How necessary are cardiac stress tests?
Encouraged that recent studies have shown conservative treatment for heart disease may be just as effective as a more aggressive treatment program? Well, it’s important to read the details of the results to know if you would qualify for the lesser treatment. And, importantly, it does not mean you should forego a cardiac stress test.
“You need to apply the data and the science to the individual patient and not broad-brush an entire population,” said Cardiologist Lawrence McAuliffe, MD, at Cape Cod Healthcare Cardiovascular Center in Hyannis.
A large new study published in the The New England Journal of Medicine last spring suggested that conservative treatment was just as effective at preventing death or future heart attack as aggressive treatment, for people with stable coronary disease and moderate to severe ischemia. Ischemia is an inadequate supply of blood to the heart, usually due to a buildup of plaque in the blood vessels.
The International Study of Comparable Health Effectiveness with Medical and Invasive Approaches (ISCHEMIA) trial randomly assigned 5,179 patients with moderate to severe ischemia to a treatment strategy of either an invasive procedure like cardiac catherization or stenting, or conservative treatment with medication and close follow-up in case the treatment needed to be changed to more aggressive strategies.
After the study was published, some major news outlets suggested that the fact that aggressive treatment didn’t lower risk of death or heart attack meant that cardiac stress tests might not offer much value for those with heart artery blockages, because those tests could lead to invasive and expensive procedures that wouldn’t do any good anyways.
The ISCHEMIA study was a follow-up to the earlier Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation (COURAGE) trial in 2007 that came to the same conclusion about death and heart attack rates. For that reason, the new study wasn’t particularly controversial to Dr. McAuliffe, but he didn’t agree with the news outlets’ claims that stress tests are unnecessary.
Dr. McAuliffe said the clue to understanding the implications of the study was found right in the title of the study: “Initial Invasive or Conservative Strategy for Stable Coronary Disease.” The key word was “stable.” When Dr. McAuliffe read the details of the study, he noted that researchers tested all patients to eliminate high-risk people with left main disease and proximal LAD lesion, the so-called “widow-maker.”
“Those people were discovered by conventional testing and angiogram, so for them that made a huge difference and probably saved their lives,” Dr. McAuliffe said. “But the vast number of patients in the study could have been managed through the best medical practice, and by the guidelines, in terms of blood sugar, cholesterol, blood pressure, exercise, weight, smoking cessation - all those things we normally talk about. If you maximize that therapy they do pretty well.”
Both the ISCHEMIA trial and the COURAGE trial found that there was no significant difference in heart attack or death by treating stable heart patients conservatively. But neither trial proved that heart stress tests were unnecessary. In fact, there are many instances when they are very helpful and can save lives.
Who Benefits From Stress Tests?
Dr. McAuliffe identified several groups of patients who do benefit from stress tests. The first group was patients who have all of the risk factors of heart disease. In those cases, the stress test establishes the presence or absence of heart disease.
“Another group of patients are those who present symptomatically with chest discomfort or any angina equivalent, like shortness of breath, exercise intolerance, and who have never had testing,” he said. “With those individuals you are trying to discriminate between a cardiac and a non-cardiac cause for their symptoms because the treatment is completely different.”
The third group of patients who he identified as benefitting are those with established coronary disease that was revealed by a heart attack, a positive catheterization before bypass or a positive non-invasive test. This is a group with known angina, but their symptoms may have worsened.
Examples would include patients who used to be able to walk two miles on the beach and now struggle to walk to the corner. Or they might be having difficulty doing house or yard work or their activities of daily living.
“If there has been a significant change symptomatically then that becomes a group who merits stress testing and non-invasive imaging,” Dr. McAuliffe said.
Both the COURAGE trial and the ISCHEMIA trial showed that if a patient has a stable pattern, they don’t necessarily have to be tested aggressively and they certainly don’t need to be sent for a stent or bypass, he said. Even if a patient has a progressive blockage that looks bad, it doesn’t mean you have to correct it.
That said, a patient with progressive blockage that is causing an anginal burden and limiting that patient’s lifestyle would benefit from revascularization, either by stenting or bypass because their physiologic demands outstrip their ability to deliver blood and oxygen to the heart. Dr. McAuliffe compared it to trying to fill a kiddie pool with your finger over the nozzle of the hose. Eventually the pool will fill up but it will take a long time as opposed to if you opened up the nozzle.
“All of the studies do show that you require less medicine and have fewer symptoms if you correct the blockage,” he said. “You don’t make them live longer. You don’t prevent a heart attack. You don’t prevent them from dying. You reduce the number and dosage of medicines required to prevent angina.”
This is especially pertinent for a younger, more active patient who may not want to take four medications. The medications will slow their heart rate down and lower their blood pressure, but also have side effects, such as depleting their energy. If a doctor can improve their blood supply through a stent or bypass, they will need fewer medications to prevent angina.
The final group of patients that need a different approach and more aggressive use of stress tests are people who have high-risk professions like first responders, firefighters and airline pilots. In those patients, you can’t afford to miss something important just because they don’t have symptoms or because things sound good.
“There are certain groups of patients whose professions or lifestyles or some other independent factor necessitates being more aggressive in terms of either making the diagnosis and/or treating what you find once you’ve found it,” he said. “You can’t have the pilot of a 747 having a heart attack at 35,000 feet.”
He also pointed out that doctors don’t make these decisions on a whim. The American College of Cardiology has published guidelines and there is guideline approved therapy for every condition, both medical and interventional. Guideline Directed Therapy is designed to maximize treatment of heart conditions while also minimizing unnecessary testing, Dr. McAuliffe said.