Abstract
Objective Exercise therapy as part of cardiac rehabilitation is one of the most effective treatments for patients with chronic heart failure (HF). The anaerobic threshold (AT) determined by an exhaled gas analysis during cardiopulmonary exercise testing (CPX) is used to prescribe the appropriate level of exercise therapy. However, CPX using an exhaled gas analysis is not widely performed because of its cost, complexity, and the need for skilled staff. Therefore, a simpler and inexpensive method for determining AT without respiratory gas measurements is required in patients with HF. The present study elucidated the relationship between the AT determined by the CPX ventilatory method (CPX-AT) and the AT determined by cardiac acoustic biomarkers (CABs), which are measured by acoustic cardiography (CAB-AT), in HF patients. Methods Patients underwent symptom-limited ramp CPX twice using a cycle ergometer. The ATs determined from the exhaled gas analysis were identified by three independent physicians. CABs, including the first heart sound (S1) and the second heart sound intensities (peak-to-peak amplitudes), electromechanical activation time (EMAT) defined as the time interval from the Q wave onset on electrocardiography to S1, heart rate, and other parameters, were collected during CPX. Patients Forty patients with HF were included in this study. Results A significant correlation (R=0.70; p<0.001) was found between CPX-AT and CAB-AT, using the double product of S1 intensity and heart rate. CAB-AT using S1 intensity also showed a significant correlation with CPX-AT (R=0.71; p<0.001). Conclusion The present study suggests a possible new method for determining AT without respiratory gas measurements in patients with HF.