Stress test vs flipping a coin: which is more accurate?

1 Mar

by Carolyn Thomas  @HeartSisters

You may not have any signs or symptoms of coronary artery disease while you are just sitting there quietly reading this post. In fact, your symptoms may occur only during exertion, as narrowed arteries struggle to carry enough blood to feed a heart muscle that’s screaming for oxygen under increased demand. Enter the diagnostic stress test, used to mimic the cardiac effects of exercise to assess your risk of coronary artery disease.

During stress testing, you exercise (walk/run on a treadmill or pedal a stationary bike) to make your heart work harder and beat faster.  An EKG (aka ECG) is recorded while you exercise to monitor any abnormal changes in your heart under stress, with or without the aid of chemicals to enhance this assessment.

So for doctors who like to order stress tests for their patients with possible heart issues, imagine their reaction to this blunt warning from Dr. David Newman:   

“It appears that flipping a coin would be a more sensitive mechanism for detecting coronary artery disease than relying on a stress test.”   

Dr. Newman, director of clinical research at Columbia University and author of the book Hippocrates’ Shadow, adds that despite clear clinical guidelines about using stress tests, concern and confusion apparently exist among our physicians, according to his Special Report: The Truth About Stress Tests that he co-authored for the journal, Emergency Physicians.

For instance, he cites guidelines from the National Institute for Health and Clinical Excellence that state:

“Do not use exercise EKG to diagnose or exclude stable angina* for people without known coronary artery disease.”

Cardiologist Dr. Richard Fogoros also explains another potential limitation to the exercise stress test:

“The stress test can only help to diagnose coronary artery disease (CAD) that is producing partial blockages in the arteries – so-called obstructive CAD. But CAD often produces plaque in the arteries that may not actually be causing obstruction, and these non-obstructive plaques can (and do) rupture, causing acute blood clot formation, which produces an acute obstruction of the artery, often leading to myocardial infarction (heart attack).

“So it is certainly possible to have a ‘normal’ stress test while still having CAD.

“In some patients, EKG changes can occur even in the absence of CAD. (In other words, ‘false positive’ stress tests are not uncommon.) In other patients, no significant EKG changes are seen even in the presence of CAD. (So ‘false negative’ stress tests can be seen.)

False positive and false negative studies can significantly limit the usefulness of the stress test in many patients.

“By adding a nuclear perfusion study to the stress test, this limitation may be minimized, and the diagnostic capacity of the stress test is greatly improved.”**

It almost seems counter-intuitive, but cardiologists like Dr. Seth Baum confirm that most heart attacks actually happen in what is called non-obstructive CAD (i.e. in vessels that are less than 70% blocked). He adds: 

“This actually is one of the reasons why stress testing is such a bad screening test. Stress tests detect lesions that are greater than 70%. If an individual has multiple 50% blocked arteries, you’re going to miss that on a stress test, yet that individual is likely at significant risk for a future cardiac event.”

Dr. Kevin Klauer, who is Chief Medical Officer and Editor-in-Chief for the journal, Emergency Physicians, is equally cautious about the treadmill stress test, particularly when it comes to women, pointing to studies that suggest 50% of women with reversible coronary artery blockages actually had “normal” exercise treadmill test results.(1)  Dr. Klauer even adds bluntly:

“Exercise treadmill tests are not very good tests.”

And cardiologist Dr. Martha Gulati, director for preventive cardiology and women’s cardiovascular health at the Ohio State University Medical Center, warns:

“What is surprising is the fact that all the research that describes stress testing, and that has gone on for more than 40 years, was only done on men.”

More recently, some researchers who have specifically studied accuracy in stress tests for female patients have made some interesting observations unique to women. For example:

  • In pre-menopausal women, EKG results taken during exercise appear to vary with the women’s menstrual cycles. (2)
  • Post-menopausal women receiving oral estrogen therapy are more likely to have exercise-induced EKG changes than post-menopausal women who aren’t on estrogen replacement(3).
  • Women are generally older when they undergo stress testing and may have decreased exercise tolerance, limiting the ability to accurately identify women with coronary artery disease (4)

Here’s how the National Heart Lung & Blood Institute lists the most common types of stress tests (and for a glossary of cardiac terminology, read this):

  • Exercise echocardiogram or exercise stress echo
  • Exercise test
  • Myocardial perfusion imaging
  • Nuclear stress test
  • PET stress test
  • Pharmacological stress test
  • Sestamibi stress test
  • Stress EKG (or ECG)
  • Thallium stress test
  • Treadmill test

One of the most serious concerns about tests that are commonly used despite  important diagnostic accuracy issues is that an initial “normal” test may lead to misdiagnosis. No further tests will be ordered. Doctors like Duke University’s Dr. Pamela Douglas call this phenomenon “verification bias”.  As she warned in her editorial called  “Is Noninvasive Testing for Coronary Artery Disease Accurate?” in the journal Circulation:(5)

“Patients with positive tests are more likely to have their results verified with further testing, while those with negative tests are rarely referred for subsequent studies. False-negative results are unlikely to be discovered, and true-negative results will be less likely to be confirmed and therefore will be underrepresented.

“For every cardiovascular non-invasive test analyzed for the effects of verification bias (exercise ECG, exercise thallium, exercise radionuclide angiogram, and exercise echocardiography), results are similar, according to research by Roger et al.

“No type of test escapes this verification bias effect.”

Dr. Douglas then added that, in populations with sex-based differences in disease prevalence and extent, there will be sex-based differences in the accuracy of test results:

“This suggest that test results must be analyzed in a sex-specific fashion and that the decision to proceed to the anatomic gold standard of angiography must take into account sex-based differences in measures of test accuracy.”

Dr. David Newman offers this straightforward conclusion:

“The stress test is the elemental unit of diagnostic cardiology, and patients know of stress tests all too well. Unfortunately, both doctors and laypeople have been taught and trained wrong.

“I, for instance, was trained to believe in the general utility of stress testing. This was wrong. I was taught to obtain a stress test history, and to be comforted by normal results. Also wrong. I was taught to believe in the power of stress tests to establish safety and identify disease in low risk chest pain patients before they leave the hospital. Wrong.

“Sensitivities and specificities for stress tests are often reported as being between 70% and 90%, but these numbers are misleading. Studies of stress tests have rarely used a proper gold standard (i.e. coronary angiography), and in the one reasonably sized, high quality study to be performed rigorously, the test’s sensitivity for coronary stenosis was only 45%.”

For more on this, read the special report The Truth About Stress Tests, from the journal, Emergency Physicians.

.* stable angina: chest pain or discomfort that comes on with exertion and lessens during rest, due to poor blood flow through narrowed or blocked coronary arteries

** See my glossary for patient-friendly definitions of some cardiac terminology

(1) Hoilund- Carlsen, P.F. et al, Am J Card 95:96, January 1, 2005
(2) Grzybowski A et al. How to improve noninvasive coronary artery disease diagnostics in premenopausal women? Am Heart J. 2008;156:e961–e965
(3) Morise AP et al.  The specificity of exercise electrocardiography in women grouped by estrogen status. Int J Cardiol. 1997;60:55–65
(4) Mieres JH et al.  Role of noninvasive testing in the clinical evaluation of women with suspected coronary artery disease. American Heart Association. Circulation. 2005;111:682–696.
(5) Douglas PS: Is Noninvasive Testing for Coronary Artery Disease Accurate? American Heart Association.  Circulation. 1997; 95: 299-302 doi: 10.1161/​01.CIR.95.2.299

Q: Have you ever had a “normal” stress test despite being later diagnosed with heart disease, as I was?

See also:

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24 Responses to “Stress test vs flipping a coin: which is more accurate?”

  1. Stella Alexandri September 22, 2014 at 6:08 am #

    I wander if a treadmill stress test is enough to exclude coronary disease? I had a stress test 2 weeks ago. My HR at rest was 116 and blood pressure 130/80. During the second part of the test HR increased to 155 and at the beginning of the 3rd part reached 179, which is considered as maximum for my age (42 yrs). There was an ST depression during the second part of the test 1, 1mm and 2,8mm at the 3rd. But it was signed as negative. The total time was 7:16 minutes. There was not enough time to see the reaction of my body. It was a completely confusing result.

    The point that I usually have a very high heart rate at rest was not taken into account. The fact that I asked the doctor to stop the test because I was up to collapse was not taken into account too. I am still not sure if it was really negative. I still have chest pain and shortness of breath when I walk fast, or when I carry things, or when I am under emotional stress. The stress test was signed as negative but Duke Treadmill score was -5 meaning moderate risk of having CAD.

    Like

    • Carolyn Thomas September 22, 2014 at 6:57 am #

      Hello Stella and thanks for sharing your experience here. As the cardiologists in this post remind us, stress testing is certainly not enough to exclude a diagnosis of coronary artery disease. If your symptoms continue, seek further medical help.

      Like

  2. Elizabeth Y., RN, BSN August 25, 2014 at 6:05 am #

    The Physicians Assistant I see for cardiac is insisting I have another Treadmill Stress test in the near future, as the last stress test (nuclear) was over a year ago. I fail to see the benefit in this as I am walking/jogging 3-4 miles 6 days a week with no chest pain. I ride my bicycle all over town on weekends, no chest pain. But, she insists it is important.

    I hate treadmill tests…

    Like

    • Carolyn Thomas August 25, 2014 at 6:58 am #

      Hi Elizabeth! Send her a copy of this article (including the list of journal references) and see what she thinks. Good luck!

      Like

      • Elizabeth Y., RN, BSN August 25, 2014 at 9:07 am #

        Thank you, Carolyn! I’ll send her the link!

        Like

  3. Nancy June 21, 2014 at 8:09 am #

    So if the stress test is not very useful as a first stop diagnostic tool for women after an EKG, what is? (Recently referred for nuclear stress test, do not want to do it)

    Like

  4. Eve Zavodnick March 4, 2014 at 4:52 am #

    The thing about Stress Tests for those of us with known heart disease is that it’s like a check up every 2 to 3 years. I had one recently and my own situation hasn’t changed. I still have an EF of only 14, but I function and appear as “normal” as anyone else. People are still floored when I tell them that I nearly died from a serious heart attack 3 years ago. The “funny” part about all of this was the look on the Nuclear Tech’s face when he saw the scans after the comparisons. All of a sudden, he was looking at me as if I had one foot in the grave. He really needs to work on his poker face!

    Like

    • Carolyn Thomas March 4, 2014 at 5:24 am #

      An ejection fraction of 14% is indeed enough to “floor” most techs, for sure. No wonder he couldn’t keep a poker face during your nuclear stress test! It’s amazing that you’re able to function and appear “normal” – given that normal is typically in the 55-70% range! Good luck to you…

      Like

      • Stella Alexandri September 22, 2014 at 6:15 am #

        EF 14% is very low. I had 56% and they thought it was not enough.

        Like

        • Carolyn Thomas September 22, 2014 at 7:01 am #

          56% EF sounds within normal limits, Stella. As Eve demonstrates, you can still function and appear as “normal” even with an EF that may at first glance appear to be in the heart transplant zone! Conversely, a significant number of patients with heart failure have a “normal” EF. It’s just one number.

          Like

  5. Nitro Mama March 3, 2014 at 11:20 am #

    My feelings about stress tests are confused. A few months ago the cardiologist I saw prescribed one for me. I chose not to take it. I know I have ischemia, I couldn’t understand what could that test could tell me that isn’t already known. I decided after that visit that I will see another cardiologist in the future. He was so rushed, was annoyed when I had questions about my medications.

    Like

    • Carolyn Thomas March 3, 2014 at 11:35 am #

      Hello Nitro Mama – getting a second opinion is always an option, particularly when you’re experiencing a doc who’s “rushed” and “annoyed”. Good luck to you…

      Like

  6. Deborah Walker March 2, 2014 at 10:35 am #

    Don’t get me started about stress tests!

    My mother, who had angina and then suffered a heart attack, was hospitalized for the latter. In the hospital she was given a stress test on a treadmill. During the exercise, increased blood pumping, etc., an undiagnosed blood clot elsewhere in her body broke loose and entered her brain, causing a stroke! We learned later that this is quite common and yet none of her care providers bothered to consider that she might be at risk for this kind of thing; even though her family history was chock full of heart and stroke victims and this history was recorded in detail on her chart.

    My dear mom went from a lively intelligent person to a confused little old lady overnight.

    Now I’m going to be all Canadian and apologize for the rant, but I wanted your readers to know about the stroke risk connected to stress tests too.

    Like

    • Carolyn Thomas March 2, 2014 at 12:33 pm #

      Hello Deborah – I’m so sorry about your mother’s experience. We know that there is indeed a link between elevated blood pressure during this test and stroke risk for some patients (a Finnish study published in the journal, Stroke – a study done on men, mind you – suggested that a systolic blood pressure rise two minutes after exercise began was “directly and independently associated with the risk of stroke”.

      Like

  7. Deanna Rush March 1, 2014 at 4:51 pm #

    I too, have had negative stress tests, and I had angina while on the treadmill!

    The last one 10 weeks prior to having emergency triple bypass surgery. One artery was 100% occluded and two were 99% occluded.

    That was 4 years ago and after a very long recovery period I am doing well. I tell my family and friends no matter what the outcome of your stress test, if you continue to have symptoms you need to have further testing.

    Your articles are very informative, and at times humorous; please continue. They have been very beneficial for me.

    Thank you.

    Liked by 1 person

    • Carolyn Thomas March 1, 2014 at 10:20 pm #

      Thanks Deanna – your story is a good example of why some doctors (like the ones quoted in my post) consider treadmill stress tests to be “not very good tests” for many patients. Glad you are now doing well. Take care…

      Like

    • Stella Alexandri September 22, 2014 at 6:23 am #

      Very useful advice. Why do they sign as negative tests that are inconclusive? That’s my question. It is a great risk to say a test is negative if you have experienced angina during it. There are some signs on the ekg that are usually neglected because they are based on the fact that you managed to pass it and that you are a woman. They tend to exclude CAD in women just because of the sex.

      Like

  8. Tricia March 1, 2014 at 10:57 am #

    My cardiologist stopped my stress test after being on the tread mill 2 minutes. He honestly felt I would have a heart attack right there and then! He immediately called the intervention team to schedule a heart cath. He said the stress test EKG showed blockage and I would need a triple bypass.

    Yikes! Imagine my delight when the heart cath showed 50% blockage and surgery would not be necessary at this time. In the future I will need bypass, but for now I’m ok! Testing false positive was nerve racking to say the least.

    Liked by 1 person

    • Carolyn Thomas March 1, 2014 at 11:19 am #

      Thanks Tricia for this example: stress tests can indeed show false positives as well as false negatives. As for predictions that your blockages will “need bypass” in the future, few if any doctors could accurately promise this outcome for 50% blockages. Best of luck to you!

      Like

  9. cave76 March 1, 2014 at 7:35 am #

    Wow—- thanks for yet another informative post that points out the problems with ‘established’ tests. (Not that ALL tests are wrong, I want to make clear!)

    Liked by 1 person

    • Carolyn Thomas March 1, 2014 at 7:40 am #

      Good point, Cave. Even stress tests get it right on occasion!

      Like

      • Barbara Keddy March 2, 2014 at 6:27 am #

        Hi Carolyn:

        I keep wondering why I ask health professionals questions when I eventually get the real and detailed information from you!

        During my stay in hospital after my heart attack and stent I heard the cardiac team outside my cubicle door decide I would have a MiBi instead of a tread mill stress test. New language for me!

        No one explained to me the difference, nor why I was now having one. I didn’t ask many questions cause I was still in shock over everything that had happened. The words MiBi were new ones I was too exhausted to ask about.

        Other than telling me that I was on a ‘blood thinner’ and HAD to come off it in 365 days (!) I don’t remember any discussion about anything of consequence. Maybe I was too rattle brained to absorb much but they were very adamant about the blood thinner, a detail I was too stressed to care about at the time.

        I recently saw the cardiologist, at my request to the family doctor, for a referral since I had not seen one for a year. I asked him for a stress test so I could see how my heart has healed (or not) on the advice of a friend, a retired cardiologist. During the cardiologist visit he told me some of the information that this blog of yours explains (thankfully in detail). Otherwise, I would not have known nor thought anything much about stress tests and their unreliability. He would not order one for me.

        As an added problem unrelated to stress tests, I have just found out that I cannot be insured for the stent for travel outside the country until one year AFTER I have come off the Plavix! However, the whole year I was on it I could have been granted health insurance, had I not had a heart attack. One is required to wait one year after a heart attack and one year after coming off the blood thinner. So, in essence for travel outside the country one has to wait two years before being eligible to buy travel insurance following a heart attack and stent.

        NO ONE EXPLAINED THAT TO ME! I have been very anxious about even leaving my city let alone the country, now that I want to test my courage I find these loopholes! Guess the safest is to stay inside Canada where I don’t need travel insurance(blessedly) !

        What else don’t I know about heart disease and all that condition entails? Plenty, I suspect.

        Without you I would have been in the dark about so many things!
        Thank you, thank you once again!

        Liked by 1 person

        • Carolyn Thomas March 2, 2014 at 6:52 am #

          Thanks for this, Barbara. You bring up such an important point – that overwhelming shock following a catastrophic diagnosis like heart attack that makes it so challenging to comprehend what’s going on or even being said to us! I recall trying to explain to my daughter after being discharged from hospital that I had seen the cardiologist’s lips moving and I’d heard sounds coming out of his mouth, but it was as if he were speaking Swahili to me . . .

          That’s amazing about your out-of-country travel insurance! Does this depend on your insurance company? I flew from my home here in Canada to the U.S. five months after my MI (and while taking Plavix) to go to Mayo Clinic, and that Plavix issue didn’t come up while I was purchasing my out-of-country medical insurance.

          Like

          • Barbara Keddy March 2, 2014 at 3:07 pm #

            It is the same with all travel insurance companies. As long as you are on Plavix it is ok but after you come off of it they will not insure for one year!?

            Like

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