Each year hundreds of thousands of Americans, including some 700,000 Medicare recipients, get on a treadmill not for exercise but to try to determine if their hearts are healthy.
Tim Russert, the NBC journalist, had such an exam, called an exercise or treadmill stress test, six weeks before he died of a heart attack last month at age 58. His results had been deemed normal, prompting people to question how worthwhile this test could be.
Two weeks before Mr. Russert died, Dr. Todd D. Miller, a cardiologist and co-director of the Mayo Clinic's Nuclear Cardiology Laboratory in Rochester, Minn., published an assessment of the test's ability to predict the presence of potentially life-threatening cardiac problems. Dr. Miller elaborated on his report, in The Cleveland Clinic Journal of Medicine, in a telephone interview.
The test is meant to be used ''almost exclusively'' for people who have symptoms of heart disease, Dr. Miller emphasized.
''But in the real world,'' he said, ''it is often used as a screening test for people without symptoms who are worried about their risk. The accuracy of the test depends on whom it is used. It is most accurate among populations with a high prevalence of coronary disease. But in most people without symptoms, the prevalence of disease is so low that the accuracy of the test is low, too.''
Limitations and Advantages
In fact, this test is unable to detect the kind of problem that caused Mr. Russert's death -- a plaque within the wall of a coronary artery that ruptured, resulting in a clot that set off a rapidly fatal heart rhythm abnormality. If not for the rhythm disturbance, Mr. Russert would have had a far greater chance of surviving his heart attack, said Dr. Miller, who was not one of his physicians.
Mr. Russert's treadmill test may have put him in the low-risk category, Dr. Miller said, ''but that doesn't mean no risk.''
''Maybe 3 patients in 1,000 with a low-risk test will die from heart disease within a year,'' he said. ''Among those deemed at high risk, more than 3 patients in 100 would die within a year.''
Furthermore, when the stress test is used for people who are at low risk for heart disease, an abnormal finding is most often a false positive that prompts further testing that is far more costly, Dr. Miller said.
The stress test's main advantages are its rapidity and low cost -- one-fifth to one-quarter the cost of more definitive and often more time-consuming tests like a nuclear stress test, CT coronary angiogram or standard angiogram. Medicare pays about $150 for a standard stress test, though hospitals typically charge three to four times that when the test is done on younger patients.
Regardless of cost, the test has no value unless its findings are interpreted in the context of a person's other risk factors for heart disease: age, sex and heart disease symptoms, as well as smoking, being overweight, hypertension, high cholesterol, diabetes and family history.
Three main arteries feed the heart, and the ability of a stress test to pick up narrowing of an artery depends on which one is involved, Dr. Miller said. It is better at picking up coronary disease if more than one artery is clogged.
The treadmill test seeks to answer two questions: ''Does the patient have coronary artery disease, and is he or she likely to die or suffer a coronary event soon?'' Dr. Miller wrote in the Cleveland Clinic journal. But at best it can provide only an estimate of someone's risk of having a heart attack or dying of heart disease within a given period of time.
Interpreting the Results
During a treadmill test, patients are hooked up to an electrocardiogram machine (often abbreviated EKG, for the German spelling) that records the workings of the heart as the duration, speed and difficulty of the exercise increase.
