Abstract 12358: Achievement of 85% of Maximal Age Predicted Heart Rate Is Not an Appropriate Exercise Stress End Point and May Result in Underestimation of Inducible ECG Ischemia
There is a strong relationship between maximal exercise capacity (duration and METs) and cardiac outcomes. These parameters play a key role in the evaluation of patients with suspected coronary artery disease. Although there is a linear relationship between exercise METs and maximal achievable heart rate (HR), there is substantial variability in maximal HR among individuals of the same age. Nevertheless, in many clinical laboratories it has become customary to consider achievement of 85% of maximal age predicted heart rate (MPHR) the criterion for adequate exercise performance and exercise endpoint. We hypothesized that this approach may underestimate a patient's exercise capacity and inducible ischemia.
Methods: Exercise data of 183 consecutive patients with ischemic exercise ECG by clinical reports were analyzed retrospectively. All patients had symptom-limited exercise and computerized ECG tracings. METs achieved and maximal ST segment depression were noted at 85% of MPHR and at peak exercise. Computerized exercise ST segment depression of ≥1 mm was considered positive.
Results: Of 183 patients with positive ECG reports, 20 (11%) did not achieve 85% MPHR, whereas 163 (89%) achieved ≥85 % MPHR. Of the latter group, the mean peak exercise HR was 98 ± 7% MPHR. Only 17 (9%) patients stopped exercise <1 min after reaching 85% MPHR. Mean workload at the time of 85% MPHR was 7.6 ± 2.5 METs and at peak exercise 10.8 ± 2.5 METs (p <0.001). At 85% MPHR, 120 (74%) patients had positive ECG compared to 146 (90%) at end of exercise (p>0.001). 17 patients with positive ECG report did not have 1 mm by computer analysis. Mean computer ST segment depression at 85% MPHR was 1.5 ± 0.8 mm and at peak exercise 2.0 ± 0.9 mm (p>0.001). Of 126 patients who achieved 10 METs, exercise ECG was positive in 65% at 7 METs and in 87% at 10 METs (p<0.001).
Conclusion: In this cohort of patients with positive exercise ECG, 89% of patients exercised beyond 85% MPHR. If 85% MPHR had been used as an exercise endpoint, positive exercise ECGs would have been missed in 26(16%) patients. Moreover, the degree of ECG ischemia would have been underestimated. Thus, achievement of 85% MPHR is not an appropriate exercise endpoint, nor an indicator of adequate diagnostic stress testing. Exercise testing must be symptom limited.
- Exercise tests
- Heart rate/Heart rate variability
- Metabolic equivalents
- Ischemic heart disease
- © 2010 by American Heart Association, Inc.