pharmacology of antidysrhythmic and vasoactive medications
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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
Pharmacology of Antidysrhythmic and Vasoactive Medications
Class I Antidysrhythmics Lidocaine (Xylocaine) Procainamide (Pronestyl) Propafenone (Rythmol) Flecainide (Tambocor)
Lidocaine (Class Ib) Binds fast sodium channels, inhibiting
recovery after repolarization Suppresses spontaneous depolarization of
the ventricles during diastole Acts on ischemic myocardium
Lidocaine Onset of action: 45-90 seconds Indications:
Ventricular dysrhythmias and ectopy Sinus maintenance after pulseless VT/VF Second-line for hemodynamically stable VT
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
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
Procainamide
Onset: 5-10 min
Indications: Recurrent ventricular dysrhythmias
stable VT & wide complex tachycardia Pulseless VT/VF Converting PSVT, a fib, a flutter
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
Class II Antidysrhythmics BETA BLOCKERS
Treatment of hypertension Decrease morbidity and mortality:
Acute MI (metoprolol and atenolol)CHF (metoprolol and carvedilol)
Beta Blockers Cardioselective (specific for β1
receptors): atenolol, esmolol, metoprolol Useful with asthma, COPD, or diabetes Cardioselectivity lost at high doses
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
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
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
Class III Antidysrhythmics Amiodarone (Cordarone) Dofetilide (Tidosyn) Ibutilide (Corvert)
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
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%
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
Class IV Antidysrhythmics: Calcium Channel Antagonists
Diltiazem (Cardizem) Verapamil (Verelan, Calan, Isoptin)
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
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)
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
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
Other Dysrhythmics/Vasoactives Adenosine Digoxin Atropine Dobutamine Vasopressin
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.
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
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.
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
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
Digoxin Indications:
Improve cardiac output in CHF Control ventricular response in atrial
fib/flutter and PSVT
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
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
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
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
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
Atropine Adverse effects:
Dry mouth, CNS stimulation, hallucinations, blurred vision, and tachycardia
Potential ischemia and ventricular tachydysrhythmia in hemodynamically stable bradycardic patients
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
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.
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
Nitroglycerin Enters vascular smooth muscle Converts to nitric oxide
direct vasodilator produces systemic venodilatation
Venodilation at <100 μg/min Arteriolar vasodilation >200 μg/min
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
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
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
Vasopressin Onset = immediate Indications:
Alternative to epinephrine as nonadrenergic peripheral vasoconstrictor during CPR
Pulseless VT/VF
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
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
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
Answers 1. B 2. E 3. T 4. C 5. A