SECTION A. Clinical Entities COPYRIGHTED MATERIAL

Transcription

1 SECTION A COPYRIGHTED MATERIAL

2

3 1 Heart Murmurs and Gallop Heart Sounds Key Points Cardiac murmurs can be present due to primary heart disease (for example, hypertrophic obstructive cardiomyopathy with systolic anterior motion of the mitral valve), high - output heart disease (for example, anemia), or they can be innocent. It is usually impossible to differentiate between these possible underlying etiologies on physical examination alone. However, higher - intensity murmurs, such as those that produce a precordial thrill, are more likely to be associated with underlying structural heart disease. Although early heart disease can be present in cats without cardiac enlargement on thoracic radiographs, over time the left (most commonly) atrium typically enlarges due to elevated ventricular fi lling pressures associated with cardiomyopathy. Usually left atrial enlargement is present prior to the development of congestive heart failure. Therefore, thoracic radiographs are a reasonable screening tool when a murmur or gallop sound is detected on physical examination. Because early disease can be missed radiographically, echocardiography is the most appropriate screening tool for breeding stock of high - risk breeds (such as Maine coon cats), and in clinical situations where defi nitive ruling in or ruling out of heart disease is desirable (e.g., preanesthetic evaluation, owner s desire to know, etc.) because cardiomyopathy may be clinically silent. Echocardiography is the best diagnostic modality to defi ne underlying cardiac disease and identify the cause of the murmur. It is the only diagnostic tool that allows the clinician to defi nitively identify the cause of a cardiac murmur that has been noted on physical examination. A gallop sound is said to be present when S 3 or S 4 (the diastolic fi lling sounds) are auscultable. A summation gallop can be ausculted in normal cats when the heart rate is fast enough to allow superimposition of early and late ventricular fi lling (S 3 and S 4 ). However, auscultable gallop sounds most often indicate cardiac disease in cats. INTRODUCTION A thorough clinical examination is of critical importance for complete investigation of the heart no matter how many advanced diagnostic tests are available. It can provide valuable information about cardiac functional status, circulatory physiology, and the likely etiology of heart disease. History taking and a complete physical examination are always the essential first steps that should guide the choice of diagnostic tests. It is optimal to measure the respiratory rate in the cage or carrier before the patient is stressed by removal for physical examination (Bond 2005 ). The auscultatory examination of the heart and lungs should include the identification of auscultable normal heart sounds (S 1 and S 2 ) and the identification of any abnormal heart sounds (Figure 1.1 ). The most important part of becoming adept with a stethoscope is experience; however, its proper use is essential (Box 1.1 ). Approach to Auscultation Prior to auscultation, the chest should be palpated for the apex beat (the palpable heart beat on the chest surface). The examiner s palpation identifies the location of the strongest apex beat which is a useful place to begin auscultatation and, without compressing the chest, characterizes its strength and position. With experience, the astute clinician will come to appreciate the difference between an increased apex beat caused by excitement (which will decrease as the patient calms) and an increased apex beat due to cardiac enlargement (which will be present in a calm patient). Feline Cardiology, First Edition. Etienne Côté, Kristin A. MacDonald, Kathryn M. Meurs, Meg M. Sleeper John Wiley & Sons, Inc. Published 2011 by John Wiley & Sons, Inc. 5

4 6 Section A: ECG Phono Phono P Q R S S 1 S 1 T Systolic click S 2 S 3 S 4 S 1 Split S2 S 2 S 2 Split S 1 Figure 1.1. Illustration of relationships between the electrocardiogram (ECG) and timing of heart sounds. Box 1.1. Anatomy of the stethoscope A good stethoscope should have comfortable earpieces that angle slightly toward the examiner s chin to direct sounds down the ear canals. The chest piece should be capable of detecting high - frequency (normal heart sounds and most murmurs) or low - frequency sounds (S 3 and S 4 ). When the bell is placed gently against the skin, it accentuates low - frequency sounds, but this capacity is lost if the bell is placed too fi rmly against the skin because the stretched skin acts as a diaphragm. When the diaphragm side of the chest piece is placed against the chest wall, it tends to minimize the low - frequency sounds and accentuates high - frequency sounds (such as the normal heart sounds, S 1 and S 2 ). Some chest pieces are capable of acting as both a bell and a diaphragm depending on how fi rmly they are placed against the chest wall. Such a stethoscope design is actually intended for human cardiology. It may be suboptimal in most cats (exception: Sphynx) because the haircoat interferes with the dual diaphragm - bell function. Stethoscope chest pieces/heads come in a variety of sizes. The pediatric size is advantageous for more specifi c sound localization in cats; it is often diffi cult to localize a murmur s point of maximal intensity to the heart base or apex with an adult size chest piece in small animals. The stethoscope diaphragm is optimal for hearing higher frequency sounds such as the normal first and second heart sounds. Abnormal heart sounds can be defined as either transient (brief in duration) such as split heart sounds or gallop sounds (S 3 or S 4 ), or of longer duration (e.g., most murmurs). Gallop sounds are low - frequency, diastolic sounds heard best with the bell of the stethoscope (see Box 1.1 ). Cardiac murmurs are usually associated with turbulent or high - velocity blood flow in the heart or great vessels. A quiet environment is essential for successful auscultation. Extraneous sounds, such as purring, can make auscultation very difficult in some cats. Restraining the animal near a sink with slowly running water or placing a cotton ball soaked with isopropyl alcohol near the cat s face can sometimes be useful to make the cat stop purring. Occasionally, breath sounds or fur rubbing against the stethoscope can be mistaken for sounds originating from the heart. Careful auscultation while watching the cat s breathing pattern can be useful to differentiate heart sounds from breath sounds. Location and Characterization of Heart Sounds It is very important that complete auscultation is performed in order to identify all abnormal sounds and rhythms. A simple approach is to auscult the left heart base, medial to the triceps musculature (which is the region of the aortic and pulmonic valve areas) and the left apex (which is the mitral valve area). The right heart base and apex should also be ausculted. The right apex is the area over the tricuspid valve area and tricuspid regurgitation is usually loudest in this region. Murmurs associated with ventricular septal defects are usually loudest at the right heart base but often radiate ventrally to the sternum. In cats, cardiac murmurs of many origins are often loudest over the parasternal region because of the cardiac positioning in this species, particularly as cats age and a greater amount of contact occurs between the sternum and the heart. Therefore auscultation along the left and right parasternum is crucial for a complete assessment. In cats, systolic murmurs loudest at the left apex are most often due to systolic anterior motion of the mitral valve (SAM; most often seen with hypertrophic obstructive cardiomyopathy). Murmurs caused by congenital cardiac malformations are much less common than those caused by myocardial disease because of the distribution of congenital versus myocardial disease in this species. In one echocardiographic survey of 92 cats in shelters, 18 62% had left ventricular concentric hypertrophy but none had a congenital cardiac lesion (Wagner et al ), and in over 400 cats presented to a referral hospital for another study, the ratio of cats with myocardial disease to cats with congenital heart defects was approximately 23:1 (Ettinger 2010 ). Systolic murmurs that are loudest at the left heart base may be caused by SAM, congenital aortic stenosis, incompletely ausculted patent ductus arteriosus, or physiologic (benign) murmurs. A common cause of physiologic murmurs in cats is mild, dynamic right ventricular outflow tract obstruction, which can produce a systolic

5 Chapter 1: Heart Murmurs and Gallop Heart Sounds 7 Box 1.2. Websites with libraries of digital heart and respiratory sounds Veterinary Human html/surface/thorax/hsounds.html heartsou.htm medic.htm sounds.htm murmur along the right or left parasternum (Rishniw and Thomas 2002 ; Allen 2010 ). There are several good websites, which include libraries of normal and abnormal heart and respiratory sounds, that are excellent for educational purposes. See Box 1.2 for a list of these sites. HEART MURMURS Cardiac murmurs are most often caused by the vibrations associated with high - velocity, disturbed, and turbulent blood flow. Such disturbances may be caused by valvular insufficiency (regurgitation), valvular stenosis, or the presence of a shunt. Disturbed flow that is low velocity, such as pulmonic valve regurgitation/ insufficiency, may not be auscultable. Low - velocity abnormal flow often is of no consequence (e.g., pulmonic valve regurgitation) but in some instances may exist with a severe cardiac lesion (e.g., low - velocity flow through a large atrial septal defect). Murmurs can also be created by other physiologic or pathological processes. For example, murmurs are often heard with changes in the viscosity of blood (anemia), and high - output diseases such as hyperthyroidism can be associated with the development of murmurs due to increased velocity of ejected blood. The Reynolds number is used for predicting whether a flow pattern is likely to be laminar or turbulent. Typically it is defined as v s L/v, where v s is the mean fluid velocity in ms 1, L is the characteristic length of the blood vessel in meters, and v is the kinematic fluid viscosity in m 2 /s. Simplified, the relationship is inertial forces/viscous forces. Therefore, in a large - diameter Box 1.3. Grading of murmurs (6 grade scale) Grade 1 : a very soft, localized murmur detected only in a quiet room after intense listening Grade 2 : a soft murmur, heard immediately, localized to a single area Grade 3 : a moderate - intensity murmur that is evident at more than one location Grade 4 : a moderate - intensity to loud murmur that radiates well, but a consistent precordial thrill is not present Grade 5 : a loud murmur accompanied by a palpable precordial thrill Grade 6 : a loud murmur with a precordial thrill, audible when the stethoscope is removed from the thorax vessel with rapid flow, or when blood viscosity is decreased (with anemia), there is a tendency toward turbulence. Rapid changes in vessel diameter such as occurs with stenotic lesions may also lead to turbulent flow. Classification of Heart Murmurs Murmurs are classified in several ways: Timing in the cardiac cycle (systolic, diastolic, continuous). While most common cardiovascular diseases in the cat result in systolic murmurs, occasionally feline patients will present with diseases such as mitral stenosis (which results in a diastolic murmur) or patent ductus arteriosus (which results in a continuous cardiac murmur). Intensity is the loudness of the murmur most often graded using a 6 - tier scale. See Box 1.3 for definitions in this classification scheme. The intensity of the murmur does not necessarily correlate with the severity of the underlying heart disease, as some well tolerated abnormalities (such as restrictive/resistive ventricular septal defects) produce very loud murmurs, while some severe lesions may produce soft murmurs (i.e., large unrestrictive/unresistive ventricular septal defect or severe tricuspid regurgitation). Point of maximal intensity is the area at which the murmur is loudest, and it generally relates closely to the underlying source of turbulent flow. For example, a left - to - right patent ductus arteriosus murmur is usually heard loudest over the left heart base at the pulmonary artery, because high - velocity flow from the aorta is shunting through the duct into the pulmonary artery at this location. Radiation of a murmur refers to how widely the murmur can be heard from the point of maximal intensity. Generally, the wider the radiation of the murmur, the greater the amount of turbulence being generated. Pitch and quality are subjective descriptions of the character of a murmur (i.e., coarse, musical, etc.). These descriptors are not precise and do not have the same objectivity as timing and point of maximal intensity.

6 8 Section A: Associations between Heart Murmurs and Cardiovascular Disease Certain murmurs are pathognomonic for specific diseases. For example, a continuous murmur at the left heart base is almost always caused by a patent ductus arteriosus (although rarely an aortic - pulmonary window or an arteriovenous fistula can produce a similar murmur). A systolic murmur with a point of maximal intensity at the right heart base is usually associated with a ventricular septal defect. See Box 1.4 for a list of murmur characteristics for the common feline cardiac diseases. However, it is often impossible to differentiate innocent (benign) murmurs from those murmurs secondary to heart disease based on auscultation alone particularly in the cat, where innocent murmurs are very common. Benign dynamic right ventricular outflow Box 1.4. Murmur characterization based on point of maximal intensity and timing Left heart base Systolic Aortic stenosis (dynamic or fi xed; including hypertrophic obstructive cardiomyopathy) Pulmonic stenosis (dynamic or fi xed) Tetralogy of Fallot Physiologic (benign) Continuous Patent ductus arteriosus Diastolic (rare) Aortic regurgitation Left heart apex Systolic Mitral regurgitation Physiologic (benign) Diastolic (rare) Mitral stenosis tract stenosis is an important and common cause of innocent murmurs in cats (Rishniw and Thomas 2002 ; Allen et al ). In the authors experience, soft ( grade 4/6), musical quality murmurs at the heart base that disappear at slower heart rates are more likely to be innocent, particularly if thoracic radiographs reveal a normal heart size; however, enough overlap exists with mild forms of HCM and other disorders to prevent any definitive conclusion from being reached on auscultation alone. While ausculting the feline patient, it is often possible to slow the heart rate by covering the cat s face in the examiner s hand or in the crook of the examiner s arm (Figure 1.2 ). Changes in heart murmur characteristics are common when a cat s heart rate changes. The clinical significance of this phenomenon is mixed: in many instances, a murmur that appears only during tachycardia can be benign (e.g., dynamic RVOT outflow obstruction). But in many other cases such a murmur is associated with structural heart disease: a cat with a murmur audible only when the cat is provoked or aroused is 6.1 times more likely to have dynamic ventricular outflow tract obstruction than a cat that does not develop a murmur under the same circumstances (Paige et al ). Therefore, the appearance of a heart murmur, or an increase in murmur intensity, when the heart rate increases is not a finding that definitively confirms either a benign or a pathologic condition. It is also important to remember that it is possible to create murmurs, particularly in lean small animal patients, by applying excessive pressure to the cat s thorax with the stethoscope chest piece/head. When a murmur is ausculted, it is useful to reduce the pressure with which the stetho- Parasternal Systolic Left ventricular outfl ow tract obstruction (dynamic or fi xed; including hypertrophic obstructive cardiomyopathy) Dynamic right ventricular outfl ow tract obstruction Ventricular septal defect Physiologic Right heart base Systolic Ventricular septal defect (left to right) Dynamic right ventricular outfl ow tract obstruction Right heart apex Systolic Tricuspid regurgitation Figure 1.2. During auscultation, gently covering the feline patient s face with the hand or in the crook of the arm often results in appreciable slowing of the heart rate. This technique is useful to aid in accurately determining the timing of heart sounds, as well as to see whether the murmur character changes.

7 Chapter 1: Heart Murmurs and Gallop Heart Sounds 9 scope is applied to the thorax and evaluate whether the intensity of the murmur changes. These false murmurs are easiest to produce at the heart base and likely represent compression of the great vessels in an animal with a compliant chest wall. Prevalence of Heart Murmurs Heart murmurs are a common finding in the general cat population. Various screening studies have identified a prevalence of heart murmurs in overtly healthy cats of 21% (blood donor candidates; n = 103) (C ô t é et al ), 16% (privately owned cats; n = 103) (Paige et al ), 27% (same privately owned cats after provocation, wherein the examiner quickly lifted the cat in the air twice) (Paige et al ), and 34% (cats in shelters; n = 199) (Wagner et al ). No association between heart murmurs and overt physical characteristics (coat color, eye color, or breed) has been identified (C ô t é et al ). Echocardiography in these groups has revealed structural heart disease in a substantial proportion of cases: 16 (16%) of 103 seemingly healthy cats had hypertrophic cardiomyopathy (HCM) in 1 study (5 with a heart murmur, 11 without a heart murmur) (Paige et al ), and 18 62% of 92 cats (depending on criteria used for defining ventricular wall thickness) had left ventricular concentric hypertrophy in another study (Wagner et al ). The presence of a heart murmur does not confer a diagnosis of a structural cardiac lesion. Between 25% (Bonagura 2000 ) and 69% (Paige et al ) of cats with murmurs on physical examination have no echocardiographic evidence of heart disease, showing that no conclusions can be drawn about the structure of a cat s heart based on the detection of a heart murmur. Moreover, although they are a common finding, murmurs in cats can be challenging for many practitioners to evaluate for several reasons. The rapid resting heart rate of many cats (routinely > 200 beats/minute), particularly when nervous at a veterinary hospital, can abbreviate the duration of murmurs to such a point that they are not auscultable. Making murmur characterization even more difficult in cats is the close proximity of heart valve areas on the thorax, so clear definition of valve areas is less certain in this species. Additionally the heart position in the thorax changes with age in cats resulting in all valve areas becoming more parasternal in location (Figure 1.3 ). Despite these difficulties, characterizing murmurs by timing in the heart cycle and the point of maximal intensity is a critical part of the physical examination and should be undertaken using the suggestions presented earlier in this chapter. This accurate characterization of murmurs is crucial for the development of a thorough, specific differential diagnostic list, particularly in young animals. Once the differential diagnosis A B Figure 1.3. Left lateral radiographs from a young cat (A) and from a middle - aged cat (B) showing the fl attened cardiac angle (yellow line), which can occur normally as cats age and which can further concentrate normal and abnormal heart sounds in the parasternal region in adult, older cats. list is formulated, further diagnostic tests such as thoracic radiography and/or echocardiography can help to establish a definitive diagnosis. Although findings on physical examination may suggest the cause of a murmur, echocardiography is the only readily available way to identify the specific cause of a murmur (and the type of heart disease, if heart disease is present). However, echocardiography may not be feasible in all patients with murmurs, due to various constraints. In these individuals, a reasonable approach is serial radiography. If the heart size is normal, hemodynamically significant structural heart disease is unlikely and regular monitoring of heart size with this modality is a reasonable alternative when echocardiography is not available. For example, if the heart size is normal and remains normal over subsequent studies, the patient is unlikely to benefit from cardiac medications. It is important to remember that cardiac medications are not instituted to treat murmurs, but to treat the underlying diseases that produce the murmurs.

8 10 Section A: Murmur character can change (e.g., become louder) due to physiologic changes in the patient that do not necessarily reflect the presence or progression of cardiac disease. The mere existence of a heart murmur does not justify beginning cardiac medications. A common conundrum is the cat with an incidentally found heart murmur and grossly apparent cardiac changes on radiographs but no evidence of congestive heart failure and no overt clinical signs whose owner is unable or unwilling to pursue echocardiography. At least two approaches are recognized by cardiologists in such cases, and each carries substantial advantages and drawbacks. First, it may be inferred that in a cat with a murmur and heart enlargement noted radiographically, cardiac medications (an angiotensin - converting enzyme inhibitor for concentric or eccentric hypertrophy suggested by generalized cardiomegaly and aspirin for blood stasis associated with atrial enlargement) may be warranted because these abnormalities suggest that cardiac remodeling has occurred. If bursts of tachycardia or an irregularly irregular rhythm at an elevated heart rate is persistent, a drug such as atenolol may be beneficial. On the other hand, echocardiography allows a noninvasive and detailed assessment of cardiac structure and basic cardiac function. The advantages of deciding whether to pursue treatment based on cardiac appearance on radiographs alone are Simplicity of diagnostic testing Lower expense The advantages of deciding on whether to pursue treatment based on echocardiographic findings are Elimination of misdiagnosis when the heart is in fact structurally normal (but peritoneopericardial diaphragmatic hernia, pericardial effusion, or an artifact such as patient obliquity, expiratory - phase films, or ventrodorsal projection instead of dorsoventral, give the mistaken impression of cardiomegaly on radiographs) Quantification of structural lesions (e.g., atrial enlargement, outflow tract velocities associated with obstruction, Doppler assessment of diastolic function) that help in deciding whether to initiate treatment, and may help stratify risk and owner concern/monitoring for the future It must also be considered that the physical administration of medications to an asymptomatic cat for a period commonly lasting months to years and attendant dis- couragement of the patient, the client, or both may compromise the willingness to pursue later treatment when it becomes indispensable (e.g., CHF, ATE; see Chapter 11 ). Therefore, a reasonable approach to the overtly healthy cat with an incidentally discovered heart murmur appears to be to 1. Consider the context of the case, since preanesthetic evaluations or evaluations of breeding stock carry greater implications for the cardiovascular health of patients immediately or for many generations, respectively (and echocardiography would be more immediately important in such patients). 2. Discuss the advantages and drawbacks of echocardiography with the cat s owner, recommending echocardiography if it is feasible. 3. Pursue treatment if indicated based on diagnostic imaging findings following a realistic and comprehensive discussion with the owner of advantages and drawbacks of such treatment, particularly when cardiac morphology has not been determined. GALLOP HEART SOUNDS Key Point The term gallop rhythm is a misnomer because the underlying cardiac rhythm is most often sinus. The additional heart sound, which results in a triple cadence in conjunction with the normal fi rst and second heart sounds, is more accurately called a gallop heart sound. The third (S 3 ) and fourth (S 4 ) heart sounds are not normally audible during cardiac auscultation in small animals. When present in dogs or cats, the extra sound results in a triple beat cadence reminiscent of a cantering horse. Because of this similarity, some refer to it as a gallop rhythm; however, this term leads to confusion because a true arrhythmia (change in the rhythm of cardiac electrical activity) is not present. In fact, gallop sounds are usually associated with sinus rhythms. An extra heart sound (and this triple - sound, galloping character of each heartbeat) can be noted due to the presence of auscultable S 3 or S 4 sounds, a systolic click, or a split heart sound, but only the diastolic sounds (S 3 and S 4 ) are correctly termed gallop sounds. The various extra sounds occur secondary to differing abnormalities and mechanisms, so accurate identification is important. S 3 and S 4, as diastolic filling sounds, are best ausculted using the bell of the stethoscope (see Box 1.1 ).

9 Chapter 1: Heart Murmurs and Gallop Heart Sounds 11 In small animals, gallop sounds (S 3 and S 4 ) are generally reflective of abnormal diastolic function. As blood from the atria fills the ventricles during diastole, rapid deceleration of the blood column in a stiff, noncompliant ventricle (such as occurs with hypertrophic or restrictive cardiomyopathy) results in auscultable vibrations. S 3 sounds are generated by rapid ventricular filling during early diastole (see Figure 1.1 ). When present in a cat, they imply ventricular dilation and/or systolic dysfunction. Other possible causes include hyperthyroidism and anemia. The S 4 sound is associated with active ventricular filling caused by atrial contraction and occurs late in diastole (see Figure 1.1). S 4 sounds are most commonly ausculted in cats with hypertrophic cardiomyopathy. However, it is often difficult to differentiate between S 3 or S 4 when the heart rate is fast, and when they merge, the result can be a single auscultable extra sound, called a summation gallop. Summation gallop sounds occasionally can occur in some normal cats when their heart rates are fast enough that S 3 and S 4 become audible and are superimposed. However, in general, gallop sounds suggest underlying structural heart disease and further diagnostic tests are warranted. Because their presence is often associated with elevated left ventricular filling pressure, the presence of a gallop sound (S 3, S 4, or summation) is highly suggestive of imminent or existing congestive heart failure in a cat exhibiting respiratory distress or receiving fluid therapy. Systolic clicks are a different type of third heart sound with a very different causative mechanism and character. Systolic clicks are short, midsystolic sounds that are higher in frequency than gallops sounds. When systolic clicks are present, the result is a triple cadence, which can be confused with that produced by a gallop sound, especially given the rapid heart rate of many cats in the clinical setting. However, the high - frequency sound of a systolic click is distinctly different from the low frequency of a gallop sound; therefore, the two can be differentiated by their frequency, with clicks mimicking the normal heart sounds (which are high - frequency and thus more easily heard with the diaphragm of the stethoscope) and gallops being more prominent during light application of the bell of the stethoscope to the chest surface (low - frequency sounds). Systolic clicks are most often associated with abnormalities of the atrioventricular valves, such as mitral valve prolapse. In general, systolic clicks, and specifically, mitral valve prolapse, are rare in the feline population, although anecdotally such clicks may be noted in cats with hypertrophic cardiomyopathy. Split heart sounds can also produce a triple cadence as already described and thus constitute another differential diagnosis for gallop sounds. Asynchronous closure of the atrioventricular valves (S 1 ) or the semilunar valves (S 2 ) can result in split heart sounds. Split first heart sounds and split second heart sounds are very rare in cats. In humans and dogs, split second heart sounds can occur with pulmonary hypertension and delay of pulmonic valve closure, but this finding has not been recognized in cats with pulmonary hypertension (see Chapter 25, Pulmonary Thromboembolism and Pulmonary Hypertension ). REFERENCES Boldface font indicates key references. Allen JW, Yee K, Buckner MH, Ettinger SJ. NT-proBNP levels in 30 cats with dynamic right ventricular outflow obstruction [abstract]. J Vet Intern Med 2010 ;24 :695. Bonagura JD. Feline echocardiography. J Fel Med Surg 2000 ; 2 : Bond BR. Fine tuning the history and physical examination: correlations with miscellaneous techniques. Clin Tech Small Anim Pract 2005 ;10 : Côté E, Manning AM, Emerson D, et al. Assessment of the prevalence of heart murmurs in overtly healthy cats. J Am Vet Med Assoc 2004 ; 225 : Ettinger SJ. NT-proBNP: The cat is not a dog. Oral scientific sessions, 28th Annual ACVIM Forum, Anaheim, CA, June 12, Paige CF, Abbott JA, Elvinger F, Pyle RL. Prevalence of cardiomyopathy in apparently healthy cats. J Am Vet Med Assoc 2009 ; 234 : Rishniw M, Thomas WP. Dynamic right ventricular outflow obstruction: A new cause of systolic murmurs in cats. J Vet Intern Med 2002 ;16 : Wagner T, Luis Fuentes V, Payne JR, McDermott N, Brodbelt D. Comparison of auscultatory and echocardiographic findings in healthy adult cats. J Vet Cardiol 2010 ;12 :

10