Electronic stethoscopes: What’s new for auscultation

The stethoscope is perhaps the most iconic device associated with medical practice, and the most important part of the stethoscope will always be the part “between the ear tips.” Because I last reviewed high-tech stethoscopes 5 years ago, I thought it appropriate to discuss the new technologies that can improve our ability to auscultate.

Murmurs are common

The incidence of heart murmurs can be as high as 80% to 90% in children, yet the vast majority of auscultated murmurs in children are not associated with structural heart disease and therefore are considered merely “functional” or “innocent” murmurs.^1,2 This creates a dilemma for the pediatrician who, upon hearing a previously undocumented murmur in a child, must decide whether the murmur merits further investigation.

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The ability of pediatricians to distinguish innocent from pathologic heart murmurs pales in comparison with that of the pediatric cardiologist. A study performed at Duke University showed that pediatric residents could distinguish innocent murmurs from 4 common heart conditions with an accuracy of only 33%, while experienced pediatricians did slightly better at 55%.^3,4 In contrast, pediatric cardiologists usually do not need to corroborate their auscultation diagnosis with an echocardiogram. In 2 separate studies, pediatric cardiologists demonstrated the ability to distinguish innocent from pathologic heart murmurs with sensitivities as high as 98%.^5,6 As a result of the poor auscultation skills of primary care physicians (PCPs), at least 60% of “suspicious” murmurs referred to pediatric cardiologists end up being innocent murmurs.⁵ This is not to say that such referrals are inappropriate, but any way we can improve our auscultation skills would save significant medical expenses and unwarranted parental concern.

Murmur interpretation software

Five years ago, murmur interpretation software was available from Zargis Medical, which had established a relationship with 3M Corporation (St Paul, Minnesota), manufacturer of the Littmann Model 3200 electronic stethoscope. The software, called Cardioscan, communicated via Bluetooth wireless connectivity to the stethoscope and prompted the user to record heart sounds from 4 positions on the patient’s chest. The software would then analyze the recordings, report whether a murmur was present, and specify whether an echocardiogram was indicated.

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Unfortunately, Zargis Medical went out of business, and its excellent murmur analysis software became unavailable. However, a South African company, Diacoustic Medical Devices (Stellenbosch, South Africa) recently introduced its own SensiCardiac software to analyze murmurs. One study performed in Australia on a limited number of patients indicated that the SensiCardiac software has a sensitivity and specificity for detecting pathologic murmurs of 82% and 88%, respectively.⁷ This is much better than the performance of PCPs in identifying pathologic murmurs, but less than that of cardiologists.

The SensiCardiac software is used in conjunction with the Littmann Model 3200 stethoscope and is accessed via a subscription service that costs $25 per month for up to 20 tests; $49 per month for up to 100 tests; and $99 per month for unlimited testing. The software is growing in popularity in areas of the world where access to cardiologists is limited.

Keep in mind that the majority of heart sounds and murmurs occur in the frequency range of 5 Hz to 800 Hz. Because human ears are most sensitive to sounds in the 500-Hz to 4000-Hz frequency range, many murmurs ideally need to be amplified for them to be appreciated by examiners.⁸ Computers have no frequency limitations, and computer-assisted auscultation software such as SensiCardiac can improve the ability of physicians to diagnose pathologic murmurs.

Advantages of digital stethoscopes

As a reviewer of medical devices, over the years I have had the opportunity to use a variety of electronic stethoscopes. These stethoscopes convert the acoustic signal of auscultated sounds into digital signals that can be processed for optimal listening. While we refer to these devices as electronic stethoscopes, it is more appropriate to refer to them as digital stethoscopes.

I have been an avid user of the Littmann 3200 stethoscope for many years and I will never go back to using a traditional stethoscope. Chief advantages of going electronic are the reduction or elimination of external sounds that interfere with optimal auscultation, as well as amplification of sounds across selected frequency ranges. Despite poor hearing, I can detect murmurs and lung sounds with my Littmann Model 3200 that colleagues using standard stethoscopes sometimes miss. The Littmann Model 3200 displays the detected heart rate and also enables me to record up to 12, 30-second periods of auscultation. Later, I can replay the recording for the parent merely by pushing a few buttons on the headpiece and placing the earpieces in the parent’s ears. I find this extremely helpful in explaining a murmur or lung findings with parents and, as a consequence, they are more likely to understand and follow my recommendations.

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While I have found the Littmann Model 3200 useful in detecting murmurs, its true utility, I think, lies in auscultation of lung sounds. Because it facilitates the auscultation of rales and rhonchi, I find I have substantially reduced the number of chest x-rays that I order. It does take time to learn the subtleties associated with auscultation with a digital stethoscope (distinguishing pathologic sounds from normal sounds), but given time and patience I am confident that most providers can become expert users of these devices.

Littmann Models 3200 and 3100

In addition to the features discussed above, the Model 3200 is powered by a single AA battery and has a bell, diaphragm, and combined frequency mode. You can download the free StethAssist Heart and Lung Sound Visualization Software from the 3M website (bit.ly/StethAssist-software) to either a Mac or PC for storage and display. The recordings also can be sent to cardiologists for analysis via the Internet. The Littmann Model 3200 is quite affordable at about $400. If you want the acoustics of the 3200 but are not interested in its recording capability, combined frequency mode, and its ability to wirelessly connect to diagnostic software, you can purchase the Littman Model 3100 for about $60 less.

An iconoclastic electronic stethoscope

Thinklabs (Centennial, Colorado) is an interesting company headed by a very interesting entrepreneur. Clive Smith is both a musician and an electrical engineer with a graduate degree from the California Institute of Technology, Pasadena. After years of research and development, Thinklabs has developed a new digital stethoscope that utilizes an electromagnetic diaphragm with a conductive inner surface to provide outstanding acoustics for auscultation.

The device is called the Thinklabs One, and it is iconoclastic in that it does away with the tubing associated with traditional stethoscopes. The user connects the One stethoscope either to high-quality earphones provided with the device or noise-cancelling headphones or earphones of your own choosing. The stethoscope sells for $500. Until recently, the One digital stethoscope was in short supply because the device was used in medical facilities caring for Ebola patients, where traditional stethoscopes could not be used without violating strict isolation protocols.

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According to Smith, the quality of auscultation with the One is “all about the bass.” It can magnify sounds 100 times (compared with 24 times in the Littmann Model 3200), and provides adjustable sound-filtering capability. I have been using the One for several weeks, and I have found the acoustics exceptional. I must admit it was difficult to break with tradition and lose the tubing, but this is how technology moves forward. I am replacing my Littmann 3200 with the One digital stethoscope for everyday use. I encase the earphone tubing in a fabric sleeve that enables me to carry the One stethoscope comfortably around my neck (available at www.etsy.com/shop/relaine) when not in use with the headpiece in my shirt pocket.

The One encourages experimentation. It can connect to a small $30 Bluetooth transceiver that transmits auscultated sounds to Bluetooth headphones or earphones. It can also connect to smart devices to record the auscultated sounds for transmission to specialists. Many of my patients think it’s “cool” that I use earphones to listen to their heart and lungs in much the way they listen to their hip-hop music. Also, I can plug into their mobile phones to “sample” their favorite music.

Smith recently contacted me to let me know Thinklabs is considering adding a tube headset for physicians who want a more traditional look, and interested physicians should contact Thinklabs for availability (www.thinklabs.com).

ViScope MD and CardioSleeve

Two other electronic stethoscopes are worth your consideration. The ViScope MD from HD Medical Group (Santa Clara, California) is the first “visual” stethoscope that displays a simultaneous phonocardiogram on a high-resolution color screen.

With this device, you can essentially “see” what you hear. It can capture 4, 10-second recordings and transfer this data to a computer to document the sounds auscultated. Like the Littmann Model 3200, it features noise cancellation as well as sound amplification, and it has a bell, diaphragm, and combined frequency mode. The ViScope MD integrates an internal algorithm that indicates whether a murmur is present. It has a rechargeable battery and sells for $600.

Finally, in the next quarter of this year, physicians can look forward to a unique stethoscope accessory that not only provides improved auscultation and Bluetooth connectivity to mobile devices, but also adds 3-lead electrocardiogram capabilities as well. The device is called the CardioSleeve from Rijuven Corporation (Wexford, Pennsylvania) and it connects to most standard stethoscopes. The CardioSleeve communicates with a smartphone to display its results that can be uploaded to Rijuven servers for review and analysis. It is being promoted as a device that will improve our ability to detect pathologic murmurs as well as dysrhythmias, and it may be helpful in diagnosing long QT syndrome that is associated with sudden death in pediatric patients. The stethoscope accessory will be priced at $400, and a subscription to its online services will be reasonably priced. I look forward to trialing the device when it becomes available.

Stay tuned

I hope this update will encourage you to do some personal research. Although there is nothing wrong with your traditional stethoscope, taking the time and effort to learn the nuances of digital auscultation will improve your diagnostic capabilities. And, yes, even with digital auscultation, the most important part of the stethoscope will always be between the ear tips (or earphones)!

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REFERENCES

1. Hoffman JI. Incidence of congenial heart disease: I. Postnatal incidence. Pediatr Cardiol. 1995;16(3):103-113.

2. Gaskin PR, Owens SE, Talner NS, Sanders SP, Li JS. Clinical auscultation skills in pediatric residents. Pediatrics. 2000;105(6):1184-1187.

3. Rajakumar K, Weisse M, Rosas A, et al. Comparative study of clinical evaluation of heart murmurs by general pediatricians and pediatric cardiologists. Clin Pediatr. 1999;38(9):511-518.

4. Smythe JF, Teixeira OP, Vlad P, Demers PP, Feldman W. Initial evaluation of heart murmurs: are laboratory tests necessary? Pediatrics. 1990;86(4):497-500.

5. McCrindle BW, Shaffer KM, Kan JS, Zahka KG, Rowe SA, Kidd L. Factors prompting referral for cardiology evaluation of heart murmurs in children. Arch Pediatr Adolesc Med. 1995;149(11):1277-1279.

6. Geva T, Hegesh J, Frand M. Reappraisal of the approach to the child with heart murmurs: is echocardiography mandatory? Int J Cardiol. 1988;19(1):107-113.

7. Botha JS, Scheffer C, Lubbe WW, Doubell AF. Autonomous auscultation of the human heart employing a precordial electro-phonocardiogram and ensemble empirical mode decomposition. Australas Phys Eng Sci Med. 2010;33(2):171-183.

8. Pelech AN. The physiology of cardiac auscultation. Pediatr Clin North Am. 2004;51(6):1515-1535, vii-viii.

Computer-Assisted Auscultation and Sports Exams

Computer-assisted auscultation (CAA) eventually may play an important role when used in conjunction with the preparticipation sports exam. The American Heart Association (AHA) and American Academy of Pediatrics recommend that at such exams pediatricians take a thorough family history, looking for significant heart disease or sudden death from cardiac disease, as well as a patient history to identify patients with a history of chest pain, palpitations, or syncope.

The exam should include documentation of blood pressure and auscultation in both the supine and standing positions. The reason for this is that the most common cause of sudden cardiac death among young athletes in the United States is hypertrophic cardiomyopathy (HCM). While 60% of HCM patients have no murmurs, the remainder have obstruction to blood flow from the left ventricle and also have an associated systolic murmur that increases in intensity when a patient moves from the supine to standing position.¹

Unfortunately, preparticipation sports screening is often performed without the benefit of preparticipation sports screening questionnaires recommended by the AHA. Additionally, pediatricians rarely examine patients in both supine and standing positions during these exams, and the majority of sports teams physicians are orthopedists with little training or experience with auscultation.^2,3

A pilot study has shown that CAA may have potential utility in helping screen patients who may have the obstructive form of HCM by identifying patients with systolic murmurs with grade 3 intensities that are louder when the patient is repositioned from supine to standing.⁴ An advantage of CAA is that it can be performed by medical assistants or nurses, and results can be reviewed by physicians upon completion. Because results are digital, they also can be shared via the Internet so that a second opinion can be solicited from pediatric cardiologists to see if a referral is appropriate.

REFERENCES

1. Maron, BJ. Cardiology patient pages. Hypertrophic cardiomyopathy. Circulation. 2002;106(19);2419-2421.

2. Gómez JE, Lantry BR, Saathoff KN. Current use of adequate preparticipation history forms for heart disease screening of high school athletes. Arch Pediatr Adolesc Med. 1999;153(7):723-726.

3. Koester MC. A review of sudden cardiac death in young athletes and strategies for preparticipation cardiovascular screening. J Athl Train. 2001;36(2):197-204.

4. Watrous RL, Bedynek J, Oskiper T, Grove DM. Computer-assisted detection of systolic murmurs associated with hypertrophic cardiomyopathy: a pilot study. Tex Heart Inst J. 2004;31(4):368-375.

Dr Schuman, section editor for Peds v2.0, is clinical assistant professor of pediatrics, Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire, and editorial advisory board member of Contemporary Pediatrics. He has nothing to disclose in regard to affiliations with or financial interests in any organizations that may have an interest in any part of this article.