CHRONOTROPIC INCOMPETENCE IN AN APPARENTLY HEALTHY. SELF-REFERRED MIDDLE-AGED POPULATION.

Abstract

663 Chronotropic incompetence (CI) has been defined as failure to attain 85% of age-predicted maximal heart rate (PMHR). Using this criteria, a recent report from Framingham (Lauer et al, 1997) suggested the prevalence of CI was 21% in a healthy, middle-aged cohort, and associated CI with cigarette smoking (SM). However, due to the submaximal nature of their exercise test (85% of PMHR), the maximal heart rate reserve (MHRR) was not assessed. The purpose of this study was to assess the prevalence of CI and the association of CI with SM in a self-referred, mostly middle-aged (42±11 years) population of men (N = 1606) and women (N = 1156) who completed a maximal treadmill test to volitional fatigue. Maximal heart rate (MHR) and oxygen consumption (VO2peak) were measured by ECG and open circuit spirometry, respectively. Subjects were excluded due to beta blockers, history of myocardial infarction, or failure to attain a respiratory exchange ratio at peak exercise of > 1.0. SM was assessed using an ordinal code scheme (1-7). CI was defined as 1) failure to attain 85% of PMHR, or 2) lower quartile of maximal heart rate reserve (MHRR). The prevalence of CI based on failure to attain 85% PMHR was 1.7% (46/2762), with no gender difference in prevalence (1.5 vs. 1.9% for men & women, respectively). The prevalence of SM within the cohort was only 11.8%. Those who failed to attain 85% of PMHR were more likely to smoke (19.6 vs. 11.6%), however the difference was not statistically significant (P=.10). The mean MHRR values for the low to high quartiles were 89, 107, 118 & 131 beats per minute, respectively. After adjusting for age, resting heart rate and VO2peak, SM remained inversely associated with MHRR (p<0.001). These results show a considerably lower prevalence of CI in healthy, middle-aged adults compared to the Framingham cohort, but confirm the association between SM and CI. Reasons for the lower prevalence of CI are not clear, but may be due in part, to the lower SM prevalence (11% vs. 38%).