pharmacology of antidysrhythmic and vasoactive medications
DESCRIPTION
Pharmacology of Antidysrhythmic and Vasoactive Medications. dr shabeel pn. Class I Antidysrhythmics. Lidocaine (Xylocaine) Procainamide (Pronestyl) Propafenone (Rythmol) Flecainide (Tambocor). Lidocaine (Class Ib). Binds fast sodium channels, inhibiting recovery after repolarization - PowerPoint PPT PresentationTRANSCRIPT
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Pharmacology of Antidysrhythmic and Vasoactive Medications
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Class I Antidysrhythmics Lidocaine (Xylocaine) Procainamide (Pronestyl) Propafenone (Rythmol) Flecainide (Tambocor)
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Lidocaine (Class Ib) Binds fast sodium channels, inhibiting
recovery after repolarization Suppresses spontaneous depolarization of
the ventricles during diastole Acts on ischemic myocardium
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Lidocaine Onset of action: 45-90 seconds Indications:
Ventricular dysrhythmias and ectopy Sinus maintenance after pulseless VT/VF Second-line for hemodynamically stable VT
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Lidocaine Dosing:
Load 1-1.5 mg/kg, max of 3 mg/kg Infuse at 1-4 mg/min (maintenance usually 2
mg/min) Adverse effects:
Above 9 mg/min, may cause CNS depression, seizures, respiratory depression
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Procainamide (Class Ia)
Prevents ectopic or reentrant dysrhythmias Anticholinergic properties in large doses Potentially pro-dysrhythmic
Prolonged QRS and QT intervals, PVCs, VT, VF, complete AV block
Beware hypotension secondary to peripheral vasodilation
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Procainamide
Onset: 5-10 min
Indications: Recurrent ventricular dysrhythmias
stable VT & wide complex tachycardia Pulseless VT/VF Converting PSVT, a fib, a flutter
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Procainamide
Contraindications: Torsades & all blocks except first degree Myasthenia gravis (will increase weakness)
Dosing: Load 20 mg/min up to 17 mg/kg then
infuse at 1-4 mg/min to maintain suppression
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Class II Antidysrhythmics BETA BLOCKERS
Treatment of hypertension Decrease morbidity and mortality:
Acute MI (metoprolol and atenolol)CHF (metoprolol and carvedilol)
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Beta Blockers Cardioselective (specific for β1
receptors): atenolol, esmolol, metoprolol Useful with asthma, COPD, or diabetes Cardioselectivity lost at high doses
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Labetalol (Normodyne) Non-cardioselective β-blocker and
selective α1-adrenergic blocker The β-blocker effects exceed the α1-
blocking effects at a 7:1 ratio if given IV Decreases heart rate, contractility, cardiac
output, cardiac work, and peripheral resistance
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Labetalol Onset: 2-5 min; duration 2-4 hrs Indications:
HTN in patients with myocardial ischemia Minimally changes heart rate and cardiac output
Acute neurological emergencies little effect on cerebral perfusion pressure or ICP
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Labetalol Dosing:
IV bolus 20 mg, repeat 40-80 mg q10 min prn up to 300 mg
Infuse 0.5-2 mg/min to desired effect Adverse effects:
orthostatic hypotension, heart failure, lethargy, increased liver enzymes
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Class III Antidysrhythmics Amiodarone (Cordarone) Dofetilide (Tidosyn) Ibutilide (Corvert)
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Amiodarone Inhibits sodium channels and β-adrenergics Prolongs action potential duration &
effective refractory period delays repolarization
Impairs SA and AV nodal function and prolongs refractory period in accessory pathways
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Amiodarone Indications:
Ventricular and supraventricular dysrhythmias
Recurrent VF and VT, atrial fib/flutter, and junctional & wide-complex tachycardias
Pulseless VT/VF and atrial dysrhythmias with LVEF<40%
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Amiodarone Dosing:
Pulseless VT/VF: Load 300 mg IV, repeat 150 mg IV
Other dysrhythmias: Load 150 mg IV, then infuse 1 mg/min X 6 hours,
then 0.5 mg/min thereafter Adverse effects:
Hypotension, bradycardia, asystole, cardiac arrest, shock
Contains iodine – avoid if allergic to iodine or shellfish
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Class IV Antidysrhythmics: Calcium Channel Antagonists
Diltiazem (Cardizem) Verapamil (Verelan, Calan, Isoptin)
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Diltiazem1) Interferes slow channel extracellular
calcium influx in cardiac smooth muscle
2) Inhibits sodium influx through fast channels
Slows AV nodal conduction/prolongs refraction Dilates coronary vasculature
decreases O2 consumption/ improves O2 delivery
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Diltiazem Onset: 2-3 min IV; 15-60 min PO
Indications: Rapid conversion of PSVT to NSR Ventricular slowing in atrial fib/flutter Do NOT use for wide-complex
tachydysrhythmias suggesting an accessory bypass tract (i.e. WPW syndrome)
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Diltiazem Dosing:
Load 0.25 mg/kg (max 20 mg) IV push over 2 min, repeat in 15 minutes with 0.35 mg/kg (max 25 mg) IV push over 2 minutes if patient not responsive
Infuse at 5 mg/hr (max 15 mg/hr) Adverse effects:
Angina, bradycardia, asystole, CHF, AV block, bundle branch block, hypotension, peripheral edema
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Verapamil Action & Adverse Effects similar to Diltiazem Indications:
As in Diltiazem Essential HTN Avoid in WPW patients (may accelerate
bypass tract conduction) Dosing:
For PSVT: 5-10 mg IV push over 2 min
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Other Dysrhythmics/Vasoactives Adenosine Digoxin Atropine Dobutamine Vasopressin
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Adenosine (Adenocard) Transient AV nodal block
breaks re-entrant circuit of AV nodal atrial tachydysrhythmia
No effect on non-AV nodal re-entrant SVTs or anterograde conduction over accessory pathways in WPW
As rapid IV bolus - slows cardiac conduction and restores sinus rhythm
Infused - acts as a potent vasodilator.
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Adenosine Onset: 20-30 seconds; Half-life <10 seconds Indications: Emergency treatment of SVT
Distinguish Afib/AFlutter from other tachydysrhythmias
Contraindications: 2nd and 3rd degree AV block or sick sinus
syndrome
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Adenosine Dosing:
6 mg rapid IV bolus, most proximal port then 12 mg rapid IV bolus every 1-2 min prn x2 doses
Follow bolus immediately with 10-20 cc flush
Adverse effects (usu. minor and well-tolerated) Dyspnea, syncope, vertigo, metallic taste, flushing,
chest pain, bradycardia, and sense of impending doom.
Bronchospasm in asthmatics.
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Digoxin 3 basic actions:
Positive inotrope = Increases force, strength, and velocity of contractions
Negative chronotrope = Slows heart rate, improving coronary blood flow and myocardial perfusion
Negative dromotrope = Slows conduction velocity through AV node
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Digoxin Inhibits Na+K+ATPase pump gain of
intracellular Na+
Extra Na+ removed via Na+Ca2+ exchange channel
Increased intracellular Ca2+ improves myocyte contractility
Onset: 5-30 min IV; 30-120 min PO
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Digoxin Indications:
Improve cardiac output in CHF Control ventricular response in atrial
fib/flutter and PSVT
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Digoxin Dosing:
10-15 μg/kg or 0.75-1.5 mg IV 0.125-0.5 mg/day PO
Adverse effects:
GI: abdominal pain, N/V, diarrhea Cardiac: sinus bradycardia, AV or SA nodal
block, ventricular dysrhythmias
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Digoxin Toxicity:
Can be fatal if not properly treated Symptoms are varied and can be vague
Altered mentation, visual disturbances, seizures PVCs, VT, junctional tachycardia, high-degree
AV block, SVT, and sinus arrest Hyperkalemia
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Digoxin Toxicity Treatment:
Lidocaine, phenytoin and/or atropine Digibind (antibody fragments) IF:
Tachydysrhythmias Sinus bradycardia Severe AV blocks K+ >5mEq/L secondary to digoxin use
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Atropine Antagonizes acetylcholine & muscarinic agents Increases sinus node automaticity and AV
conduction by blocking vagal activity (parasympatholytic)
Onset: 2-4 minutes Indications:
Symptomatic sinus bradycardia PEA and asystole
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Atropine Dosing:
For bradycardia = 0.5mg IVP q 3-5min For PEA/asystole = 1mg IVP q 3-5min Maximum total dose of 0.04 mg/kg
produces complete vagal blockade
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Atropine Adverse effects:
Dry mouth, CNS stimulation, hallucinations, blurred vision, and tachycardia
Potential ischemia and ventricular tachydysrhythmia in hemodynamically stable bradycardic patients
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Dobutamine (Dobutrex) Sympathomimetic - inotropic and
chronotropic effects β1/ β2-adrenergic and α-adrenergic offset
by α-adrenergic antagonist activity increase in myocardial contractility and
systemic vasodilation
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Dobutamine Onset: 1-2 min Indications:
Positive inotropic support for cardiovascular decompensation secondary to ventricular dysfunction or low-output heart failure.
Preferred agent to manage cardiogenic shock. increases CO and renal/mesenteric blood flow w/o direct stimulation of the heart rate.
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Dobutamine Dosing:
2-20 μg/kg/min Monitor patient with CVP or pulmonary
artery catheter. Adverse effects:
Increases in heart rate, blood pressure, and ectopic dysrhythmias
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Nitroglycerin Enters vascular smooth muscle Converts to nitric oxide
direct vasodilator produces systemic venodilatation
Venodilation at <100 μg/min Arteriolar vasodilation >200 μg/min
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Nitroglycerin Indications:
Angina pectoris Acute decompensated CHF Hypertensive crisis Perioperative hypertension in CV procedures
Dosing: SL, lingually, intrabuccaly, topically or IV Multiple formulations with specific dosing
regimens
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Nitroglycerin Adverse effects:
Headache, dizziness, hypotension, syncope Remove transdermal patches and ointments
before defibrillation or cardioversion Concurrent use of sildenafil (Viagra) has
been reported to cause excessive refractory hypotension
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Vasopressin (Pitressin) Directly stimulates smooth muscle V1
receptors vasoconstriction Decreased splanchnic, coronary, GI, skin, and
muscular system blood flow May be beneficial during resuscitation
attempts
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Vasopressin Onset = immediate Indications:
Alternative to epinephrine as nonadrenergic peripheral vasoconstrictor during CPR
Pulseless VT/VF
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Vasopressin Dosing:
Cardiac arrest: 40 units IV push single dose Epinephrine 1 mg IV should be given after 10
minutes if adequate response is not seen. Adverse effects:
HTN, bradycardia, dysrhythmias, PACs, heart block, peripheral vascular constriction, and decreased cardiac output
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Questions 1. Which of the following is indicated for symptomatic sinus bradycardia?
A. Labetalol B. Atropine C. Neseritide D. Vasopressin E. Digoxin
2. Nitroglycerin may not be given: A. Sublingually B. Topically with cardioversion C. Via IV infusion D. With concomitant Viagra use E. B & D
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3. True or False?
Amiodarone is a good treatment choice for wide-complex tachydysrhythmias in patients with unknown underlying EF.
4. Which of the following is false regarding adenosine? A. Is indicated for emergency treatment of SVT. B. Has a half-life of about 10 seconds. C. Blocks anterograde conduction over accessory pathways. D. Produces transient AV nodal block. E. A sense of impending doom is a common side effect.
5. What is the appropriate dose of vasopressin for pulseless VT/VF? A. 40 units IV push B. 1 mg IV C. 1mg/kg/min D. 6 mg rapid IV push E. 300 mg IV
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Answers 1. B 2. E 3. T 4. C 5. A