A treadmill exercise score predicted survival in outpatients with suspected coronary artery disease
ACP J Club. 1992 Jan-Feb;116:23. doi:10.7326/ACPJC-1992-116-1-023
Mark DB, Shaw L, Harrell FE Jr, et al. Prognostic value of a treadmill exercise score in outpatients with suspected coronary artery disease. N Engl J Med. 1991 Sep 19;325:849-53.
To assess the prognostic value of a score based on treadmill exercise test results in outpatients referred for noninvasive evaluation of possible coronary artery disease.
Consecutive outpatients with suspected coronary disease referred to a cardiac noninvasive diagnostic unit and meeting all inclusion criteria.
Tertiary cardiac care center between March 1983 and January 1985.
613 patients who were scheduled for a treadmill test, had not had cardiac catheterization, had no evidence of serious valvular, congenital, or cardiomyopathic disease, and had an interpretable ST-segment response participated.
Assessment of prognostic factors
After providing a cardiac history and having a physical examination and electrocardiogram, patients underwent a standard Bruce-protocol treadmill test that continued until the development of limiting symptoms, abnormalities of rhythm or blood pressure, or marked and progressive ST-segment deviation (≥ 0.20 mV in the presence of typical angina or in the first stage of exercise). Treadmill score was calculated as: Duration of exercise in minutes - (5 × the maximal net ST-segment deviation during or after exercise, in mm) - (4 × the treadmill angina index).
The angina index was 0 for no angina, 1 for nonlimiting angina, and 2 for limiting angina. Treadmill scores ranged from -25 (highest risk) to +15 (lowest risk). ST-segment deviation was measured 0.06 s after the J point by a computerized system with manual review by 2 cardiologists.
Main outcome measures
All patients were contacted annually by questionnaire or telephone interview. 4-year survival was available for 98% of patients.
The treadmill score predicted 4-year survival better than clinical data alone. For the 62% of patients with high treadmill scores (≥ +5), indicating low risk, the 4-year survival rate was 99%, for the 34% of patients with moderate scores (+4 to -10), the rate was 95%, for the 4% of patients with low scores (< -10), the rate was 79%.
In patients referred for noninvasive testing for suspected coronary disease, a score based on the results of exercise treadmill testing provided better prognostic stratification than clinical factors alone.
Sources of funding: Agency for Health Care Policy and Research; National Heart, Lung, and Blood Institute; Robert Wood Johnson Foundation.
Address for article reprint: Dr. D.B. Mark, P.O. Box 3485, Duke University Medical Center, Durham, NC 27710, USA.
Exercise testing according to the treadmill protocol of Bruce and colleagues has become an important clinical tool. Mark and colleagues demonstrated, in their patient population, the strength of a score based on treadmill results to predict 4-year survival. The appeal of this method over clinical assessment alone for selecting patients for cardiac catheterization or arteriography is its simplicity, predictive power, and objectivity. The incremental value of the diagnostic properties of this exercise test over clinical assessment alone in predicting survival could be compared with the incremental value of ferritin levels over red blood cell mean volumes in diagnosing iron-deficiency anemia (1). In this latter case, the areas under the receiver operating characteristic (ROC) curve (a measure of a test's discriminating properties, with higher values indicating a better test) are 0.91 for ferritin and 0.78 for red cell volume. For predicting survival in the study by Mark and colleagues, the areas under the ROC curve are 0.85 for the exercise test and 0.80 for clinical assessment. Obviously, this additional diagnostic power is obtained at some extra cost in terms of time and money.
Ideally, the treadmill prognostic score should be validated in other outpatient populations before it is advocated for widespread use. The scoring system, however, is likely to be robust because it was derived from inpatients in the same setting (with both a training and test sample) and performed equally well in all 3 samples.
Thus, physicians who routinely administer and interpret exercise tests may benefit by becoming familiar with this prognostic score, deriving it for patients, and assessing its use in their practice.
Claudia Kozinetz, MPH, PhD
Baylor College of MedicineHouston, Texas, USA
Claudia Kozinetz, MPH, PhD
Baylor College of Medicine
Houston, Texas, USA