and inhibition of rapid component of delayed rectifier potassium current.
What are the indications for Dofetilide?
Conversion of atrial fibrillation and atrial flutter to sinus rhythm and maintenance of sinus rhythm.
What characterizes Vernakalant’s mechanism of action?
Blocks Ikr and is more selective for ultra-rapid current (Ikur) in the atria.
What are the indications for Class IV antiarrhythmics?
- Stable Angina
- Coronary artery spasm
- Hypertension
- Supraventricular arrhythmias.
What is the primary difference between dihydropyridines (DHPs) and non-DHPs?
DHPs have greater vascular selectivity and primarily cause peripheral vasodilation.
What are the common adverse effects of calcium channel blockers?
- Hypotension
- Bradycardia
- AV block
- Constipation
- Peripheral edema.
What is the contraindication for DHPs in the context of angina?
They are contraindicated in unstable angina.
What effect do calcium channel blockers have on oxygen demand?
Decrease oxygen demand by reducing heart rate and afterload.
What is the effect of DHP calcium channel blockers on the heart rate?
They may decrease heart rate.
Fill in the blank: Class IV agents are _______.
calcium channel blockers or antagonists.
True or False: Non-DHP calcium channel blockers do not affect the SA or AV nodes.
False.
What is the action of Diltiazem compared to Verapamil?
Diltiazem has a moderate dilation effect on arteries and a less pronounced action on the AV node compared to Verapamil.
