LAUSR

Attenuated chronotropic index and heart rate recovery, documented during treadmill exercise testing in 13,887 patients without known cardiovascular disease, were both associated with worse cardiovascular outcomes and mortality. Their predictive value was independent of cardiorespiratory fitness, and was more pronounced when the two abnormal heart rate measures coexisted. Purpose: Heart rate response during exercise testing (ET) provides valuable prognostic information. Limited data are available regarding the prognostic interplay of heart rate (HR) measured at rest, exercise and recovery phases of ET, and its ability to predict risk beyond exercise capacity. Methods: Retrospective analysis of treadmill ETs was performed by the Bruce protocol in patients aged 35-75 yr without known cardiovascular disease (CVD; n = 13 887; 47% women). Heart rate recovery at 2 min (HRR2; defined abnormal <42 beats) and chronotropic index (CI; defined abnormal <80%, determined as age-predicted HR reserve) were analyzed in association with the risk of developing myocardial infarction, stroke, or death (major adverse cardiovascular event [MACE]) during median follow-up of 6.5 yr. Results: The HRR2 <42 beats and CI <80% were each associated with increased risk of MACE: adjusted hazard ratios with 95% confidence interval 1.47: 1.27-1.72 and 1.66: 1.42-1.93, P < .001, respectively, evident also when analyzed as continuous variables. Strength of association of HRR2 and CI with outcome was attenuated but remained significant with further adjustment for exercise duration and metabolic equivalents. Having both HRR2 and CI abnormal compared with only one measure abnormal was associated with hazard ratios with 95% confidence interval of 1.66: 1.38-2.00 and 1.48: 1.22-1.79 for MACE, before and after adjustment for cardiorespiratory fitness (CRF). The degree of CRF (low vs mid/high) did not modify the prognostic effect of HRR2 and CI (P-for-interaction nonsignificant). Conclusions: Both HRR2 and CI provide independent prognostic information beyond CRF in patients without CVD referred for ET. The predictive ability is more pronounced when both abnormal HR measures coexist.