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What are the 3 categories of anti-arrhythmic drugs?
sodium influx inhibitors or blockers, beta blockers, calcium channel blockers
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How do sodium influx inhibitor drugs work to prevent arrhythmias?
they slow down the movement of Na+ across cardiac cell membranes, and so slow down the rate of spontaneous depolarization of ectopic foci, a decrease in automaticity. the sinoatrial node can regain control of the heart rate
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Name 4 sodium influx inhibitor drugs
- quinidine
- procainamide
- lidocaine
- mexiletine
- (remember mainly quinidine and lidocaine for testing purposes)
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what is the drug of choice for long term PO therapy of atrial fibillation?
quinidine
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Procainamide is similar to quinidine. What is its advantage over quinidine?
causes fewer GI side effects
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What sodium influx inhibitor is the IV drug of choice for controlling PVC's?
lidocaine
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What are the clinical signs of a slight lidocaine overdosage?
- drowsiness
- ataxia
- depression
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What are the clinical signs of a larger lidocaine overdosage?
- excitement
- muscle tremors
- seizures
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What is lidocaine with epinephrine used for?
local anesthesia - local analgesia
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Why is epinephrine added to lidocaine for local analgesia?
vasoconstrictor - prolongs numbing effect, reduces bleeding, reduces chance of too much lidocaine reaching systemic circulation too fast and causing toxicity
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Should you avoid giving IV lidocaine with epinephrine for heart problems? Why or why not?
yes. we give lidocaine IV for cardiac arrhythmias, and if we gave epinephrine at the same time, it would speed up the heart reate, destabilize the heart, and make the heart even more prone to arrhythmias
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What drug is similar to lidocaine, but can be used PO for long-term maintenance?
mexiletine
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Are beta 1 receptors on the heart sympathetic or parasympathetic receptors? What does stimulation of beta 1 recpetors on the heart cause?
sympathetic. causes the heart to beat faster, to beat with more force of contraction and makes the heart more unstable and more prone to arrhythmias
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Do beta blocker drugs cause sympathetic or parasympathetic effects on the heart? What does blockage of beta receptors on the heart cause?
parasympathetic. causes the heart to beat slower, to beat with less force of contraction, and makes the heart more stable and less prone to arrhythmias
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What is a negative inotropic drug?
a drug that decreases the force of contraction of the heart
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Are beta blocker drugs negative or positive inotropic drugs?
negative inotropic
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What stimulation of beta 2 receptors cause?
bronchodilation, and relaxation of certain other smooth muscle cells, as in blushing
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What does blockage of beta 2 receptors cause?
bronchoconstriction
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Is beta 2 blockage with bronchoconstriction more likely to be helpful or harmful to a patient with heart problems?
harmful
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If we give a heart patient a general beta blocker drug (blocks beta 1 and beta 2) for an arrhythmia, and he gets bronchoconstriction, what type of bronchodilator should we use - a beta agonist such as isoproterenol, or a methylxanthine such as aminophylline?
methylxanthine - does not interfere with beta receptors
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In general, what is better for treatment of cardiac arrhythmias - a general beta blocker or a selective beta 1 blocker?
selective beta 1 blocker
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Name 1 general beta blocker drug
propranolol
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Name 5 selective beta 1 blocker drugs.
- atenolol
- nadolol
- timolol
- metoprolol
- carvediolol
- (remember mainly atenolol for testing purposes)
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Over time, a patient may need a larger dose of a beta 1 blocker drug due to "up-regulation". What is up-regulation?
cardiac cells produce more beta 1 receptors, so it takes more drug to block them
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Once up-regulation with a beta 1 blocker drug has occurred, if the patient must be taken off of the drug, should it be done abruptly or gradually? Why?
gradually - give the cardiac cells a change to eliminate excess beta 1 receptors. if the drug is stopped abruptly, the cardiac cells will be extra sensitive to epinephrine due to their extra beta 1 receptors, and may have extreme tachycardia and severe arrhythmias
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How do calicum channel blocker drugs reduce cardiac arrhythmias?
reduce movement of calcium into cardiac cells, decreasing their ability to contract as fast or as strongly. decrease automaticity
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Name 2 calcium channel blocker drugs
- verapamil
- diltiazem - Cardizem
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What effect does a positive inotropic drug have on the heart?
increases the heart's force of contraction
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Name 2 types of positive inotropic drugs
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Do adrenergic drugs, or catecholamines, give sympathetic or parasympathetic effects in the patient?
sympathetic
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Are adrenergic drugs used for short - term or long - term positive inotropic effects?
short - term
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Name 3 adrenergic drugs.
- epinephrine
- dopamine
- dobutamine
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What is the drug of choice for long-term positive inotropic effects?
digoxin
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What flowering plant is digoxin derived from?
foxglove
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How does digoxin act to increase the strength of cardiac muscle contractions?
makes calcium more available
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Can digoxin therapy cause cardiac arrhythmias?
yes
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What effect does digoxin have on the sinoatrial node?
parasympathetic effect - slows down the heart rate
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What effect does digoxin have on the atroventricular node?
delays conduction - can control ventricular tachycardia due to atrial fibrillation - more effective ventricular contraction
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Is the therapeutic range of digoxin wide or narrow - in other words, is it easy or hard to overdose the patient?
narrow therapeutic range - it is easy to overdose the patient - the therapeutic dose is close to the toxic dose
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If we have to put a pet on digoxin, how important is it to educate the client about the signs of digoxin overdosage?
very important
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What are some early clinical signs of digoxin overdosage?
GI signs - vomiting, diarrhea, anorexia
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If the client detects these early OD signs, what should she do?
stop giving digoxin, call her vet, bring the pet in for evaluation and an EKG. we will probably have to adjust the dose
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What are some EKG signs of more serious digoxin overdosage?
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What drug can we use to treat heart block due to digoxin OD, if it becomes necessary?
atropine
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Does hypokalemia make digoxin toxicity more of less likely? What is the most likely way for a cardiac patient to become hypokalemic?
digoxin toxicity more likely. cardiac patients are more often put on furosemide, which can cause hypokalemia.
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Who tolerates digoxin better - dogs or cats?
dogs
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Digoxin is available as tablets and as an elixir. If your patient was taking a 20mg table BID, could you switch him to 20 mg of digoxin elixir BID?
no
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Does digoxin have a lot of interactions with other drugs? What should you do about this?
yes - look up interactions
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When a diseased heart first starts to pump less effectively, what happens to the patient's blood pressure?
it decreases - hypotension
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If the heart patient's blood pressure drops, what does the brain (autonomic nervous system) do about it?
causes vasoconstriction to bring the blood pressure up. causes the body to retain fluid to bring blood volume up, increasing blood pressure
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Are vasoconstriction and higher blood volume necessarily good for a patient with a weak heart?
no. vasoconstriction makes it harder for the heart to pump blood through blood vessels, and higher blood volume also increases the workload of the heart.
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Which is easiest for the heart to pump blood through - blood vessels with vasoconstrictions or vasodilation?
vasodilation
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What effect on blood pressure does vasoconstriction have?
increases blood pressure
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Does hypertension (increased blood pressure) cause more or less work for a weak heart?
more
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Does vasoconstriction of renal blood vessels cause more or less urine to be formed? Does this cause more or less water to be retained by the body? Does this cause an increased or decreased workload for the heart?
less urine formed. more water retained. increased workload for the heart.
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When vasoconstriction of renal blood vessels occurs, what substance is released?
renin
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Is the release of renin good or bad for the cardiac patient?
bad
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What happens to renin after it is released?
it is metabolized through a couple of stages until one of its products (angiotension I) is formed. this product is acted on by ACE - angiotension converting enzyme - to produce angiotension II.
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What does "ACE" stand for?
angiotension converting enzyme
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Is angiotension II good or bad for the cardiac patient?
bad
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What effect does angiotension have on blood vessels?
causes vasoconstriction - vasoconstriction is already a problem in the heart patient - it does not need to be worse
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Angiotension also stimualtes the release of a hormone. Name the hormone, and briefly describe its effects.
aldosterone - is a mineralocorticoid hormone which causes Na+ resorption and water retention
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What effect does sodium resorption and water retention have on blood volume and the workload of the heart?
increases blood volume, increases the workload of the heart.
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Since vasoconstriction causes all of these problems in a heart patient, it makes sense to treat the patient with drugs that cause vasodilation. Can we "overdo" the vasodilation and cause more problems for the patient?
yes
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List the undesirable side effects of vasodilator drugs.
hypotension - syncope, lethargy, ataxia. tachycardia.
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What is "synocope"?
fainting
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How should we avoid causing the undesirable side effects of vasodilator drugs in a patient?
start with a low dose of vasodilator drug, gradually work up to the desired clinical effect
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How does vasodilation help a weak heart?
less resistance of blood flow, lower blood pressure, less work for the heart.
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List the 3 categories of vasodilator drugs
- direct vascular smooth muscle relaxers
- alpha 1 blocker
- ACE inhibitors
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List 2 direct vascular smooth muscle relaxers. Which one can be applied topically?
- hydralazine
- nitroglycerine
- nitroglycerine can be applied topically
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List an alpha 1 blocker drug
prazosin
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How do ACE-inhibitor drugs act?
block ACE - angiotension converting enzyme. this prevents the formation of angiotension 2 (a potent vasoconstrictor) and the release of aldosterone (which cause sodium and water retention - increased blood volume - increased workload for the heart).
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List 4 ACE-inhibitor drugs.
- captopril - Capoten
- enalapril - Enacard
- benazepril
- lisinopril
- (remember captopril and enalapril for testing purposes)
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What is a diuretic?
a drug that increases urinen formation, promotes water loss
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How do diuretics help a patient with a weak heart?
decrease excess body fluid, decrease blood volume, reduce pulmonary edema, reduce ascites, reduces workload of the heart.
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How do diuretics work?
cause Na+ or K+ to be secreted into renal tubules, or prevent their resorption - then the Na+ or K+ is lost in the urine, and pulls water out by osmosis
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How do loop diuretics work?
inhibit Na+ resorption from the lood of Henle, then K+ is exchanged for Na+ in the distal convoluted tubule. K+ is lost from the body, Na+ is not lost.
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Can loop diuretics cause hypokalemia?
yes
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Can loop diuretics cause ototoxicity?
yes
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List 3 diuretic drugs.
- furosemide - Lasix
- chlorthiazide
- spironolactone
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What is the most commonly used diuretic in veterinary medicine?
furosemide - Lasix
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Is furosemide a loop diuretic?
yes
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Can furosemide cause hypokalemia?
yes
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Hypokalemia can cause increased toxicity of which cardiac drug?
digoxin
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Which diruetic is "potassium-sparing"?
spironolactone
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How can aspirin be useful in cardiac therapy?
reduces blood clot formation, possiblity of vessel occlusion
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How can bronchodilators be useful in cardiac therapy?
improve oxygenation of blood, increase lung perfusion, more oxygen dilates pulmonary blood vessels leading to easier pulmonary blood flow with less resistance, less work for heart
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Name 2 methylxanthine bronchodilators used in cardiac therapy.
- aminophylline
- theophylline
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How can sedatives and tranquilizers be useful in cardiac therapy?
calm down an anxious patient, decrease oxygen demand, decrease release of epinephrine (fight or flight sympathetic reaction).
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Name 2 types of sedative and tranquilizers appropriate for use in cardiac therapy
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