Heart failure Tx/Drugs (pt 2) Flashcards
Direct effects of Digoxin
a. Positive inotropic effect – Due to a direct effect to increase the contractile state of the myocardium – Increases stroke volume b. Increases vagal tone – Slows heart rate
Do we see a change in AP when we give pt Digoxin?
NO change in AP but we do see increased Ca+ thus increasd force of contraction
Secondary affects of Digoxin
Decreased heart rate
- Arterial and venous dilation
- Decreased venous pressure
- Normalized arterial baroreceptors
Molecular site of action of Digoxin
• Positive inotropic effect due to inhibition of the Na+,K+ ATPase
– results in increased intracellular [Na+] – decreasing driving force for Ca2+ extrusion by Na+/Ca2+exchanger
– indirectly results in increased intracellular concentration of Ca2+
WHy do we worry about hypokalemia in pts that take Digoxin?
• K+ competes for binding of digoxin to the Na+,K+-ATPase thus end up with low K+ levels
What electrophysiological actions does Digoxin have?
Electrophysiological actions:
• At therapeutic concentrations, mainly related to increased vagal nerve activity
– Reduced firing rate of SA node
– Decreased conduction velocity in AV node
– Heart block can develop
Main effect of Digoxin on ECG?
increased PR interval
Key pharmK of Digoxin
1/2life?
absorption and excreation?
when do we see best benefits for contractility vs neurohormonal
1/2 = 36 hrs
oral absorption with renal excreation
best cnx benefits at 1.4ng/ml and best neurohormonal at 0.8 ng/ml
What are the adverse effects/toxicity related to Digoxin
Low therapeutic index (~2)!!!!!
Affects all excitable tissues
a. GI tract (most common)- anorexia,, vomiting, diarrhea
b. Visual disturbances- Blurred vision, photophobia, color disturbances
c. Neurologic- disorientation, hallucinations
d. Muscular- muscle weakness, fatigue
e. Cardiac – arrhythmias (any type)
Toxicity with Digoxin is enhanced when pt is
hypokalemic.. may be related to diuretic use
What effect does Digoxin have on CHF progression?
debated.. some say helps, others say you only see benefit vs placebo when taking pts off because they were on a medince for long period of time, much like you would have withdrawl from other drugs
What effect does Digoxin have on overall mortality in CHF pts?
NONE!!! we see no overall benefit, also this drug has narrow tx window so it’s difficult to monitor.
Better to use in pts with atrial fib or if pts have severe heart fail and this helps reduce symptoms
clincial Uses of Digoxin
Use limited to heart failure patients with LV systolic
dysfunction in atrial fibrillation or in some cases to patients in sinus rhythm who remain symptomatic despite maximal therapy with other therapies
• If used, administer a low doses
dobutamine, dopamine are what type of drugs and when do we use them for heart fail pts?
b adrenergic agonists
– Used i.v. for temporary hemodynamic support for
acutely ill patients (acute decompensated heart
failure)
Milrinone is what type of drug and when do we administer to heart fail pts?
• Phopsphodiesterase inhibitors (
– Use limited to i.v. administration for acutely ill patients
– Positive inotrope and also produce vasodilation
Mainstay of heart failure management
• Reduce fluid volume and preload
• Reduction in heart size improves efficiency and reduces wall stress
• Reduce edema (and its symptoms)
Diuretics!
Diuretics reduce:
fluid volume and preload and edema
Furosemide is what type of dieuretic?
loop diuretic
Widely used – most heart failure patients require chronic
therapy with a loop diuretic to maintain euvolemia
– Promote K+loss - hypokalemia
Chlorothiazide is what type of diuretic?
Thiazide; Rarely used alone
– Combination therapy with loop diuretics in patients refractory to loop diuretics alone
– Promote K+loss - hypokalemia
Issue with loop diuretics and thiazides?
promote K loss–hypokalemia
Amiloride and Triamterene are what kind of diuretic?
K sparing diuretic
Weak diuretic activity but limited K+ and Mg2+ wasting