Antiarrhythmics Flashcards
Adenosine
1) Indications
2) Half Life
3) Metabolism
1) “Treat paroxysmal SVT
Differential diagnosis of tachyarrhytmia
Coronary vasodilator in nuclear stress tests
Temporary asystole during deployment of vascular stents”
2) “E1/2t = 30 secs
E1/2 life = 10 sec”
3) “Intracellular enzyme metabolism – phosphorylation by adenosine kinase or deamination by deaminase.
Hepatic and renal function do not effect metabolism.”
Adenosine
1) Class
2) Action
1) “Endogenous nucleoside
Adenine and pentose sugar”
2) “Adenosine acts on adenosine A1 receptors in the cardiac conduction system that are linked to Ach activated G-coupled potassium channels (Kach) = slowing of cardiac conduction tissue and slowing SA node conduction = delay AV node conduction. Also blocks stimulation of cAMP and thus Ca+ influx.
Local tissue hypoxia stimulates adenosine production = inhibits NE release via A1 receptor activation. = ↓sympathetic tone = ↓cardiac workload and O2 demand via coronary vasodilation.”
Adenosine: Adverse Effects
"Headache, dizziness, parasthesia Facial flushing, palpitations, chest pain, hypotension Dyspnea Chest pressure Numbness"
Adenosine
1) Contraindications
2) Dosage
1) "Hypersentivity 2nd or 3rd degree heart block SSS without pacer Bronchospastic and restrictive lung disease (not effective in afib, aflutter, VT)"
2) “PSVT = 6mg IV, if not effective give 12mg, if not effective give 18mg
Controlled hypotension = 220mcg/kg/min”
Amiodarone
1) Class
2) Action
1) “Class III antiarrhytmic (also has Class I, II, IV effects)
Benzofurane derivative containing iodine that resembles thyroxine.
Atrial and ventricular dysrhythmic”
2) “Amiodarone alters the lipid membrane where ion channels are located.
Class I agent = blocks Na+ = decreased firing of pacemaker
Class II agent = noncompetitively antagonizes alpha and beta
Class III agent = inhibits repolarization = prolongs refractory period by blocking K+ channels responsible for repolarization = prolonged plateau
Class IV agent = Ca++ channel blocker = decreases AV conduction and sinus node function
Coronary vasodilator”
Amiodarone
1) Indications
2) Onset, Peak, Vd, & Half life
3) Metabolism
1) “Recurrent VF, unstable VT, a-fib, SVT
Pre op oral admin = decreased risk of afib after cardiac sx
Decreased mortality post MI”
2) "Onset – Iv is rapid (PO 3d-3wks) Peak effect = PO 1wk-5mon bc need to accumulate metabolite Vd 66L/kg 96% PB E1/2t = 29days Duration after DC therapy = 7-50days"
3) “CYP450 microscomal enzymes with biliary excretion
DEA = N-desethylamiodarone = active metabolite has longer minimally dependent on renal excretion”
Amiodarone: Adverse Effects
“Hypotension, bradycardia
AV block, prolonged QTc and VT, torsades,
Decreased response to catecholamines bc A and B stim.
Pulm fibrosis, alveolar pneumonitis, ARDS (2% of pts)
Hyper/hypothyroidism, photosensitivity”
Amiodarone
1) Contraindications
2) Dosage
1) “Hypersensitivity to amio or iodine
Cardiogenic shock, SB, 2nd or 3rd degree heart block
Pregnancy
Bradycardia with syncope
*inhitbits Cyp450 enzymes = increased conc of warfarin, procainamide, digoxin
*fentanyl = cardiac arrest, bradycardia, hypotension”
2) “A-flutter, Stable VT/SVT = 150mg IV over 10 mins, 360mg over next 6 hrs(1mg/min) and 540mg over next 18hrs (0.5mg/min)
Pulseless VT/VF = 300mg IVP, than 150mg IVP, then gtt”
Digoxin
1) Class
2) Action
1) Cardiac Glycoside
2) “Digoxin directly inhibits Na+/K+/atpase pump = ↑ Na+ in cardiac myocytes = ↓ extrusion of Ca++ by Na+/Ca++ pump. = ↑Net Ca++ available for subsequent cardiac muscle contractions. (each contraction = more Ca+ released from SR = more myofibril contraction = ↑inotropy)
↓sympathetic tone and ↑vagal tone = slowed conduction through SA and AV node = AV block.”
Digoxin
1) Indications
2) Onset, Peak, half life, & Vd
3) Metabolism
1) “+ inotrope in systolic heart failure
Rate and rhythm control in SVT or a-fib/flutter or paroxysmal”
2) "Onset = 5-30mins IV (1.5-6hrs po) Peak 1-5 hrs E1/2life = 30-48hrs Vd 7L/kg 25% PB"
3) Hepatic metabolism, 50% Excreted by kidneys unchanged.
Digoxin: Adverse Effects
“Prolonged PRI, ST depression Twave changes
Dysrhythmias, heart block, blurred vision
NV, diarrhea, headache, fatigue”
Digoxin
1) Contraindications
2) Dosage
1) “Vfib, v-tach, heart block
Hypertrophic subaortic stenosis
Renal impairment – decrease dose
DIG toxicity potential with hypokalemia, hypomag, hyperCa”
2) “Loading dose = 0.75-1.5mg PO or 0.5-1.0mg IV
Maint dose = 0.125-0.5mg PO or 0.25mg IV
Therapeutic index 0.5-2.0ng/mL”
