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Class I drugs
Inhibit fast sodium channels
Affect primarily myocardial tissue
- Sub-classes differ by variations in drug binding to and dissociation from the channel
- receptors
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Class IA
Reduce automaticity
Reduce conduction velocity
Increase refractory period
Reduce contractility
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Quinidine
Class IA
- May slow heart rate, widen QRS
- complex, prolong QT interval
- Cardiac monitoring when starting Rx
- Interacts with several drugs
- Increase risk of digoxin toxicity
- Uses—ventricular arrhythmias
- Supraventricular arrhythmias
- —tachycardia, atrial fibrillation and flutter
- Adverse effects
- Diarrhea—up to 30% can’t tolerate
- Cinchonism—toxicity
- Tinnitus, ototoxicity—deafness
- Headache, blurred vision
- Nursing—monitor effects and adverse effects
- Monitor QRS duration and rate
- Teach—to report adverse effects
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Lidocaine (xylocaine)
Class IB
- Decrease automaticity of His-Purkinje system
- Less effect on atria, in ischemic heart--block re-entry
- *No decreased contractility
- *Little effect on BP, pulse
- Adverse effects--CNS-- numbness, tingling
- Drowsiness (dose-related),
- Toxicity--confusion, blurred vision, paresthesias, seizures, widened QRS
- Uses: Acute Rx ventricular dysrhythmias
- Especially in diseased heart (CHF, MI)
IV only--bolus followed by drip
Nursing: Requires cardiac monitoring--rhythm, observe QRS width
- For acute therapy only
- Observe for therapeutic and toxic effects
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Class II
- Beta Adrenergic Blockers
- Affect sympathetic nervous system to
- Decrease heart rate and automaticity
- Mild inhibition of Na+ channels
- Increase refractory period of AV node
- Decreases contractility
- Uses: treat ventricular dysrhythmias
- Prophylactically after MI
- Digitalis-induced dysrhthmias
- Slows ventricular rate with atrial fibrillation
- Nursing:
- Monitor BP—hold for systolic <100
- Monitor P—hold for pulse <60 (50)
- Observe for S/S CHF
- Greater risk with calcium channel blockers
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Propranolol
Class II
- Beta blocker
- Used for: tremors, angina, hypertension, dysrhythmias, and other heart or circulatory conditions. It is also used to treat or prevent heart attack, and to reduce the severity and frequency of migraine headaches.
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Class III
- Blocks potassium channels, calcium channels
- Prolong action potential
- Slows AV conduction
- Prolongs QT interval, widens QRS
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Amiodorone (cordarone)
Class III
- Also block Na+ channels, Ca+ channels, adrenergic receptors
- Slow onset, long half life
- *Primary use for ventricular tachycardia and fibrillation
- Hypotension with IV use-give slowly
- Bradycardia common—monitor
- Longterm Therapy: Monitor liver enzymes, thyroid levels
- May cause pulmonary toxicity—pneumonitis, fibrosis
- Monitor for dyspnea, cough, chest pain
- High incidence of nausea, vomiting, anorexia
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Class IV
Calcium channel blockers
- Reduce AV conduction
- *Increase AV refractory period
- *Affects AV node – decreases automaticity
- *Decreases myocardial contractility
- Uses: treat Supraventricular Tachycardias
- Slow ventricular rate in atrial fibrillation & atrial flutter
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- Adverse Effects: CHF, bradycardia, hypotension
- Give slowly iv, with cardiac monitoring
- Monitor BP—hold for systolic < 100
- Monitor P—hold for pulse < 60
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Diltiazem (cardizem, ziac)
Class IV
- calcium channel blocker
- It works by relaxing the muscles of your heart and blood vessels. Diltiazem is used to treat hypertension, angina, and certain disrrhythmias.
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Adenosine (adenocard)
Class IV
- Naturally occurring nucleosideàpurinergic receptor antagonist
- Inhibits camp induced Ca++ influx
- Depress AV nodal activity
Use—Convert supraventricular tachycardia
- Serum half life 1.5 – 10 seconds
- *Give rapid IV bolus (1-2 seconds)
- *Requires cardiac monitoring
- May see chest pressure, nausea
- Short term asystole (usually 5-6 seconds)
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