Exercise stress testing to diagnose heart disease has a long history. This year, cardiologists can celebrate the 50-year anniversary of a study connecting abnormal stress test results and obstructive coronary artery disease (CAD).
The basic stress test procedure can involve walking on a tilting treadmill as the heart is monitored via electrocardiogram. A variant called the nuclear stress test involves introducing a radioactive tracer into the body to visualize alterations in blood flow within the heart.
Some stress tests are considered inappropriate, leading to additional medical costs. Arshed Quyyumi and colleagues from Emory Clinical Cardiovascular Research Institute presented research on Sunday at the American Heart Association Scientific Sessions meeting on the use of a blood test along with an exercise stress test. First author Bryan Kindya is a 2017-18 internal medicine resident.
The blood test detects troponin, a sign of recent damage to the cardiac muscle. Very high levels indicate that someone is having a heart attack. As testing for troponin has become more sensitive in recent years, the implications of lower but still detectable troponin levels need to be backed up by follow-up outcomes. That’s what the Emory data can provide.
Quyyumi’s team found that more than 25 percent of CAD patients will have troponin levels below a certain cut-off (2.45 picograms per milliliter), predicting that they have a low risk of having heart problems during a stress test or adverse events (hospitalization/heart attack/death) over the next three years.
The researchers conclude that measuring troponin in CAD patients before embarking on stress testing “may provide major cost-savings.” Disclosure: the research was done in cooperation with Abbott Labs, the maker of the high-sensitivity troponin test.
Clinical research presentations at 2016 American Heart Association Scientific Sessions: telomeres + circulating progenitor cells, food deserts, and troponin as risk marker for atrial fibrillation.
Telomere Shortening, Regenerative Capacity, and Cardiovascular Outcomes Nov. 13, 4:45 pm, Room 346-347
Aging, in general, depletes our bodies’ regenerative capacities. Arshed Quyyumi, MD and colleagues at Emory Clinical Cardiovascular Research Institute have shown how circulating progenitor cells or CPCs, which regenerate blood vessels and correlate with outcomes in cardiovascular disease, are a finite resource.
Working with Quyyumi, research fellow Muhammad Hammadah, MD is presenting data on how telomere length interacts with the levels of CPCs, in a study of mental stress ischemia in 566 patients with stable coronary artery disease. Telomeres tend to shorten with ageing and cellular stress, and their length has been a widely studied biomarker.
Hammadah concludes that low leukocyte telomere length is associated with decreased regenerative capacity, independently of age and cardiovascular risk factors. However, telomere length and CPC levels are independent and additive predictors of adverse cardiovascular outcomes (such as death, heart attack, stroke, or hospitalization for heart failure), he finds. Hammadah is a finalist for the Elizabeth Barrett-Connor Research Award for Young Investigators in Training. Read more
Some people with heart disease experience a restriction of blood flow to the heart in response to psychological stress. Usually silent (not painful), the temporary restriction in blood flow, called ischemia, is an indicator of greater mortality risk.
Cardiologists at Emory University School of Medicine have discovered that people in this group tend to have higher levels of troponin — a protein whose increased presence in the blood that is a sign of recent damage or stress to the heart muscle– all the time, independently of whether they are experiencing stress or chest pain at that moment.
The results were presented Sunday by cardiology research fellow Muhammad Hammadah, MD at the American College of Cardiology meeting in Chicago, as part of the Young Investigator Awards competition. Hammadah works with Arshed Quyyumi, MD, and Viola Vaccarino, MD, PhD, and colleagues at the Emory Clinical Cardiovascular Research Institute.
â€œElevated troponin levels in patients with coronary artery disease may be a sign that they are experiencing repeated ischemic events in everyday life, with either psychological or physical triggers,â€ Hammadah says.
Doctors test for troponin in the blood to tell whether someone has recently had a heart attack. But the levels seen in this study were lower than those used to diagnose a heart attack: less than a standard cutoff of 26 picograms per milliliter, in a range that only a high-sensitivity test for troponin could detect.
In a separate study, Emory investigators have shown that elevated troponin levels (especially: more than 10 pg/mL)Â predict mortality risk over the next few years in patients undergoing cardiac catheterization, even in those without apparent coronary artery disease.
There is already a lot of information available for doctors about the significance of elevated troponin. It has even been detected at elevated levels after strenuous exercise in healthy individuals. One recent study suggested that low levels of troponin could be used to rule out heart attack for patients in the emergency department.
More information about the mental stress ischemia study: Read more
This recent paper in Circulation, from Arshed Quyyumi and colleagues at the Emory Clinical Cardiovascular Research Institute, can be seen as a culmination of, even vindication for, Â Dean Jones’ ideasÂ about redox biology.
Let’s back up a bit.Â Fruit juices, herbal teas, yogurts, even cookies are advertised as containing antioxidants, whichÂ could potentiallyÂ fight aging. This goes back to Denham Harman and the free radical theory of aging.Â [I attemptedÂ to explain this several years ago in Emory Medicine.]
We now know that free radicals, in the form of reactive oxygen species, can sometimes be good, even essential for life. So antioxidants that soak up free radicals to relieve you of oxidative stress: that doesn’t seem to work.
Dean Jones, who is director of Emory’s Clinical Biomarkers laboratory,Â has been an advocate for a different way of looking at oxidative stress. That is, instead of seeing cells asÂ big bags of redox-sensitive chemicals, look at cellular compartments. Look at particular antioxidant proteins and sulfur-containing antioxidant molecules such asÂ glutathione and cysteine.
That’s what theÂ Circulation paper does. Mining the Emory Cardiovascular Biobank, Quyyumi’s team shows that patients with coronary artery disease have a risk of mortality that is connected to the ratio of glutathione to cystine (the oxidized form of the amino acid cysteine).
How this ratio might fit in with other biomarkers of cardiovascular risk (such as CRP, suPAR, PCSK9,Â more complicated combinationsÂ and gene expression profiles, even more links here) and be implemented clinically areÂ still unfolding.
Cardiologist Bob Taylor and colleagues have a new paper in PLOS One this week, looking at the biomechanical forces behind plaque erosion.
Plaque erosion is a mechanism for blood clots formation in coronary arteries that is not as well-understood as its more explosive counterpart, plaque rupture. Plaque erosion disproportionally affects women more than men and is thought to account for most heart attacks in younger women (women younger than 50).
“We believe that this work has implications for our better understanding of the underlying biology of coronary artery disease in women,” Taylor says. The first author of the paper is biomedical engineering graduate student Ian Campbell, who now has his PhD. The team collaborated with cardiovascular pathologist Renu Virmani in Maryland.
Cardiologists have well-developed ideas for how plaque rupture works*; see the concept of vulnerable plaque. Cholesterol and inflammatory cells build up in the coronary arteries over several years. At one point in a particular artery, the plaque has a core of dying inflammatory cells, covered by a fibrous cap. If the cap is thin (the patterns of blood flows near the cap influence this), there is a risk that the cap will break and the contents of the core will spill out, triggering a blood clot nearby.
Plaque erosion is more mysterious and can occur more gradually, the researchers have found. Read more
John Puskas, chief of cardiac surgery at Emory University Hospital Midtown, recently had an editorial in the journal Circulation on the topic of coronary bypass surgery.
John Puskas, MD
Specifically, he says that many cardiac surgeons are reluctant to employ bilateral internal thoracic artery grafts (as opposed to a single graft), even though there is a long-term benefit, because of perceived risk of infection and suboptimal financial incentives.
Puskas’ key message paragraph was so clear that it demands reposting here:
Why are American surgeons doing so few BITA [bilateral internal thoracic artery] grafts? Fundamentally, U.S. surgeons are responding to their practice environment, especially to a fear of deep sternal wound infection in an increasingly obese, diabetic population of patients. The surgeon pays a large and immediate political price for a deep sternal wound infection and receives relatively little credit for the extra years that BITA grafting adds to a patient’s life in the future. There is also a relative Ray Ban outlet financial disincentive to perform BITA grafting: incremental payment for the second internal thoracic artery graft is small considering the extra time required in the operating room. Moreover, the Centers for Medicare and Medicaid Services no longer reimburse for extra care necessary for treatment of mediastinitis [internal chest inflammation/infection] after cardiac surgery, because this is now deemed a never event. Thus, surgeons, who are increasingly employed by hospitals and hospital systems, are under intense pressure to perform CABG surgery that is safe and cost-effective according to short-term metrics.
Puskas and his colleagues have published an analysis of bilateral vs single grafting at Emory, as well as a proposed metric for when single grafting should be used in the context of patients with diabetes:
Our present practice is generally to use BITA grafting in patients who are <75 years, have suitable coronary artery targets, are not morbidly obese, and whose glycosylated hemoglobin level is <7.0% to 7.5%.