hronotropic incompetence, or an attenuated heart rate response to exercise, is considered to be associated with the presence and severity of coronary heart disease, [1][2][3][4] and has proved a useful prognostic tool for patients with coronary heart disease, [5][6][7][8][9][10] and predictor of allcause mortality. 11 Chronotropic incompetence is also seen in children and adolescents who have undergone intracardiac repair for congenital heart disease, [12][13][14][15][16][17][18][19] or who have congenital long QT syndrome. 20,21 The chronotropic response in adults is assessed by the chronotropic index (CRI), which utilizes the linear relationship between heart rate reserve and metabolic reserve during incremental exercise testing, 22,23 and this has become the standard method. [3][4][5][6][7][8][9][10] The main advantages of using the CRI are, first, that it enables evaluation of the chronotropic response at any point in the exercise protocol and, second, that it is independent of age, sex, functional capacity and resting heart rate. 22,23 To our knowledge, however, the clinical diagnosis of chronotropic incompetence in children and adolescents is almost exclusively based on a failure to reach standard heart rate at peak exercise or at each stage of treadmill testing as estimated according to age and sex. [13][14][15][16][17][18][19][20][21]24 Therefore, in the present study we tested the hypothesis that the CRI is not influenced by exercise intensity, and is also independent of Circulation Journal Vol.69, April 2005 age, sex, functional capacity, and resting heart rate in young patients.
Methods
SubjectsA total of 132 normal Japanese children and adolescents (64 boys, 68 girls) were recruited to participate in the study. Clinical consultation and examination, including auscultation, chest X-ray, exercise ECG, and echocardiography, revealed that all the subjects were in good health. The subjects and their parent(s) gave informed consent for participation, in accordance with the requirements of the institutional review board. Subjects who did not reach maximal exercise, defined as a peak exercise gas exchange ratio less than 1.05 during exercise testing, were excluded (n=3), leaving a total of 129 subjects (63 boys and 66 girls) ( Table 1). None of the subjects failed to reach a peak heart rate below -2SD of age-and sex-predicted standard values. 24 All subjects were moderately or highly active.
Is the Chronotropic Index Applicable to Children and Adolescents?Reizo Baba, MD; Suketsune Iwagaki, PhD; Nobuo Tauchi, MD*; Masahito Tsurusawa, MD** Background The aim of the present study was to investigate whether the chronotropic index (CRI) is independent of age, sex, stage of exercise testing, functional capacity and resting heart rate in children, as it is in adult populations. Methods and Results A total of 129 normal children and adolescents underwent maximal treadmill exercise testing according to the Bruce protocol. Submaximal chronotropic response was assessed by the CRI at the end of stages 1, 2, 3, and 4...
