Many people who have had angioplasty or heart bypass surgery may undergo Exercise stress testing too soon after the procedures, a new study suggests.

Recently developed guidelines from the American College of Cardiology and other groups state that routine stress tests are inappropriate within two years of angioplasty and five years of bypass surgery. That is, patients who do not have potential symptoms of artery blockages - like chest pain or breathlessness upon exertion - do not need to have a stress test just to check on their condition.

However, in a study of more than 28,000 U.S. patients who’d undergone angioplasty or bypass surgery, researchers found that 59 percent had at least one stress test within two years of the procedure.

The findings, reported in the Journal of the American College of Cardiology, are based on billing records for patients at one large national health plan. So it’s not clear why the stress tests were ordered, and what portion of them were done to evaluate symptoms.

“A portion of these tests would be symptom-driven for sure,” said lead researcher Dr. Bimal R. Shah, of Duke University Medical Center in Durham, North Carolina.

However, he noted in an interview, it is safe to assume that 59 percent of the study group did not have symptoms warranting stress testing within two years.

Based on data from a National Institutes of Health registry, for example, about 18 percent of angioplasty patients report chest pain within a year of the procedure.

Shah pointed out, however, that patients in this study were followed from 2004 to 2007, and the guidelines on stress testing came out in the middle of the period. So, he said, studies are now needed to see whether the guidelines have created a shift in clinical practice.

The main problem with performing cardiac stress tests on symptom-free individuals is that it can lead to needless invasive procedures, Shah said.

During a standard Exercise stress test, the patient walks on a treadmill or pedals a stationary bike while electrodes placed on the skin gather information on the heart’s activity.

The test may also involve an echocardiogram, where ultrasound is used to produce images of the heart, or nuclear imaging. In the latter case, a radioactive dye is injected into the bloodstream and then picked up by a special scanner resembling an X-ray machine; this can allow the doctor to see whether there are areas of the heart that are not getting adequate blood flow.

Abnormal results on any of these tests may be followed up with coronary angiography, a more invasive test where a catheter is inserted into a blood vessel and a dye is injected to allow X-ray images of any blockages within the heart arteries.

But stress testing, Shah pointed out, can result in “false-positives” - abnormal results that, upon further testing, turn out not to be caused by clogged arteries. That means that some proportion of patients who have stress testing will undergo unnecessary angiograms.

In their study, Shah and his colleagues found that 11 percent of patients who had a stress test ended up having an angiogram. Of those patients, about half needed a repeat angioplasty or surgery.

Those rates, the researchers write, indicate that all of that stress testing yielded little real benefit for patients.

The risks of serious complications from coronary angiography, such as heart attack, heart rhythm disturbances or an allergic reaction to the dye, are low - generally ranging from 1 in 500 to 1 in 1,000.

But more testing means more costs, Shah and his colleagues point out. And in the case of nuclear stress tests and follow-up angiography, it means more radiation exposure for patients.

The issue of patients’ cumulative radiation exposure - from a range of medical tests and procedures - has received increasing attention in recent years. Last year, the American Heart Association issued a statement calling on doctors to carefully weigh the pros and cons of nuclear stress testing, angiography and other radiation-based tests for any one patient before ordering the tests.

In the current study, nuclear stress testing accounted for most of the stress tests performed.

As for why so many patients underwent stress testing within two years, the reasons are not clear, Shah said. But the lack of clear guidance for doctors, at least for part of the study period, could be one factor. Other potential reasons include patient preferences and doctors’ worries over being sued should they miss a potential problem, according to Shah.

The researchers also found that rates of early stress testing varied significantly according to where patients lived. Rates were lowest - hovering around 50 percent to 55 percent - in cities such as Chicago, New Orleans, and Columbus and Cincinnati in Ohio. Phoenix had the highest rate, at about 70 percent.

Again, Shah said, further research is needed to uncover the reasons for that geographic variation.

For patients, Shah noted, the finding that only 5 percent of study patients who underwent stress testing ultimately needed a repeat angioplasty or surgery should be reassuring: It bolsters the guideline that symptom-free patients need not have a stress test in the two to five years following their heart procedure.

SOURCE: Journal of the American College of Cardiology, October 12, 2010.