Was your stress test smarter than your doctor?
For decades, the Exercise Treadmill Stress test has been the mainstay option for heart doctors to evaluate their patients’ hearts. This low tech test simply involves having the patient walk on a treadmill while wearing stickers (“electrodes”) attached to 10 wires placed in very specific positions. More than 90% of the time, patients are asked to exercise according the “Bruce” protocol, named after Dr. Robert Bruce who published a specific protocol in 1963 that is able to efficiently characterize the functional capacity and physical limitations of a patient, while simultaneously looking for “ischemia” or strain on the heart. If there is plaque buildup in the arteries of the heart that is significantly blocking blood flow, then at peak exertion (whatever level that may be for you), the electrical patterns of the heart will change in a characteristic and visible way. This identifiable pattern clues the doctor in on the likely presence of disrupted blood flow to your heart, and often prompts a recommendation for further investigation.
For years, however, the medical community has known that the routine exercise treadmill stress test has a high rate of “false positives”. This means that even though the test was abnormal, when the person undergoes further testing, no obvious blockage is found. In some settings, this false positive rate has been found to be as high as 35%! Additionally, research showed that this situation was far more common in women. This is a big issue. Obviously, you would not keep doing something that had a chance of being wrong one out of every three times you did it, would you?
So over the years, doctors began adding components to the stress test that would improve its accuracy. Taking pictures of the heart, either with special nuclear cameras or ultrasound (“echo”) machines. Through lots of research, we found that combining these pictures of the heart WITH the exercise stress test improved the accuracy to 80-90%, reducing the “false positive” rate significantly. In fact, some authorities went so far as recommending NEVER doing a “plain old” exercise stress test in women because of the high rate of false positives.
But a recent study in the Journal of the American College of Cardiology sheds some new light on the exercise stress test, and suggests that we’ve been going about this all wrong.
In recent years, the cardiology world has come to learn that people can have “ischemia” or strain on the heart WITHOUT having major blockages in the large blood vessels of the heart. These large blood vessels are the ones that are visible to the naked eye during cardiac catheterizations and angiograms, and the ones that we can put stents in to move blockages out of the way. It turns out that you can ALSO have problems with the tiny blood vessels that branch off those larger ones. These tiny vessels can be dysfunctional in that they don’t squeeze and relax appropriately. As a result, abnormal function of these tiny vessels can still deprive the heart of needed nutrients and energy.
In this recent study, the researchers took a group of patients who had heart catheterizations and did not have any blockages but did have dysfunction of their tiny blood vessels (diagnosed by specialized testing during the heart catheterization). They then took this group of patients without blockages and had these patients do an Exercise Treadmill Stress Test. And guess what they found? All the patients with abnormal stress tests also had abnormal function of the tiny blood vessels. And remember, NONE of these patients had blockages. In the past, we would’ve called these “false positives”, because these patients had abnormal stress tests but “normal” heart catheterizations. But in reality, they ALL had dysfunctional tiny blood vessels that were incapable of providing their hearts with sufficient energy at peak exertion. And of course, the majority of the patients with this pattern of findings were women. In the past, these women would’ve been told that their chest pain wasn’t from their hearts, when in reality it probably was!
So what does this tell us? We may have been interpreting these “false positives” incorrectly for decades. These patients truly had problems, we just didn’t recognize them because we weren’t doing the right kind of follow-up testing.
Moving forward, maybe instead of doing expensive “nuclear” stress tests routinely as a first step, we should return to the days of the simple, exercise treadmill stress test. These tests seem to be able to tell us a lot of useful information, even if us doctors don’t always understand or appreciate what they have to say.
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