WEEK 6- Positive Inotropic Agents: Flashcards
Positive Inotropic Agents
Drugs that increase the force of myocardial contraction Used to treat heart muscle failure Cardiac glycosides -Digoxin -Phosphodiesterase inhibitors -Amrinone and Milrinone
left-ventricular-end-diastolic volume
More blood accumulates in the ventricles as a result of incoming blood plus that which was not effectively ejected from the previous contraction
This leads to pressure build up in the blood vessels leading to the heart which eventually leads to further build up (ie like a chain reaction)
L VS R SIDED FAILURE
Left ventricular failure—elevated left ventricular pressure produces pulmonary edema (pulmonary congestion) resulting in cough, SOB & air hunger
LUNGS=LEFT
Right ventricular failure—elevated right ventricular pressure leads to venous congestion & peripheral edema i.e. edema of the ankles, jugular venous distention, ascites (abd distention) & hepatic congestion
SA node: pacemaker of the heart
HR 60-100
AV node: controls the rate of impulses arriving to the ventricles
HR 40-60
Inotropic
increase the Force of myocardial contraction. this is what dig.
INCREASE CONTRACTILITY
Chronotropic
Heart rate in the only med crash cart if they are bradycardic and dilates
MED:ATROPINE
Dromotropic
Speed of conduction of electrical impulses through the SA (sinoatrial) & AV (atrioventricle)nodes
Cardiac Drugs Work By:
Increasing the force of contraction referred to as “positive inotropic drugs”
Increasing the heart rate referred to as “positive chronotropic drugs”
Increasing conduction of electrical impulses through the SA (sinoatrial) & AV (atrioventricle) nodes referred to as “positive dromotropic drugs”
Cardiac Glycosides: Digoxin
need to know
Used in heart failure and to control ventricular response to atrial fibrillation or atrial flutter
Referred to as positive inotropic agents
Loading dose of digoxin is necessary to establish a therapeutic blood level and to prevent toxicity
Digitilization
Cardiac Glycosides:Mechanism of Action
Increase myocardial contractility
Enhances the vagal tone therefore resulting in elevated diastolic filling time
Change electrical conduction properties of the heart Decrease rate (velocity) of electrical conduction Prolong the refractory period between the SA node and AV node
Digoxin and Digitalis
Positive inotropic effect FOR CARDIAC GLYCOSIDES DRUG EFFECTS
Increase in force and velocity (rate) of myocardial contraction (without an increase in oxygen consumption)
Negative chronotropic effect FOR CARDIAC GLYCOSIDES DRUG EFFECTS
Reduced heart rate
Negative dromotropic effect FOR CARDIAC GLYCOSIDES DRUG EFFECTS
Decreases automaticity at SA node; decreases AV nodal conduction (controls conduction of electrical impulses)
Cardiac Glycosides:Drug Effects
Increased stroke volume
Reduction in heart size during diastole
Decrease in venous BP and vein engorgement
Increase in coronary circulation
Promotes diuresis due to improved blood circulation
Reduce pressure and back up of fluids in the lungs
Cardiac Glycosides:Indications
Heart failure
Supraventricular dysrhythmias
->Atrial fibrillation and atrial flutter
Digoxin (Lanoxin)
Very V. V. narrow therapeutic window
– Drug levels must be monitored to prevent toxicity
Normal lab values 0.5 to 2mmol/l -NORMAL DIG LVLS
PROB Q6
– Low potassium (HYPOKALEMIA) levels increase its toxicity
Digoxin: Side/Adverse Effects
Cardiovascular
Dysrhythmias, including bradycardia and hypotension
CNS
Headaches, fatigue
Eye
**Colored vision (seeing green, yellow, purple), halo vision, flickering lights (sign of toxicity)
GI
Nausea, vomiting, diarrhea
Digoxin ToxicityAntidote
Digoxin Immune Fab (Digibind) therapy is indicated for:
Hyperkalemia (serum potassium >5 mmol/L) in a digitalis-toxic patient
Life-threatening cardiac dysrhythmias
Life-threatening digoxin or digitoxin overdose which leads to severe bradycardia, hypotension, heart block
Normal lab values 0.5 to 2mmol/l
Phosphodiesterase Inhibitors
Work by inhibiting the enzyme phosphodiesterase (thereby allowing more calcium to the heart muscles)
Results in:
Positive inotropic response (^ contraction)
Vasodilation (positive lusitropic effects)
Decreases work load, better perfusion to heart due to relaxed blood vessels
Two agents
Amrinone and Milrinone
Phosphodiesterase Inhibitors:Indications
Short-term management of heart failure
Given when patient has not responded to treatment with digoxin, diuretics, and/or vasodilators
Often given as weekly 6-hour infusions for:
- Improved quality of life
- Mainly for congestive heart failure
- Decreased readmissions for heart failure episodes
- For end stage heart failure
Phosphodiesterase Inhibitors:Side/Adverse Effects
Amrinone
Thrombocytopenia, most worrisome
Dysrhythmia, nausea, hypotension
Milrinone
Dysrhythmia, mainly ventricular
Hypotension, angina, hypokalemia
Thrombocytopenia
is a condition in which you have a low blood platelet count. Platelets (thrombocytes) are colorless blood cells that help blood clot. Platelets stop bleeding by clumping and forming plugs in blood vessel injuries.
Positive Inotropic Agents:Nursing Implications
Assessment of VS
BP
ALWAYS DO Apical pulse for 1 full minute (especially when pt is on Digoxin)
Hold Digoxin dose if apical pulse is 120BPM
Heart sounds, breath sounds HEAVY BREATHING (COULD BE DEVELOPING LEFT HEART FAILURE
Weight, I&O measures
ECG
Serum labs: potassium (hypokalemia can lead to Digoxin toxicity), sodium, magnesium, calcium, renal and liver function studies
signs/symptoms of toxicity
Anorexia, nausea, vomiting, diarrhea Visual disturbances (blurred vision, seeing green or yellow halos around objects – mainly seen with Digoxin toxicity)
Avoid giving digoxin with high-fiber foods (fiber binds with digitalis)
Decreases absorption
PPL WHO ARE ON DIGITLALIS
ARE AROUND 3RD OR 4TH DEGREE HEART FAILURE
