Impaired heart rate response during incremental exercise in patients with acute myocardial infarction and after coronary artery bypass grafting evaluation of coefficients with Karvonen's formula

Abstract

Heart rate (HR) response during exercise in patients with ischemic heart disease was evaluated, and the appropriateness of Karvonen's method for determining rehabilitation exercise target HR was investigated. The study group comprised 24 patients with acute myocardial infarction (AMI) and 37 patients who had undergone coronary artery bypass grafting (CABG). Cardiopulmonary exercise testing (CPX) was performed with a cycle ergometer and changes in HR (ΔAHR)/changes in work rate (ΔWR) and interval changes of the coefficient of Karvonen's formula were evaluated. In the AMI group and the CABG group, ΔHR/ΔWR were significantly lower than those of age-matched control subjects (p<0.01). Karvonen's coefficients ranged from 0.37 to 0.54 when calculated from actual peak HR and 0.21 to 0.32 calculated from the predicted peak HR. An impaired HR response was found in patients with AMI and those who had had CABG up to 6 months previously. Because the Karvonen's coefficient values, which ranged from 0.6 to 0.8, were elevated for these patients, and considering the data from the CPX, increased exercise is recommended for such cases.