CARDIAC GLYCOSIDES
CARDIAC PHYSIOLOGY
ELECTRICAL CONDUCTION
Sino-atrial node - pacemaker
Atrio-ventricular node - regulator
Bundle of His
Purkinje fibers
CONTRACTION PHYSIOLOGY
ELECTRICAL CURRENT
CALCIUM RELEASED TO SARCOPLASM
INERACTS WITH TROPONIN
ACTIN-MYOSIN COUPLING
CONTRACTION
ACTION POTENTIAL
PHASE 0 - Fast sodium Channel
PHASE 1 - Mild repolarization
PHASE 2 - Slow calcium channel
PHASE 3 - Repolarization (potassium enters cell)
PHASE 4 - Resting (sodium/potassium pump)
ACTION POTENTIAL GRAPH
FRANK-STARLING CURVE
CARDIAC OUTPUT (heart rate times stroke volume) graphed versus left
ventricular end diastolic pressure
Cardiac Output increases with pressure up to a point of congestive
heart failure.
Cardiac glycosides shift the curve of the graph
LOW OUTPUT FAILURE
Congestive Heart Failure
Treatment
Diet - weight loss/low sodium/low fat
Diuretics
Cardiac Glycosides
ACE inhibitors
CARDIAC GLYCOSIDE PHARMACOLOGY
INCREASED CONTRACTILITY OF HEART
Increased inotropic effect
Cannot pump calcium out of cardiac cell
Leads to greater contractility and duration
DECREASED A-V NODE CONDUCTION
Decreased chronotropic effect
Used in atrial fibrillation
THERAPEUTIC MONITORING
Apical Pulse
Hold dose for <60
Serum drug level
Narrow therapeutic index
Serum potassium- caution in hypokalemia
Serum Calcium- caution in hypercalcemia
EKG
PHARMACOKINETICS
Five half lives leads to steady state
Loading Doses required
Toxicities - reversed by digoxin immune fab (Digibindฎ)
HALF LIFE
DIGOXIN - 24 HOURS
DIGITOXIN - 5 days
BIOAVAILABILITY
INTRAVENOUS - 100%
INTRAMUSCULAR - 80%
TABLET - 70%
TOXICITIES
A-V BLOCK
SINUS BRADYCARDIA
ARRHYTHMIAS
YELLOW-GREEN HALO VISION
CNS: Headache, weakness, anorexia
TOXICITY THERAPY
Discontinue Cardiac Glycoside
Digoxin immune fab (Digibindฎ)
Correct hypokalemia
Antiarrhythmic Agents
THERAPEUTIC USES
CONGESTIVE HEART FAILURE
ADJUNCT THERAPY FOR ATRIAL FIBRILLATION