Chapter 8 Cardiovascular Drugs Copyright © 2011 Delmar, Cengage Learning

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 Copyright © 2011 Delmar, Cengage Learning

Basic Anatomy and Physiology Copyright © 2011 Delmar, Cengage Learning

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 Copyright © 2011 Delmar, Cengage Learning

Basic Anatomy and Physiology Heart rhythm –Contractions at regular intervals –Systole is contraction of heart chambers –Diastole is relaxation of heart chambers –Normal heart beat is called normal sinus rhythm Copyright © 2011 Delmar, Cengage Learning

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 Copyright © 2011 Delmar, Cengage Learning

Basic Anatomy and Physiology There are 3 major types of blood vessels: arteries, veins, and capillaries –An artery is a blood vessel that carries blood away from the heart –Veins are low-pressure collecting system that returns blood to the heart –Capillaries are single-cell-thick vessels that connect the arterial and venous systems Copyright © 2011 Delmar, Cengage Learning

Basic Anatomy and Physiology Blood pressure –Flows from areas of higher pressure to areas of lower pressure –Determined by heart rate, stroke volume, peripheral resistance Copyright © 2011 Delmar, Cengage Learning

Basic Anatomy and Physiology Blood supplies body tissues with oxygen, nutrients, and various chemicals Blood transports waste products to various organs for removal from the body Blood cells also play an important role in the immune and endocrine systems Copyright © 2011 Delmar, Cengage Learning

Cardiovascular Conditions Congestive heart failure is a syndrome that can occur with any disorder that damages or overworks the heart muscle –Conditions that lead to congestive heard failure include: Cardiomyopathy (caused by infections, genetic disorders, or degeneration) Hypertension Valvular disease Copyright © 2011 Delmar, Cengage Learning

Cardiovascular Conditions Cardiac arrhythmias is a disruption in the cardiac rate or rhythm –Arrhythmias interfere with the work of the heart and can disrupt cardiac output –Can be caused by changes in the rate, stimulation from an ectopic focus, or by alterations in conduction of the muscle –These changes can be caused by electrolyte disturbances, decrease in oxygen delivered to the cells, structural damage, accumulation of waste products, and acidosis Copyright © 2011 Delmar, Cengage Learning

Cardiovascular Disease Alterations in blood pressure may result in hypertension (increased blood pressure) or hypotension (decreased blood pressure) –Hypertension results in prolonged force put on the vessels of the vascular system Leads to left ventricle thickening –Hypotension results in the tissues of the body not receiving sufficient amount of oxygenated blood Allows wasted products to accumulate and cells to die from lack of oxygen Copyright © 2011 Delmar, Cengage Learning

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 Copyright © 2011 Delmar, Cengage Learning

Increasing Force 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 Copyright © 2011 Delmar, Cengage Learning

Increasing Force Positive inotropes – Benzimidazole-pyridazinones: Increase the force of contraction Cause widening of the blood vessels Side effects include anorexia, lethargy, diarrhea, and dyspnea Copyright © 2011 Delmar, Cengage Learning

Fixing the Rhythm 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 –For examples of antiarrhythmic drugs refer to Table 8-3 in your textbook Copyright © 2011 Delmar, Cengage Learning

Correcting Constriction 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 Copyright © 2011 Delmar, Cengage Learning

Correcting Constriction Calcium channel blockers are used to treat CHF and hypertension Calcium channel blockers inhibit the movement of calcium through the the myocardial cell membranes and vascular smooth muscle –Decreases the force of cardiac contractions –Side effects include hypotension and anorexia Copyright © 2011 Delmar, Cengage Learning

Losing Fluid 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 –For examples refer to Table 8-4 in your textbook Copyright © 2011 Delmar, Cengage Learning

Clot Stopping 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 Copyright © 2011 Delmar, Cengage Learning

Clot Stopping Clopidogrel bisulfate is an oral platelet aggregation inhibitor –May prevent thrombi in cats –Improves circulation in cats following an embolic event –Side effects are gastrointestinal in nature and include vomiting and anorexia Copyright © 2011 Delmar, Cengage Learning

Bleeding Control Hemostatic drugs –Help promote the clotting of blood –May be parenteral or topical –Parenteral Vitamin K 1 Protamine sulfate –Topical Silver nitrate, hemostat powder, gelfoam gelatin sponges, thrombogen topical thrombin solution Copyright © 2011 Delmar, Cengage Learning

Blood Enhancing Drugs Affect RBCs Affect the production or quality of RBCs Examples: –Iron –Erythropoietin Copyright © 2011 Delmar, Cengage Learning

Blood Enhancing Erythropoietin is a protein made by the kidneys that stimulates the differentiation of bone marrow stem cells to form red blood cells –Used to treat anemia in animals with chronic renal failure –Allergic reactions are sometimes seen with erythropoietin products –Erythropoietin products must be refrigerated Copyright © 2011 Delmar, Cengage Learning

Blood Enhancing Cyanocobalamine is B 12 and is used to treat B 12 deficiencies –Oral forms are not appropriate for small animals Folic acid is a B vitamin needed for normal erythropoiesis –May be seen in dogs, cats, and horses due to small intestinal disease –Very few side effects Copyright © 2011 Delmar, Cengage Learning