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Wearable Technology is Here to Stay

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woman checking smart watch on wrist

The number of smart wearable devices on the market and the types of activities they monitor have increased dramatically over the last few years. An estimated 20% of U.S. residents currently own a smart wearable device and the global market is expected to reach $70 billion by 2025.

Tracking health with purpose
These digital devices are usually worn on the wrist like a watch but can also be attached to belts, shirts, shoes, socks and even glasses. These devices contain tiny sensors that collect information and send it to a smart phone or computer. Different health-related wearable devices can measure and monitor a variety of parameters related to health including:

  • Heart rate and rhythm
  • Blood oxygen and sugar levels
  • Blood pressure
  • Temperature
  • Gait speed
  • Sedentary versus active behavior
  • Energy expenditure
  • Ultraviolet light exposure
  • Body position and body movement
  • Sleep behavior
  • Respiratory rate
  • Lung function
  • Snoring, wheezing and coughing
  • Dietary behavior
  • Mood and stress levels

These wearable health care technologies provide information that may advance one or more of the following health goals:

  • Maintaining good health and preventing disease
  • Identifying the presence of new clinical conditions early on
  • Improving management of chronic diseases to prevent complications and prolong life

Ideally, wearable technologies could improve the quality of health care while also reducing the cost of that care.

Starting with steps
Wearable technology is here to stay. These devices have the potential to play important roles in the prevention, detection and treatment of common cardiac conditions. However, like with any technology, we need to be aware of its limitations of data collection and management.

In general terms, wearable devices can be categorized as consumer-grade or medical-grade. In my cardiology practice, my patients send me data from their consumer-grade wearable devices to describe and quantitate health habits such as physical activity, calorie intake and sleep patterns as well as health biometrics including weight, resting heart rate and blood pressure.

As wearable technology became more user friendly and affordable, step counting became the most popular variable measured by my patients. They traded in their clunky pedometers for wristwatch type wearables that count daily steps using triaxial accelerometer technology which detects posture, acceleration and whole-body movement. The devices send information directly to apps that can track the information in a number of formats and then send it off to family, friendly virtual competitors and health care providers. This kind of tracking resulted in improvements in health behaviors and biometrics. In an analysis of 26 studies with almost 2,800 participants, investigators found that the behavior of habitually tracking steps was associated with an increase in physical activity of about 2,200 steps per day as well as a decrease in body mass index and blood pressure.

However, step counting technology is not 100% accurate. Where the wearable device is placed on the body is one of the most important factors affecting step measurements. A centrally located sensor on the chest, which are embedded into vests or mounted onto chest straps, offers the least amount of data errors compared with other body locations. They are most accurate in detecting posture, acceleration of movement forward and whole-body movements.

While wrist placement is the most common of consumer wearables due to the convenience easy accessibility, ankle-mounted sensors are better suited to measure steps and energy expenditure. I personally noticed I often accumulated more steps when I wore my device on the wrist of my right (dominant) hand because it is more active in isolation (like petting my dog). When I moved the device to my non-dominant arm, I noticed a small but consistent decrease in my daily step count without any change in my general routine.  

The heart of health tracking
Step counting was quickly followed by an increased popularity in heart rate monitoring whether it be one’s heart rate at rest, during exercise, during recovery from exercise or during sleep.  

Heart rate tracking is important as changes in the average resting heart rate over time may indicate an increase or decline in health. For example, a person’s resting heart rate may decrease due to their fitness level increasing or as a side effect of a new medication. It may also increase due to dehydration or stimulant use such as decongestants. 

Heart rate during exercise is often a reflection of exercise intensity or effort. Cardiorespiratory fitness and the number of calories burned improves over time as the intensity of the exercise increases. If you are walking a dog that stops often to sniff, your heart rate is unlikely to increase very much. While this activity is better than sitting on the couch, its intensity is insufficient in improving overall fitness.

Experts recommend getting at least 150 minutes a week of moderate aerobic activity or 75 minutes a week of vigorous aerobic activity (or a combination of both). As a general rule of thumb, the target heart rate during moderate-intensity physical activity is 50-70% of one’s maximum predicted heart rate and 70-85% during vigorous physical activity.

Awareness of accuracy
Most wearable devices monitor resting heart rate with reasonable accuracy when the rhythm is normal. However, consumer grade wearable devices are often less accurate when tracking higher heart rates due to movement of the limbs and sweat—both of which can affect the contact of the sensors with the skin.  

ECG sensor measurements are the gold standard of which newer wearable devices are compared to in studies of accuracy. While the newer devices on the market are not perfect, a number of studies performed on generally healthy individuals who were engaged in a wide range of activities have demonstrated an accuracy rate of less than 10% absolute error. In a study of older patients with heart disease undergoing cardiac rehabilitation, 5% of heart rate measurements detected by wrist worn devices were substantially inaccurate.

Tracking abnormal heart rhythm
The newest application of heart rate monitors is the detection of abnormal heart rhythms, specifically atrial fibrillation. Atrial fibrillation is abnormal heart rhythm characterized as “irregularly irregular,” which is often substantially faster than the normal resting heart rate. I use the example of the sound of popcorn popping in the microwave to describe this abnormal heart rhythm. In some patients, atrial fibrillation is associated with symptoms of a rapid or irregular heart rate, fatigue or reduced exercise tolerance. Other patients may be completely asymptomatic. In older patients and those with chronic diseases such as hypertension, diabetes or heart failure, the presence of atrial fibrillation increases the risk of stroke. The early identification of atrial fibrillation provides an opportunity to prescribe treatments aimed at reducing this risk.

The Apple Heart Study was a landmark study designed to determine the utility and accuracy of the Apple Watch Series 1 through 3 in identifying atrial fibrillation in adults. In this study, 34% of individuals who received a notification of arrhythmia were later found to have atrial fibrillation using traditional ECG based monitoring. It is important to note the device obtained “spot” tachograms to detect irregular heart rates—indicating the device does not monitor the heart rhythm continuously. If an irregular heart rate were detected during one of these spot checks, it would initiate a cascade of more frequent tachogram collections. Then, if five out of six sequential tachograms were classified as irregular within a 48-hour period, the user was notified of the potential arrhythmia.

Starting with the Apple Watch Series 4, the device began using electrodes to generate a single-lead ECG providing two mechanisms for rhythm assessment—the first being rhythm notification and the second being single-lead ECG downloaded as a PDF for interpretation.

Cleared by the FDA, this single-lead technology is particularly useful for individuals with symptoms such as palpitations or irregular heart rate to determine if the heart rhythm is abnormal during these symptoms. It may also be useful in detecting atrial fibrillation in the patient who is having frequent bouts of atrial fibrillation lasting hours or days because the technique of “spot” monitoring is more likely to detect something that is occurring frequently. 

For my patients in whom I want to be confident they are not having short bouts of intermittent atrial fibrillation, I recommend that an ECG based heart monitor be worn for two weeks. 

Future of wearables
Since wearables are here to stay, maximizing their utility in health management is key. Important objectives must be met by the technology industry as it advances including:

  • Data accuracy
    It is vital to ensure the accuracy of these devices so the information gathered is actionable in terms of improving clinical care.
  • Data privacy
    It is also important to prioritize managing wearable data in ways that are secure, private and efficient.
  • Device availability
    If these devices are shown to improve clinical outcomes, the next step is to make them widely available to the population, regardless of socioeconomic status.

Heart health and fitness are key components to a healthy mind, body and lifestyle. To learn more about Cooper Clinic preventive exams and how an annual exam can help you manage and improve your health, click here or call 866.906.2667

Article provided by Nina B. Radford, MD, Cooper Clinic Cardiologist and Director of Clinical Research.