What a Stress Test Can (and Can’t) Tell You

Plaque in arteries causes bad things. 

It causes heart attacks, the #1 cause of death (CDC, “Heart Disease Facts,” 2020). It causes strokes, the #1 cause of permanent disability (CDC, “Stroke Facts,” 2020). Scientists also continue to debate the linkage between plaque and Alzheimer’s, which may rival both heart attacks and strokes (Hughes, 2013). 

Given plaque’s importance, it’s surprising just how much we don’t know about measuring arterial plaque. The most common methods used nowadays are woefully inadequate.

What’s even more surprising is the fact that so few of us are aware of the problem. When someone we know has a heart attack, we worry about the possibility of having a heart attack as well. So we rush to the doctor and ask, “how about a stress test?”

Stress tests are the go-to measurement for arterial plaque. Its supposed goal is to predict a heart attack.

Unfortunately and ironically, stress tests don’t measure plaque—they only measure blood flow. Still, they are popular. In the US alone, over 8 million nuclear stress tests are done every year (Gluckman, 2019).

Here some questions surrounding stress testing:

1. Can a stress test predict a heart attack?
2. Can a stress test tell if you have plaque in your arteries?
3. What exactly can a stress test tell you?
4. What are the things a stress test cannot tell you?
5. Which standards groups don’t recommend stress tests?
6. What do cardiologists say when you ask about the accuracy of stress tests?
7. What is a stress test?
8. What are the types of stress tests?
9. How accurate are stress tests?
10. Why are more stress tests being done instead of less?
11. How can we do better? Are there alternatives?

In this article, let’s describe what a stress test is, and the answers to the above questions.

1. Can A Stress Test Predict A Heart Attack?

The short answer is no. A stress test cannot predict a heart attack (Harvard health Publishing, 2020).

 

2. Can A Stress Test Tell If You Have Plaque In Your Arteries?

Again, no (Princeton Longevity Center, 2018; Harvard Health Publishing, 2020). 

Exercise stress tests are just flow studies. They only measure the flow of blood in arteries. Doctors usually assume that plaque causes a decrease in blood flow based on the patient’s history, labs, and other imaging studies. 

But stress tests can’t detect plaque unless there is more than 50-70% blockage of blood flow in the artery. Also, increased blockage does not correlate with a plaque’s susceptibility to rupture and cause a heart attack (Princeton Longevity Center, 2018; Gibbons, 1997; Falk, 1995).

That’s why many people (like Tim Russert) died after getting a negative stress test result. 

In case you don’t remember, Russert was the host of NBC’s “Meet the Press” for 17 years until his fatal heart attack on June 13, 2008. Six weeks earlier, he had a stress test done in the office of Michael Newman, Rusert’s doctor.  

The stress test yielded a “negative” result; meaning, there should be nothing big to be worried about. Though Russert had enough plaque that could cause a heart attack, it was not enough plaque to generate a 50-70% blockage of blood flow. Still, despite the negative stress test, Russert succumbed to a heart attack later. 

 

Cases like Russert’s are more common than most of us think. 86% of heart attacks occur in people with less than 70% occlusion in their arteries, while 68% of heart attacks occur in people with less than 50% occlusion. So, heart attacks could happen, even though a stress test wouldn’t show anything (Gibbons, 1997; Falk 1995).

3. What Exactly Can A Stress Test Tell You?

Mayo Clinic and Harvard Health Publishing give 2 different perspectives of what a stress test can (and cannot) tell. 

According to Mayo Clinic (2018), a stress test:

…shows how your heart works during physical activity…

 

…can reveal problems with blood flow within your heart…

 

…may also guide treatment decisions, measure the effectiveness of treatment or determine the severity if you’ve already been diagnosed with a heart condition…

 

…diagnose(s) coronary artery disease…

 

…diagnose(s) heart rhythm problems…

 

…guide(s) treatment of heart disorders…

Given all the Mayo Clinic says about a stress test, it’s no wonder that more than 10 million stress tests are done in the US each year (Rahsepar 2015). 

While stress tests only measure blood flow and not arterial plaque, the information they provide can still be useful. For example, if a patient needs to end a stress test early, that may be a sign of a health risk. 

A group of researchers following 2,014 men aged 40-59 years old found that men who stopped their stress test had high mortality. The only reason why these men terminated their stress test early is because of breathlessness (Bodegard 2005).

There are many reasons why a stress test is being stopped, like:

• A decrease (or increase) in blood pressure;
• Moderate to severe chest pain;
• Dizziness;
• Signs of poor blood flow (e.g., bluish tinged skin);
• Technical difficulties in monitoring ECG or systolic blood pressure;
• The patient wants to stop;
• Various EKG changes; 
• Fatigue, shortness of breath, wheezing, leg cramps.

In the end, all these reasons are implications that the patient has an underlying health issue (Gibbons, 1997; Fletcher, 2013).

4. What Are The Things a Stress Test Cannot Tell You?

Harvard Health Publishing published an article titled “Cardiac exercise stress testing: What it can and cannot tell you.” 

Here are a few facts quoted from the article:

“… expert guidelines now discourage such ‘just in case’ stress testing.”

 

“… is not 100% accurate…”

 

“If stress testing were 100% accurate, everyone would have them regularly.”

 

“It can’t absolutely rule (coronary artery disease) out or diagnose it.”

 

“A ‘normal’ stress test can’t rule out the chance that a plaque will later rupture and block an artery…”

 

“The U.S. Preventive Services Task Force… urges physicians not to routinely offer … exercise stress testing…”

 

“…. the tide has turned against exercise stress testing of otherwise healthy men…”

 

“An exercise stress test is designed to find out if … coronary arteries …contain fatty deposits (plaques) that block a blood vessel 70% or more.”

 

“You could still have a heart attack if a smaller blockage (less than 70%) ruptures…”

With these lines, we get a better understanding of why so many medical advisory committees discourage stress tests. 

5. Which Standards Groups Don’t Recommend Stress Tests?

For almost a decade, most medical standards committees have discouraged the current high rates of stress testing. Some groups that have long advised against stress tests in low risk, asymptomatic (without signs or symptoms) individuals include:

• The US Preventive Services Task Force (Moyer, 2012);
• The American Academy of Family Physicians (AAFP, 2017);
• The American College of Cardiology (Greenland, 2010);
• The American Heart Association (Hendel, 2009);
• Choosing Wisely® advisory group (Choosing Wisely®, 2020).

6. What Do Cardiologists Say When You Ask About The Accuracy Of Stress Tests?

I tried searching the term “accuracy of stress tests” on Google, and the snippet for my search came from a post by Dr. Douglas Dawley, a cardiologist from Providence Health & Services in Oregon and Southwestern Washington (Dawley 2012). When I look closely, the article raises several questions about the accuracy of stress tests.

For example, even though Dawley describes the standard treadmill as “safe, accurate and inexpensive,” he later states that it is “between 60 and 80 percent accurate.” And patients relying on a stress test to predict their heart attack won’t see “between 60 and 80 percent” as reassuring. 

To Dr. Dawley’s credit, he did mention that many standards committees discourage stress testing for the following reasons:

• Patients without cardiac symptoms; 
• Patients at low risk;
• Use as a preoperative assessment.

After the snippet on Dawley’s article, my search then showed a blog written by and for emergency medicine physicians (Morgenstern, 2019). The article is titled “Stress Tests Part 3: Stress test accuracy,” and it comes from a well-researched, accurate website named First10EM. The article quotes:

The quick summary… is that stress testing does not pick out patients at risk of MI (myocardial infarction) or death, has a high rate of false positives, and probably leads to unnecessary invasive procedures.

Many cardiologists do a lot of stress tests. If you challenge one about the accuracy of such tests, their usual response is to imply confusion in the terminology. You can expect them to give quotes similar to what Dawley said in his write-up. 

One problem is that most people conflate the terms when discussing stress tests. So to clear up the confusion, let’s define, describe, and list the common variations of stress tests.

7. What is a Stress Test?

A stress test is a procedure used to measure how the heart works during physical activity. It typically involves assessing heart function while exercising on a treadmill or exercise bike, or through drug-induced heart stress. 

There are multiple types of stress testing, like nuclear, echo, and drug-induced stress testing. These have various names too, like stress echo, nuclear stress, and drug-induced stress test. 

Other names and types of stress tests include stress EKG, exercise EKG, exercise electrocardiogram, and functional testing (as opposed to anatomical imaging) of the coronary arteries. 

8. What Are The Types of Stress Tests?

There are 4 basic types of stress tests: drug-induced stress tests, stress EKG (or ECG), stress echo, and nuclear stress tests. 

A. Drug-induced Stress Tests

Drug-induced stress tests use drugs to stress the heart and cause the arteries to dilate. 

A drug-induced stress test bypasses exercise. Instead, it directly infuses a chemical called adenosine. This adenosine causes arteries of the heart to dilate, which in turn, increases pump function. With adenosine, doctors can measure the heart’s reaction to stress even though the patient cannot walk, run, or cycle.

B. Stress EKG/Stress ECG

Stress EKG (or stress ECG) is the original stress test. 

EKG or ECG is an electronic cardiac response measurement tool. (EKG is an acronym for the German word for electrocardiogram.) It can measure the electrical pulse or waveforms created via the sympathetic nervous system during complete cardiac cycles. 

In stress EKG, the patient walks for about 10 minutes on a treadmill. The full process, though, takes about an hour, including undressing, dressing, shower, and preparation time. 

In stress EKG, the doctor creates 4 records:

• the amount of work as measured by speed and incline on the treadmill;
• the EKG waveform patterns created during the cardiac cycle;
• the patient’s biometrics (e.g., heart rate and blood pressure);
• any symptoms reported by the patient (e.g., breathlessness, levels of fatigue, or pain).

C. Stress Echo

The stress echo is the same as the stress EKG, except that it adds a cardiac ultrasound or ‘echo’ before and after the stress events. The goal here is to get the second echo reading within 1 minute the patient gets off the treadmill. 

In stress echo, the sonographer records Doppler images and waveforms of the blood flow in large vessels and chambers throughout the cardiac cycle. The resulting images would provide insight into the presence of a blockage. However, that only happens when the blockage exceeds 50%.

In stress echo, the total patient time required for this exam is about an hour, including the time to prepare, and time to undress and dress. The doctor generates the same 4 records of a stress EKG, with the echo reading in response to cardiac stress added as a 5th record. 

D. Nuclear Stress Test

Nuclear stress tests are, by far, the most common stress tests. They outnumber the rest by 10 to 1. In the mid-90s, just over half of all stress tests performed (59%) included nuclear imaging. By 2009, the percentage had swollen to 87% (Ladapo, 2014). 

The nuclear stress test is similar to the stress EKG and stress echo. Instead of using an EKG or a cardiac echo, doctors inject radioactive thallium tracers into the patient’s vein. 

In a nuclear stress test, it takes 15 minutes to give the intravenous infusion of the tracer. It would then take a couple of hours to read the distribution of the tracer. The typical patient involvement time for a nuclear stress test is 3-4 hours. 

In a nuclear stress test, the doctor supplements the other 4 records (work done, symptoms, biometrics, and EKG) with images of the radioactive thallium tracer as it pulsates through the patient’s vasculature. 

Nuclear stress test subcategories

SPECT (Single Photon Emission Computerized Tomography) and PET (Positron Emission Tomography) are names of 2 nuclear imaging tests. SPECT generates images that are more detailed than other nuclear imaging tests. On the other hand, PET creates images that are more precise than other stress tests. 

SPECT and PET are combined with stress testing to create 2 subcategories of nuclear stress tests—SPECT and PET scan stress tests. Together, SPECT and PET scan stress tests are called MPI (Myocardial Perfusion Imaging). (Perfusion refers to the flow of blood or fluid through the blood vessels.)

Stress EKG vs. nuclear stress tests: Which is more popular?

The average cost range for a stress EKG is $200 to $300. On the other hand, the average of a nuclear stress test is $600 to $14,000. 

With stress EKG’s lower cost, you might expect to see more stress EKGs being done. The higher cost of nuclear stress tests suggests that they should be reserved for more complicated cases. 

That’s not the case, though. 

Despite being the least expensive, stress EKG is just not popular anymore. On average, simple stress EKGs account for only around 10% of the total stress tests. 

The plethora of stress tests performed annually shows that many patients and their doctors assume they’ll get more value out of a nuclear stress test. In fact, around 8 million nuclear stress tests are performed in the US per year (Gluckman 2019). 

If you ask me why this is the case, the reason seems obvious. A stress EKG doesn’t accomplish much in ensuring future health, as we saw in Tim Russert’s cases. 

Do nuclear stress tests cause radiation? 

Yes. Each nuclear stress test delivers radiation equivalent to 400 chest X-rays. This amount of radiation is not insignificant. Nuclear stress tests contribute to hundreds of additional cancer cases in the US each year (Gluckman 2019).

9. How Accurate Are Stress Tests?

The accuracy of nuclear stress tests is higher than those of the exercise EKG (at least given leeway on the definition of a “true positive” test). As I mentioned earlier in section 6, Dawley (2020) listed the accuracy of stress tests as “between 60 and 80 percent,” while nuclear stress tests as 80-90% accurate. 

Why was there so much variation in the accuracy range of stress tests? And what exactly is accuracy? 

Definition of accuracy

Accuracy is a measure of how well a test measures what it’s supposed to measure. Imagine a target with a bull’s eye—an accurate test will hit that bull’s eye. 

 

Baratloo et al. (2015) describe accuracy with the following equation:

Accuracy = (true positives + true negatives)/all tested

What are true (and false) positives, and true (and false) negatives then? Here are simple descriptions:

• True positives are cases correctly identified as positive for a condition.
• False positives are cases incorrectly identified as positive for a condition.
• True negatives are cases correctly identified as negative for a condition.
• False negatives are cases incorrectly identified as negative for a condition. 

Stress tests (like humans) make mistakes or errors too, and doctors label such errors as “false positive” and “false negative” results. 

In Tim Russert’s case, his stress test result is “negative,” which should mean he is negative for the disease (heart disease in his case). However, we knew he succumbed to a heart attack 6 weeks later. We can say that his stress test result was a “false negative.” 

So, does a true positive stress test mean there’s an impending heart attack? 

Not necessarily. According to Harvard Health Publishing (2020), “true positive” stress tests do not automatically equate to heart attacks. They just indicate the presence of certain types of cardiac pathology.

Believe it or not, the accuracy of a test varies by the prevalence of the condition (the proportion of people tested with the disease). We won’t explain that further. We just mention this because it helps explain even more of the problem with stress test accuracy.  

Tests are also not only about accuracy. Aside from accuracy, a test must also exhibit these other characteristics (Lab Tests Online Australasia, 2020):

• Sensitivity: the ability of a test to correctly determine true positive results.
• Specificity: the ability of a test to correctly determine true negative results.
• Precision: the tendency of a test to produce results that are close to each other or with the least variation.

Comparing sensitivity and specificity of stress tests

The sensitivity and specificity of nuclear and echo stress tests are better than that of the stress EKG, at least as demonstrated in most peer-reviewed studies. Most doctors can tell you that, even though they cannot define sensitivity and specificity. 

Here’s a good comparison of sensitivity and specificity results of different stress tests, obtained from a meta-analysis published in the Annals of Internal Medicine (Garber, 1999):

Stress type	Sensitivity	Specificity	Data Source
Exercise (or stress) EKG	68%	77%	132 studies of over 24,000 patients
Stress echo	76%	88%	6 studies of 510 patients
Nuclear stress test	79%	73%	6 studies of 510 patients
SPECT MPI	88%	77%	10 studies of 1,174 patients
PET scan stress tests	91%	82%	3 studies of 206 patients

10. Why are More Stress Tests Still Being Done Instead of Less?

Many hoped that the advisory group recommendations that discouraged the use of stress tests (see section 5) would help reverse the overutilization of such tests. 

That didn’t happen. Instead, overutilization increased. In fact, nuclear stress tests doubled from 1995 to 2010, and they continue to skyrocket. 

If standards committees recommend fewer stress tests, why are doctors doing more instead of less?

Here are some reasons:

• Stress tests do provide a certain degree of information about CV (cardiovascular) disease (see section 3). Patients, unfortunately, don’t know that stress tests can’t predict heart attacks (see section 4).
• These medical advisory committees that discourage stress tests have been slow to adopting other methods of heart attack risk assessment, such as inflammation testing, calcium scores, CIMT, and CT angiograms.
• Before the procedure, patients, payors, and sometimes even physicians don’t know whether the information from a stress test will be worth it.
• Loss of stress test income would financially devastate cardiologists, clinics, and hospitals.

 

 

Runaway Healthcare Inflation: The Human ATM

The US fails to control surgical and medical procedure utilization. You do not have to be a doctor or a medical economist to know that. 

Atul Gawande, MD, moved this discussion to center stage over a decade ago with his article in The New Yorker magazine, “The Cost Conundrum” (Gawande, 2009). He did not say that all doctors practice medicine for financial gain; just a lot of them, enough to drive runaway healthcare costs. 

A decade after Gawande’s article, the situation became worse. Neither insurance nor government control of healthcare has been effective at controlling the cost or quality of stress tests.

Even a decade ago, almost half (43%) of primary care physicians believed that much of the provided healthcare is unnecessary, according to a study in the Archives of Internal Medicine. Physicians point to other physicians (and themselves to a much lesser extent) as responsible for unnecessary care. 

Here are some numbers that reflect the state of US healthcare (Sirovich, 2011). 

• Only 28% said that they were testing and referring more than the ideal.
• 76% blamed the practice on malpractice concerns.
• 83% of doctors feared litigation for not ordering a test.
• Only 21% feared litigation for ordering an unnecessary test.
• Over half (52%) said they were ordering tests due to performance measures in their contracts.
• 40% said it was due to a lack of time.
• Over one third (39%) believed other primary care physicians would order fewer diagnostic tests if those tests did not generate extra income.
• Almost two thirds (62%) said specialists were ordering tests due to financial incentives.
• These physicians said 10% of the patients they see each day do not need it.
• 95% said that doctors vary in the testing and treatment choices for similar patients.

Physicians as a group are not alone in stating there is much waste in medical care. In 2010, NAM (National Academy of Medicine, formerly the IOM or Institute of Medicine) said that if prices had grown as quickly as healthcare, a gallon of milk would cost $48 (Institute of Medicine (US) Roundtable on Evidence-Based Medicine, 2010). 

The Overuse Of Stress Tests Prevails

2014 and 2015 were significant years for increasing awareness that we do too many stress tests. 

The New York Times once published the article titled “Too Much Cardiac Testing” from pediatrician Nikolas Bakalar. Here, Bakalar quoted a new guideline from the American College of Physicians.

There is no evidence that stress tests, electrocardiograms or myocardial perfusion imaging (the so-called nuclear stress test that involves exposure to radiation) have any advantages over routine risk assessment in asymptomatic people. All the tests commonly produce false positives that lead to further unnecessary testing. All involve extra expense.

Bakalar further quoted the author of the guidelines article (Chou, 2015) as saying, “doing a stress test doesn’t give you extra information that is helpful” in an asymptomatic person. Chou chose strong words, yet he did it as a spokesman for America’s internists. 

Furthermore, in the Annals of Internal Medicine, Ladapo et al. (2014) stated that:

• Over one third (at least 34.6%) of cardiac stress tests are inappropriate.
• These unnecessary tests cost over half a billion dollars ($501 million). Other estimates (2.7 million nuclear stress test times $630/test) indicate it may be at least 3 times that amount. 

Medical boards, professional associations, and foundations have also developed efforts to help. 

For example, the ABIM (American Board of Internal Medicine) joined forces with Consumer Reports to inform the American public about the dangers and costs of physician-driven over-testing (Gann, 2012). They cited the Consumer Reports study indicating that 44% of asymptomatic adults aged 40 to 60 had unnecessary stress tests. 

In 2019, the problem of overusing stress tests continued with no end in sight (Gluckman, 2019). 

Dilemmas: Logical, Therapeutic, Financial, and Ethical

If you are a physician, what are you supposed to say to those patients coming through your door? 

They are sitting in your waiting room. They are waiting to tell you that their uncle just had a fatal heart attack. They want you to make sure they aren’t the next to have one. They are worried. 

If they can just pass a stress test, isn’t that the best assurance that they do not have a CV risk problem? 

These patients do not know the revelatory information that we’ve just covered in this article. Unfortunately, only a few doctors are familiar with this information too. Patients have expectations, and doctors attempt to meet those expectations. 

For many physicians, it’s not just the financial concern of losing patients. Doctors went into medicine with a desire to help people. They want to make their patients healthy and happy. 

If doctors cannot do both, they’ll settle for one or the other. Too often, with stress tests, doctors give patients the comfort that they’ve “done all that could be done.” 

Unfortunately, that relief comes at the cost of thousands of dollars. Worse yet, it brings a false sense of security. That false sense of security, in turn, can lead to fatal relaxation of lifestyle rules.

I think the pasta and dessert—and maybe another pound or two—will be OK. I did pass my stress test, after all.

Many doctors lack knowledge about other screening tools (like CIMT, coronary calcium score, and CT angiograms), and this leads to gross overuse of stress tests. This potentially leads to severe heart attack outcome, and the supposed lack of solutions lead to additional financial and ethical dilemmas. It is a trap for medical overuse. 

Heart disease is estimated to cost the public over 1.1 trillion dollars annually by 2035 (Thompson, 2017). That’s a big number. Most of us don’t deal with numbers with that many zeros in it. 

Let’s put this cost into perspective:

• The standard HUD Point In Time (PIT) count for homelessness in the US was 567,715 in January of 2019 (Schneider, 2020). Half of that $1.1 trillion projected cost of heart disease could already build 1 million $500,000-cost community centers, with each center able to house 280 homeless people (Dukes, 2019).
• There are approximately 20 million students registered for college. The other half of that $1.1 trillion could already pay $25,000 for tuition and annual expenses for every person registered for college.

To get a few more images of $1 trillion, watch this video by Koch (2015).

 

11. How Can We Do Better? Are There Alternatives?

There is no way to predict the timing of heart attacks. That’s not different from other types of traumatic life events, like car wrecks. However, in such events, we know what causes risk. 

With a car wreck, it’s driving too fast, under the influence, while distracted with phones or other technology, in poor conditions, or with poor breaks or tire treads. With a heart attack, it’s obesity, diabetes (or far more often, prediabetes), aging, genetics, or inflammatory diseases.

We mentioned in the beginning that stress tests don’t measure arterial plaque. We also mentioned that there is immense pressure for a doctor to offer something to patients worried about heart attack and stroke risk. 

While many medical advisory groups discouraged stress testing, unfortunately, the same groups also voiced their opinions against what they call “non-traditional risk testing,” like CV inflammation testing, calcium scores, CIMTs, and CT angiograms. 

Take calcium scores, CIMTs, and CT angiograms as an example. They have major advantages over stress tests when it comes to measuring plaque, but they still aren’t usually ordered by doctors.

 

The car wreck analogy has another powerful aspect. The most significant modifiable risk factor for both car wrecks and heart attacks is… 

Human behavior. 

The biggest current risk for wrecks is distraction (like driving while using a phone). The biggest current risk for heart attacks is the way we eat. Thus, these behaviors—eating and distracted driving—could kill us. 

What will it take to change those habits and save some lives? It depends on many things. 

But one thing is certain—getting a stress test isn’t going to help that much.
 If you found this article helpful and want to start taking steps toward reversing your chronic disease, Dr. Brewer and the PrevMed staff are ready to serve you no matter where you’re located.

To find out more, schedule a consult here: prevmedhealth.com 
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