Cardiovascular 3 Flashcards
What is an arrhythmia? do we need to intervene?
An abnormal heart rate and/or rhythm that results from…..
- Disturbances in impulse formation or in impulse conduction, or both
- Arrhythmias may/may not require intervention
Consider treating arrhythmias when…..
Patient is symptomatic
- Causes hemodynamic compromise
- When it may degenerate into a more unstable condition that is life threatening
- Tachyarrhythmia—sustained
- Bradyarrhythmia—sustained
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Bradyarrhythmias may require treatment
- Often long term treatment requires pacemaker
What are the classes of antiarrhythmics used to treat tachyarrhythmias
- Class I (Na+ channel blockers)
- Class II (β-blockers)
- Class III (K+ channel blockers)
- Class IV (Ca2+ channel blockers)
Sodium Channel Blockers
- mechanism, what they do?
- uses
This class blocks fast sodium channels that are important during phase zero of depolarization
- Slows conduction velocity in the myocardium
- Known as “membrane stabilizers”
- These agents prolong the refractory period
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These agents are used most commonly to treat ventricular tachyarrhythmias (VA’s)
- Ventricular premature contractions (VPCs)
- Ventricular tachycardia (VT)
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Occasionally may also be used to treat some supraventricular arrhythmias (SVA’s)
- Paroxysmal supraventricular tachycardia (PSVT)
- Atrial fibrillation
Sodium Channel Blockers that we use
- Class 1A: Quinidine, Procainamide
- Class 1B: Lidocaine, Mexiletine
Quinidine, Procinamide
- use?
- Limited use in small animals due to adverse effects— proarrhythmic
- Are both available for oral and injection
- CV monitoring needed for both drugs
- Quinidine may still be used in atrial fibrillation in the horse
Class 1B sodium channel blockers vs class 1A
Class 1B has more profound effects in abnormal cardiac tissue than Class 1A
Lidocaine, Mexiletine
- uses
- Lidocaine licensed in vet medicine as local anesthetic, not antiarrhythmic
<><> - Lidocaine has value in treatment of VA’s; no value with SVA’s
- Drug is often given as a loading dose followed by a CRI; extensive first pass metabolism if given orally
- Lidocaine most effective if serum K+ levels are high normal
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Lidocaine, Mexiletin toxicity
- Ataxia, drowsiness, seizures (treat with diazepam)
- Cats sensitive to adverse effects; use not recommended
- Do not use lidocaine-epinephrine formulations
β-Blockers as antiarrythmics
- how they work?
- uses
- cautions
Exert their antiarrhythmic effects thru inhibition of sympathetics
- Reduces AV nodal conductivity and increased myocyte refractoriness
- Reduces SA firing (depolarizing) rate
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In veterinary medicine β-blockers are used……
- Primarily for mgmt. of supraventricular tachyarrhythmias
- May be helpful with ventricular tachyarrhythmias (VTA)
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- Careful with decreased contractility in HF eg. DCM
commonly used beta blockers and their individual properties
Atenolol, Esmolol
- Esmolol is an injectable selective β1-blockers with a very short half-life; Used for acute antiarrhythmic therapy
- Atenolol is an oral selective β1-blockers used for chronic tx
Potassium channel blockers
- what they do?
As a group these agents prolong the action potential duration and the refractory period
- Act primarily by blockade of K+ channels
- They reduce automaticity of myocardial cells
- May be safer than class I agents for preventing
sudden death in ventricular arrhythmias
Sotalol
- what is this drug?
- properties and use?
- Non-selective β-blocker that also blocks myocardial K+ channels
> β-blocking properties are less than propranolol
> Also slows AV nodal conduction and will also slow heart rate
> Maybe of value in treating ventricular tachyarrhythmias in dogs
> Negative inotropic and proarrhythmic effects are possible
Amiodarone
- what is this drug? what is its use?
- mechanism?
- adverse effects?
Potassium channel blocker
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Amiodarone is reserved for refractory arrhthymias not responding to sotalol or mexiletine
- Produces an increase in refractory period
- Can also block sodium channels, calcium channels and possibly adrenergic receptors
- Amiodarone can also suppress supraventricular tachyarrythmias, such as atrial fibrillation
- Usually used orally, but is available as an injectable
- Potential for serious adverse effects
> Hepatotoxicity, neutropenia, and thrombocytopenia possible
> Holter monitoring recommended
Potassium channel blockers commonly used
- sotalol
- Amiodarone
Calcium channel blockers
- which are commonly used?
- diltiazem
Calcium channel blockers mechanism
- Effects due to blockade of cardiac calcium channels
- Slow calcium channel activity is important for depolarization in the SA and AV nodes
> Slowing of SA depolarization & AV conduction
> Prolongs AV node refractory period - Results in ventricular response to supra-ventricular tachyarrhythmias
> Atrial fibrillation
> Paroxysmal supraventricular tachycardia
Diltiazem
- properties
- Calcium channel blocker
> Has minimal effects on VSM calcium channels
> Available as injectable and oral tablet including extended release forms
Digoxin
- use?
- Primary indication in veterinary medicine is for therapy of supraventricular tacharrhythmias including atrial fibrillation
> May be used in combination with other agents (CCB’s, β-blockers)
> Moderately effective treatment of supraventricular tachyarrhythmias
<><><><> - increase parasympathetic nerve activity at the SA node, atria and AV node > decrease heart rate
> Slows the ventricular response
> Improved baroreceptor function yielding:
=> increased vagal tone
=> decreased sympathetic tone (neuromodulatory)
when may we need to treat bradyarrythmias? when can drugs benefit?
Treatment of bradyarrhythmias may be necessary when CO is substantially reduced
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Drugs may be of benefit in some cases of bradycardia
- Sinus bradycardia
- Sick sinus syndrome
- Heart block (2nd, 3rd deg)
what drugs can be used in the treatment of bradyarrhythmias?
- Anticholinergics (muscarinic blockers): atropine, propantheline
- Sympathomimetics: isoproterenol
Anticholinergics (muscarinic blockers): atropine, propantheline
- when to use for bradyarrhythmia
- Conditions with high vagal tone; block muscarinic receptors
- Injectable atropine available; oral tablets for both drugs
- Chronic oral therapy (tablets) may be possible with propantheline
Sympathomimetics for bradyarrhythmias
- what do they do?
- which do we use and what are possible adverse effects?
- Sympathomimetics; increase conduction via cardiac β1 receptor
> Isoproterenol (β1, β2 agonist); given by CRI
=> Can cause hypotension and arrhythmias; ECG monitoring needed
