Stress tests for healthy people
What a stress test does and does not tell you about heart disease risk
Have you ever heard of an executive physical?
One large language model’s definition is “comprehensive health assessment typically designed for busy corporate executives, business leaders, or other high-level professionals. It offers a more thorough and time-efficient approach to preventive healthcare compared to standard annual check-ups.”
I would simplify that: an executive physical is a term that describes a doctor’s appointment that is part in-depth primary care visit, part cardiovascular screening, and part marketing nonsense.1
I’ve had quite a few patients (and even some friends) come to see me after going for an executive physical.
They bring in tons of bloodwork and often a handful of imaging tests for us to review.
One of the things that I think is most interesting about these visits is that they often come with an exercise stress test, which is often being used incorrectly and where the results are communicated in a way that misinforms the patient.
Even though they are incredibly common, stress tests are probably the most poorly understood - and most commonly misused - test that can be done for heart disease screening.
So I wanted to talk today about what a stress test can tell a healthy person about their cardiovascular health.
The usual point of a stress test is to figure out if there is a severely blocked artery in the heart
Stress tests are done in regular medical practice either to investigate symptoms or to do something called “risk stratify” someone, or better triangulate a person’s cardiovascular risk.
But the concept of the stress test is that you’re trying to figure out if there’s a critical blockage in an artery to the heart.
The reason it’s called a stress test is that when the heart is under stress from having to do more work, it beats faster and with more force, which can bring out evidence of decreased blood flow related to the blockage in question.
Not all stress tests are the same - these tests come in many forms.2
When you’re ordering one of these tests, you need to decide both how to stress someone as well as how to image them.
The preferred method of stressing someone3 is by putting them on a treadmill to follow something called the Bruce protocol, a standardized testing method that starts a treadmill at a slow speed (1.7 mph) and 10% incline, and then every 3 minutes the treadmill gets a little bit faster and 2% steeper:
You can image people in multiple different ways. Everyone gets an EKG, and you can add in ultrasound or nuclear scanning to increase the sensitivity of the test.4
The results of a stress test can be pretty nuanced, but when they are reported out, they’re often just reported to a patient as normal or abnormal.
And if you’ve had a stress test, you probably got some variation of “you passed!” as the report from the doctor.
But that’s a pretty unhelpful piece of information to get as part of an executive physical, because “passing” tells you very little about how your heart is actually doing.
A stress test only comes out as abnormal when there’s a greater than 70% blockage
It’s almost wild to think about the fact that a stress test looks normal until blockages have progressed pretty far.
And so if you’re getting on that treadmill and you have a major artery in the heart that is 69% blocked, the stress test isn’t going to pick that up.5
So what about that idea that you “passed” the stress test and so everything is great? It’s not an accurate representation of what the test tells you.
It *might* be correct, but it also might be really misleading.
You may have noticed that in my other pieces on heart disease screening, there isn’t any mention of stress tests.
That’s because most of the information you get from a stress test isn’t helpful for a healthy person trying to figure out if they have heart disease.
A stress test is a really important part of figuring out whether symptoms that someone has are related to a heart problem, but I don’t think that stress tests - as currently utilized - aren’t informative for heart disease screening.
If you want to know about subclinical or asymptomatic heart disease, you need an imaging test.
But stress testing does have a place in an overall preventive evaluation, just not really in the way that you might think.
The useful information from a stress test in a healthy person tells us about someone’s fitness level, which is a major predictor of death and disability
That top line “normal or abnormal” question may not provide much information as part of an overall cardiac assessment in healthy people, but if you dig into the numbers, you can get a lot of really useful information from an exercise stress test.
First, what was their exercise capacity?
High exercise capacity on a stress test portends a better prognosis when it comes to cardiovascular risk.
But you can take this even farther - how long you can go on a stress test can tell us about how likely you are to die from any cause.
That’s because high levels of aerobic capacity are consistently linked with a better lifespan.
You know how longevity gurus are preaching about the importance of VO2 max testing?
Well consider a stress test an easier method of figuring out your fitness level6 - you may not be precisely measuring oxygen consumption and thus getting your VO2 max, but evaluating how far someone can go on the Bruce protocol provides a standardized method of assessing overall cardiovascular capacity.
Objectively assessing fitness is important beyond just what it tells us about our potential longevity - it also tells us about whether we are exercising enough and at a high enough intensity.
Second, what is their heart rate recovery?
Better heart rate recovery has been linked to lower risk of death from all causes in this paper in the New England Journal of Medicine:
It’s a powerful relationship - people in the lowest quintile of heart rate recovery had a 6-fold increase in their risk of death compared to the fittest people.7
So a good heart rate recovery - defined as a drop in heart rate in the one minute period after maximal activity - suggests a lower risk of death.
You can think of heart rate recovery the same way you think about VO2 max or performance on the Bruce protocol: it is a quantifiable metric that helps to assess your level of fitness.
It’s shouldn’t necessarily be the target of your training, but as your fitness level improves, your heart rate recovery should improve as well.
If you’re getting a stress test done as a means of preventive testing, you should use the information from it in a way that’s useful, not a way that’s useless
If you just think about a stress test as a test that tells you whether you have heart disease or not, that’s probably missing the mark.
And the traditional way that a stress test is used - to figure out whether someone may need an invasive procedure or medical therapy - isn’t a particularly useful set of information if you’re getting it done as part of a health assessment.
But used in the correct way, it seems clear that a stress test can be a helpful part of a preventive cardiovascular assessment.
Unfortunately, that isn’t the way it’s used most of the time.
Not all of these are the same. And there’s no standard definition of the term “executive physical.” Some executive physicals do heart disease screening in a useful way and provide actionable and personalized insight and some of the doctors who perform these are really providing a high-end service.
You’ve probably heard of a nuclear stress test and a treadmill stress test before. But a nuclear stress test may or may not include a treadmill component. This can get confusing, which is why I’m discussing it.
If you can’t go on a treadmill, some places will offer an exercise bike. If you can’t do any exercise, you have an option of medications that either dilate blood vessels in the heart or medications that make the heart contract more quickly and with more force.
I don’t want to get into a detailed discussion of the ischemic cascade, but if you want to better understand the mechanism behind the increased sensitivity of either echo or nuclear compared to EKG imaging, “ischemic cascade” is what you should look into.
And the inability of a stress test to figure out a blockage is complicated even more by how high the patient got their heart rate up as well as the quality of the imaging that was done. We often think of these tests as infallible, but there are a lot of little things that can ultimately make the results less reliable.
The question of whether VO2 max is the best or most important marker of aerobic capacity is an interesting question. I think that for most people, it’s not all that important to harp on getting this tested specifically, but rather it’s a marker for maintaining high levels of aerobic conditioning in general. The downstream question of whether training to improve this metric specifically is the “optimal method” of aerobic training is also interesting (and I think kind of unanswerable).
This is an association - it’s not causative. This type of data supports the “healthier people are healthier” conclusion of most observational data. It’s interesting because this is one method of figuring out how healthy someone is.