Lecture 8 - Arrhythmias 2 Flashcards
goals of anti arrhythmic therapy
- Dec or inc conduction velocity
- alter excitability of cardiac cells by changing the duration of the effective refractory period
- Suppress abnormal automaticity
Vaughan-williams Classification
Class 1- 1A, 1B, 1C
Class 2
Class 3
Class 4
Class 1A drugs
Moderate Na+ blockers = fast fibers
Drugs: Quinidine, Procainamide, Disopyramide
What do Class 1A drugs do?
Dec conduction velocity
Inc refractory period
Dec automaticity
Prolongs QT
What are Class 1A drug used for?
useful for Supraventricular and ventricular dysrhythmias
Class 1B drugs
Weak Na+ blockers = fast fibers
Drugs: Lidocaine, Mexilitine, Phenytoin
What do Class 1B drugs do?
No effect on conduction velocity
Dec refractory period
Dec automaticity
** More effect on Fast HR, no real effect on slow **
Class 1B used for?
Ventricular dysrhythmias only
Class 1C drugs?
Strong Na+ blockers = fast fibers
Drugs: Flecainide, Propafenone
What do Class 1C drugs do?
Profoundly dec conduction velocity
No sig effect on refractory period
Dec automaticity
What are Class 1C drugs used for?
effective in both supraventricular and ventricular dysrhythmias
** don’t use in pts w/ CVD secondary to pro arrhythmia and mortality **
Class 2 Drugs
Work at SA/AV nodal tissue
Drugs: Beta-blockers
What do Class 2 Drugs do?
Block catecholamines
Dec conduction velocity
Inc refractory period (nodal tissue)
Dec automaticity
What are Class 2 drugs used for?
slowing ventricular response to supraventricular tachycardias (A-Fib)
Class 3 Drugs
K+ blockers = fast fibers
Drugs: Amiodarone, Dofetilide, Dronedarone, Ibutilide, Sotalol
What do Class 3 Drugs do?
don’t effect conduction velocity (except amiodarone/dronedarone)
profound inc in refractory period
no effect of automaticity (except amiodarone/dronedarone/sotalol)
**prolongs QT (rare with amiodarone)
What are Class 3 drugs used for?
both supraventricular and ventricular dysrhythmias
Class 4 drugs
Blocks Ca Channel
Drugs: Diltiazem, Verapamil
What do Class 4 drugs do?
Dec conduction velocity
Inc refractory period (nodal tissue)
Dec automaticity
What are Class 4 drugs used for?
slowing ventricular response to supraventricualr tachycardias (A-Fib)
Class I mortality info
Avoid in pts for short or long-term use
Ok in pt without CAD or CHF (studies show inc morality)
Class 3 mortality info
class of choice for pt with CAD and CHF
Avoid Sotalol and Dronedarone in pt w/ CHF
Amiodarone may have mortality benefit
Amiodarone MOA
- Prolongs repolarization, lengthen refractoriness, slows AV conduction, inhibits automaticity, and has nonspecific B-blocking properties
- QT prolongation is minimal
Amiodarone Uses
- Ventricular and atrial arrhythmias
- considered most effective anti arrhythmic available
- Can be used in pts w/ CVD and decompensated HF
Amiodarone Dosing IV (Supraventricular arrhythmias)
150 mg over 10-30 min, followed by 1mg/min X 6hrs, then 0.5mg/min X 18hrs, then 400 mg PO BID-TID until 10 grams total….then maintenance therapy with 200-400 mg/day
Amiodarone Dosing Oral (Supraventricular arrhythmias)
1.2-1.8 g/day in divided doses until 10g total, then 200-400 mg/day
Amiodarone Toxicity: CVD
Hypotension
AV block
Bradycardia
V-tach
** careful in elderly**
Amiodarone Toxicity: Endocrine
Hypo-/Hyperthyroidism (Hypo most common)
Amiodarone Toxicity: Dermatological
Photosensitivity
Bluish-slate gray discoloration of skin
Phlebitis (if using IV)
Amiodarone Toxicity: Opthalmologic
Visual disturbances
Halo vision
Corneal microdeposits
Optic neuritis (rare)
Amiodarone Toxicity: Pulmonary
Pulmonary pneumonitis
Risk factors: >400mg/day, COPD+Asthma, Elderly, Smoking
Two types of Pulmonary pneumonitis
Hypersensitivity pneumonitis (ARDS) (within weeks) Interstitial pneumonitis ( ~ about a month)
Amiodarone Toxicity: Neurologic
Abnormal gait/ataxia Dizziness Fatigue insomnia poor coordination peripheral neuropathy Tremor
Amiodarone Toxicity: Hepatic
AST or ALT > 2x ULN, hepatitis or cirrhosis
Amiodarone Toxicity: GI
N,V, anorexia
Constipation, abdominal pain
abnormal salivation and taste
Amiodarone Drug Interactions
Inc lvls of…
CSA, digoxin, flecainide, statins, warfarin, many more
Dofetilide MOA
Blocks K+ channels and profoundly inc refractory period but doesn’t alter conduction velocity or automaticity
Strong QT-prolonging agent
No negative inotropic effects and no significant effects on HR or BP
Dofetilide Uses
A-fib/A-flutter (not for ventricular arrhythmias)
Can be used in pts w/ CVD and decompensated HF
Dofetilide Dosing
500mcg PO BID
Dosing dependent on QTc + Renal function
QTc must be determined prior to 1st dose
1st time starters must stay in hospital for min of 3 days
Dofetilide CI
- Weak substrate of CYP3A4
2. Avoid drugs that strongly inhibit CYP3A4 or prolong QT interval
Absolute CI for Dofetilide
- Long QT Syndromes
- Baseline QTc > 440 msec
- CrCl < 20ml/min (known how to calc)
which drugs cant you use with Dofetilide
Cimetidine Dolutegravir HCTZ itraconazole Ketoconazole megestrol proclorperazine trimethoprim verapamil
Chest X-Ray & Opthalmologic eval timeframe (amiodarone)
BL, Q12 months
Pulmonary function test & ScCR/Electrolytes, Neurologic/GI/Derm eval time (amiodarone)
BL, PRN
Thyroid & Liver function Test Eval time (amiodarone)
BL, Q6 months
ECG eval time (amiodarone)
BL, q3-6 months
