Cardiac Glycosides

• –   Sino-atrial node - pacemaker 
• –   Atrio-ventricular node - regulator
• –   Bundle of His
• –   Purkinje 

• - electrical current
• - Ca released to sarcoplasm
• - interacts with troponin
• - actin-myosin coupling
• - contraction

• PHASE 0 - Fast sodium Channel
• PHASE1 - Mild repolarization
• PHASE2 - Slow calcium channel
• PHASE 3 - Repolarization (potassium exits the cell)
• PHASE 4 - Resting (sodium/potassium pump)

• FS Law: Cardiac Output increases with pressure up to a point of congestive heart failure.
• Cardiac output (V pumped by H in 1 min) = Stroke volume (V_blood in one ventricle before systole) * heart rate.
• Systole=Contraction, Diastole=Resting
• Patients with CHF have low cardiac output, b/c heart lost its contractility => FS curve shifts down. When this occurs SV ⇓ and ⇑ preload (LEVP). 
• Symptoms associated w/ CHF:
• 1. Edema: ♡ can't pump anymore => fluid is building up in lungs and lower extremities. Use Loop Diuretics, b/c too much fluid.
• 2. Shortness of breath and exercise intolerance.
• Cardiac glycosides shift the curve of the graph up

• Congestive Heart Failure
• Treatment
•         Diet - weight loss/
•                   low sodium/fat
•         Diuretics: Loop and K⁺ Sparing
•         Cardiac Glycosides
•         ACE inhibitors

• 1. Increase Contractility of ♡ (for longer and stronger contaction) (LOW DOSE)
• (↑ inotropic effect)
• Cardiac Glycosides decrease ability of myocardial cells to pump Ca⁺⁺ out => Ca⁺⁺ stays longer in the cell => longer and stronger contraction => ↑ CO

• 2. Decrease AV node conduction (in order to prevent V fib) (HIGH DOSE)
• –   Decreased chronotropic effect (↓ heart rate)
• –   Used in atrial fibrillation
• AV node prevent conduction of AP from atruim. Person can live with A-fib, but V-fib is fatal. In order to prevent V fib we use Glycosides. Glycosides ↓ AV node conduction => amount of electrical activity going to the ventricles is ↓ 

• Therapeutic index is narrow: ng/dL
• CHF dose: 1-2 ng/dL
• Afib: 1.5-2.5 ng/dL
• Toxic: >3 ng/dL

• p - atrial contraction
• QRS- ventricular contraction
• T - repolarization (phase 3)

• 1. Apical Pulse
• Nurse should always measure apical pulse before administering drug. Do not administer drug if apical pulse <60, b/c patient may be toxic.
• Cardiac glycosides work on AV node, they prevent conduction from atria. Higher dose => longer P-R interval (time btw atrial and ventricular conduction)=> 1⁰ block has less ♡ beats=>WARNING: b/c patients apical pulse is <60 they could be in 1⁰ block. If ignore warning => 3⁰ block. 
• In 3⁰ degree block the gate is completely closed, nothing goes through AV node (person is toxic with cardiac glycosides)
• 
• 2) Serum drug level
• Cardiac glycosides have a narrow therapeutic index. Easy to get toxic: ng/dL
• 3) Serum potassium- caution in hypokalemia
• We need K in phase 3 (repolarization), if person doesn't have enough K, he can't recover from phase 2 => toxic. Diuretics also  ↓ K level
• 4) Serum Calcium- caution in hypercalcemia
• Ca found in phase 2(longer and stronger contraction), to much Ca, person can't get to phase 3. 
• If patient doesn't have toxic blood level of cardiac glycosides, hypokalemia or hypercalcemia can make them TOXIC

 5) EKG

• •    Five half lives leads to steady state
• •    Loading Doses required
• •    Toxicities - reversed by digoxin immune
• fab (Digibind®)
• •    HALF LIFE
• –   DIGOXIN - 24 HOURS
• –   DIGITOXIN - 5 days

•    INTRAVENOUS - 100%

•    INTRAMUSCULAR - 80%

•    TABLET - 70%

A-V BLOCK

SINUS BRADYCARDIA

ARRHYTHMIAS

YELLOW-GREEN HALO VISION

CNS: Headache, weakness, anorexia

Discontinue Cardiac Glycoside

Digoxin immune fab (Digibind®)

Correct hypokalemia

Antiarrhythmic Agents

CONGESTIVE HEART FAILURE

 ADJUNCT THERAPY FOR ATRIAL FIBRILLATION