Reduced chronotropic reserve to the metabolic requirement during exercise in advanced heart failure with old myocardial infarction.

We studied the metabolic and cardiac responses to exercise by expiratory gas analysis in 40 patients with old myocardial infarction and 33 normal sedentary males. On the basis of exercise energy metabolism, the elevation of the respiratory quotient (RQ; RQ = VCO2/VO2) during exercise is caused by the increase of blood lactate due to the augmented anaerobic metabolism. Functional aerobic impairment (FAI) in our study was significantly advanced in the control group and the NYHA functional class I, class II and class III groups, that is, -2.3 +/- 11.2%, +14.8 +/- 10.4%, +27.8 +/- 13.8% and +49.4 +/- 2.8%, respectively. The delta RQ values were similar among all groups; 0.29 respectively. The delta RQ values were similar among all groups; 0.29 +/- 0.06, 0.28 +/- 0.07, 0.27 +/- 0.07 and 0.29 +/- 0.09, respectively. Functional chronotropic impairment (FCI) for the same groups was -0.9 +/- 7.0%, +1.4 6.1%, +3.8 +/- 4.8% and +8.7 +/- 6.0%, and that of the class III group was significantly larger than that of the control group. Thus, in the class III congestive heart failure group, the chronotropic response to the metabolic requirement was impaired in comparison to the control group. It was concluded that the reduced chronotropic reserve was present in NYHA class III patients with old myocardial infarction, and that this mechanism might contribute to a decrease in the pump reserve of the heart, resulting in further impairment of physical capacity in these patients.