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(Circulation. 1996;93:1250-1253.)
© 1996 American Heart Association, Inc.

Articles

Cardiac Auscultation

A Glorious Past—But Does It Have a Future?

Morton E. Tavel, MD

From the Indiana Heart Institute and St Vincent Hospital, Indianapolis, Ind.

Key Words: auscultation • diagnosis

	Introduction

Top Introduction Why Do We Still... How Accurate Is Cardiac... Methods to Improve the... Conclusions References

 
For most of this century, the stethoscope has served as a critical diagnostic tool in cardiovascular evaluation. With the advent of numerous new diagnostic modalities, however, especially ultrasonic imaging and Doppler techniques, cardiac auscultation is receiving less emphasis in teaching and practice.¹ To compound this problem further, phonocardiography, ie, the graphic recording of heart sounds, which had served as a valuable means for teaching and documenting auscultation, has been largely discarded in this country. Although medical training directors and their students generally believe that cardiac auscultation is a skill that physicians should master,¹ there appears to be a widespread belief that this skill is of secondary importance because the same information is readily obtainable through newer technological means. Possibly as a result of this attitude, there is no structured teaching of cardiac auscultation in three fourths of American internal medicine programs and two thirds of cardiology programs.¹ This will inevitably lead to poor practice and teaching of this technique at all levels of training. Although not as well documented, the same process of attrition is probably affecting the other cognitive skills of history taking and bedside examination.^{2 3 4}

Conventional wisdom dictates that auscultation not only provides important clinical information in itself but also is a cost-effective means to select additional tests.⁵ To support these assumptions, however, we must evaluate contemporary information concerning not only how auscultation can be used for additional test selection but also how it might, in comparison with other testing methods, provide a source of information of independent clinical value. For this reason, we shall examine a few specific examples in which auscultation can be used to achieve these ends. To maximize information gained through auscultation, however, we must attempt to identify sources of inaccuracy and suggest methods to correct these deficiencies, thereby allowing for more uniform and effective teaching and practice of this method.

	Why Do We Still Need Cardiac Auscultation?

Top Introduction Why Do We Still... How Accurate Is Cardiac... Methods to Improve the... Conclusions References

 
Auscultation represents the acquisition of mechanical vibrations from the surface of the body that encompass the frequency range of sound. Vibrations below this range (<20 cycles per second) are defined as "infrasonic," and although not audible, they are usually readily palpable or visible and constitute a source of information supplementing that obtained from the sounds alone.⁶ Examples of infrasonic vibrations are provided by precordial motion (thrusts or heaves) and arterial and venous pulses. Although the general subject of cardiac auscultation has been reviewed recently,⁷ the diagnostic value of this technique and how it relates to other testing modalities are presented specifically in a few important examples below.

The audible fourth heart sound (and its simultaneous accentuated presystolic apical thrust) usually provides evidence of a forceful left atrial contraction⁸ combined with reduced left ventricular compliance—findings indicating diastolic dysfunction of the left ventricle.^{9 10} Studies of the accentuated and palpable presystolic apical thrust ("A" wave of the apexcardiogram), which usually accompanies the fourth sound, have provided direct evidence for increased ventricular stiffness (reduced compliance) in such cases.^{11 12} In general, Doppler and echocardiographic techniques (E/A velocity ratio, E-wave deceleration time, isovolumic relaxation time, and atrial filling fraction) and nuclear ventriculography (peak filling rate, time to peak filling rate, and one-third filling rate) have had some success in the detection and confirmation of diastolic dysfunction of the ventricles, but factors such as ventricular preload and the gradient of pressure between left atrium and left ventricle may influence diastolic filling patterns independent of ventricular stiffness.^{13 14 15} Thus, the fourth sound may provide one of the few direct clues of diastolic dysfunction, a finding of clearly useful and independent value.

The third heart sound, when encountered in the older individual without primary valvular disease or states marked by high cardiac output, usually signifies reduced systolic function of one or both ventricles together with increased filling pressure within the affected chamber.¹⁰ When encountered in this setting, this sound virtually ensures that the left ventricular ejection fraction is below 50%; moreover, it is regularly present when the ejection fraction drops below 30%.¹⁶ The presence of this sound has even been found to signal the likely efficacy of inotropic agents such as digitalis glycosides in treatment of the underlying disorder.¹⁷ Even when found in the setting of primary valvular disease (except for mitral regurgitation), the third sound usually signals the presence of systolic dysfunction together with elevation of left ventricular filling pressure.^{18 19} Imaging techniques that demonstrate ventricular enlargement and reduced systolic wall motion provide similar information, but the third sound additionally signifies the presence of an abnormally high filling pressure, and thus decompensation, of the involved ventricle.

A diastolic sound resembling the third sound but earlier in timing characterizes the pericardial "knock" sound of pericardial constriction; when such a sound is combined with careful evaluation of the precordial motion and jugular venous pulse, this diagnosis is strongly supported.²⁰ Although imaging techniques may demonstrate pericardial thickening or calcification, they do not provide prima facie evidence for hemodynamic interference of ventricular filling. A variety of echocardiographic signs have been described in pericardial constriction, but to date no single sign is best or pathognomonic in making this diagnosis.²¹ Even hemodynamic information obtained through cardiac catheterization may not provide clear differentiation between pericardial constriction and myocardial restrictive disease²² ; however, if one combines this information with precordial motion and timing of the early diastolic sound, clear diagnosis may become possible.

The presence of an ejection sound (ejection click) or opening snap usually signifies improper opening of semilunar valves or atrioventricular valves, respectively.^{23 24 25} For example, an ejection sound in an ostensibly normal individual generally signifies abrupt cessation of the motion of an abnormal semilunar valve before it reaches full opening. This finding usually indicates the need for an echocardiogram, which can identify and characterize an abnormal semilunar valve, such as a malformed or bicuspid aortic valve. On the other hand, opening sounds usually indicate proper functioning of mechanical prosthetic valves, and their loss may warn us of impending or actual malfunction of these devices. Thus, serial auscultatory evaluation may provide important collateral information in the assessment of prosthetic valves²⁶ and lead to proper selection of imaging techniques, such as transesophageal echocardiography.

A mid or late systolic click is most likely diagnostic of mitral (or tricuspid) valve prolapse, even though echocardiograms may fail to confirm this finding.²⁷ Echocardiograms commonly fail to demonstrate prolapse when an isolated systolic click is found in the absence of a systolic murmur of mitral regurgitation, a fact probably attributable to the inability of this technique to detect minor prolapse of limited portions of the leaflets. On the other hand, "prolapse" is often diagnosed from the echocardiogram in the absence of any auscultatory abnormalities. This is generally considered a benign clinical finding and, for the most part, probably reflects the inaccuracies of echocardiographic criteria for diagnosis. Thus, to avoid overdiagnosing this disorder, with its attendant psychological and insurance problems, careful auscultation of the patient in different positions and at different times must be considered in arriving at a final diagnosis²⁸ and also is superior to echocardiography for clinical management and follow-up.²⁹ Therefore, in the total absence of auscultatory abnormalities, there is usually little justification for performing an echocardiogram to search for mitral prolapse³⁰ and no need for prophylaxis against infective endocarditis.^{31 32}

Proper identification and classification of audible systolic murmurs usually enables us to identify their mechanism and likely source. Very often, Doppler techniques demonstrate minor regurgitation across atrioventricular valves that does not produce audible murmurs,³³ a finding that is usually clinically insignificant, for such patients generally suffer from no hemodynamic consequences and there is no evidence that antibiotics are necessary to prevent bacterial endocarditis. Conversely, Doppler study may not reveal the origin of audible murmurs, as exemplified by many crescendo-decrescendo murmurs produced by ejection of blood into the great vessels. Thus, to understand the origin and significance of a given systolic murmur, one must first categorize its type on the basis of its auscultatory characteristics and then consider this in the light of the Doppler results. By use of certain appropriate maneuvers, one can usually distinguish between ejection murmurs originating in the aortic outflow tract in contrast with pansystolic murmurs produced by mitral or tricuspid regurgitation.³⁴ If such a murmur is characterized by skilled examiners as an innocent-type ejection murmur, further testing is generally unnecessary.³⁵ On the other hand, a long, late-peaking, crescendo-decrescendo murmur may signal the presence of severe aortic³⁶ or pulmonic³⁷ stenosis and require confirmation by echo-Doppler techniques.

Hypertrophic obstructive cardiomyopathy can be diagnosed easily, or at least suspected, through the use of auscultation combined with simple bedside maneuvers, such as changes of position, Valsalva maneuver, and squatting.³⁴ Although this condition usually can be diagnosed through Doppler echocardiography alone, we have encountered occasional situations in which such study was technically difficult or it was unclear whether stenosis was valvular or subvalvular in location. Under such circumstances, definitive diagnosis was possible only when the results of auscultation were also taken into account.

The examples above represent but a few of the many practical applications of cardiac auscultation, sometimes coupled with other phases of the bedside examination. The accurate gathering and assessment of sonic vibrations from the body's surface, therefore, continue to serve an important need in clinical medicine and warrant further measures to preserve this technique.

	How Accurate Is Cardiac Auscultation?

Top Introduction Why Do We Still... How Accurate Is Cardiac... Methods to Improve the... Conclusions References

 
The examples cited above represent instances in which experienced examiners can make definitive diagnoses or acquire information leading to proper selection of additional tests. The information so obtained, however, is subjective, is dependent on the expertise of the examiner, does not result in permanent objective records, and often is not easily duplicated by other examiners. Improper interpretation of auditory information does not stem entirely from inexperience or ineptitude of examiners. In a recent study,³⁸ we found that even experienced physicians often disagreed about heart sounds, especially about the various brief sound phenomena, such as the low-frequency third and fourth heart sounds, or about narrowly split sound transients. Previous studies have also disclosed similar inconsistencies^{39 40} only partially attributable to examiner inexperience.³⁹ These results appear to expose certain human auditory limitations, which include insensitivity to low frequencies, slow responses to rapidly occurring, brief sonic events, and the masking of soft sounds by loud sounds in close proximity.⁴¹ These shortcomings provide a clear explanation for the severe limitations currently existing in both teaching and learning of auscultation. Unless we can develop better means to improve the accuracy of this technique and at the same time standardize its results, this method of examination, as we know it, will probably not endure.

	Methods to Improve the Practice and Teaching of Auscultation

Top Introduction Why Do We Still... How Accurate Is Cardiac... Methods to Improve the... Conclusions References

 
Because of the limitations described above and because of the need to address cost containment by avoiding primary use of expensive diagnostic facilities, we must consider means by which the practice of auscultation could be improved. Two major areas in which this could be achieved are (1) correcting certain deficiencies in reception and interpretation of auditory data and (2) extending data gathering beyond the sense of hearing alone.

With regard to problems presented by limitations in reception, human hearing is notoriously insensitive to low-frequency sounds,⁴² as exemplified by diastolic gallop sounds and the diastolic murmur of mitral stenosis. We typically compensate for this insensitivity through the use of the bell pickup device of the stethoscope, a method that tends to preserve low-frequency sound intensity but provides no significant amplification within this realm.⁴³ To overcome the insensitivity to low-frequency sounds, the process of amplifying all sounds equally through electronic means would provide selective enhancement of the subjective reception of sounds in this frequency domain.⁴⁴ Personal experience with equipment of this type leads me to conclude that this would allow us to detect sounds that are otherwise inaudible or, at best, indeterminate. Alternatively, the process of electronically amplifying or increasing the frequency of poorly audible low-frequency sounds would render them more easily detectable.⁴⁵ Another method of signal processing with which I have had personal experience is the process of converting sounds into a digital form and playing them back at slower speeds, a process that can be accomplished without a drop in sound frequency, thereby avoiding auditory distortion. This method can also allow for better sensitivity and recognition of low-frequency and individual sounds by reducing the subjective masking effect produced when multiple sounds occur in rapid sequence. One can also more easily recognize the temporal sequential intensity of murmurs (for instance, a crescendo-decrescendo pattern) and relate murmur timing more accurately to heart sounds. Although these various methods of signal processing are technologically oriented, they can be accomplished through the development of lightweight portable equipment that can be made relatively inexpensive.

To transcend certain limitations of human hearing, visual display of sound data has proved enormously helpful in the past, not only for purposes of teaching but also in producing diagnostic information per se and in providing permanent records.⁴⁶ Miniaturized devices now commercially available are capable of conveniently providing immediate graphic representation of cardiovascular sounds,³⁸ a technique previously achievable only through the relatively cumbersome technique of phonocardiography. Through this means, one can make accurate measurements of time intervals, clearly display low-frequency sounds that are difficult to hear, accurately characterize closely split and multiple brief sound transients occurring in rapid sequence, display contours of murmurs and their temporal relation to various other sound events, and provide permanent records of all acoustic information. The limitations of graphic display are much the same as those of phonocardiography in general, especially in the detection and display of high-frequency murmurs such as those produced by aortic regurgitation. In this latter case, owing to the noise produced by ambient or muscular factors, these murmurs are often submerged into the baseline of the recording. At this time, therefore, graphic display is effective only as a means to supplement auditory analysis.

Future developments in signal processing of sonic waves will undoubtedly not only lead to better auscultation but also provide more information of diagnostic value.⁴⁷ Stethoscopes could be equipped with advanced methods of noise rejection that would provide the ear with "cleaner" sounds free of background interference. At the same time, this would result in the accurate collection of signals that could be stored and analyzed in many ways. Data collection and analysis in this fashion are not possible through the use of the standard acoustic stethoscope, and thus, I believe that within the next few years, this instrument, in its present form, probably will be used less often for cardiac auscultation. More likely, miniature portable electronic stethoscopes will become available and allow the clinician to perform standard bedside examinations while at the same time providing a means for simultaneous listening by two or more individuals and allow the generation of permanent records and data storage for additional analysis.

	Conclusions

Top Introduction Why Do We Still... How Accurate Is Cardiac... Methods to Improve the... Conclusions References

 
The collection of sonic waves from the surface of the body, as performed with the stethoscope, continues to provide an important source of clinical information that, together with the overall bedside examination, not only is cost-effective but also cannot be totally replaced by alternative technological methods. Limitations of human hearing and stethoscope design, however, have hampered the physician's ability to accurately collect, reproduce, and document acoustic data obtained in this fashion. These limitations also threaten to disrupt the teaching of cardiac auscultation. Paradoxically, however, modern electronic means of data collection, which could be made portable and inexpensive, could provide the human ear with more perceptible and interpretable sound waves and at the same time provide for permanent records and advanced signal processing. This would bring cardiac auscultation into the modern era, abreast of the wide array of techniques grounded in modern technology. Many physicians resist innovations of this type, perhaps because of the mistaken notion that this will interfere with the "hands-on" and personal bedside contact with the patient and thus alter the traditional physician's "image" or relationship with the patient. Although this concern has merit, I believe that the time has come to devote our efforts toward developing newer methods of perception, display, and analysis of cardiovascular sound events. Through this means, the general physician not only should be able to continue active participation at the bedside but also should be far more effective in this role.

	Footnotes

 
Reprint requests to Morton E. Tavel, MD, 8333 Naab Rd, Suite 200, Indianapolis, IN 46260.

(Circulation. 1996;93:1250-1253.)

Received August 16, 1995; revision received October 19, 1995; accepted October 20, 1995.

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Top Introduction Why Do We Still... How Accurate Is Cardiac... Methods to Improve the... Conclusions References

 

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