Dysrhythmics Flashcards
Autorhythmic cells
Cardiac cells that create their own resting membrane potential
(SA and AV node cells)
Contractile cells
Cardiac cells responsible for the heart’s pumping activity
Automaticity
Heart’s ability to spontaneously generate an electrical impulse
Depolarization
Electrical stimulation/impulse that generates an action potential
(cell becomes less negative)
Repolarization
Membrane potential returns to resting/polarized state (more negative)
Conduction velocity
Speed in which electrical impulses are transmitted
Refractory period
Time frame after depol. where cells can’t be excited again
Absolute refractory period
In-excitable period regardless of impulse strength
Relative refractory period
The cell is partially repolarized
A strong stimulus could cause depolarization
Vaughan-William Class I Agents
Sodium Channel blockers
Vaughan-William Class II Agents
Beta blockers
Vaughan-William Class III Agents
Potassium channel blockers
Vaughan-William Class IV Agents
Non-dihydropyridine calcium channel blockers
Class IA agents and MOA
Double, Quarter, Pounder
Disopyramide, Quinidine, Procainamide
Moderate inhibition of phase 0
Prolongs absolute refractory period/repolarization (QT interval)
Class IB agents and MOA
Lettuce, Mayo, Pickles
Lidocaine, Mexiletine, Phenytoin
Mild inhibtion of Phaso 0,
Shortens absolute refractory period/repolarization (good for VT/VF
Class IC agents and MOA
Fries, Please
Flecainide, Propafenone
Major inhibition of Phase 0
Minimal effect on absolute refractory period/minimal prolongation of repolarization
Class I agents MOA
Na+ channel blockade (C>A>B)
delay automaticity
slows conduction velocity
varying effects on repolarization
Procainamide
IV
Ventricular arrhythmias
LD: 500-600mg IV over 25-30 mins
MD: 2-6 mg/min by cont. IV infusion
AEs: hypotension, HF, 1st degree AV block, lupus erythematosus-like syndrome, blood dyscrasias (agranulocytosis, bone marrow suppression, neutropenia, thrombocytopenia)
Active metabolite acts as Class III agent
Substrate of CYP 2D6
Ethanol reduces serum conc.
dose adjust in renal (CrCl<50)/hepatic impairment
TDM: procainamide: 4-10mcg/ml, NAPA: 12-25mcg/ml, combo: 10-30 mcg/ml
Disopyramide
Norpace
Oral
Ventricular arrhythmias
IR: 100-150mg q6h ATC
CR: 200-300mg q12
Dose adjust in renal dysfunction (CrCl <40) and hepatic dysfunction
CYP3A4 substrate
TDM: 3-7mcg/mL
Beers list: HF inducer, anticholinergic AEs
Take on empty stomach
AEs: hypotension, exacerbate HF, xerostomia, constipation, urinary hesitancy
Quinidine
Atrial fibrillation/atrial flutter, Ventricular arrhythmias
Gluconate: ER: 648mg PO q8
Sulfate: IR: 200-400mg PO q6h, ER: 300mg q8-12h
(267mg quinidine gluconate = 200mg quinidine sulfate)
Metabolized by CYP3A4 (maj) and eliminated by P-gp
Strong inhibitor of CYP 2D6/P-gp
Dose adjust in CrCl <10, use caution in hepatic impairment
Contraindications: thrombocytopenia, 2nd/3rd degree heart block, concurrent use of quinolone antibiotics (prolong QT interval)
TDM: 3-8mcg/ml
AEs: GI distress, diarrhea, dizziness, fatigue, HA, palpitations, cinchoism
Class IA pearls
use dependence, TDM, all can be pro-dysrhythmic
avoid in structural heart disease and/or CAD
Notorious for QT-prolongation
Class IB Pearls
treatment of ventricular arrhythmias
use caution in hepatic disease and HF
higher CNS-related AEs
avoid in pts w/ structural heart disease and/or CAD
Lidocaine
Xylocaine
VF/pulseless VT, hemodynamic monomorphic VT
1-1.5 mg/kg bolus
Refractory VF/pulseless VT: 0.5-0.75 mg/kg bolus every 5-10 mins (max cumulative dose: 3 mg/kg)
Cont infusion: 1-4mg/min
AEs: heart block, CNS toxicity (seizures, altered mental status, somnolence), N/V
Pearls: lower dose w/ hepatic dysfunction, maj substrate of CYP1A2 and CYP3A4
Contraindications:allergy to corn/corn-related products, severe degrees of SA/AV block(except in artificial pacemakers)
TDM: avoid levels >5 mcg/ml (CNS toxicity)
Mexiletine
Ventricular arrhythmias
200-300mg PO q8 initially, after dysrhythmia is controlled q12h
Max/day: 1.2g
AEs: GI distress, N/V, dizziness, ataxia, hepatotoxicity, blood dyscrasias, DRESS
Pt counseling: take w/ food, avoid diets/meds that increase urinary pH
Pearls: maj substrate of CYP 1A2 and 2D6, caution in hepatic impairment and/or HF
Contraindications: 2nd/3rd degree AV block (except w/ artificial pacemaker), cardiogenic shock
Class IC clinical pearls
primarily for supraventricular tachycardia in outpatient setting, avoid in pts w/ structural heart disease and/or CAD
Flecainide
Tambocor
Paroxysmal a-fib, paroxysmal supraventricular tachycardia
50-100mg PO q12h (max/day 300-400mg)
Pearls: maj substrate of CYP 2D6, caution in hepatic dysfunction, dose adjust in CrCl<35ml/min
Contraindications: ritonavir, pre-existing 2nd/3rd degree AV block
Pt counseling: strict vegetarian diet decreases clearance due to increased urinary pH, milk may decrease absorption
AEs: dizziness, HA, fatigue, nausea, visual disturbances, dyspnea
Propafenone
Rythmol
Paroxysmal a-fib, paroxysmal supraventricular tachycardia
ER cap: initial 225mg q12 may increase to max of 425mg q12
IR tab: initial: 150mg q8, may increase to max of 300mg q8
Monitor: CBC w/ differential for agranulocytosis, LFTs, ECG for heart block/bradycardia
Pearls: use w/ caution in pts on BBs, CYP2D6 substrate, inhibits P-gp, dose adjust in hepatic dysfunction, avoid grapefruit juice
AEs: unusual taste, n/v, dizziness, fatigue, blurred vision
Vaughan-William Class II MOA
Autorhythmic cells: inhibits sympathetic activity decreasing SA/AV node automaticity and conduction velocity
Contractile cells: membrane stabilizing activity, increases AP duration and effective refractory period
Beta blockers w/ MSA: propranolol and metoprolol
Beta blockers w/o MSA: esmolol
Propranolol
Inderal
30-320 mg/day divided q6-8h (Max/day 640mg)
Pearls: non-selective beta blocker, can be used to treat arrhythmias caused by hyperthyroidism
Drug-drug interactions: metabolized by CYP1A2 and 2D6 (fluoxetine), ethanol increases/decreases plasma levels
high protein diet can increase bioavailability (~50%)
Esmolol
Brevibloc
Continuous infusion: 500mcg/kg/min over 1 min, then 50mcg/kg/min (max 200mcg/kg/min)
Pearls: good for low BP/HR, short half-life (9mins) metabolized by blood cell esterases
Transition to oral BB: reduce infusion by 50% 30mins after first dose of oral alternative
Vaughan-William Class III MOA
K+ channel blockade (inhibits Phase 3)
Prolongs refractory period/repolarization
Vaughan-William Class III agents
Amiodarone (Pacerone/Cordarone)
Dofetilide (Tikosyn)
Sotalol (Betapace/Betapace AF)
Amiodarone
blocks all 4 Vaughan-William Classifications
treats atrial and ventricular arrhythmias
oral: 200-1600 mg/day
IV: 150-300mg rapid bolus, then 1mg/min for 6hrs, tehn 0.5mg/min for 18hrs
AEs: hypotension, bradycardia, hypothyroidism, hyperthyroidism, n/v, acute/chronic liver impairment, photosensitivity, pulmonary toxicity (pneumonitis, fibrosis), peripheral neuropathy, optic neuritis
