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 (Vblood in one ventricle before systole) * heart rate.
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
Low output failure: treatment
Congestive Heart Failure
Diet - weight loss/
Diuretics: Loop and K+ Sparing
CARDIAC GLYCOSIDE PHARMACOLOGY
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 PulseNurse 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 hypercalcemiaCa 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