Exam Prep Flashcards
(26 cards)
Mechanism of Action and Risk of TDP
- Lengthens action potential duration by prolonging repolarization which prolongs the QT interval.
- QT prolongation with hypokalemia (↓ K+),
hypomagnesemia (↓ Mg+), or bradycardia (↓ HR) may predispose to torsades de pointes. - Torsades de Pointes (TDP) – polymorphic ventricular tachycardia.
- Polymorphic → poly – many, morphic – QRS shape.
Cardiac Cell Properties and the Action
Potential.
- Contractility.
- Automaticity.
- Excitability.
- Conductivity.
Class
III
Potassium channel blockers or antagonists:
* Sotalol
* Amiodarone
* Ibutilide
* Dofetilide
* Dronedarone
Amiodarone
- Lengthens effective refractory period in all cardiac tissues, including accessory pathways
- Class III
- Class IA
properties for lengthening action potential
potent sodium channel blocker
Sotalol
Class II
beta-blocker properties, sinus and AV node depression
Class III
lengthens action potential in atrial and ventricular
Ibutilide
Prolongs repolarization by activation of a slow inward sodium current, as well as by inhibition of rapid component of delayed rectifier potassium current (Ikr), during repolarization.
* Administered intravenously.
* Conversion of atrial fibrillation or atrial flutter to sinus rhythm.
Dofetilide
Similar to Ibutilide and prolongs repolarization by inhibiting only rapid component of delayed rectifier potassium current (Ikr)
* Mild negative chronotropic (rate) effect
* Administered orally
Vernakalant
Blocks Ikr just like other class III agents, but is more selective for ultra-rapid current (Ikur), which is more predominant in the atria as well as blocking other ion currents selectively in the atria.
* Rate-dependent slowing (more potent at higher heart rate).
* Administered intravenously due to short half-life.
* Indicated for acute cardioversion of atrial fibrillation and atrial flutter to sinus
rhythm.
How do class III antiarrhythmics treat
re-entry rhythms?
A: Increase effective refractory period
prolonging the repolarization phase
Class IV agents
calcium channel blockers or antagonists
Non-Dihdropyridines
Diltiazem
Verapamil
Dihdropyridines
Nifedipine
Amlodipine
Felodipine
CCB group 1
L channel blockers
No action on SA or AV nodes
Dihydropyridines (DHP)
Nifedipine
Amlodipine
Felodipine
CCB group 2
L channel blockers, some T channel blockade Action on SA and AV nodes (Affects pacemaker action Non-dihydropyridines (Non-DHP)- Benzothiazepines
: Diltiazem- Phenylalkylamines
: Verapamil
CCB group 3
T type channel blocker
No current agents on the market
How does CCBs decrease oxygen demand and increase O2 supply.
Decreased Oxygen Demand
* +(DHP) or ↓ (non-DHP) heart rate
* ↓↓ (non-DHP) or ↓↓↓ (DHP) afterload
* ↓ BP
* + preload or ↓↓ contractility
Increased Oxygen Supply
* ↑ coronary dilation
* ↑ collateral coronary blood flow
* ↑↑↑ vasodilation
Indications for CCBs.
Indications
* Stable Angina – second line agents- ↓ BP, ↓ contractility, ↓ HR- ↑ coronary dilatation
* Coronary artery spasm- Coronary artery vasodilation
* Hypertension- Arterial vasodilation
* Supraventricular arrhythmias- Verapamil and Diltiazem- ↓ AV node conduction
Contraindications for CCBs
Contraindications
* Acute MI
* Unstable Angina – DHPs are contraindicated
* Bradycardias and AV blocks with Verapamil and Diltiazem
Nifedipine
Indications
* Vasospastic angina
* Hypertension
* Raynaud’s syndrome
- DHP calcium channel blocker
- Powerful vasodilator
- Mild negative inotropic
- Grapefruit and grapefruit juice increase nifedipine levels
Amlodipine
DHP calcium channel blocker
Felodipine
Indications
* Hypertension
* Raynaud’s syndrome
- DHPcalcium channel blocker
- Hypertension
- Decreases risk of stroke in hypertension
- Reduce dosage in elderly and liver dysfunction
- Grapefruit and grapefruit juice increase felodipine levels
Diltiazem
Indications
* Angina - vasospastic
* Hypertension
* Supraventricular Arrhythmias
- A benzothiazepine Non-DHP calcium channel blocker
- Moderate dilation of arteries, < Nifedipine or other DHPs
- Effect on SA node > Verapamil
- Action on AV node < Verapamil
- ↓ rate pressure product (RPP) at any given level of exercise
Verapamil
Indications
* Angina - effort, vasospastic
* Hypertension
* Arrhythmias, supraventricular
- A phenylalkylamine Non-DHP calcium channel blocker
- Moderately potent vasodilator
- Marked negative inotropic effect
- Mild depression of sinus node function and AV nodal conduction
Why are DHP calcium channel blockers
(CCB’s) preferred in the treatment of
hypertension over non-DHP CCB’s?
DHP CCB’s have greater vascular
selectivity, reducing afterload more than
non-DHP CCB’s.
Adenosine
Indications: Terminating narrow-complex PSVTs,
pharmacological stress-testing, and diagnostic testing (e.g. for atrial flutter or wide-complex tachycardia)
Mechanism: Class V – Adenosine acts on adenosine receptor, especially the AV node.
-Interrupts re-entry rhythms.
-Can also dilate coronary arteries, increasing risk for coronary steal
Ivabradine does not fit into a pre-defined class
Mechanism: selectively inhibits the funny current (If), which modulates slow depolarization phase of the action potential in the SA node.
Results in decreased heart rate by inhibiting phase 4 of the SA node action potential.
