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Examination of the Cardiovascular System
Symposium on Physical Diagnosis
Examination of the Cardiovascular System
Allen W. Hahn, D.V.M., Ph.D.*
In view of the seemingly endless stream of technologically sophisticated medical instrumentation, especially in the area of cardiovascular function, one wonders why any effort at all is devoted to mundane technique of physical examination. Yet, with each new technologic introduction, the basic techniques of cardiovascular physical examination receive further substantiation. The observations from echocardiography, nuclear imaging, cardiac catheterization and other types of studies have elucidated and verified the observations obtained from such inexpensive and simple techniques as auscultation. The main reason clinicians must become and remain proficient in the technique of physical examination is that they may be applied to every patient, both inpatient and outpatient. About one in every ten dogs presented to a veterinary hospital will have some form of cardiovascular disease (less with cats). These techniques take relatively little time to perform, the investment in equipment is minuscule, and the amount of data available on which to base clinical judgments is formidable. Thus, physical examination techniques are probably the most cost effective of any in clinical practice.
HISTORY
In retrospect, it is easy to see how the signs related to the clinician by an owner should be interpreted. It is much more difficult, however, when presente d with an unknown disease entity to obtain all the relevant information necessary to thoroughly document the disease process. Standard practice calls for a systematic way for obtaining information about environmental factors, past medical proble ms (including vaccination history), present medical problems, and chief complaint. Under the category of environmental influences, the examiner should document the type and amount of diet that the patient is *Professor of Veterinary Medicine and Surgery, University of Missouri College of Veterinary Medicine, Columbia, Missouri Veterinary Clinics of North America: Small Animal Practice- Vol. 11, No.3, August 1981
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receiving. This is important, especially in older dogs, in order to define the total sodium intake. The type of housing should also be documented, as outdoor dogs have greater exposure to insect-borne diseases, especially heartworms. Water intake and urinary and bowel patterns can also be noted here, as concomitant problems are often elucidated. It is helpful also to attempt to define the growth pattern and relation to growth rate of littermates, if this information is available. These types of data may reveal certain congenital anomalies. If possible, attempts should be made to establish if any littermates had cardiac-related problems. There are breed predilections to cardiovascular abnormalities, which may be very helpful in establishing a differential diagnosis. Ventricular premature complexes and idiopathic myocarditis are commonly associated with the Boxer breed. Pugs are prone to stenosis of the His bundle; this can often be associated with sudden death and fainting episodes. The male of the Newfoundland breed is prone to aortic stenosis . The Beagle breed is congenitally prone to pulmonic stenosis; the Poodle breed, to patent ductus arteriosus; and the Keeshound breed, to tetralogy of Fallot. The breed most often affected with fainting from cardiac disease, referred to as the "sick sinus syndrome," is the Schnauzer. The Siamese and Burmese breeds of cats have a predilection for the dilated form of cardiomyopathy. Major effort should be given to documenting present medical problems, especially coughing and/or dyspnea, syncopal episodes, weight gain or loss, tiring easily, poor tolerance of exercise, and client-noted cyanosis. Frequent coughing accompanies congestive heart failure and may signify the onset of this life-threatening syndrome. These coughs should be documented as to their relationship to exercise, feeding, and sleeping. Animals are often presented because of persistent coughing at night which may be accompanied by dyspnea. Hemoptysis is a sign of serious pulmonary disease and refers to the expectoration of blood from the respiratory passages. Because animals often swallow the ir sputum, hemoptysis may not be recognized. The clinical signs of hemoptysis in the dog are associated with a ruptured chordae tendineae, eosinophilic pneumonitis, pulmonary edema, lungworms or heartworm infestation, neoplasia, foreign bodies, or severe bronchial infections. Syncopal "seizures" or collapse may signal certain, often subtle, cardiovascular problems. During syncopal seizures, dogs simply collapse and do not have the convulsive tonic-clonic patte rn seen in disorders that originate in the central nervous system. This syncope frequently results from cardiac arrhythmias, where cerebral hypoxia occurs due to severely and acutely depressed cardiac output. Discuss with your client whether there has been a rapid gain or loss of weight. Weight gains due to accumulation of fluid usually occurs during congestive heart failure when ventricular function is unable to keep up with the demands placed upon it. Other types pf cardiac disease may be accompanied by debilitating weight loss, and
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hequently the weight gain will follow a slower, progressive weight loss. The weight loss is primarily the result of loss of muscle mass. Always weigh the animal as part of routine physical examination. The animal's tolerance to exercise is extremely important in order to determine the condition of the cardiovascular system. Normal, healthy dogs are capable of exercising far beyond the limits of their owners, unless their owners happen to be Olympic class marathon runners. Certainly, the loss of exercise tolerance in an athletic-type hunting breed is easy to determine and often will be the reason for presentation. On the other hand, dogs kept indoors most of the time are really never stressed to their full level, and it is difficult to decide whether or not this animal has acceptable exercise tolerance. Veterinary medicine has yet to establish an adequate means of assessing exercise tolerance, although this is under research by various groups. It is important to listen to the client's description of exercise. Animals that tend to lag during walking or are dyspneic during exercise present important clues to establishing a diminished tolerance to exercise. Cyanosis observed by either client or clinician can be an important clue to congenital or acquired heart disease although respiratory problems can also cause it. Cyanosis is an infrequent finding but must be further examined when it is present. It is also extremely important to query the owner in regard to previous or present therapy, especially if it involves one of the digitalis glycosides, diuretics, or cough suppressants. Very often an animal may have been treate d by another veterinarian and brought to you with or without his or her knowledge. Clients often will attempt to hide this information, especially if they might have been dissatisfied with the animal's slow response to previous therapy.
PHYSICAL EXAMINATION Inspection By merely looking at a patient and observing its general attitudes and conformation, we are often able to add much to our preliminary data base. One of the primary characteristics of certain cardiac diseases is the position assumed by an animal with respiratory distress: the elbows are adducted and a sitting position is assumed so that the chest cavity may have the largest volume possible to compensate for fluid within the chest. Observe the peripheral vessels, notably the jugular veins, to note if they are distended and/or pulsating, an indication of abnormal filling of the right ventricle. Increased venous pressure may accompany right ventricular failure and insufficie ncy of the tricuspid valve will cause venous pulsations. Observe also the general state of the animal: whether or not it is debilitated, if gross fluid is present in the abdominal cavity or in the
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limbs, etc. Edema of the limbs is an uncommon feature of congestive cardiac failure to quadrupeds. Palpation Palpation refers to that technique of the physical examination that uses the hands to gather, by means of tactile senses, data about pathophysiologic conditions. In cardiology, palpation is used first on the precordium, or the chest wall, where it is important to determine the location of the point of maximal intensity (PMI) of the cardiac thrust. Place the hands on either side of the ventral thorax at about the fifth intercostal space . With the fingertips laid lightly on the chest, it is possible to locate the PMI on either the left or the right chest wall and whether it is displaced either cranially or caudally. The PMI should occur on the left side, approximately at the fifth intercostal space at the level of the costochondral junction. Often, however, in thin-chested breeds the intensity of this cardiac thrust will be approximately equal on both sides. If one finds the PMI displaced to the right, there is very good probability that the right ventricle is enlarged beyond its normal limits. Similarly, space-occupying tumors and masses in the chest may also displace the PMI. If one feels vibrations of low frequency in addition to the pulse thrust from a cardiac contraction, this is termed a "thrill" and its radiation and PMI should also be carefully noted on the examination record form. These low frequency vibrations are an indication that a severe murmur exists. Palpation of the peripheral pulses is also a significant portion of a cardiac physical examination. It is important to palpate both femoral pulses, using the sensitive portions of the fingertips, and to assess them in terms of their equality on left and right and also in terms of their fullness. The fact that a peripheral pulse is faint is not necessarily an indication that there are problems with low pressure within the systemic circulation, but rather an indication of low pulse pressure. The peripheral pulse is merely an indication of how far the walls of the vessel move. For large systolic to diastolic pressure variations, the peripheral pulse will feel full and bounding. When these variations are less, the peripheral pulse feels fainter. Palpate the femoral pulse while simultaneously auscultating the h eart. Determine if a pulse deficit is present. The re should be one pulse for each heartbeat. A pulse d e ficit occurs when severe arrhythmias such as atrial fibrillation or frequent premature contractions are present. The normal pulse rate is 70 to 160 beats per minute (up to 180 in toy breeds and 220 in puppies). For cats, 90 to 240 beats per minute is normal. The a bdomen should be palpated so that the p resence of pain or abdominal masses can be note d. An attempt should be made to d efine the borders of the liver. The borders of the liver are not palpable in the
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normal dog, and when they are felt beyond the costal margins this is evidence that the liver is enlarged. Percussion Percussion of the chest and abdomen is an old technique that should play a role in our physical exam. Though largely replaced in small animal medicine by thoracic radiography, percussion still stands as the only means of determining the "cardiac silhouette" in large species such as horses and cattle. Its place in small animal practice is best in the rapid determination of the presence or absence of fluid or the progression of fluid lines within the chest when repeated thoracic radiographs are neither indicated or desirable. Percussion is done by striking a sharp blow to the chest wall through either a pleximeter or two fingers of the examiner. One then listens and feels for a sound that has been variously described as dull or resonant or by other descriptive terms. When percussing over the cardiac "shadow," one receives back a dull impulse; that is to say, the cardiac tissue rapidly absorbs the sound. By the same token, when one percusses over a lung that is not fluid-filled, a resonant sound is heard. These two areas may then be separated as the examiner moves over the chest. These areas may then be delineated in each intercostal space, and a merging pattern of areas of cardiac dullness can be "plotted" and documented. Measurement of Blood Pressure The noninvasive techniques for measuring systemic arterial blood pressures are not so easy to apply in the dog as in humans. Recent studies, however, have shown that by using ultrasonic detection of arterial wall motion, .these pressures may be accurately obtained. It is beyond the scope of this article to completely examine these techniques, but a brie f me ntion is in orde r. A pneumatic cuff and ultrasonic transducer are applied around a peripheral vessel. In the dog and cat, the tibial artery has been found to be the most satisfactory. The pneumatic cuff is inflated to a pressure level about that of expected peak systolic pressure. An ultrasonic beam directed at the arterial wall detects vessel motion under the cuff. As the cuff is deflated by approximately 3 to 5 torr per second, the examiner listens for the initiation of a tapping sound, indicative of the arterial wall motion as systolic pressure is crossed. A change in the character of the signal received indicates that diastolic pressure is reached. Normal blood pressures in the dog, recorde d with the indirect Doppler technique, are estimated to be 155 ± 27 torr systolic and 73 ± 14 torr diastolic. Auscultation of the Heart Cardiac auscultation is the art and science of listening to and interpreting sounds from the heart. It is certainly the most cost-
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effective of all the methods that are used in examinations. The equipment necessary involves a good stethoscope and a quiet room. A good stethoscope should fit well in the ears, without pressing unduly on the tissues; it should provide a good seal. It should also be one with which the examiner has had considerable experience in recognizing the nature of the sound that finally reaches his ear. It is unwise to use three or four stethoscopes of different design. The overall length of the stethoscope from earpieces to chestpiece should be approximately 18 to 22 in. Excessively long tubing accentuates the sound; tubing that is too short makes it difficult to move the chestpiece to different locations. The earpieces should be placed into the ears with the bend of the earpieces toward the nose. The chestpiece should be switchable between bell and diaphragm. The bell is used to listen to tones of low frequency. The diaphragm chestpiece, which filters these low frequency sounds, allows the higher frequency sounds to reach the earpieces. A brief word about electronic stethoscopes and others of rather bizarre design-unless one has a noticeable low frequency hearing loss, the use of an electronic stethoscope is probably ill advised. The reason for this is that unless the sound pickup microphones necessary for electronic stethoscopes are extremely expensive and well made, they are very inadequate for low frequency sounds generated by the heart. Other types of stethoscopes of a more bizarre design first need to prove their claims by rigorous acoustical testing before they should be accepted into routine clinical use. A System for Auscultation. When listening to the heart, it is extremely important that two facets be rigidly followed. The first is preservation of a good physical environment for conducting an auscultatory exam. This includes a quiet room and, if possible, a quiet patient. The room should have drapes to help dampen sound reflections in the room, and if at all possible, acoustical tile or other sound-absorbing ceiling material. There is nothing more distracting when attempting to listen to the heartthan to have sharp noises from outside sources coming at irregular intervals throughout the exam. It is also important that the client be asked to remain quiet so that the clinician might devote all of his energies to listening. Just as important is what might be called the "spiritual" environment necessary for adequate auscultation. If this technique is not mastered, subtle features may often be missed by the clinician. Spiritual environment means the ability to concentrate one's full attention on the sounds coming through the stethoscope. Sounds produced at or around the various structures of the heart are best heard at certain places in the chest wall. One should listen with both the bell and the diaphragm of the stethoscope in all of these areas on all examinations (Fig. 1). The first area is commonly known as the mitral area, and sounds coming from the mitral valve are best heard here. That is not to say that these sound will not be heard in any other areas of the chest wall, but it is here that they are heard best. In most dogs, this area is located
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Figure 1. Areas for auscultation: mitral valves (A), aorta (B), lungs (C), and tricuspid valve (D).
at the fifth intercostal space on the left side of the chest in the region of the costochondral junction. The examiner next moves the stethoscope to the aortic area near the base of the heart. In most dogs this is located at the level of the point of the shoulder, approximately the third intercostal space on the left side of the chest. After examining this area with the bell and diaphragm of the stethoscope, the examiner next moves to the pulmonic area located above the costochondral junction at the second or third intercostal space. On some heavily muscled dogs and on large species, it is necessary to force the stethoscope under the axilla to gain access to this region. It is extremely important to listen to both the aortic and pulmonic areas at the base of the heart because it is here that murmurs originating from the great vessel are often heard best. Also, in some cases of patent ductus arteriosus, the classic continuous murmur can be heard only in this region. After listening to each of these points on the left side of the chest, the examiner should next move to the right side of the chest. The best place to listen here is the fourth intercostal
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Figure 2.
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Documentation of first and second heart sounds.
space at approximately the costochondral junction. Usually sounds emanating from the tricuspid valve (the right atrioventricular valve) are best heard at this point. While these four regions should be auscultated in all cases, occasionally it is necessary, when one hears a murmur or abnormal extra sound, to also listen elsewhere. One should auscultate at the thoracic inlet and also move the stethoscope to the more dorsal regions of the chest to determine how abnormal sounds radiate throughout the chest. The actual process of auscultation takes much less time to perform than it does to read about or describe. The clinician should take the opportunity to review his findings and document them thoroughly in the case record. As we discuss the various types of normal and abnormal sounds, we will use a technique of graphic illustration suggested by Segall. In this process, normal first and second heart sounds are depicted as "bars," appropriately timed with an electrocardiogram, to indicate the intensity and duration of the sound and its place in the cardiac cycle (Fig. 2). These are labelled S 1 for first heart sound and S2 for the second. Normal Heart Sounds and the Cardiac Cycle. During each contraction of the heart, a specific set of events leading to the ejection of blood from the cardiac chamber takes place in a specified sequence called a "cardiac cycle." The cardiac cycle starts with the generation of an electrical impulse by the sinoatrial (SA) node located in the right atrium. This electrical impulse travels over both the right and left atria. As the electrical impulse passes over and through the muscula-
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ture of the atrial myocardium, an electrical signal that can be recorded at the body surface is generated. This is the P wave of the electrocardiogram and can be used as a correlation for other events that will occur throughout the cycle. Following this electrical activity, the musculature of the atria begins to contract. As the atria contract, they force an additional volume of blood into the ventricles through the atrioventricular (AV) valves. As this blood (from atrial contraction) flows rapidly into the ventricles, vibrations are created in the heart. These are low frequency vibrations but may be recorded with sensitive instruments at the skin surface. In certain species, particularly the horse and the ox and occasionally in humans, these vibrations are intense e nough to cre ate an audible sound. This low fre quen~y, low intensity sound is known as the atrial or fourth heart sound (SJ (Fig. 3). This sound is not normally heard in dogs or cats, and when it occurs, is indicative of severe cardiac disease and congestive heart failure. The electrical impulse that had previously spread over the atria now reaches the AV node of the specialized cardiac conduction system. This node the n "fire s" on its own and propagates an e lectrical impulse down the spe cialized cardiac conduction system to stimulate the ventricular musculature to contract. As the electrical impulse travels over the ventricular musculature, the large QRS complex of the electrocardiogram is inscribed. During and shortly following this inscription, the active contraction of the ventricle begins to take place. Pressure rises within the ventricular chambe rs and whe n it exceed s p ressure in the atria (usually around 5 mm Hg or torr) the right and left AV valves (tricuspid and mitral) close vigorously and suddenly. During this closure, vibrations are transmitted to th~est w all and
Figure 3.
Atrial contraction , or fourth heart sound.
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Ventricular contraction, or first heart sound.
are audible with a stethoscope. The sound created at this time is known as the first heart sound (S 1) (Fig. 4). In the dog it lasts approximately 50 to 100 msec (111000 of a second). This first heart sound signifies the onset of cardiac contraction, or systole. Shortly following this first heart sound, the semilunar valves of the pulmonic and aortic outflow tracts open and blood is active ly ejected into pulmonary arteries and aorta. Opening of these valves is silent. After active contraction has passed, the pressure in the ventricle begins to rapidly decrease toward its diastolic level, which is approximately atmospheric pressure. Early in this relaxation phase, the pressure in the ventricles drops below that in the aortic and pulmonary arteries and semilunar valves close rapidly and quickly. This closure again creates vibrations that can be heard at the chest wall. These vibrations are known as the second heart sound (S 2) (Fig. 5), signifying the end of the systole and the beginning of the cardiac relaxation, or diastole. The pressure in the ventricles is now approximately atmospheric. Atrial pressure is slightly above that of the ventricles, and thus blood flows passively through the AV valves to refill the recently emptied ventricles. The mitral and tricuspid valves then open (they do so silently), and this large volume of blood passively fills the ventricle during a phase known as rapid ventricular filling. During this time, the rapid volume flow into the chambers creates low frequency vibrations. These vibrations are inaudible in normal dogs and cats although they may be heard in normal horses and cattle. Vibrations may be recorded at the chest surface with sensitive recording instruments. When they are h eard it is d efinite ly an abnormality, again
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Figure 5.
Ventricular relaxation, or second heart sound.
indicative of cardiac failure. This sound is known as the third heart sound (S 3 ) (Fig. 6). After the venticles have filled to about 70 per cent of their diastolic volume, the SA node again discharges, the atria contract, the end diastolic volume is complete, and the cardiac cycle begins again. Extra Cardiac Sounds. There are times when, for various pathologic reasons, the ventricles do not contract synchronously or one spends longer in contraction than the other. This results in · splitting the sounds. While detectable with high speed phonocardiography in dogs, this splitting is almost never detectable in a normal
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Figure 6.
Early diastolic or filling sound, or third heart sound.
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animal. Splitting of the second heart sound with respiration is heard in normal people. Splitting of the second heart sound in the dog is usually the result of pulmonary hypertension, that is, increased pressure in the pulmonary arteries and right ventricle. The most frequent cause of this in a dog is severe infestation with the canine heartworm, Dirofilaria immitis. Occasionally, for reasons still obscure, a high frequency click may occur during systole. This click may or may not be accompanied by a murmur.. It is thought to be due to an abnormally formed mitral valve that billows into the left atrium in midsystole. Apparently, this billowing tenses elements of the valve and causes high frequency vibrations to occur during systole. The clicking sound occurs during systole between the first and second heart sounds, and by this means it can be differentiated from a split second heart sound. As mentioned earlier, the pathologic significance of this is still somewhat obscure, but it is definitely an auscultatory abnormality. Third and Fourth Heart Sounds. In the dog and the cat, the presence of audible third and fourth h eart sounds is indicative of increased ventricular filling due to chronic congestive heart failure These abnormal sounds occur early in diastole for the third h eart sound and late in diastole (just before the first heart sound) for the atrial or fourth heart sound. When the heart rate is such that the third and the fourth heart sounds merge, they create a sound known as a summation gallop; summation because the third and fourth heart sounds occur together with an increased intensity. The term gallop is used because the three-beat cadence resembles the rhythm of the equine gallop. These are called diastolic gallops since they are caused by sounds occurring during diastole. They are always abnormal, and these animals should be carefully investigated for severe cardiac pathology. Remission of the gallop sound usually signifies improvement of cardiac failure. Murmurs. A murmur is an abnormal sound that has a longer duration than any of the heart sounds-first, second, third or fourth. Murmurs may occur anywhere in the cardiac cycle and their presence may either indicate a severe cardiac abnormality or be p erfectly innocent. It is a task of the clinician to differentiate between them. Murmurs are generated when flow conditions within the vascular system are disturbed and generate sufficient energy to transmit these sounds to the chest wall. Though the pathologic conditions in which murmurs occur will be discussed, the emphasis will be on characterization of the sounds heard so that this information can be transferred to a permanent record and compared with later observations. The same information can also be transmitted to a colleague when it is necessary to ask for a consultation. However, the sounds h eard by one person may be interpreted considerably differently than those heard by another. We should strive to maintain some degree of uniformity in describing abnormal heart sounds.
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Murmurs are characterized on the basis of five features: timing, intensity, shape, quality, and radiation. Timing. Is the murmur systolic, that is, does it occur between the first and second heart sound? Is it diastolic-occur between the second and the next first heart sound. Is it continuous, being present during both systole and diastole? Intensity. There are several different methods for characterizing the intensity or loudness of a murmur; the one I prefer is that suggested by the American College of Cardiology. This scheme divides murmurs into six categories of loudness: the loudest being grade six (6), and the softest murmur, grade one (1). A grade 1 murmur is one that can be heard only after several seconds of careful auscultation. A grade 2 murmur is very soft murmur but one heard immediately upon applying the stethoscope to the chest wall. A grade 3 murmur is louder than a grade 2 but is not accompanied by a thrill or vibration of the chest wall. A grade 4 murmur is a loud murmur accompanied b.Y a thrill. A grade 5 murmur is louder than a grade 4 but is not heard when the stethoscope head is moved out of contact with the skin of the chest wall. A grade 6 murmur is the loudest possible murmur and may still be heard when the stethoscope is removed several millimeters from contact with the chest wall. Since this system is not universally accepted in veterinary medicine, it is best to denote the grade of a murmur by placing the slash after the grade and then the number indicating the total range of grading scale; thus a grade 3 murmur would be recorded as a 3/6. Shape. How are the murmurs modulated during the cardiac cycle? The various shapes that may be encountered are the plateau or sustained murmur, which does not change its intensity; a crescendo murmur, which builds up in intensity; a decrescendo murmur, which starts loud and decreases in intensity; and a diamond-shaped or crescendo-decrescendo murmur, which starts soft and builds to a peak and then drops off. A particular shape of these murmurs is often characteristic of a certain valvular abnormality. Quality or Character. This is a descriptive term and is extremely subjective. The observer must attempt to describe the overtones that are present by terms such as blowing, harsh, musical, and so forth. A long list of the descriptive terms can be compiled, but it is beyond the scope of this presentation to cover all of them. Radiation. The radiation of the murmur to different parts of the chest wall should be noted and used to characterize the particular abnormal sound. Frequently, murmurs occurring at the aortic or pulmonic outflow tract will radiate to the thoracic inlet. Murmurs of mitral insufficiency, as they become more severe, will radiate to the more dorsal portions of the left chest wall. Systolic Murmurs. Systolic murmurs are those that occur during cardiac contraction, or systole. By definition, they occur at some time between the first and second heart sounds. In the dog, they are caused most frequently by insufficiency of the atrioventricular valves, the
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mitral valve being the most commonly affected. They may, however, be caused by stenosis at the aortic or pulmonic valve or by ventricular atrial septal defects, or they may be of an innocent (sometimes termed functional) nature and are not due to any underlying cardiac disease. Similarly, systolic murmurs may also be present during anemia, as blood viscosity has decreased and the tendency toward disturbed flow has been greatly enhanced. The most common type of murmur heard in the dog is the holosystolic, or plateau murmur of mitral insufficiency. This murmur is characterized by occupying all of systole and by being sustained in its shape (Fig. 7). Its intensity can vary, its character is usually blowing, and late in the disease it may radiate to the dorsal portions of the chest wall. The holosystolic, sustained character of the murmur is also frequently heard in ventricular septal defect, although it can also be of an ejection nature. Other types of systolic murmurs may have different shapes. A crescendo murmur is one that starts low in intensity and builds up in a peak. A decrescendo murmur starts with a higher intensity and decreases (before the second heart sounds) to a low intensity. These types of murmurs may accompany canine mitral valve disease, but their prevalence and diagnostic importance are unknown at this time. Ejection murmurs are characteristically harsh and are usually accompanied by a thrill. This is a typical type of murmur that is heard in both pulmonic and aortic stenosis and occasionally may be heard in ventricular septal defect. These murmurs have a modulation envelope that resembles a "diamond" -increasing to a p eak in midsystole and decreasing to end before the second heart sound (Fig. 8). Innocent or functional murmurs are always systolic in nature and
F igure 7.
Holosystolic murmur.
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Figure 8.
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Crescendo-decrescendo systolic murmurs.
occur usually in early systole. They are seldom louder than grade 2 or grade 3. Diastolic Murmurs. Murmurs occurring during diastole, that is, after the second heart sound and before the first heart sound, are quite rare in the dog. When they do occur, they are usually associated with either pulmonic or aortic valvular insufficiency, which may be due to bacterial endocarditis resulting from infection of these valves. Occasionally heartworm disease due to stretching of the valve ring may produce a diastolic rpurmur. A different type of diastolic murmur, called a diastolic rumble, is heard rarely in mitral insufficiency, when there is a large volume of diastolic flow crossing the mitral valve. These are generally higher in frequency than systolic murmurs and less noisy in their character of a decrescendo nature. Diastolic rumbles are much harsher in character than the insufficiency murmurs, and occur at about mid-diastole. Continuous Murmurs. Continuous murmurs are those occurring during both systole and diastole. They are most frequently heard accompanying arteriovenous shunts. The most prevalent type of arteriovenous shunt in the dog is congenital patent ductus arterious (PDA). With PDA a murmur is always present. This has also been described as a machinery murmur since it resembles the sounds heard in an old machine shop. In some cases, PDA presents with a systolic murmur only when auscultated over the apex. It is not until one moves the stethoscope head to either the pulmonic or aortic area, at the base of the heart, that the total continuous murmur becomes obvious. Arrhythmias. Arrhythmias may often be detected by careful auscultation. Their presence needs to be confirmed by electrocardiog-
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raphy, but these sounds, which are really breaks in the normal pattern, frequently confront the examiner upon routine physical examination and should be further documented by electrocardiography. Sinus Rhythm. Sinus rhythm is a normal, reguiar rhythm occurring at any rate but being perfectly regular. Dogs usually have a sinus rhythm when excited. Sinus tachycardia is the term applied when a regular rate occurs faster than 150 per minute. Sinus Arrhythmia. Sinus arrhythmia is frequently heard in the resting dog. It is a regular waxing and waning of the heart rate, speeding and slowing down, usually in concert with respiration. This is a perfectly normal rhythm for the dog but is abolished by sympathetic activity. An arrhythmia heard on auscultation in the cat is usually abnormal. Sinus arrhythmia is rare in the cat whereas in the dog it is very common. Sinus bradycardia in the cat is most often associated with the dilated form of cardiomyopathy. · Premature Atrial or Ventricular Contractions. When an ectopic focus causes the sinus node to fire early and out of synchrony with the normal sinus rhythm, a premature atrial contraction is created. The sound pattern of this arrhythmia is that of a normal sinus rhythm interrupted by a normal first and second heart sound occurring early and usually following a compensatory pause. The normal sinus rhythm again results. Premature ventricular contractions are more serious than premature atrial contractions, and frequently, because of their site of origin, do not open an aortic valve so that the first heart sound is all that is heard. These beats have a totally different sound character than the normal heart sounds. Many times, these beats do not propagate an arterial pulse and a pulse deficit is encountered when the femoral pulse is simultaneously palpated. Paroxysmal Atrial Tachycardia. At times the sinus node is given to periods of rapid discharge in which heart rate goes from a modest rate of 100 to 120 per minute to a very rapid rate of 150 to 200 or above. This may last for five or ten beats or may continue for as long as 30 minutes to an hour. Atrial Fibrillation. Atrial fibrillation is a severe arrhythmia that frequenly accompanies enlarged atria in cardiomyopathies and mitral insufficiency. It is very frequently seen in the giant breeds, including Great Danes, St. Bernards, Irish Wolfhounds, and Newfoundlands. It is rare in toy breeds and is less frequently seen in medium sized animals. It is characterized by a random nature of the heart sounds and by a pulse deficit.
SELECTED READINGS 1. American Heart Association: Physiologic principles of heart sounds and murmurs. American Heart Association Monograph No. 46, 1974. 2. Glossary of cardiologic terms related to physical diagnosis and history. 1: H eart murmurs. J.A.M.A., 200:1041, 1967. 3. Detweiler, D. K., and Patterson, D. F.: A phonograph record of heart sounds and murmurs of the dog. Ann. N.Y. Acad. Sci., 127:322, 1965.
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4. Gould, L., Ettinger, S. ]., and Lyon, A. F.: Intensity of the first heart sound and arterial pulse in mitral insufficiency. Dis. Chest, 53:545, 1968. 5. Hahn, A. W.: Auscultation of the canine heart. Parts I-IV. Small Anim. Clin., 1:320, 348, and 377, 1961; 2:10, 1962. 6. Hahn, A. W.: Cardiac murmurs in the dog. Small Anim. Clin., 2:319, 1962. 7. Hamlin, R. L., Robinson, F. R., Smith, C. R., eta!. : Heart sounds of healthy Macaca mulatta. J. Appl. Physiol., 17:199, 1962. 8. Hamlin, R. L., Muir, W. W., Gross, D. R., eta!.: Right and left ventricular systolic intervals during ventilation and sinus arrhythmia in the dog: Genesis of physiologic splitting and of the second heart sound. Am. J. Vet. Res., 35:9, 1975. 9. Humphries, J. 0., and Criley, J. M.: Comparison of heart sounds and murmurs in man and animals. Ann. N.Y. Acad. Sci., 127:347, 1965. 10. Patterson, D. F., and Detweiler, D. K.: The diagnostic significance of splitting of the second heart sounds in the dog. Zentralbl. Vet. Med., 2:121, 1963. 11. Patterson, D. F ., Detweiler, D . K., and Glende nning, S. A.: Heart sounds and murmurs of the normal horse. Ann. N.Y. Acad. Sci., 127:242, 1965. 12. Ravin, A.: Auscultation of the heart. Edition 2. Chicago, Year Book Medical Publishers, 1967. 13. Smetzer, D. L., and Smith, C. R.: Diastolic heart sounds of horses.]. Am. Vet. Med. Assoc., 146;931, 1965. 14. Smetzer, D. L., Smith, C. R., and Hamlin, R. L.: The fourth heart sound in the equine. Ann. N.Y. Acad. Sci., 127:306, 1965. College of Ve te rinary Medicine University of Missouri Columbia, Missouri 65211
Examination of the Cardiovascular System
Allen W. Hahn, D.V.M., Ph.D.*
In view of the seemingly endless stream of technologically sophisticated medical instrumentation, especially in the area of cardiovascular function, one wonders why any effort at all is devoted to mundane technique of physical examination. Yet, with each new technologic introduction, the basic techniques of cardiovascular physical examination receive further substantiation. The observations from echocardiography, nuclear imaging, cardiac catheterization and other types of studies have elucidated and verified the observations obtained from such inexpensive and simple techniques as auscultation. The main reason clinicians must become and remain proficient in the technique of physical examination is that they may be applied to every patient, both inpatient and outpatient. About one in every ten dogs presented to a veterinary hospital will have some form of cardiovascular disease (less with cats). These techniques take relatively little time to perform, the investment in equipment is minuscule, and the amount of data available on which to base clinical judgments is formidable. Thus, physical examination techniques are probably the most cost effective of any in clinical practice.
HISTORY
In retrospect, it is easy to see how the signs related to the clinician by an owner should be interpreted. It is much more difficult, however, when presente d with an unknown disease entity to obtain all the relevant information necessary to thoroughly document the disease process. Standard practice calls for a systematic way for obtaining information about environmental factors, past medical proble ms (including vaccination history), present medical problems, and chief complaint. Under the category of environmental influences, the examiner should document the type and amount of diet that the patient is *Professor of Veterinary Medicine and Surgery, University of Missouri College of Veterinary Medicine, Columbia, Missouri Veterinary Clinics of North America: Small Animal Practice- Vol. 11, No.3, August 1981
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receiving. This is important, especially in older dogs, in order to define the total sodium intake. The type of housing should also be documented, as outdoor dogs have greater exposure to insect-borne diseases, especially heartworms. Water intake and urinary and bowel patterns can also be noted here, as concomitant problems are often elucidated. It is helpful also to attempt to define the growth pattern and relation to growth rate of littermates, if this information is available. These types of data may reveal certain congenital anomalies. If possible, attempts should be made to establish if any littermates had cardiac-related problems. There are breed predilections to cardiovascular abnormalities, which may be very helpful in establishing a differential diagnosis. Ventricular premature complexes and idiopathic myocarditis are commonly associated with the Boxer breed. Pugs are prone to stenosis of the His bundle; this can often be associated with sudden death and fainting episodes. The male of the Newfoundland breed is prone to aortic stenosis . The Beagle breed is congenitally prone to pulmonic stenosis; the Poodle breed, to patent ductus arteriosus; and the Keeshound breed, to tetralogy of Fallot. The breed most often affected with fainting from cardiac disease, referred to as the "sick sinus syndrome," is the Schnauzer. The Siamese and Burmese breeds of cats have a predilection for the dilated form of cardiomyopathy. Major effort should be given to documenting present medical problems, especially coughing and/or dyspnea, syncopal episodes, weight gain or loss, tiring easily, poor tolerance of exercise, and client-noted cyanosis. Frequent coughing accompanies congestive heart failure and may signify the onset of this life-threatening syndrome. These coughs should be documented as to their relationship to exercise, feeding, and sleeping. Animals are often presented because of persistent coughing at night which may be accompanied by dyspnea. Hemoptysis is a sign of serious pulmonary disease and refers to the expectoration of blood from the respiratory passages. Because animals often swallow the ir sputum, hemoptysis may not be recognized. The clinical signs of hemoptysis in the dog are associated with a ruptured chordae tendineae, eosinophilic pneumonitis, pulmonary edema, lungworms or heartworm infestation, neoplasia, foreign bodies, or severe bronchial infections. Syncopal "seizures" or collapse may signal certain, often subtle, cardiovascular problems. During syncopal seizures, dogs simply collapse and do not have the convulsive tonic-clonic patte rn seen in disorders that originate in the central nervous system. This syncope frequently results from cardiac arrhythmias, where cerebral hypoxia occurs due to severely and acutely depressed cardiac output. Discuss with your client whether there has been a rapid gain or loss of weight. Weight gains due to accumulation of fluid usually occurs during congestive heart failure when ventricular function is unable to keep up with the demands placed upon it. Other types pf cardiac disease may be accompanied by debilitating weight loss, and
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hequently the weight gain will follow a slower, progressive weight loss. The weight loss is primarily the result of loss of muscle mass. Always weigh the animal as part of routine physical examination. The animal's tolerance to exercise is extremely important in order to determine the condition of the cardiovascular system. Normal, healthy dogs are capable of exercising far beyond the limits of their owners, unless their owners happen to be Olympic class marathon runners. Certainly, the loss of exercise tolerance in an athletic-type hunting breed is easy to determine and often will be the reason for presentation. On the other hand, dogs kept indoors most of the time are really never stressed to their full level, and it is difficult to decide whether or not this animal has acceptable exercise tolerance. Veterinary medicine has yet to establish an adequate means of assessing exercise tolerance, although this is under research by various groups. It is important to listen to the client's description of exercise. Animals that tend to lag during walking or are dyspneic during exercise present important clues to establishing a diminished tolerance to exercise. Cyanosis observed by either client or clinician can be an important clue to congenital or acquired heart disease although respiratory problems can also cause it. Cyanosis is an infrequent finding but must be further examined when it is present. It is also extremely important to query the owner in regard to previous or present therapy, especially if it involves one of the digitalis glycosides, diuretics, or cough suppressants. Very often an animal may have been treate d by another veterinarian and brought to you with or without his or her knowledge. Clients often will attempt to hide this information, especially if they might have been dissatisfied with the animal's slow response to previous therapy.
PHYSICAL EXAMINATION Inspection By merely looking at a patient and observing its general attitudes and conformation, we are often able to add much to our preliminary data base. One of the primary characteristics of certain cardiac diseases is the position assumed by an animal with respiratory distress: the elbows are adducted and a sitting position is assumed so that the chest cavity may have the largest volume possible to compensate for fluid within the chest. Observe the peripheral vessels, notably the jugular veins, to note if they are distended and/or pulsating, an indication of abnormal filling of the right ventricle. Increased venous pressure may accompany right ventricular failure and insufficie ncy of the tricuspid valve will cause venous pulsations. Observe also the general state of the animal: whether or not it is debilitated, if gross fluid is present in the abdominal cavity or in the
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limbs, etc. Edema of the limbs is an uncommon feature of congestive cardiac failure to quadrupeds. Palpation Palpation refers to that technique of the physical examination that uses the hands to gather, by means of tactile senses, data about pathophysiologic conditions. In cardiology, palpation is used first on the precordium, or the chest wall, where it is important to determine the location of the point of maximal intensity (PMI) of the cardiac thrust. Place the hands on either side of the ventral thorax at about the fifth intercostal space . With the fingertips laid lightly on the chest, it is possible to locate the PMI on either the left or the right chest wall and whether it is displaced either cranially or caudally. The PMI should occur on the left side, approximately at the fifth intercostal space at the level of the costochondral junction. Often, however, in thin-chested breeds the intensity of this cardiac thrust will be approximately equal on both sides. If one finds the PMI displaced to the right, there is very good probability that the right ventricle is enlarged beyond its normal limits. Similarly, space-occupying tumors and masses in the chest may also displace the PMI. If one feels vibrations of low frequency in addition to the pulse thrust from a cardiac contraction, this is termed a "thrill" and its radiation and PMI should also be carefully noted on the examination record form. These low frequency vibrations are an indication that a severe murmur exists. Palpation of the peripheral pulses is also a significant portion of a cardiac physical examination. It is important to palpate both femoral pulses, using the sensitive portions of the fingertips, and to assess them in terms of their equality on left and right and also in terms of their fullness. The fact that a peripheral pulse is faint is not necessarily an indication that there are problems with low pressure within the systemic circulation, but rather an indication of low pulse pressure. The peripheral pulse is merely an indication of how far the walls of the vessel move. For large systolic to diastolic pressure variations, the peripheral pulse will feel full and bounding. When these variations are less, the peripheral pulse feels fainter. Palpate the femoral pulse while simultaneously auscultating the h eart. Determine if a pulse deficit is present. The re should be one pulse for each heartbeat. A pulse d e ficit occurs when severe arrhythmias such as atrial fibrillation or frequent premature contractions are present. The normal pulse rate is 70 to 160 beats per minute (up to 180 in toy breeds and 220 in puppies). For cats, 90 to 240 beats per minute is normal. The a bdomen should be palpated so that the p resence of pain or abdominal masses can be note d. An attempt should be made to d efine the borders of the liver. The borders of the liver are not palpable in the
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normal dog, and when they are felt beyond the costal margins this is evidence that the liver is enlarged. Percussion Percussion of the chest and abdomen is an old technique that should play a role in our physical exam. Though largely replaced in small animal medicine by thoracic radiography, percussion still stands as the only means of determining the "cardiac silhouette" in large species such as horses and cattle. Its place in small animal practice is best in the rapid determination of the presence or absence of fluid or the progression of fluid lines within the chest when repeated thoracic radiographs are neither indicated or desirable. Percussion is done by striking a sharp blow to the chest wall through either a pleximeter or two fingers of the examiner. One then listens and feels for a sound that has been variously described as dull or resonant or by other descriptive terms. When percussing over the cardiac "shadow," one receives back a dull impulse; that is to say, the cardiac tissue rapidly absorbs the sound. By the same token, when one percusses over a lung that is not fluid-filled, a resonant sound is heard. These two areas may then be separated as the examiner moves over the chest. These areas may then be delineated in each intercostal space, and a merging pattern of areas of cardiac dullness can be "plotted" and documented. Measurement of Blood Pressure The noninvasive techniques for measuring systemic arterial blood pressures are not so easy to apply in the dog as in humans. Recent studies, however, have shown that by using ultrasonic detection of arterial wall motion, .these pressures may be accurately obtained. It is beyond the scope of this article to completely examine these techniques, but a brie f me ntion is in orde r. A pneumatic cuff and ultrasonic transducer are applied around a peripheral vessel. In the dog and cat, the tibial artery has been found to be the most satisfactory. The pneumatic cuff is inflated to a pressure level about that of expected peak systolic pressure. An ultrasonic beam directed at the arterial wall detects vessel motion under the cuff. As the cuff is deflated by approximately 3 to 5 torr per second, the examiner listens for the initiation of a tapping sound, indicative of the arterial wall motion as systolic pressure is crossed. A change in the character of the signal received indicates that diastolic pressure is reached. Normal blood pressures in the dog, recorde d with the indirect Doppler technique, are estimated to be 155 ± 27 torr systolic and 73 ± 14 torr diastolic. Auscultation of the Heart Cardiac auscultation is the art and science of listening to and interpreting sounds from the heart. It is certainly the most cost-
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effective of all the methods that are used in examinations. The equipment necessary involves a good stethoscope and a quiet room. A good stethoscope should fit well in the ears, without pressing unduly on the tissues; it should provide a good seal. It should also be one with which the examiner has had considerable experience in recognizing the nature of the sound that finally reaches his ear. It is unwise to use three or four stethoscopes of different design. The overall length of the stethoscope from earpieces to chestpiece should be approximately 18 to 22 in. Excessively long tubing accentuates the sound; tubing that is too short makes it difficult to move the chestpiece to different locations. The earpieces should be placed into the ears with the bend of the earpieces toward the nose. The chestpiece should be switchable between bell and diaphragm. The bell is used to listen to tones of low frequency. The diaphragm chestpiece, which filters these low frequency sounds, allows the higher frequency sounds to reach the earpieces. A brief word about electronic stethoscopes and others of rather bizarre design-unless one has a noticeable low frequency hearing loss, the use of an electronic stethoscope is probably ill advised. The reason for this is that unless the sound pickup microphones necessary for electronic stethoscopes are extremely expensive and well made, they are very inadequate for low frequency sounds generated by the heart. Other types of stethoscopes of a more bizarre design first need to prove their claims by rigorous acoustical testing before they should be accepted into routine clinical use. A System for Auscultation. When listening to the heart, it is extremely important that two facets be rigidly followed. The first is preservation of a good physical environment for conducting an auscultatory exam. This includes a quiet room and, if possible, a quiet patient. The room should have drapes to help dampen sound reflections in the room, and if at all possible, acoustical tile or other sound-absorbing ceiling material. There is nothing more distracting when attempting to listen to the heartthan to have sharp noises from outside sources coming at irregular intervals throughout the exam. It is also important that the client be asked to remain quiet so that the clinician might devote all of his energies to listening. Just as important is what might be called the "spiritual" environment necessary for adequate auscultation. If this technique is not mastered, subtle features may often be missed by the clinician. Spiritual environment means the ability to concentrate one's full attention on the sounds coming through the stethoscope. Sounds produced at or around the various structures of the heart are best heard at certain places in the chest wall. One should listen with both the bell and the diaphragm of the stethoscope in all of these areas on all examinations (Fig. 1). The first area is commonly known as the mitral area, and sounds coming from the mitral valve are best heard here. That is not to say that these sound will not be heard in any other areas of the chest wall, but it is here that they are heard best. In most dogs, this area is located
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Figure 1. Areas for auscultation: mitral valves (A), aorta (B), lungs (C), and tricuspid valve (D).
at the fifth intercostal space on the left side of the chest in the region of the costochondral junction. The examiner next moves the stethoscope to the aortic area near the base of the heart. In most dogs this is located at the level of the point of the shoulder, approximately the third intercostal space on the left side of the chest. After examining this area with the bell and diaphragm of the stethoscope, the examiner next moves to the pulmonic area located above the costochondral junction at the second or third intercostal space. On some heavily muscled dogs and on large species, it is necessary to force the stethoscope under the axilla to gain access to this region. It is extremely important to listen to both the aortic and pulmonic areas at the base of the heart because it is here that murmurs originating from the great vessel are often heard best. Also, in some cases of patent ductus arteriosus, the classic continuous murmur can be heard only in this region. After listening to each of these points on the left side of the chest, the examiner should next move to the right side of the chest. The best place to listen here is the fourth intercostal
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Documentation of first and second heart sounds.
space at approximately the costochondral junction. Usually sounds emanating from the tricuspid valve (the right atrioventricular valve) are best heard at this point. While these four regions should be auscultated in all cases, occasionally it is necessary, when one hears a murmur or abnormal extra sound, to also listen elsewhere. One should auscultate at the thoracic inlet and also move the stethoscope to the more dorsal regions of the chest to determine how abnormal sounds radiate throughout the chest. The actual process of auscultation takes much less time to perform than it does to read about or describe. The clinician should take the opportunity to review his findings and document them thoroughly in the case record. As we discuss the various types of normal and abnormal sounds, we will use a technique of graphic illustration suggested by Segall. In this process, normal first and second heart sounds are depicted as "bars," appropriately timed with an electrocardiogram, to indicate the intensity and duration of the sound and its place in the cardiac cycle (Fig. 2). These are labelled S 1 for first heart sound and S2 for the second. Normal Heart Sounds and the Cardiac Cycle. During each contraction of the heart, a specific set of events leading to the ejection of blood from the cardiac chamber takes place in a specified sequence called a "cardiac cycle." The cardiac cycle starts with the generation of an electrical impulse by the sinoatrial (SA) node located in the right atrium. This electrical impulse travels over both the right and left atria. As the electrical impulse passes over and through the muscula-
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ture of the atrial myocardium, an electrical signal that can be recorded at the body surface is generated. This is the P wave of the electrocardiogram and can be used as a correlation for other events that will occur throughout the cycle. Following this electrical activity, the musculature of the atria begins to contract. As the atria contract, they force an additional volume of blood into the ventricles through the atrioventricular (AV) valves. As this blood (from atrial contraction) flows rapidly into the ventricles, vibrations are created in the heart. These are low frequency vibrations but may be recorded with sensitive instruments at the skin surface. In certain species, particularly the horse and the ox and occasionally in humans, these vibrations are intense e nough to cre ate an audible sound. This low fre quen~y, low intensity sound is known as the atrial or fourth heart sound (SJ (Fig. 3). This sound is not normally heard in dogs or cats, and when it occurs, is indicative of severe cardiac disease and congestive heart failure. The electrical impulse that had previously spread over the atria now reaches the AV node of the specialized cardiac conduction system. This node the n "fire s" on its own and propagates an e lectrical impulse down the spe cialized cardiac conduction system to stimulate the ventricular musculature to contract. As the electrical impulse travels over the ventricular musculature, the large QRS complex of the electrocardiogram is inscribed. During and shortly following this inscription, the active contraction of the ventricle begins to take place. Pressure rises within the ventricular chambe rs and whe n it exceed s p ressure in the atria (usually around 5 mm Hg or torr) the right and left AV valves (tricuspid and mitral) close vigorously and suddenly. During this closure, vibrations are transmitted to th~est w all and
Figure 3.
Atrial contraction , or fourth heart sound.
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Ventricular contraction, or first heart sound.
are audible with a stethoscope. The sound created at this time is known as the first heart sound (S 1) (Fig. 4). In the dog it lasts approximately 50 to 100 msec (111000 of a second). This first heart sound signifies the onset of cardiac contraction, or systole. Shortly following this first heart sound, the semilunar valves of the pulmonic and aortic outflow tracts open and blood is active ly ejected into pulmonary arteries and aorta. Opening of these valves is silent. After active contraction has passed, the pressure in the ventricle begins to rapidly decrease toward its diastolic level, which is approximately atmospheric pressure. Early in this relaxation phase, the pressure in the ventricles drops below that in the aortic and pulmonary arteries and semilunar valves close rapidly and quickly. This closure again creates vibrations that can be heard at the chest wall. These vibrations are known as the second heart sound (S 2) (Fig. 5), signifying the end of the systole and the beginning of the cardiac relaxation, or diastole. The pressure in the ventricles is now approximately atmospheric. Atrial pressure is slightly above that of the ventricles, and thus blood flows passively through the AV valves to refill the recently emptied ventricles. The mitral and tricuspid valves then open (they do so silently), and this large volume of blood passively fills the ventricle during a phase known as rapid ventricular filling. During this time, the rapid volume flow into the chambers creates low frequency vibrations. These vibrations are inaudible in normal dogs and cats although they may be heard in normal horses and cattle. Vibrations may be recorded at the chest surface with sensitive recording instruments. When they are h eard it is d efinite ly an abnormality, again
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Figure 5.
Ventricular relaxation, or second heart sound.
indicative of cardiac failure. This sound is known as the third heart sound (S 3 ) (Fig. 6). After the venticles have filled to about 70 per cent of their diastolic volume, the SA node again discharges, the atria contract, the end diastolic volume is complete, and the cardiac cycle begins again. Extra Cardiac Sounds. There are times when, for various pathologic reasons, the ventricles do not contract synchronously or one spends longer in contraction than the other. This results in · splitting the sounds. While detectable with high speed phonocardiography in dogs, this splitting is almost never detectable in a normal
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Figure 6.
Early diastolic or filling sound, or third heart sound.
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animal. Splitting of the second heart sound with respiration is heard in normal people. Splitting of the second heart sound in the dog is usually the result of pulmonary hypertension, that is, increased pressure in the pulmonary arteries and right ventricle. The most frequent cause of this in a dog is severe infestation with the canine heartworm, Dirofilaria immitis. Occasionally, for reasons still obscure, a high frequency click may occur during systole. This click may or may not be accompanied by a murmur.. It is thought to be due to an abnormally formed mitral valve that billows into the left atrium in midsystole. Apparently, this billowing tenses elements of the valve and causes high frequency vibrations to occur during systole. The clicking sound occurs during systole between the first and second heart sounds, and by this means it can be differentiated from a split second heart sound. As mentioned earlier, the pathologic significance of this is still somewhat obscure, but it is definitely an auscultatory abnormality. Third and Fourth Heart Sounds. In the dog and the cat, the presence of audible third and fourth h eart sounds is indicative of increased ventricular filling due to chronic congestive heart failure These abnormal sounds occur early in diastole for the third h eart sound and late in diastole (just before the first heart sound) for the atrial or fourth heart sound. When the heart rate is such that the third and the fourth heart sounds merge, they create a sound known as a summation gallop; summation because the third and fourth heart sounds occur together with an increased intensity. The term gallop is used because the three-beat cadence resembles the rhythm of the equine gallop. These are called diastolic gallops since they are caused by sounds occurring during diastole. They are always abnormal, and these animals should be carefully investigated for severe cardiac pathology. Remission of the gallop sound usually signifies improvement of cardiac failure. Murmurs. A murmur is an abnormal sound that has a longer duration than any of the heart sounds-first, second, third or fourth. Murmurs may occur anywhere in the cardiac cycle and their presence may either indicate a severe cardiac abnormality or be p erfectly innocent. It is a task of the clinician to differentiate between them. Murmurs are generated when flow conditions within the vascular system are disturbed and generate sufficient energy to transmit these sounds to the chest wall. Though the pathologic conditions in which murmurs occur will be discussed, the emphasis will be on characterization of the sounds heard so that this information can be transferred to a permanent record and compared with later observations. The same information can also be transmitted to a colleague when it is necessary to ask for a consultation. However, the sounds h eard by one person may be interpreted considerably differently than those heard by another. We should strive to maintain some degree of uniformity in describing abnormal heart sounds.
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Murmurs are characterized on the basis of five features: timing, intensity, shape, quality, and radiation. Timing. Is the murmur systolic, that is, does it occur between the first and second heart sound? Is it diastolic-occur between the second and the next first heart sound. Is it continuous, being present during both systole and diastole? Intensity. There are several different methods for characterizing the intensity or loudness of a murmur; the one I prefer is that suggested by the American College of Cardiology. This scheme divides murmurs into six categories of loudness: the loudest being grade six (6), and the softest murmur, grade one (1). A grade 1 murmur is one that can be heard only after several seconds of careful auscultation. A grade 2 murmur is very soft murmur but one heard immediately upon applying the stethoscope to the chest wall. A grade 3 murmur is louder than a grade 2 but is not accompanied by a thrill or vibration of the chest wall. A grade 4 murmur is a loud murmur accompanied b.Y a thrill. A grade 5 murmur is louder than a grade 4 but is not heard when the stethoscope head is moved out of contact with the skin of the chest wall. A grade 6 murmur is the loudest possible murmur and may still be heard when the stethoscope is removed several millimeters from contact with the chest wall. Since this system is not universally accepted in veterinary medicine, it is best to denote the grade of a murmur by placing the slash after the grade and then the number indicating the total range of grading scale; thus a grade 3 murmur would be recorded as a 3/6. Shape. How are the murmurs modulated during the cardiac cycle? The various shapes that may be encountered are the plateau or sustained murmur, which does not change its intensity; a crescendo murmur, which builds up in intensity; a decrescendo murmur, which starts loud and decreases in intensity; and a diamond-shaped or crescendo-decrescendo murmur, which starts soft and builds to a peak and then drops off. A particular shape of these murmurs is often characteristic of a certain valvular abnormality. Quality or Character. This is a descriptive term and is extremely subjective. The observer must attempt to describe the overtones that are present by terms such as blowing, harsh, musical, and so forth. A long list of the descriptive terms can be compiled, but it is beyond the scope of this presentation to cover all of them. Radiation. The radiation of the murmur to different parts of the chest wall should be noted and used to characterize the particular abnormal sound. Frequently, murmurs occurring at the aortic or pulmonic outflow tract will radiate to the thoracic inlet. Murmurs of mitral insufficiency, as they become more severe, will radiate to the more dorsal portions of the left chest wall. Systolic Murmurs. Systolic murmurs are those that occur during cardiac contraction, or systole. By definition, they occur at some time between the first and second heart sounds. In the dog, they are caused most frequently by insufficiency of the atrioventricular valves, the
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mitral valve being the most commonly affected. They may, however, be caused by stenosis at the aortic or pulmonic valve or by ventricular atrial septal defects, or they may be of an innocent (sometimes termed functional) nature and are not due to any underlying cardiac disease. Similarly, systolic murmurs may also be present during anemia, as blood viscosity has decreased and the tendency toward disturbed flow has been greatly enhanced. The most common type of murmur heard in the dog is the holosystolic, or plateau murmur of mitral insufficiency. This murmur is characterized by occupying all of systole and by being sustained in its shape (Fig. 7). Its intensity can vary, its character is usually blowing, and late in the disease it may radiate to the dorsal portions of the chest wall. The holosystolic, sustained character of the murmur is also frequently heard in ventricular septal defect, although it can also be of an ejection nature. Other types of systolic murmurs may have different shapes. A crescendo murmur is one that starts low in intensity and builds up in a peak. A decrescendo murmur starts with a higher intensity and decreases (before the second heart sounds) to a low intensity. These types of murmurs may accompany canine mitral valve disease, but their prevalence and diagnostic importance are unknown at this time. Ejection murmurs are characteristically harsh and are usually accompanied by a thrill. This is a typical type of murmur that is heard in both pulmonic and aortic stenosis and occasionally may be heard in ventricular septal defect. These murmurs have a modulation envelope that resembles a "diamond" -increasing to a p eak in midsystole and decreasing to end before the second heart sound (Fig. 8). Innocent or functional murmurs are always systolic in nature and
F igure 7.
Holosystolic murmur.
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Figure 8.
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Crescendo-decrescendo systolic murmurs.
occur usually in early systole. They are seldom louder than grade 2 or grade 3. Diastolic Murmurs. Murmurs occurring during diastole, that is, after the second heart sound and before the first heart sound, are quite rare in the dog. When they do occur, they are usually associated with either pulmonic or aortic valvular insufficiency, which may be due to bacterial endocarditis resulting from infection of these valves. Occasionally heartworm disease due to stretching of the valve ring may produce a diastolic rpurmur. A different type of diastolic murmur, called a diastolic rumble, is heard rarely in mitral insufficiency, when there is a large volume of diastolic flow crossing the mitral valve. These are generally higher in frequency than systolic murmurs and less noisy in their character of a decrescendo nature. Diastolic rumbles are much harsher in character than the insufficiency murmurs, and occur at about mid-diastole. Continuous Murmurs. Continuous murmurs are those occurring during both systole and diastole. They are most frequently heard accompanying arteriovenous shunts. The most prevalent type of arteriovenous shunt in the dog is congenital patent ductus arterious (PDA). With PDA a murmur is always present. This has also been described as a machinery murmur since it resembles the sounds heard in an old machine shop. In some cases, PDA presents with a systolic murmur only when auscultated over the apex. It is not until one moves the stethoscope head to either the pulmonic or aortic area, at the base of the heart, that the total continuous murmur becomes obvious. Arrhythmias. Arrhythmias may often be detected by careful auscultation. Their presence needs to be confirmed by electrocardiog-
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raphy, but these sounds, which are really breaks in the normal pattern, frequently confront the examiner upon routine physical examination and should be further documented by electrocardiography. Sinus Rhythm. Sinus rhythm is a normal, reguiar rhythm occurring at any rate but being perfectly regular. Dogs usually have a sinus rhythm when excited. Sinus tachycardia is the term applied when a regular rate occurs faster than 150 per minute. Sinus Arrhythmia. Sinus arrhythmia is frequently heard in the resting dog. It is a regular waxing and waning of the heart rate, speeding and slowing down, usually in concert with respiration. This is a perfectly normal rhythm for the dog but is abolished by sympathetic activity. An arrhythmia heard on auscultation in the cat is usually abnormal. Sinus arrhythmia is rare in the cat whereas in the dog it is very common. Sinus bradycardia in the cat is most often associated with the dilated form of cardiomyopathy. · Premature Atrial or Ventricular Contractions. When an ectopic focus causes the sinus node to fire early and out of synchrony with the normal sinus rhythm, a premature atrial contraction is created. The sound pattern of this arrhythmia is that of a normal sinus rhythm interrupted by a normal first and second heart sound occurring early and usually following a compensatory pause. The normal sinus rhythm again results. Premature ventricular contractions are more serious than premature atrial contractions, and frequently, because of their site of origin, do not open an aortic valve so that the first heart sound is all that is heard. These beats have a totally different sound character than the normal heart sounds. Many times, these beats do not propagate an arterial pulse and a pulse deficit is encountered when the femoral pulse is simultaneously palpated. Paroxysmal Atrial Tachycardia. At times the sinus node is given to periods of rapid discharge in which heart rate goes from a modest rate of 100 to 120 per minute to a very rapid rate of 150 to 200 or above. This may last for five or ten beats or may continue for as long as 30 minutes to an hour. Atrial Fibrillation. Atrial fibrillation is a severe arrhythmia that frequenly accompanies enlarged atria in cardiomyopathies and mitral insufficiency. It is very frequently seen in the giant breeds, including Great Danes, St. Bernards, Irish Wolfhounds, and Newfoundlands. It is rare in toy breeds and is less frequently seen in medium sized animals. It is characterized by a random nature of the heart sounds and by a pulse deficit.
SELECTED READINGS 1. American Heart Association: Physiologic principles of heart sounds and murmurs. American Heart Association Monograph No. 46, 1974. 2. Glossary of cardiologic terms related to physical diagnosis and history. 1: H eart murmurs. J.A.M.A., 200:1041, 1967. 3. Detweiler, D. K., and Patterson, D. F.: A phonograph record of heart sounds and murmurs of the dog. Ann. N.Y. Acad. Sci., 127:322, 1965.
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4. Gould, L., Ettinger, S. ]., and Lyon, A. F.: Intensity of the first heart sound and arterial pulse in mitral insufficiency. Dis. Chest, 53:545, 1968. 5. Hahn, A. W.: Auscultation of the canine heart. Parts I-IV. Small Anim. Clin., 1:320, 348, and 377, 1961; 2:10, 1962. 6. Hahn, A. W.: Cardiac murmurs in the dog. Small Anim. Clin., 2:319, 1962. 7. Hamlin, R. L., Robinson, F. R., Smith, C. R., eta!. : Heart sounds of healthy Macaca mulatta. J. Appl. Physiol., 17:199, 1962. 8. Hamlin, R. L., Muir, W. W., Gross, D. R., eta!.: Right and left ventricular systolic intervals during ventilation and sinus arrhythmia in the dog: Genesis of physiologic splitting and of the second heart sound. Am. J. Vet. Res., 35:9, 1975. 9. Humphries, J. 0., and Criley, J. M.: Comparison of heart sounds and murmurs in man and animals. Ann. N.Y. Acad. Sci., 127:347, 1965. 10. Patterson, D. F., and Detweiler, D. K.: The diagnostic significance of splitting of the second heart sounds in the dog. Zentralbl. Vet. Med., 2:121, 1963. 11. Patterson, D. F ., Detweiler, D . K., and Glende nning, S. A.: Heart sounds and murmurs of the normal horse. Ann. N.Y. Acad. Sci., 127:242, 1965. 12. Ravin, A.: Auscultation of the heart. Edition 2. Chicago, Year Book Medical Publishers, 1967. 13. Smetzer, D. L., and Smith, C. R.: Diastolic heart sounds of horses.]. Am. Vet. Med. Assoc., 146;931, 1965. 14. Smetzer, D. L., Smith, C. R., and Hamlin, R. L.: The fourth heart sound in the equine. Ann. N.Y. Acad. Sci., 127:306, 1965. College of Ve te rinary Medicine University of Missouri Columbia, Missouri 65211