Ellestad and Wan3
first used the term chronotropic incompetence in 1975. They defined a group of patients who achieved less than the 95% confidence limit for maximal HR adjusted for age as having CI. Further efforts to define CI clearly have been hampered by the difficulty in determining an appropriate HR response to a particular workload. Many factors may affect the maximal HR response, and they include age, gender, level of fitness, cardiovascular disease, bed rest, altitude, type of exercise, and level of effort (ie, maximal vs less than maximal exertion).,7
Astrand first documented the effects of maximal exertional HR with age and formulated the commonly used equation that maximum predicted HR is equal to 220 minus age.1
In a review of the literature, Londeree and Moeschberger8
compiled information on 23,000 patients who had undergone exercise testing and found that the 95% confidence intervals for maximum predicted HR ranged as much as 45 beats/min. Further analyses revealed that age accounted for 73% of the variability, with other factors such as mode of exercise, level of fitness, and continent of origin accounting for an additional 5%. No significant variability was found between men and women.