The treadmill exercise test for diagnosing coronary artery disease (CAD) and risk stratification is used on a routine basis to allow physicians to assess patients and determine the most appropriate intervention. The American College of Cardiology and the American Heart Association have recommended the use of the Duke treadmill score to stratify patient risk. This score was developed using a population with a median age of 49 and few elderly participants. Because the elderly have a higher prevalence of CAD that, when present, tends to be more severe than it is in younger patients, it may not be possible to generalize the Duke treadmill score to the elderly. Kwok and colleagues examined Duke treadmill scores in elderly patients (age 75 or older) and hypothesized that it would be less effective in risk stratification in these patients than in the younger population.
Patients studied included all those who received an exercise thallium test at a tertiary care center and were 75 years of age or older at the time of the test. Patients were included in the study if they had a history of chest pain and no prior cardiovascular disease. This population was compared with a control group of patients who were younger than 75 and who met the same criteria and also underwent an exercise treadmill thallium study. The results of the treadmill tests were assigned a score and risk stratum based on the Duke scoring system. Various methods were used to follow these patients over time to assess incidences of cardiac death, nonfatal myocardial infarction (MI), and late revascularization procedures. Median follow-up time for the study population was more than 6.4 years.
There were 247 patients who met the criteria for participation and were at least 74 years of age. These patients were compared with 2,304 patients younger than 75 years. The results of the Duke scoring system assigned 26 percent of the elderly patients to the low-risk category, 68 percent to the intermediate-risk category, and 6 percent to the high-risk category. The seven-year survival rates for each group were: low risk, 86 percent; intermediate risk, 85 percent; and high risk, 69 percent. These results were not statistically significant. There was no other correlation between the Duke scoring system and nonfatal MIs and revascularization events. As a continuous variable, the Duke scoring system did not predict cardiac death or acute MIs. In the control population, the Duke scoring system was highly predictive for all end points.
The authors conclude that the Duke treadmill score is not a good predictor for cardiac outcomes in patients aged 75 years and older. The use of the Duke scoring system to classify patients as low risk versus high risk assists physicians in deciding on medical and procedural interventions. In the elderly group, a substantial number of patients were in the intermediate-risk group, where clinical management guidelines are less clear. Only a minority of elderly patients in the study was categorized as low risk, but this group still had an annual cardiac mortality of 2 percent per year, which is higher than the mortality percentage in the low-risk group of the control population.
editor’s note: Physicians who provide care for the elderly have to be aware that the vast majority of studies on which we base our evaluation and treatment plans involve middle-aged adults, not elderly patients. There are few studies that provide us insight into what effect evaluation tests or treatment strategies have on elderly patients. Kwok and associates provide us with information about the Duke scoring system in predicting outcomes of coronary artery testing in the elderly. This study points out that statistical methods to predict risk stratification do not apply to patients 75 years of age and older. Even patients identified as low risk for cardiac death had the same mortality rate as patients in the intermediate category. This study points out that physicians are faced with unique challenges when trying to manage disease processes in the elderly.—k.m.