What is an AI stethoscope?

There is no medical instrument more associated with a doctor than the stethoscope. A stethoscope is used to listen to internal sounds of a human or animal body (termed auscultation). It is composed of a small disc-shaped resonator that is placed against the chest, and two tubes connected to earpieces.

The main uses of a stethoscope include:

• Listening to Heart Sounds: It allows doctors to listen to heart sounds, including the heartbeat and heart murmurs. This helps in assessing the heart's rhythm, rate, and nature of heart sounds, which can indicate conditions like heart valve abnormalities or heart defects.
• Examining Lung Sounds: Doctors use it to listen to lung sounds, which can reveal a lot about respiratory health. They can detect abnormalities like wheezing, crackles, or reduced breath sounds, which are important in diagnosing conditions like pneumonia, asthma, bronchitis, or pulmonary fibrosis.
• Checking Blood Pressure: When used with a sphygmomanometer (blood pressure cuff), a stethoscope can help measure blood pressure. The doctor listens for the sound of the blood starting to pulse through the artery as the pressure in the cuff is released, known as the Korotkoff sounds.

In practice, the stethoscope amplifies the internal sounds of the body, making it easier for the healthcare provider to hear and interpret them. This amplification occurs through the following physical mechanisms:

• Sound Collection: When the chestpiece (either the diaphragm or the bell) is placed against a patient's body, it picks up sound vibrations. For example, when placed on the chest, it can detect the sounds of the heart beating.
• The Diaphragm: The diaphragm, a thin, tight, plastic disc, is better at picking up high-frequency sounds like breathing. When sound waves hit the diaphragm, they cause it to vibrate. These vibrations are larger than the original sound waves, effectively amplifying them.
• The Bell: The bell, used for lower frequency sounds like certain heart murmurs, works similarly. It is a cup-like part that captures sound waves. When these waves hit the inside of the bell, they cause the air inside to vibrate. This vibration is then transferred up the tubing.

An alternative to mechanical sound amplification is to take advantage of electronics and especially digital electronics. For example, a hearing aid increases the loudness of sound via electronic components such as a microphone, ampli­fier, frequency filter, and mini-loudspeaker (QH). The combination of frequency filter and amplifier allows certain frequencies (high pitch or low pitch) to be selectively amplified. The microphone is a transducer that converts sound into an electrical signal through inductance, capacitance, or the piezoelectric effect.

The electronic stethoscope from the company Eko Health, which was spun off from the Mayo Clinic, has garnered the most attention. Their Eko Core 500 digital stethoscope uses a piezoelectric transducer along with various digital filtering and amplification to accentuate the most relevant heart and lung sounds. However, more importantly, they combined this traditional stethoscope functionality with an ECG to provide improved diagnosis of heart ailments (Figure 1).

As a reminder, ECG (Electrocardiography) "is the process of recording the electrical activity of the heart over a period of time using electrodes placed on a patient's body." The ECG provides valuable medical information about the heart. An ECG reading can be used to identify heart attacks, pulmonary embolism, heart murmurs, cardiac arrhythmias, and heart failure.

In the not-too-distant past, you had to go to a medical specialist to have your ECG, but more recently there has been a proliferation of consumer ECG devices touting surprising accuracy. In particular the Apple Watch ECG (introduced in Series 4) has received much fanfare. In a previous post, I described a study that showed that the Apple Watch ECG achieved roughly 99% accuracy at diagnosing atrial fibrillation (AFib), the most common cardiac arrhythmia. 

The biggest difference is that the Apple Watch ECG has 1 lead whereas the medical-grade ECG has 12. Each lead represents a different "direction" looking at the electrical signals of the heart. In addition, The medical ECG also has the advantage of having the detectors positioned closer to the heart and taped down to minimize movement resulting in a more sensitive and accurate reading that is able to diagnose a wide variety of conditions, and not just AFib.

The ECG on the Eko stethoscope contains 3 leads, and it is placed directly on the chest close to the heart. As a result, it can provide more detailed information than the typical consumer-grade ECG. According to the promotional literature, in 15 seconds, the Eko stethoscope can detect three types of heart disease: heart failure; atrial fibrillation or irregular heartbeat, which is the biggest cause of stroke; and valvular heart disease (e.g. heart murmurs). As a bonus the stethoscope provides the doctor with auscultation (internal sounds of heart and lungs) which is enhanced by electronics as described above.

Heart failure is not a general term but refers to a specific condition. According to the American Heart Association (link), "Heart failure is a lifelong condition in which the heart muscle can't pump enough blood to meet the body’s needs for blood and oxygen. Basically, the heart can’t keep up with its workload.... This can show up on an ECG as changes in the size and shape of the wave." A more complete diagnosis requires an echocardiogram (ultrasound). Over time the heart muscles can weaken, resulting in reduced pumping and ejection from the left ventricle which distributes blood to the body (termed low ejection fraction heart failure, one of the most common types of heart failure).

In April, Eko Health received FDA clearance for the diagnosis of low ejection fraction heart failure using their digital stethoscopes (Fierce Biotech). A key feature is the use of AI to assist in the interpretation of the ECG. Previously the stethoscopes had received FDA clearance for detecting atrial fibrillation and heart murmurs. 

Meanwhile over in the UK, the Eko AI stethoscope has been deployed to 200 clinics throughout north-west London and Wales, marking the country's initial introduction of this technology as part of the National Health Service (NHS). Experts suggest that this implementation may also result in substantial financial benefits, potentially saving £2,500 for each patient diagnosed with a heart ailment in primary care before they need emergency hospital treatment.

Finally it should be stated that while the device is referred to as a digital stethoscope, and looks like a stethoscope (Figure 1) which possesses an iconic status in the medical profession, most of the key functionality is coming from the integrated ECG. This clever and convenient design enables a fast and accurate ECG as part of a routine checkup.

Figure 1. The Eko digital stethoscope combines the functionality of an electronic version of the traditional stethoscope with a 3-lead ECG monitor placed on the chest. It can diagnose with high accuracy three types of heart disease. On the website, the list price is ~$500.