SUPRAVENTRICULAR
ARRYTHMIAS LECTURE |
Digoxin
for Afib/Aflutter |
Digoxin for Afib/Aflutter:
- Often ineffective and slow in onset of action
- Slowed VRR can be expected after one hour but maximal effect only after 24-48 hours
- May be superior choice for long term care of patients with systolic dysfunction (CHF)
- Often ineffective if exercise-related increases in VRR occur
Digoxin for SVT:
- Often used to control VRR in AF by enhancing vagal effects on the AV node
- Limitations are in situations with vagal tone is low (exercise, thyrotoxicosis,
hyperadrenergic states) or when a rapid response is desired. Several studies demonstrated
chronic dig therapy alone is no better than placebo in controlling VRR during AF paroxysms
- May be superior choice for long term care of patients with systolic dysfunction (CHF)
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Dosing Digoxin:
- LD: 10-15 mcg/kg (LBW*)
- MD: (14 + ClCr/5) % x LD
- Give LD 1/2 now then remainder of load as 1/4 x 2 separated by at least 6-8 hours
- Monitor: HR, BP, EKG, K+, Ca++
- Question need for LD in CHF
- Reduce load and MD in renal impairment
- V. rate is not a good measure of chronotropic effect of digoxin
*Many drugs are dosed by using lean body weight. Calculation of lean body weight (LBW)
is as follows:
- LBW male = 50 + (2.3 x + # of inches > 5 ft)
- LBW female = 45 + (2.3 x # of inches > 5 ft)
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Digoxin Toxicities:
- Poorly correlated with digoxin concentrations
- Therapeutic window 0.5-2ng/mL
- DILS (dig. immunoreactive like substance) may cause major interferrence with
interpreting normal digoxin levels in select patient populations:
- pregnant patients
- patients with chronic and possibly acute renal failure
- neonates
- Systemic toxicities
- Anorexia, N, V, diarrhea, yellow-green or blurred vision
- Cardiac toxicities:
- Heart block (2° or 3°)
- Ventricular ectopy
- PAT with 2° AV block
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