Neha Pathak, MD, FACP, DipABLM: Welcome to the WebMD Health Discovered podcast. I'm Dr Neha Pathak, WebMD's chief physician editor for health and lifestyle medicine.

Today, we're talking about the best way to leverage the information you get from your wearables, the smartwatch or fitness tracker you wear that monitors your health every day. Wearables provide valuable information about your sleep score, heart rate, step count, and blood oxygen levels, and many of us have them.

But how many of us are bringing that data into our appointments with our healthcare providers? And how many of us are using those numbers to actually change our habits? What can these numbers really tell us about our baseline and important shifts in our health? We'll talk about the difference between a meaningful change and a one-time blip, how sleep, stress, travel, exercise, and daily habits can affect your readings, and when a notification may be a reason to check in with your healthcare provider.

Whether you already track everything or are simply curious about what these devices can do, this conversation will help you turn data into useful, practical insights. But first, let me introduce my guest, Dr Calum MacRae. Dr MacRae is a cardiologist at Mass General Brigham, a professor of medicine at Harvard Medical School, and PI of the Apple Health Study.

Welcome to the WebMD Health Discovered podcast, Dr MacRae.

Calum MacRae, MD, PhD: Good morning. You're very welcome. Nice to meet you.

Pathak: I am very excited to jump into our conversation today because I get questions about wearables all the time from friends, families, and patients alike. So, before we jump into our topic for today, I'd love to ask about your own personal health discovery, your aha moment that brings you to the research that you're doing today.

MacRae: I originally trained as a physiologist and biophysicist, and so when I was an undergraduate, I had the opportunity to do a significant number of experiments on myself. And one of the things that amazed me was just how dynamic our physiology can be at times when potentially we are not paying attention.

And there is a lot of signal that is sitting in the background unrealized, undiscovered, unless you're actively measuring it. And so, from my standpoint, that really triggered a career where I've spent most of my time trying to think about how we measure biology in a way that allows us to understand the mechanisms of that biology, but also understand how people travel through life and how their final function is a real consequence of so many of the things that happened to them on that journey.

So, I have always been interested in measuring things in a more rigorous and quantitative way, and so that really fit very nicely, I think, with the wearable theme that has emerged in the last probably 10 to 15 years.

Pathak: I'm very curious then, how you think about wearables, where now you don't have to wait until you are in the doctor's office to have that potential shift identified, where people can start wearing smartwatches, fitness trackers, and everyone seems to have one, and they can now come in proactively if there is some shift in their heart rate or in their sleep parameters.

So, help us understand a little bit about the types of health information that these wearables can actually measure accurately today.

MacRae: The reality is that many of the consumer-grade tools are actually quite accurate. So, for example, on either side of peak exercise, there's a lot of information that can be captured, and the context of knowing just exactly how much exercise you did, particularly if you're aware of what you did previously, allows you to begin to anchor individual's physiology in their own past performance and their own past physiologic history.

I think the difficulty is when sometimes patients will come with an isolated variable. So, one of the most classic presentations is individuals starting to wear their wearables overnight and realizing that their heart rate goes down into the 40s or 30s overnight. Because there's often this misguided sense that the normal range is literally a hard and fast and fixed normal range for the individual, when it's really just a population distribution.

So, I think one of the things that I've found as being particularly useful about wearables is it helps you work with your patients or with users of the wearables to help them understand their own personal normal distribution. I think that's actually really important, and then that lets them annotate their lives in a way that becomes quite useful for them and potentially for their physician partners.

But I think what I've found is that oftentimes the first time that people present, there's an uncertainty simply because of the fact that it's not clear what the context is that has changed, because the only thing that is being measured is the actual wearable output. And in order to truly understand it, you need to go back and then document what is it that actually happened, what triggered that sleep disturbance, what triggered that heart rate change, and that often ends up being the way in which individuals are empowered to begin to start to think about their own physiology over a, over a lifespan, which I think is what we should be working in a preventative and lifestyle venue as you do, to try and empower the individual to understand their own physiology at a level of granularity that lets them not only identify when things have changed, but potentially also help uncover what are the triggers for that change.

So, for example, sleep is often disturbed by a whole host of external parameters, including travel, loss of day-night cycle, alcohol use. And those can be very carefully documented and accurately documented.

When we looked at sleep in the Apple Health study, it's become quite clear that there's a really wide variation in normal distribution of sleep that tends to be more constrained the older you get.

I think you learn that, in many ways, as you age, sleep is one of the things that you really need in order to preserve functionality for the following day and beyond. But I think that's probably true much earlier in life. We just have a bigger dynamic range of adaptability the following day to be able to cope with it.

You're starting to see younger and younger people realize that sleep is a fundamentally important physiologic task, and so I think that has really changed the way that people have started to think about nutrition, day-night cycle, exercise, and sleep.

I will say that's one of the things I'm particularly conscious of is trying to de-medicalize some of this so that it actually ends up being a partnership between a clinical physiologist, a primary care doctor, a lifespan physician, whatever you want to call it, and the individual to learn enough about themselves early enough in their lives that they can build those preventative strategies and also surveil what's happening to their physiology in a rigorous enough way to understand when it's beginning to deviate systematically from normal.

So, there are probably a thousand ways to get to a heart rate of 30. And if you don't know the antecedents, it's very difficult to discriminate between them immediately when you see somebody. So, I think you're gonna start to see that become a really critical part of longitudinal evaluation in health, wellness, and disease.

Pathak: As a primary care doctor, I'm also always thinking about what's actionable in your day-to-day life?

When you first start potentially using this tool, you're getting to know yourself and you're trying to figure out what is normal for you. But there are also contextual factors that might say, okay, your heart rate dipping down into the 30s associated with these symptoms, or you're exercising and this might be a new sort of exercise regimen, so yes, your heart rate is going to become more rapid, but when it becomes X and you feel the symptoms of chest pain, shortness of breath, that's actually not a time to explore your own responses.

That's a time for medical intervention. So, how do you talk to patients around that?

MacRae: I always tell people the time to call me is not when you get chest pain at rest. It's when you can no longer do your routine walk in the time that you were able to do it for the previous 12 years or whatever. A lot of it is understanding that personal baseline. The things that people love with wearables are when they give information that you yourself can deploy. So sleep disturbance is obviously one that's quite important. If you have a baseline on your sleep and you see that it's disrupted and you show people the physiologic effects of that disruption the following day, that's an incentive for people to realign their sleep behaviors in the right direction.

One of the things that I think is, at the moment, not completely clear in many instances is how to define reserve. So one of the things that we would like to do, and we're actively working on, is if you know your reserve in each domain, there are some domains where you can actually improve your reserve.

There are others where you may not at the moment be able to improve them, but we will work on ways, if we understand that biology, to begin to think about how to improve them. And then the third piece is instead of trying to measure blood pressure with wearables, looking at indices that predict the likelihood that blood pressure may be elevating, and then give the patient the tools and instruct them in how to measure their own blood pressure in a way that not only either refutes or confirms the possibility of hypertension, but also prepares them for that initial visit.

I have been consistently thinking about that transition for a long time. But I think Apple's approach to that transition was really well designed on the premise that it is not making a diagnosis, it's empowering the individual to measure their own physiology in a way that then allows them to make the choices about whether to engage their health team or not.

And I think that's gonna be a theme you're gonna start to see more and more. You're gonna start to see entities say, "Look, your exercise performance has changed over the last whatever few days or weeks. These are the potential areas that might be causing this particular pattern of decline. Here are the tools that you can use in order to be able to do that."

All of the wearable entities, they're all beginning to develop strategies for empowerment. They want to be able to identify vulnerabilities much, much earlier and begin to work to reduce the impact of those vulnerabilities or to reverse them completely.

Pathak: Where is it that you find wearables the most helpful when someone has a condition that they're seeing you for? So whether it's heart disease, diabetes, high blood pressure, sleep disorders, where do we see the biggest value in these tools?

MacRae: I have to say, the biggest value in my practice has been in rhythm detection with ECG. That in the past, we would have relatively rare events. We would do 7-, 15-, 30-day telemetry and still not be able to pick it up. And now we actually have the ability to get a rhythm strip in real time from on the planet, and I think that's been very useful and has helped my practice dramatically.

I think it's really one of the signature outputs of wearable tools. The other area I think that's been quite powerful from my standpoint is just documenting how much exercise people actually do, is showing step counts in a quantitative way that allows you and your patient to actually agree on what the metrics are.

And you can give people concrete metrics, 'cause often what ends up happening is people are not measuring either the total distance traveled or the time they take to travel it, and wearables allow you to do that in a way that lets you actually compare people with themselves over time, and I find that particularly powerful.

I think sleep is starting to be an area where that is also helpful. People are beginning to use it in that way, but the reality is that this is a rapidly evolving field. I think you're gonna see more and more metrics. Over time, you've started to see some of the wearable makers begin to predict ovulation, menstrual cycle. There's a whole slew of things that I think are tractable in this space if you have the right contextual information.

Pathak: So let's dig into the abnormal rhythm detection that you mentioned, because I have noted that a lot in even just folks in my life who've talked about, "Oh, I found out I had AFib because my smartwatch told me." So help us understand a little bit, what does that mean?

What are they detecting? What would one be seeing? How would your device help you identify that?

MacRae: So again, I'll speak about the system that I know the best, the Apple system. Their watch PPG at the wrist can actually detect irregular rhythm. And so if you don't have the diagnosis, there's an irregular rhythm notification. That then could, for example, trigger you, it's the way it's set up is not necessarily in that domain at the moment, trigger you to take an electrocardiogram using the single-lead ECG at the wrist, which then can confirm or refute the diagnosis of atrial fibrillation, and you can then send that to your physician.

The other way that we've seen it is to have people come in and complain of palpitations, but relatively infrequently not really know, have had negative telemetry on a couple of occasions. And there, people are actually buying the watch or being advised to buy the watch or similar devices so that they can then assess their rhythm, take a rhythm strip, a 30-second rhythm strip. And there I've found that the most useful thing is to get them to get the device, bring it to the next clinic visit, and then instruct them on how to use it. 'Cause oftentimes, people know how to collect the ECG is the single most important thing.

Although there are lots of really helpful YouTube videos on all of this as well. And then the final space in which this has been very useful is looking at rate control in people that are in atrial fibrillation, so that you can either, using just the PPG data or the ECG data, document very clearly whether a change in rate control using different doses of nodal blockers is adequate or inadequate, both at baseline and during exercise.

And I think that's been a real advance, 'cause we used to have to either take a resting ECG and then do a stress test to assess rate control, and now we have it in the real world in a much more rigorous and quantitative way than used to be possible.

Pathak: That's really helpful. So, essentially we are saying that you are able to adjust medications based on this information rather than the sort of long tail of diagnostic information that you'd need to collect with these various tests, stress testing, et cetera.

MacRae: That's exactly right. And it's, it has definitely condensed my approach to atrial fibrillation quite substantially. It makes it much more of a partnership. You're educating the individual on the biology of atrial fibrillation. They're educating you on their lifestyle and other factors that are important to them.

That's, that's exactly what being a physician should be in a deep therapeutic relationship.

Pathak: And as we're coming to the end of our time together, I'd love to ask you about how you counsel patients, because it can at once be empowering to be able to have this information at your fingertips, but it can also conversely be really stressful and, in some cases, anxiety-provoking. And we know stress is a major pillar of lifestyle intervention as well.

So how do you counsel your patients around using this technology so that we can manage that pillar as well?

MacRae: So I'm obviously very conscious of the fact that, particularly in a medical setting, it's our duty to tailor our advice to the whole person. And so there are some people for whom too many triggers are, as you point out, so stressful and detrimental that it's difficult for them to manage that.

So part of the initial counseling is having them understand what the normal range looks like, what we're trying to accomplish, what they're trying to accomplish, what we're trying to do together with the wearable tools that will be helpful for them, when to be concerned, when not to be concerned.

And in many instances, what I've done is, and that you can often manage this remotely, and you can say, "Look, show me what it is that you're worried about." You can help put their mind at ease, and then that literally changes their entire approach to how they use the devices going forward.

You know, there are lots of people who will come to physicians for a set of symptoms or a set of metrics that they themselves have defined about which they're becoming anxious. And a lot of it is how do you establish where they are within their own normal range, within a broader setting, whether or not there's anything physiologically detrimental going on.

And reassurance is as much a part of what it is to be a physician as therapy and intervention. So, as I said earlier, it's a partnership. The process of empowerment takes different steps and different stages with different people. That applies both on the physician side and on the patient or consumer side.

And I think we just have to, as we, I think, are talking about here, we have to build the tools that allow this to be done in a way that benefits the individual rather than as a sort of broad-based, one-size-fits-all. And I think, at the end of the day, that's also what you're seeing in precision medicine.

So precision health and precision medicine are clearly overlapping concepts, and when you have more precision in your wellness, you're gonna have better precision in your health. And I think you're gonna start to see that happen over time.

In fact, I, to be 100% honest, I think it's much easier to get precision, i.e. real detailed information on the individual in the wellness space at the moment than it is to do it in the health space. Which is one of the reasons you're starting to see consumers bypass the medical system and go direct to the source for not only wearable physiologic data, but also lab data and a whole host of other biological parameters, scans and skin surveys and the like.

And I think that's a message to the medical profession that we're not doing what we said we were planning to do 40 years ago. It's taken us a long time to begin to really introduce precision at the medical side of the equation. Maybe it's gonna be easier to do it at the wellness side of the equation.

And as we come to our the close of our conversation, I'm gonna cede the floor to you.

Pathak: I'd love to hear what you're most excited about, and then your piece of advice to someone who is about to get their first wearable or has their first wearable, just advice you would want them to know as they embark on this journey.

MacRae: The things I'm most excited about are the new sensors that are likely to come in the next, you know, decades. The integration of existing information with sensor-driven information to build a much more complete picture of the individual, and to do it much, much earlier in life.

I mean, the current model for prevention is show that it works in a disease and then progressively edge it back into earlier stages of the disease. Wouldn't it be fantastic if we actually had prevention for prevention's sake? Here are your baseline vulnerabilities. Let's work on those for decades before you ever need to see a clinician.

So I think that, from my standpoint, is super exciting. And I think it's a vista that many people in this field share. I'm excited because so many primary care physicians are beginning to recognize that this is actually the real way to maintain health, and waiting for a magic biomarker to come from existing care and move backwards takes a long, long time.

It's much better to do this in collaboration with the public and the consumer before they ever become patients. The second thing that you asked me to address was advice to the new wearable user is literally learn about your device. I think one of the things that we realize, this is the case just even for the basic communication functions of the phone, is that the vast majority of people use only a fraction of the functionality.

And I think one of the things that I've learned as a clinician with the devices that we all use, echocardiography, electrocardiography, you can do so much if you're properly trained in it. And I think one of the things I would just advise people who buy a wearable is to use the web to really understand how to not only collect data better, but then use—I mean, one of the nicest things I've seen in the last six months even, is almost all of my patients are now bringing not only their own analysis of their own wearable data from one of the existing large language models, one of the existing AI vendors, but they're also bringing their synthesis of what it is that they want to talk about.

And what I've realized is that even there, bringing not just the output, the final output of the AI model, but actually understanding the conversation that the patient has had with the model or with the wearable or with whatever other data they're collecting, that's actually where you learn most about the individual.

So thinking about these things not as traditional point-of-care or point-of-delivery interpretations, but thinking of them much more as longitudinal partnerships, data collection, data interpretation, and iterative remodeling of lifestyle as well as medical care. Those are the ways that I think wearables should be used, and investing the time and energy in learning about how to use your wearable best is really important.

Pathak: I want to thank you so much for your time and for this conversation. I know I've certainly learned a lot, and maybe I will turn back and find that wearable that I have somewhere and start using it. So thank you so much.

MacRae: You're very welcome. It was a pleasure to be here. Thank you.

Pathak: I'd like to share my three key takeaways from this discussion. First, wearables are not just vanity metrics to compare yourself to others or to be rigid with yourself and your own activities. They can be a valuable tool for your health and well-being. They allow your healthcare visit to extend beyond the exam room.

You're monitoring your health not just when you're in the office with your healthcare provider, as in blood pressure, heart rate, weight, BMI, but also bringing important information like your daily heart rate pattern, sleep patterns, and activity levels into your health and wellness conversations. By tracking your health, you can also monitor changes over time, which is really important when it comes to shifts that may be indicating a new health condition.

Second, wearables remind us that context matters by encouraging us to pay attention to the factors contributing to our health. A change in sleep patterns, heart rate, or activity may be related to some of our habits, it may be related to something that just happened in our lives, or the information can be related to something that's gonna happen to our bodies on the horizon.

The information we receive through wearables is an invitation to get curious about lifestyle changes and things we can do to support our health and well-being. And finally, wearables are not a replacement for medical care and treatment. They allow us to notice it's time to talk to our healthcare provider if consistent shifts are happening that may indicate a health problem.

To find out more information about Dr Callum MacRae and wearable technology, make sure to check out our show notes. Thank you so much for listening. Please take a moment to follow, rate, and review this podcast on your favorite listening platform.

If you'd like to send me an email about topics you're interested in or questions for future guests, please send me a note at [email protected]. This is Dr Neha Pathak for the WebMD Health Discover podcast.