Correspondence Address: Dr. Karishma Landge Department of Cardiology, AIIMS, New Delhi India
Source of Support: None, Conflict of Interest: None
The rapid technological advancements in field of cardiovascular medicine over the years has led to the decreased utility of conventional stethoscope. Attempts to improve the flaw in previous versions of stethoscope has led to new enthusiasm in the art of clinical cardiology again. In this article, we try to briefly describe how an electronic stethoscope operates, its difference from conventional stethoscope and what are its potential utility in modern clinical cardiology with the available evidences so far.
How to cite this article: Landge K, Kidambi BR, Singhal A, Basha A. Electronic stethoscopes: Brief review of clinical utility, evidence, and future implications. J Pract Cardiovasc Sci 2018;4:65-8
How to cite this URL: Landge K, Kidambi BR, Singhal A, Basha A. Electronic stethoscopes: Brief review of clinical utility, evidence, and future implications. J Pract Cardiovasc Sci [serial online] 2018 [cited 2022 Dec 1];4:65-8. Available from: https://www.j-pcs.org/text.asp?2018/4/2/65/240969
The stethoscope was introduced by a French Physician René Laennec in 1818. Since then, 200 years has passed and there have been immense advancements in the field of radiology and cardiac imaging. The major cause of death and morbidity is still cardiovascular disease, and early diagnosis is quintessential to saving their lives. There are a number of noninvasive investigational modalities for early diagnosis of cardiac disorders, such as electrocardiography, echocardiography, cardiac computed tomographic (CT) scan, and cardiac magnetic resonance imaging, which have devalued the use of conventional stethoscope in modern times. The important limitations inherent to these advancements are the necessity of trained personnel to do these investigations and for their interpretation. The other important limitations are their cost and availability only in advanced centers. Compared to this, the stethoscope is relatively easier to use, cost-effective, and easily available and can be used by paramedics and nurses. This is important in a developing country like India where a penetration of advanced cardiac imaging into the rural areas is less. Digital stethoscopes offer a new perspective over the conventional stethoscope and would be an effective arsenal in armamentarium of modern healthcare workers. This article provides a detailed outlook on the clinical utility of electronic stethoscope and modern smartphone applications.
The parts of the conventional binaural stethoscope are shown in [Figure 1]. It basically consists of chest piece which has diaphragm and bell for picking up high- and low-frequency sounds, respectively. These sounds are transmitted as sound energy through hollow tubing which is usually 18–26 inch in length conventionally. The hollow tubing splits into a binaural which is attached to the pair of ear pieces. When a physician uses the stethoscope to auscultate, he/she closes a circuit where sound energy is transmitted with some minimal energy loss from the patient's chest to the physician's ear for interpretation.,, Multiple variables are involved which can affect the sound quality in a traditional acoustic stethoscope such as:
Figure 1: Parts of a conventional stethoscope, the chest piece consists of diaphragm and bell connected to the ear piece through hollow tubing.
Sound quality is usually low, especially so in obese and in patients with thick chest wall
Any break in circuitry can dampen (e.g., air leak from hollow tubing) or sometimes cause complete abolition of sound transmission
Sound data obtained cannot be analyzed, processed, or utilized in any other way.
Electronic stethoscope attempts to improve on some of the features of the traditional acoustic stethoscope. The parts of an electronic stethoscope are shown in [Figure 2]a and [Figure 2]b. There are three important steps before a sound arriving at the chest piece is transmitted to the ear piece [Figure 3].
Figure 2: (a and b) The electronic stethoscope Littmann M3200 contains a large chest piece with a battery case below it. The rest of the parts are similar to the conventional stethoscope. The chest piece contains the LED display showing volume control, battery status, heart rate and a control mode to choose between bell, diaphragm, and extended mode. Not shown in picture is the Bluetooth connectivity option.
Heart sound is converted into digital analog by either using microphone or the piezoelectric sensor to acquire and transduce the sound energy into electrical energy. This is then amplified and processed by passing through a band pass filter to reduce the unwanted noise corrupting the sound signal.
A second round of denoising is done with a digital filter, to extract the signal of interest from the frequency band. Some advanced artifact removal techniques are incorporated here. The heart sounds obtained in the process are normalized to a particular scale and are segmented into cycles. This helps us in detecting the heart sound components clearly.
Signal processing module
The raw data obtained as an electrical signal are further represented in parametric form and are classified. This helps in decision-making.,, For example, the sound data obtained from electronic stethoscope can be transferred via Bluetooth to laptop and analyzed by special software. One such example given along with Littmann M3200 model is the Littmann Steth assist software (St. Paul, Minnesotta, U.S.A) [Figure 4].
Figure 4: Littman Steth assist software provides sound in digital data expressed as phonocardiogram.
Using these new software, the sound can be converted into digital data and expressed as phonocardiogram or spectral graph. It can be converted into other common audio formats such as wav. It can be played in half speed for better appreciation of sounds.
Some sounds recorded by Littmann 3M3200 are provided in [Audio 1] and [Audio 2]. For best-quality listening, any standard earphones can be used.
Various Electronic Stethoscopes in Market
There are various electronic stethoscopes available. The two most common ones used are the Littmann 3M model and the Thinklabs One Digital. There are other models which are not used as popularly as the former two. These are Welch Allyn Elite electronic stethoscope, Cardionics E-scope II, EcoScope, and ViScope. Some of these models, for example, the Welch Allyn Elite electronic stethoscope, are no longer available. The comparison between the two popular stethoscopes is elaborated in [Table 1].
Table 1: Comparison of different popular electronic stethoscopes
NCT01040923: Validation of the cardio sound sonospectrographic digital electronic stethoscope in diagnosing coronary artery disease versus CT angiography; patients presenting themselves for cardiac CT angiography (n = 200) sensitivity: 89.5%, specificity: 57.7%
NCT01605669: Correlation of auscultatory severity of aortic stenosis with transthoracic echocardiography; patients with aortic stenosis seen in the internal medicine clinic (n = 50), sensitivity: 85.7%, specificity: 72.4%, accuracy: 75%
NCT01665820: Study EM-05-012530 benefit of auscultation with 3M™ Littman 3200 electronic stethoscope to diagnose murmurs and heart pathologies in overweight and obese patients with increased layers of adipose tissue; patients with a body mass index >30 and who have been scheduled for an echo examination (n = 30), sensitivity and specificity not mentioned.
There has been a rapid development in smartphone applications and mobile health technology. This implies the use of mobile phone for:
Collecting patient data
Delivery of healthcare information to doctors and patients
Limitations of Smartphone Applications and Electronic Stethoscope
Independent clinical studies which showed promising results of these applications and stethoscope were done in an ideal setting without much ambient noise. This is in stark contrast to the real-world scenario, with a plenty of background noises corrupting the recorded sound data
Heart sound and murmurs have complex characteristics which are dynamic in nature, i.e., the same disease can have different types of murmurs and different diseases can have similar murmurs. The murmur can even vary within the same patient with the onset of arrhythmia or cardiac dysfunction. This requires the development of complex algorithms and use of machine learning. This is the subject of future research going on in this area
The dataset which has been used in the studies may vary from population to population and between different ethnic races. Validation would need to be done with larger datasets and with properly blinded trials
Well-designed double-blinded controlled trials are required for approval of devices from Food and Drug Administration (FDA) and other health professionals
Early diagnosis of cardiovascular disorders carries tremendous implications in terms of morbidity and mortality. The conventional stethoscope is almost outdated today due to rapid development of robust cardiovascular imaging techniques. However, with the advent of electronic stethoscopes and smartphone applications, which overcomes the usual limitations of conventional models, there has been resurgence in the use of stethoscope once again. A brief difference is mentioned in [Table 2].
Table 2: Brief difference between electronic and conventional stethoscope
If proper validated automated cardiac disorder detection technologies are incorporated, the target user of stethoscope will slowly shift from doctors and nurse to patients for self-use. However, no such device exists as of now, and further large-scale validated trials are required for these newer devices to be approved by the FDA and come into routine clinical practice.
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