85% of maximal age-predicted heart rate is not a valid endpoint for exercise treadmill testing.

BACKGROUND

Exercise testing should be symptom-limited. Nevertheless, 40% of clinical laboratories applying for ICANL accreditation use 85% of maximal age-predicted heart rate (MPHR) as the primary exercise endpoint. We hypothesized that this approach importantly may underestimate exercise capacity and inducible ischemia.

METHODS

Two patient cohorts were studied. 1. A prospective registry of patients referred for exercise testing. 2. A retrospective cohort of patients with positive exercise ECG.

RESULTS

Of 306 registry patients, 211 (69%) continued exercising after reaching 85% MPHR to maximal HR of 101% ± 7% of MPHR. Forty-two patients (14%) stopped <1 minute after achieving 85% MPHR; 53 (17%) did not achieve 85% MPHR. More women (75%) than men (64%) achieved >85% MPHR (P = .02). Of 300 patients with positive ECG, 232 patients (77%) exercised to >85% MPHR. At 85% MPHR 144 patients (62%) had positive ECG (1.2 ± .7 mm ST depression) compared to 232 patients (100%) at peak exercise (2.3 ± .9 mm ST depression, P < .001). Mean workload at 85% MPHR was 7.3 ± 2.4 METs compared to 10.6 ± 2.8 METs at peak exercise (P < .001).

CONCLUSION

Achievement of 85% MPHR is not a valid diagnostic or functional exercise endpoint because it significantly underestimates exercise capacity and inducible ischemia.