March 2013 A publication of the Center for Equine Health • School of Veterinary Medicine • University of California, Davis The Equine Heart: Power Plant Unequaled!

This Horse Report was made possible by the invaluable contributions of the following veterinary faculty: Dr. Bill Thomas, Dr. Gary Magdesian, Dr. Gregory Ferraro, Dr. Claudia Sonder, Dr. Mary Beth Whitcomb, Dr. Tania Kozikowski-Nicholas, and Dr. Monica Aleman.

or as long as horses have been bred, raised and used by humans, Ftheir owners and caretakers have praised their "heart". This reputation for quality or quantity of "heart" is obviously based on a horse's psychological rather than anatomical characteristics: stoicism, bravery, dedication and nobility of character. In fact, these attributes of character also reflect the typically robust nature of the horse's anatomical heart and cardiovascular system as well.

A horse’s heart supplies blood to all parts of one of the largest domesticated land mammals (1,000 pounds or more), not only at rest and during routine activities, but also during periods of extreme physical stress such as encountered during performing, racing and the training required for those activities. It is a power plant unequaled in any other creature! That it is able to do so attests to the system’s remarkable efficiency and The left heart collects blood returning adaptability. from the lungs via the pulmonary and pumps it to the body via the aorta. INSIDE THIS ISSUE … The cardiovascular system of a horse The right heart collects blood returning The Equine Heart: Power Plant consists of a pump (the heart), a from the body via the large veins and Unequaled!...... 1 distribution system (), exchange directs it to the lungs via the pulmonary Director’s Message ...... 2 areas (capillary beds), and a collection . The output of each ventricle in an and return system (veins). The heart of adult horse at rest is about 25 to 40 liters/ Message from Dr. Gregory Ferraro ....3 a 1,000-pound adult horse is about the minute (approximately 7 to 10 gallons), Baby Kaya Gets a Pacemaker...... 10 size of a large melon and weighs about compared with 4 to 5 liters/minute in an The Art of Listening to Your 10 pounds. As in all mammals, it consists average adult human (1 liter ≈ 1.05 quart). Horse’s Heart ...... 11 of the left and right atrial receiving Cash: The Little Horse with a chambers, left and right atrioventricular This Horse Report describes some Big Hole in His Heart...... 13 inflow valves, left and right pumping conditions most often encountered by Cardiology Service at the VMTH .... 14 ventricles, and aortic and pulmonic One More Word About semilunar outflow valves, plus attached —Continued on page 4 Miniature Horses...... 14 inflow veins and outflow arteries (see Oleander Poisoning: The photos on page 4). Preventable Illness...... 15 2 - The Horse Report

who needed to move quickly to stay Veterinarians will often recommend a DIRECTOR’S MESSAGE alive. Horses have incredible cardiac second exam 4 to 6 months after the reserve. They can contract their spleens original cardiac ultrasound to evaluate in moments of excitement and nearly the heart muscle’s response to altered double their oxygen carrying capacity. flow and establish prognosis for Their heart rates can jump from 30 beats athleticism. Occasionally, foals are per minute (bpm) at rest to 240 bpm in born with congenital heart defects maximal exercise. On top of that, heart including holes in the wall that disease is relatively rare in horses. divides the left and right ventricles or pumping chambers. These are Examination of the cardiovascular known as a ventricular septal defect system of the horse has come a and the size and location of the defect long way, and yet the art of cardiac determines the long-term prognosis , or listening to the of these horses. heart carefully with a stethoscope, remains the mainstay of detection of Advancements in technology have . In the 1800s, allowed us to fit Holter monitors Dr. Claudia Sonder it was a veterinary scientist that first to horses to observe the electrical described the and activity of the heart under different In the steady gaze of the horse shines a their source within the equine heart, degrees of exercise. We have silent eloquence that speaks of love and and this work was extrapolated to improved ability to diagnose loyalty, strength and courage. It is the human medicine. The detection of arrhythmias and track normal cardiac window that reveals to us how willing abnormal heart sounds or rhythms, responses to extremes of exercise. his spirit, how generous his heart. especially in performance horses, is Endurance and three-day event often a cause for concern and raises riders use heart rate monitors to s a veterinarian, and the daughter questions about future athletic direct fitness training and monitor Aof a man who lived with heart potential and performance. Many a physiologic stress in competitions. disease, I have long been fascinated pre-purchase exam has come to a halt We now have the capability to look with the resilience and simplicity upon the identification of a murmur. at cardiac enzymes such as troponin of the four chambered heart. Most As cardiac ultrasound has become in horses to detect evidence of heart of us take it for granted that this marvelous biological pump within us Despite all of our advanced testing and diagnostic capabil- functions for years on end without ities in veterinary medicine, heart rate continues to be one of our conscious input or control. What manufactured device can the best prognostic indicators associated with diseases such exist under pressure and perform as colic in the horse. at variable speeds for eighty to one hundred years without a tune more advanced and accessible, we muscle injury. Human pacemakers up? We attribute many qualities to now know that there are physiologic have been installed in horses with our hearts and we do the same to murmurs that can be quite loud arrhythmias and the prospect of animals. The words heart and horse and that are not associated with biological pacemakers introduced go together. Throughout history, underlying heart disease or pathology. through gene therapy has been horses have been praised for their These murmurs often dissipate with investigated in dogs. Thankfully, the hearts- in terms of valor, loyalty, exercise. We know that there are flow incidence of heart disease continues and strength. I have known horses murmurs that occur under physiologic to be lower in horses than in other with incredible work ethics that are stress that are transient and of little species and is not associated with devoted and committed despite consequence to athleticism. Cardiac obesity as it is in humans. Because physical limitations and I described ultrasound can reveal the source of of their size and their poor tolerance these animals as having a great deal a pathologic murmur, whether it be of thoracic surgery, open-heart of heart. The truth is that horses need a leaky valve or area of blood vessel surgery and treatment with advanced good hearts. Greater than 50% of constriction leading to or from the pharmacology is still not on the their body mass is skeletal muscle heart. immediate horizon. Sadly, horses and they evolved as prey animals with congestive heart failure pose a www.vetmed.ucdavis.edu/ceh March 2013 - 3 safety issue for those around them and options for treatment are limited. MESSAGE FROM DR. GREGORY FERRARO Early detection and management of cardiac disease carries with it the best chances for long term survival, which Therefore, with Dean Lairmore’s for the average horse is 630,720,000 endorsement, Dr. Sonder has taken heart beats in a lifetime. the reins of the CEH directorship effective January 15, 2013, while This Horse Report reviews the anatomy the formal recruitment process is and functionality of the equine heart and completed. This is a change that I discusses several of the most common welcomed and facilitated because equine heart problems. The videos I sincerely believe it is in the best contained in the electronic Horse Report interests of the CEH, the School of (Zmag) will guide the horse owner and Veterinary Medicine and the horse serve as a reference tool for veterinarians enthusiasts we serve. I ask that you as to the normal sounds of the equine welcome Dr. Sonder to her new heart and the process of auscultation. position and provide her with the The Cardiology Service at UC Davis works same enthusiastic support that you closely with the Large Animal Ultrasound have given to me during my tenure. I department to identify underlying Dr. Gregory Ferraro am certain that with your help she can heart disease and offer guidance and take the Center to new heights. treatment options for horses with ate last year while thinking about abnormalities detected in the field. Lhow far the Center for Equine As for me, I’m not going anywhere. I Health has advanced during my tenure will continue my participation in the We encourage horse owners to buy and where it needed to go in the CEH as a senior advisor for as long a stethoscope and practice listening future, it suddenly dawned on me that as needed to effect a smooth and to your horse’s heart. Despite all of at the end of 2012, I would have been productive leadership transition. I am our advanced testing and diagnostic its Director for 15 years. As rewarding also currently serving the School of capabilities in veterinary medicine, and satisfying as my job has been, 15 Veterinary Medicine as the Associate heart rate continues to be one years is a sufficient tenure for political Director of its Large Animal Clinic and of the best prognostic indicators office holders, Deans, Chancellors will be participating in any other areas associated with diseases such as colic and Center Directors. At that point I of administration that Dean Lairmore in the horse. Having the ability to realized that a change in leadership may assign. This institution has been communicate accurate heart rate to at the CEH was necessary and that a good to me and I am committed to your veterinarian in an emergency planned transition in that leadership participating in its success for as long situation can make the difference was the proper course of action. as I remain a productive member of between life and death. ❄ the team. Consequently, a formal recruitment process seeking an individual who Finally, I want to thank each and every could lead the CEH well into the future one of you, both University personnel and the public I have tried to serve, was begun. One of our applicants who have helped and supported me was Dr. Claudia Sonder, a graduate in my role as CEH Director. You all are of the UC Davis School of Veterinary responsible for any successes I may Medicine, a well-respected sport have achieved. I will always cherish horse veterinarian, and an individual my relationship with you and hope to with strong leadership qualities and continue serving you all in a different intellectual capacity. Dr. Sonder was capacity. Together our future looks initially hired as my Assistant Director bright and I am excited to explore and has been working with me and new possibilities for personal and the CEH staff for the past 12 months. institutional growth. During that period, she has excelled at every task assigned to her and has Sincerely, developed an intimate knowledge of Gregory L. Ferraro, DVM the needs and operations of the CEH.

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The Equine Heart — From page 1 The Equine Heart equine cardiologists, including some common congenital defects, some causes of heart problems, and the diagnostic methods that are currently used. In general, however, horses have excellent cardiac health.

Cardiac Disorders

Horses generally do not have the same types of cardiac problems experienced by humans, such as coronary heart disease (atherosclerosis) and heart attacks. But because most horses are not kept as companion pets and are expected to perform work or athletic feats with Photo on the left shows the outside of a horse’s heart. Photo on the right shows the inside a rider, the consequence of any kind of the left heart. Ao = aorta, PA = pulmonary artery, LA = left atrium, LV = left ventricle, RV = of cardiovascular disease in a horse right ventricle, VM = mitral valve, AoV = aortic valve. may be greater than it might be in a dog or a cat. In addition to the reveal an abnormality in the audible Most heart murmurs are caused by potential effect of a cardiac problem heart sounds or in the heart rate blood flow that becomes turbulent on performance, the safety of the and rhythm. When an abnormality because of increased velocity due to rider must also be considered in is suspected, further evaluations a leak or obstruction in one of the determining the future of the horse. by electrocardiogram (EKG) and heart valves or because of abnormal echocardiogram (ultrasound imaging) communication between different The main observable signs of a heart may be performed to more precisely parts of the heart (like the increased problem in horses include: identify the nature and severity of the velocity and spraying sound you get abnormality. Chest radiographs may when you put your thumb across  Loss of condition also be used to help determine heart the end of the hose). However,  Increased fatigue during exertion size and abnormalities in the lungs there are some soft, short, variable  Shortness of breath and chest cavity, but these are often heart murmurs that may be heard  Increased rate or effort of breathing difficult to obtain with conventional with no other detectable evidence  Weakness occasionally resulting in equipment in adult horses because of of heart disease. Such murmurs are collapse or fainting their large body size. referred to as normal or “innocent”.  Signs of fluid accumulation in the If there is uncertainty about the abdomen or beneath the skin of Heart Murmurs origin or significance of any heart the lower thorax murmur, further evaluation is usually During an examination of a horse’s performed by echocardiography, Depending on the severity of the chest and heart with a stethoscope, which provides detailed images of problem, these signs may initially a veterinarian may detect an the inside of the heart and can detect appear only when the horse is abnormality by the sound of a abnormal blood flow patterns. subjected to moderate or strenuous , which is the sound exercise. With a severe cardiac of turbulent blood flow usually Heart murmurs are graded on a scale disorder, these signs may appear caused by an abrupt increase in the of Grades 1 to 6, as follows: during normal, nonstrenuous velocity of blood flow. When blood activities or even at rest. moves smoothly through the heart Grade 1 – Very soft murmur that and blood vessels, very little sound requires extended auscultation to A physical examination in a horse is produced (like water flowing detect. with cardiac disease will usually smoothly through a hose). www.vetmed.ucdavis.edu/ceh March 2013 - 5

Grade 2 – Readily audible murmur with a stethoscope, a cardiologist vessel in the fetus that connects the that is softer than S1 or S2. will be able to assess the heart pulmonary artery with the aorta, via echocardiography (cardiac bypassing the lungs—closes more Grade 3 – Readily audible murmur ultrasound). Blood flow through the slowly after birth in horses than in that is moderately loud and similar in heart can be analyzed through color humans and dogs, so that a soft, volume to S1 and S2. flow echocardiography, pinpointing continuous murmur can be heard in the cause or causes of the murmur. newborn foals up to about a week Grade 4 – Readily audible murmur Additionally, the whole heart can be of age. Horse owners should not that radiates widely and is louder than scanned to assess chamber size and panic if their veterinarian pronounces S1 or S2. contractility. that their newborn foal has a heart murmur, although a follow-up exam Grade 5 – Very loud murmur with Congenital Heart Defects should be conducted to make sure a palpable thrill (vibration) that is the murmur disappears. detectable with fingertip pressure Congenital heart defects are over the heart. abnormalities that are present Ventricular Septal Defect (VSD). at birth. They occur much more Ventricular septal defect consists of Grade 6 – Very loud murmur commonly in humans and dogs than a hole in the muscular wall between associated with a palpable thrill that is in horses. These abnormalities are the two ventricles and is the most audible with the stethoscope held just often discovered within the first few commonly recognized congenital off the chest. weeks to months of life when a heart heart defect in horses. It also occurs as murmur is heard during stethoscopic one part of more complex defects. Heart murmurs are further classified examination of the chest and heart. by when in the cardiac cycle they occur—during ventricular filling Although rare, congenital heart (diastole, after S2 and before S1) defects can prevent the development or during ventricular contraction of an athletic career and in some (, between S1 and S2). Finally, cases can be life-threatening. For they are described by their length and this reason, every newborn foal musical qualities. should receive a thorough cardiac examination. The majority of heart murmurs heard in the horse are physiologic or A wide variety of simple or complex benign. These murmurs can increase congenital heart defects may occur, in intensity with submaximal exercise but only a few have been recognized and can also be heard with high often enough to be reported in Ventricular vagal tone or when the horse is in an more than a few individual horses. septal defect excited state. One classic example of The most accurate technique for this is colic. Often during a painful identifying specific defects and colic episode a murmur can be heard evaluating their severity is two- In simple cases, the hole results in the with a stethoscope that has not been dimensional echocardiography passage of oxygen-rich blood from heard before and that will resolve (ultrasound imaging) supplemented the higher pressure left ventricle to when the colic resolves. by Doppler echocardiography the lower pressure right ventricle and (imaging of blood flow within the pulmonary artery, primarily during It is important to know which heart heart and associated blood vessels). ventricular systole. Because some of murmurs merit further diagnostics this blood bypasses the lungs, it is and which heart murmurs can be The most commonly reported not fully oxygenated. A systolic heart considered incidental. In general, congenital heart defect in horses is murmur is usually heard on the right heart murmurs should be assessed ventricular septal defect, described side of the chest over the cranial part of by a specialist, especially when below. Another defect, patent the heart. accompanied by other signs of ductus arteriosus, which is common cardiac dysfunction or illness. In in humans and dogs, is relatively rare — Continued on page 6 addition to listening to the murmur in horses beyond 1 to 2 weeks of age. The ductus arteriosus—a large blood

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The Equine Heart — From page 5

Depending on the size of the hole and the amount of blood passing through it, the pulmonary arteries and veins and the left atrium and ventricle are subjected to an increased workload because of this extra volume of blood. If the hole and the resulting shunt are small, the adverse effect on cardiac function may be minimal, and the horse may be fully capable of engaging safely in moderate physical activities without evidence of fatigue or shortness of breath. If the hole is larger and the shunt is greater, there may be signs of cardiac insufficiency with minimal exertion, and the horse may be very limited Ventricular septal defect (VSD). Photo on left (A) shows a small VSD in the upper ventricular in its athletic ability. The nature of septum just below the aortic valve (arrow). Photo top right (B) shows an echocardiogram the defect can usually be confirmed withe the VSD opening between the left ventricle and aorta (arrow). Photo bottom right (C) using two-dimensional and Doppler shows the same view but with multicolored, disorganized turbulent flow through the VSD echocardiography. into the right ventricle during ventricular systole. RA = right atrium, RV = right ventricle, LV = left ventricle, Ao = aorta. Patent Ductus Arteriosus (PDA). The ductus arteriosus is Closure of the ductus usually occurs origin of the aorta, and right a large blood vessel connecting within the first week of life, and the ventricular hypertrophy/thickening) the fetal pulmonary artery to the murmur disappears. If the ductus or truncus arteriosus (consisting descending aorta, allowing blood remains open beyond the first week, of a ventricular septal defect and a from the right ventricle to bypass the it is called a persistent or patent single large arterial trunk exiting both nonfunctioning lungs and be directed ductus arteriosus. The resulting ventricles). toward the abdomen and placenta. shunt may cause blood volume In all mammals, the ductus constricts overload in the pulmonary arteries In the most severe cases, there may at or shortly after birth, eliminating and veins and the left atrium and be shunting of oxygen-poor, darker this fetal connection and allowing for ventricle. Although slight patency (an venous blood from the right heart the normal development of the blood open state) in the first week is very chambers to the left heart, bypassing vessels in the lungs. common in foals, patency beyond the the lungs and causing cyanosis first week is rare. (a bluish color to the membranes Unlike most other domestic animal of the mouth and eyes) at rest or species, persistent slight opening Complex Defects. Congenital heart during exertion. These defects can of the ductus arteriosus is quite defects are uncommon in horses, be diagnosed accurately only by common in newborn foals. Because but when they occur, multiple or X-ray angiography or, more recently, the pressure in the aorta is higher complex defects appear to be more two-dimensional and Doppler than that in the pulmonary artery common than in other species such echocardiography. throughout the cardiac cycle, blood as dogs and cats. These may occur flows through the ductus from the as combinations of embryologically Heart surgery is rarely performed in aorta to the pulmonary artery, and a unrelated defects, or as recognized horses. Congenital heart defects can “continuous” murmur can be heard combinations such as tetralogy of now be accurately diagnosed using over the pulmonary artery on the left Fallot (consisting of a ventricular sophisticated ultrasound imaging, but side of the chest. septal defect, pulmonic stenosis, treatment options are very limited for rightward malpositioning of the the types of defects horses tend to get. www.vetmed.ucdavis.edu/ceh March 2013 - 7

Acquired Heart Disease electrocardiogram, shown below. dilation, horses most often develop The normal resting heart rhythm of this arrhythmia with minimal or Generally speaking, acquired heart horses is usually slow (28 to 48 beats no detectable additional signs of disease is relatively uncommon in per minute) and regular (called sinus heart disease. Draft breeds are horses, although it is encountered rhythm). Many horses also have short more commonly affected. In such slightly more frequently than pauses in their resting heart rhythm cases, signs of cardiac insufficiency congenital heart defects. It occurs caused by “dropped beats” (called are usually not recognized at rest or most often in horses older than second degree AV block). These with mild to moderate exertion, but 5 years and only occasionally in are considered to be normal if they become apparent at more strenuous younger horses. Degenerative disappear during exercise. levels of exercise. changes affecting the heart valves, myocardium and lungs are associated Atrial Fibrillation. Atrial fibrillation Accurate diagnosis of arrhythmias with aging, increasing in frequency is an electrical disorder of the requires evaluation of an electro- with age. heart rhythm—also known as an cardiogram, where the lack of normal arrhythmia. There are different atrial waves and the very irregular The most commonly diagnosed kinds of arrhythmias, but the most ventricular waves can be readily conditions are heart rhythm commonly recognized one associated identified. Further evaluation of the irregularities and leaks in one or more with diminished athletic performance structure and mechanical function of heart valves. The most common signs or more serious signs of cardiac the heart by echocardiography is also associated with heart disease include insufficiency is atrial fibrillation. With recommended, because the prognosis a reduction in exercise capacity this arrhythmia, the normally regular, for treatment, recovery and return (exertional fatigue), shortness of organized atrial electrical waves to previous activity levels is directly breath especially following exertion, become irregular, disorganized and related to the presence or absence or the detection of a heart murmur, chaotic, and the atria fail to contract of underlying mechanical cardiac irregular heart beat, or other audible normally. This results in a very dysfunction. abnormality in a horse without other unpredictable, irregular heartbeat. signs of illness. If there is little or no evidence of Although atrial fibrillation often underlying cardiac dysfunction, Identification of the electrical rhythm develops in horses with advanced of the heart requires recording of an and atrial — Continued on page 8

Normal sinus rhythm

Second degree AV block

Atrial fibrillation

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The Equine Heart If serious cardiac disease with atrial leading to the affected side of the — From page 7 dilation is present, the prognosis heart increases to the point where for functional recovery is poor and fluid accumulation (edema) occurs. administration of oral or injectable conversion of the arrhythmia is usually drugs, especially quinidine, is unsuccessful or temporary. Treatment Valvular disease is initially diagnosed often successful at converting the of the signs of cardiac insufficiency by the detection of a heart murmur arrhythmia to a normal rhythm. Most with drugs such as digitalis and during a physical examination. It of these horses are able to return diuretics may be considered in is very important, however, to to their previous levels of activity selected cases where little physical understand that soft, “innocent” and performance, although some activity is expected. murmurs are often heard in normal experience one or more recurrences foals and adult horses. In order to of the arrhythmia, necessitating Valvular Heart Disease. The most advise an owner or rider about the retreatment or retirement from commonly recognized acquired significance of any heart murmur, strenuous activity. Quinidine can structural heart disorders in horses it is critical to distinguish between become toxic to horses at higher are degenerative valvular deformities. a normal murmur and a pathologic dosages and occasionally treatment The process causes thickening and murmur of valvular regurgitation, and must be suspended before conversion deformity of valve leaflets. These to assess the severity of any suspected of the rhythm can occur. A newer, defects result in incompetence and valve leaks. Two-dimensional catheter option for cardioconversion insufficiency of one or more heart and Doppler echocardiography exists for cases that do not respond valves, associated heart murmurs, and are the most accurate and least to quinidine treatment. This option dilation of the chambers that must invasive methods to help make such requires general anesthesia and handle the extra regurgitated blood determinations. specialized equipment and is still in on either side of the incompetent the developmental stages. valve. If the valve leak is severe In general, mild to moderate valvular enough, the pressure in the veins insufficiency in a horse without www.vetmed.ucdavis.edu/ceh March 2013 - 9 reported signs of illness is compatible thrombophlebitis can occur in other disease. Some heart muscle disorders with continued use for mild to large veins in the horse. have clearly been shown to have moderate physical activity. More a major genetic component, and severe valvular disease, especially Several conditions may affect the familial or breed tendencies in when it is accompanied by obvious systemic arteries in horses. The some conditions strongly suggest signs of cardiac insufficiency, atrial most common condition is parasitic that genetics play a role in these fibrillation, or severe enlargement of arteritis (inflammation of the walls conditions. the heart, is cause for a poor prognosis of the arteries) due to the vascular and a strong recommendation against migration of the larval forms of the Unlike in humans, diet and exercise any riding or forced physical activity. intestinal parasite Strongylus vulgaris. have not been shown to be factors in The resulting dilation and thrombosis heart disease in horses, since horses Myocardial Disease. Myocarditis (and potential obstruction) usually almost never develop atherosclerotic is occasionally suspected in a horse occur at the origin of the large arteries leading to stroke or that develops an arrhythmia or to the intestines, although other heart attack. Almost all heart diseases other electrical disorder following an arteries may be affected. Fortunately, except the congenital defects tend infectious disease such as strangles, this condition can usually be treated to increase with age in horses, just as influenza or an internal abscess. Toxic or prevented by an appropriate they do in humans, dogs and cats. damage to the heart muscle may antiparasitic drug treatment program. also rarely occur as a result of severe The incidence of this problem There are no known preventive dietary deficiency of vitamin E and declined significantly with the strategies to reduce the likelihood selenium, or as a result of ingesting introduction of ivermectin dewormer of heart disease in horses. However, the chemical monensin (usually from in the 1980s. owners of all animals should avoid cattle feed). inbreeding, which may increase the The other most commonly recognized risk of congenital heart defects. We Vascular Disease. Horses are known arterial disorder is called aorto-iliac strongly urge owners not to breed to develop several types of disorders thrombosis. In this condition, a any animals with known congenital that affect primarily their blood clot develops at the point where the defects of any kind, including heart vessels. However, atherosclerosis— abdominal aorta branches toward the defects. It is probably wise to also vascular disease associated with high hind legs. The resulting restriction avoid breeding horses that have blood pressure, high cholesterol and of blood flow to the hind limbs can developed an acquired heart disorder fats in humans—is exceptionally rare cause signs of lameness, stiffness, relatively early in life, as this may in domestic animals, including horses. weakness and abnormal gait that indicate an increased susceptibility for Therefore, the consequences of this develops during exercise and usually that condition in offspring. ❄ condition in humans, including heart disappears at rest. Unfortunately, this attack, stroke and other peripheral condition is often progressive and arterial disease, are also rare in horses. rarely reversible, markedly limiting the athletic uses of an affected horse. The only common condition Finally, degenerative changes in the affecting the veins of horses is wall of large arteries may weaken thrombophlebitis of the jugular a vessel and predispose to rupture (s) caused by repeated jugular and bleeding. The most commonly vein puncture, injection of material reported sites of such rupture are the outside the vein, or use of a jugular root of the aorta in stallions and the vein catheter. The resulting chemical uterine artery in mares. or physical irritation or infection in or around the vein causes inflammation, Summary swelling and tenderness, followed by formation of a firm clot in a small The causes of heart disease in horses portion or long segment of the vein. are often multiple and difficult to Treatment involves removing the determine in individual cases. There cause and applying symptomatic is increasing evidence that genetic treatment for discomfort and any background may play a major role in associated infection. Note that a horse’s susceptibility to developing

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Baby Kaya Gets a Pacemaker A Case Study from the William R. Pritchard Veterinary Medical Teaching Hospital

aya, a three-week-old which is a failure of the Kminiature donkey, presented inherent pace-keeping to her local veterinarian mechanism of the heart. because of episodes of The ultrasound showed fainting. The veterinarian that the mitral, tricuspid performed a complete physical and aortic valves were examination and heard dropped slightly leaky but that beats that he believed were the overall structure associated with the fainting. and size of the heart Additionally, he heard a were normal. Routine systolic heart murmur. After an lab work ruled out electrocardiogram confirmed infection or electrolyte an abnormal heart rhythm, the disturbances as the veterinarian referred Kaya to the underlying causes of the William R. Pritchard Veterinary arrhythmia. Medical Teaching Hospital at UC Davis. Given these findings, it was suspected Here, Kaya was seen by both the that Kaya’s third- Large Animal Internal Medicine degree AV block Service and the Cardiology might be congenital Service. They learned that not (present at birth as a only was Kaya experiencing result of hereditary fainting episodes, she was also or environmental an unusually quiet donkey baby. influences). Baby Kaya She never bucked or played like a normal baby. To treat the arrhythmia, Kaya was placed under general pacemaker placement would When UC Davis veterinarians anesthesia and a pacemaker was never be used to administer listened to her heart with a installed. The evidence of the intravenous medications or to stethoscope, both her abnormal pacemaker’s success was seen draw blood. heart rhythm and the heart immediately, as Kaya bucked for murmurs described by Kaya’s the first time that evening! The first of these considerations veterinarian were confirmed. proved to be true, as six months To understand the causes of There were some important after her initial pacemaker was these abnormal findings, both considerations for Kaya’s health placed, Kaya needed to return for an electrocardiogram (ECG) and regarding the placement of the a second, larger pacemaker to be an echocardiogram (cardiac pacemaker. First, given Kaya’s placed. Her second pacemaker ultrasound) were performed. age, it was likely that she would surgery was uneventful and Kaya is outgrow her pacemaker and a happy donkey again! ❄ The ECG showed an abnormal a second surgery would be rhythm (arrhythmia) consistent required. Second, it was critical with third-degree AV block, that the jugular vein used for the

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The Art of Listening to Your Horse’s Heart

uscultation is the action of listening to sounds the triceps muscle (requires pushing under the muscle), from the heart, lungs, or other organs, typically locate the loudest point of the heartbeat in order to get Awith a stethoscope. In human medicine, cardiac a reliable and consistent heart rate. Each lub-dub equals auscultation, long considered the centerpiece of the one heartbeat. Horses have a slow heart rate and a typical cardiac clinical examination, is becoming a lost art. Some novice mistake is to double count. Note that the heartbeat physicians believe that the availability of high-tech of a human is 60 to 80 beats per minute, almost twice as diagnostic and therapeutic methods, both more elaborate fast as that of a horse. and more expensive, has replaced auscultation to a large degree. They also believe that there is no substitute for To simplify the process of determining your horse’s resting cardiac auscultation and that, when used properly, the heart rate, listen to his heartbeat for 15 seconds and then simple stethoscope remains a valuable and cost-effective multiply that number by four to arrive at bpm. In Part 2 tool that allows physicians to make a rapid and accurate of the video contained in the Zmag edition, Peppy’s heart cardiac diagnosis. rate for 15 seconds was 10 beats, so her resting heart rate was 40 bpm. Listening to your horse’s heartbeat is also valuable for horse owners. It is another way of learning about your Increased horse’s health status and to know what is normal for heart rates your horse. Stethoscopes come in a range of prices and can be heard quality and can be purchased in many places, including in many online. The average horse owner can do very well with conditions an inexpensive one. An inexpensive stethoscope will including allow you to hear the classical “lub-dub” of the heart but colic, laminitis, will probably not allow you to hear more subtle sounds. late-term Owners of draft horses or very well-conditioned horses , may need to spend a little more on a higher quality and illness. stethoscope because the heartbeat is more difficult to During an detect in these animals with larger muscle mass. emergency, the heart The normal resting heartbeat of a horse is between 28 and rate of your 48 beats per minute (bpm). Every individual horse has its horse can be a own “normal,” so you should become familiar with what is valuable piece normal for your horse. The basic heart sounds (known as of information S1 and S2) sound like a lub-dub. This is considered ONE for your BEAT. Two additional sounds (known as S3 and S4) may veterinarian. or may not be heard as they are usually much softer in If your colicky intensity. A normal heartbeat could sound like lub-dub or horse has a it could include the two additional softer sounds to form heart rate of 36 bpm and pink mucous membranes, it is a sound like pa-lub-dub-uh. In any case, this would be likely that it is safe for your veterinarian to quickly finish the considered one beat. call they are on. If, however, your horse has a heart rate of 80 bpm and muddy mucous membranes, your veterinarian The horse’s heart is best heard on the LEFT side behind may want to head to out to see him immediately. A the elbow and below the triceps muscle. Before applying persistently increased heart rate can be a sign of cardiac the stethoscope, use the palm of your hand to feel for disease. the horse’s heartbeat (see video contained in the Zmag edition of this Horse Report, accessed via our website, www. Happy auscultating! ucdavis.edu/ceh). With the stethoscope head placed under

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www.vetmed.ucdavis.edu/ceh March 2013 - 13 Cash: The Little Horse with a Big Hole in His Heart

Thanks to Dr. Mary Beth Whitcomb of the UC Davis School of Veterinary Medicine for this story and the accompanying ultrasound images of Cash’s heart murmur.

mong the permanent residents of Athe Center for Equine Health is a little horse named Cash who was born with a ventricular septal defect, or a hole in his heart. He has been living here since he was 2 years old and is now a thriving 14-year-old. For the past 12 years, Cash has been perform- ing a valuable service for the UC Davis School of Veterinary Medicine by be- ing a model for veterinary students.

A ventricular septal defect means that Cash has an opening between the right and left ventricles of his heart, which causes blood to flow from the left to the right ventricle when the heart contracts (see illustration). Simi- Cash, pictured here with CEH Director Dr. Claudia Sonder, has lived at the Center for Equine lar to other species, VSDs are the most Health for 12 years. common congenital heart defect in horses. It is not known whether with a VSD larger than that often live Since 2001, Cash has helped teach these types of congenital defects are a shorter life but may not show any the art of cardiac auscultation (listen- hereditary. symptoms until later in life. While ing to the heart with a stethoscope) Cash did have exercise intolerance and echocardiography (cardiac While the condition may sound when put into training as a 2-year-old, ultrasound) to over 250 veterinary severe, it is important to realize that he is otherwise healthy and shows students. The students learn to hear many horses can live full lives with a no outward symptoms in his less and characterize the heart murmur normal or near-normal life expectancy demanding career as a TA (teaching and then see the structural changes as long as the hole is smaller than 2.5 assistant) at the Center for Equine that produce it. Cash also has helped cm (about 1 inch) in diameter. Horses Health. many residents in internal medicine to refine their skills in cardiac ultrasound so that more veterinarians will be skilled and familiar with this important condi- tion.

Cash always has a great demeanor, is very coop- erative, and knows his job. During ultrasound exams, he will stand with his right leg forward to ease place- ment of the probe as long These are ultrasound images of Cash’s heart. The left image shows his defect (VSD, shown by arrow) in as it takes for someone to the muscle between the left ventricle (LV) and right ventricle (RV). The defect, known as ventricular septal get an image. He is well defect or VSD, allows blood to flow through it from the left to right ventricle when the heart contracts. The right image represents the same view, but now the aortic valve (Ao) is open. This allows us to better liked by everyone. ❄ measure the size of Cash’s VSD (4.51 cm).

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Cardiology Service at the William R. Pritchard Veterinary Medical Teaching Hospital (VMTH)

The Cardiology Service at UC Davis has board-certified veteri- nary cardiologists, residents-in-training and a highly skilled technical staff dedicated to providing compassionate care to animals with known or suspected heart disease. Faculty on the Service include Dr. Leigh Griffiths, Service Chief, and Dr. Joshua Stern.

Many patients are dogs and cats, but the Service regularly examines horses and other species. Common reasons for seeking the exper- tise of a cardiologist include heart murmur, irregular heart beat, respiratory (breathing) problems, exercise intolerance, and weakness or fainting. Routine evaluations include the history and review of prior records, physical examination, an electrocardiogram, and an echocardiogram (cardiac ultrasound).

Appointments for horses may be made by calling the Large Animal Clinic at (530)752-0290. Appoint- ments are usually for Tuesdays and Thursdays, but other arrangements may be made on an individual basis. Referring veterinarians are encouraged to discuss a case with one of the cardiology faculty or residents on duty prior to the appointment if possible. Owners are asked to bring any available records or results of prior examinations for review and comparison.

One More Word About Miniature Horses

In our December 2012 Horse Report on Miniature Horses, we failed to include the American Miniature Horse Association (AMHA) among the organizations devoted to small equines. AMHA is the world’s leading Miniature Horse registry, with nearly 200,000 horses and more than 12,000 members in 38 countries and provinces. Founded in 1978, AMHA promotes the breeding, use and perpetuation of a standard of equine excellence in miniature, separate and apart from ponies and other small equine. Horses registered with AMHA must meet the Association standard of perfection and cannot exceed 34 inches in height at the withers as measured from the last hairs of the mane. For more information, please visit their website at www.amha.org.

www.vetmed.ucdavis.edu/ceh March 2013 - 15

Oleander Poisoning: The Preventable Illness

leander is an evergreen eating the day before and Oshrub that seems to grow was clearly unwell. The everywhere in California—in horse appeared to be yards, parks and along freeways. in , judging from It is often grown as a hedge that the color of its mucous can reach up to 20 feet tall. The membranes, a heartbeat leaves are thick, leathery and racing at 160 beats per dark green. White, pink or yellow minute (bpm), and a slightly flowers that are sweetly scented elevated temperature. grow in clusters at the end of (Normal heartbeat for a each branch. horse is 28 to 44 bpm.) It also had significant Oleander is one of the most discomfort from ileus—a Just four oleander leaves (shown above) can kill an poisonous plants and contains condition in which the adult horse. This plant is just as deadly dry as it is live. numerous toxic compounds, bowel does not move the many of which can be deadly contents at normal rates to people and animals. It is of flow because of lack of horse was quite weak and was especially dangerous to horses, neuromuscular control. The ileus staggering. It was immediately as it is sweet. Symptoms of a had caused a backward flow of fluid put on intravenous fluids to flush poisoned horse include severe and intestinal contents back into the out the toxins and eventually was diarrhea, colic and abnormal stomach. Since horses cannot vomit, stabilized. Meanwhile, testing heartbeat. this poses a serious problem. To treat continued to determine the exact this condition, a nasogastric tube cause of illness. The primary toxins in oleander was inserted into the horse to drain are cardiac glycosides, which the accumulating fluid while tests The diagnosis of toxicity was affect the heart. Cardiac reactions were performed to determine the confirmed by laboratory tests, consist of an irregular heart rate, underlying problem. which showed the presence of sometimes characterized by a oleander in the blood, feces and racing heart that subsequently An electrocardiogram (ECG) revealed stomach fluid. The owners of the slows to below normal further that the horse had ventricular horse had not realized that the along in the reaction. The heart , which is an irregular pasture the horse had been turned may also beat erratically with no and overly rapid heartbeat. Pleural out in days before was surrounded sign of a specific rhythm. Other effusion—fluid in the chest around by oleander. Fortunately, this toxic effects include nausea, the lungs—and — story has a happy ending. With excess salivation, abdominal pain, fluid around the heart—were continued intensive treatment and diarrhea (sometimes with blood), signs that the horse’s heart was supportive care, the horse began kidney failure and colic in horses. failing. This condition was treated to recover and was eventually Poisonings from this plant can as an emergency with lidocaine released from the VMTH. Three also affect the central nervous administered intravenously to slow months after this incident, the system and cause drowsiness, the heart rate. Eventually the heart owner reported that the horse was tremors, seizures, collapse, and rate was brought down to 60 bpm, doing very well and was back in even coma that can lead to death. substantially closer to the normal training. rate of 40 bpm than before, and the Several years ago, a sick four- arrhythmia was converted to a normal Not every case ends this well, year-old Standardbred racehorse sinus rhythm. so remember that preventing was brought to the William R. exposure to oleander is by far Pritchard Veterinary Medical Blood work and urinalysis results the best course of action for your Teaching Hospital. The owner then indicated a build-up of toxins horses and other animals. ❄ reported that it had stopped and renal failure. By now, the

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The Horse Report is now brought to you in ©The Regents of the an online format that allows us to include University of California videos. If you can access The Horse Report March 2013 from our website, you can read it sooner Center for Equine Health and save us the postage. Send your e-mail (530) 752-6433 address to [email protected] and www.vetmed.ucdavis.edu/ceh receive an e-mail notice whenever a new www.facebook.com/ucdavis.ceh publication is posted! Director: Dr. Claudia Sonder www.vetmed.ucdavis.edu/ceh [email protected]

Director Emeritus: Dr. Gregory Ferraro The Center for Equine Health is supported with funds provided by the State of California Pari- [email protected] Mutuel Fund and contributions by private donors. Senior Editor: Barbara Meierhenry The University of California does not discriminate in any of its policies, procedures or [email protected] practices. Management Services Officer: Katie Glide The University is an affirmative action/equal opportunity employer. The information you [email protected] provide will be used for University business and will not be released unless required by law. To review your record, contact Advancement Services, 1460 Drew Avenue, Ste. 100, Davis, CA Dean, School of Veterinary Medicine: 95616. A portion of all gifts is used to defray the costs of administering the funds. All gifts are Dr. Michael D. Lairmore tax-deductible as prescribed by law.