Fundamentals of Pharmacology for Veterinary Technicians

Chapter 8

Cardiovascular Drugs

Basic Anatomy and Physiology

• The functions of the cardiovascular system include delivery of oxygen, nutrients, and hormones to the various parts of the body

• The cardiovascular system also transports waste products to the appropriate waste removal system

Basic Anatomy and Physiology

Basic Anatomy and Physiology

• The electrical impulses of the heartbeat originate in the sinoatrial node (SA node)

• Heart rate is controlled primarily by the autonomic nervous system:– Stimulation of the parasympathetic

nervous system slows heart rate– Stimulation of the sympathetic nervous

system increases heart rate

Basic Anatomy and Physiology

• Workload of the heart is divided into preload and afterload– Preload: volume of blood entering the right

side of the heart– Afterload: force needed to push blood out of

the ventricles• If the heart is not working properly, it can

compensate by a few mechanisms:– Increase heart rate– Increase stroke volume– Increase efficiency– Enlarge itself

Cardiovascular Drugs

• Types of cardiovascular drugs– Positive inotropic drugs: increase the force of

myocardial contraction– Negative inotropic drugs: decrease the force of

myocardial contraction– Positive chronotropic drugs: increase heart rate by

altering the rate of impulse formation at the SA node– Negative chronotropic drugs: decrease heart rate by

altering the rate of impulse formation at the SA node– Positive dromotropic drugs: increase the conduction of

electrical impulses– Negative dromotropic drugs: decrease the conduction

of electrical impulses

Cardiovascular Drugs

• Positive inotropes– Cardiac glycosides:

• Increase the strength of cardiac contractions, decrease heart rate, have an antiarrhythmic effect, and decrease signs of dyspnea

• Side effects include anorexia, vomiting, diarrhea, and cardiac arrhythmias

• Examples include digoxin and digitoxin– Catecholamines:

• Increase the force and rate of myocardial contraction, constrict peripheral blood vessels, and increase blood glucose levels

• Examples include epinephrine, dopamine, dobutamine, and isoproterenol

Cardiovascular Drugs

• Antiarrhythmic drugs– Used to correct variation in the normal beating

of the heart (which can lead to reduced cardiac output)

– Types of antiarrhythmic drugs include local anesthetics, membrane stabilizers, beta-adrenergic blockers, action potential prolongation drugs, and calcium-channel blockers

– Examples of antiarrhythmic drugs are listed in Table 8-3

Cardiovascular Drugs

• Vasodilators– Drugs used to dilate arteries and/or

veins, which alleviates vessel constriction and improves cardiac output

– Examples include angiotensin-converting enzyme inhibitors, arteriole dilators, venodilators, and combined vasodilators

Cardiovascular Drugs

• Diuretics– Drugs that increase the volume of urine

excreted by the kidneys and thus promote the release of water from the tissues (lowers the fluid volume in tissue)

– Used in the treatment of hypertension– Categories of diuretics include thiazides, loop

diuretics, potassium-sparing diuretics, osmotics, and carbonic anhydrase inhibitors

– Examples are listed in Table 8-4

Cardiovascular Drugs

• Anticoagulants– Inhibit clot formation by inactivating one

or more clotting factors– Used to inhibit clotting in catheters, to

prevent blood samples from clotting, to preserve blood transfusions, and to treat emboli

– Examples include heparin, EDTA, coumarin derivatives, aspirin, and blood transfusion anticoagulants

Cardiovascular Drugs

• Hemostatic drugs– Help promote the clotting of blood– May be parenteral or topical– Parenteral

• Vitamin K1 • Protamine sulfate

– Topical• Silver nitrate, hemostat powder, gelfoam

gelatin sponges, thrombogen topical thrombin solution

Cardiovascular Drugs

• Blood-enhancing drugs– Affect RBCs– Affect the production or quality of RBCs– Examples:

• Iron• Erythropoietin