Elevation of end-tidal CO2 during exercise is attenuated in patients with cardiac amyloidosis

Reduced exercise tolerance is one of the hallmarks of patients with cardiac amyloidosis (CA), but detailed biological responses during exercise were not investigated. The purpose of this study was to compare the cardiopulmonary exercise test (CPX) parameters between CA patients and propensity-matched heart failure patients. This was a single-center, retrospective, observational study of patients diagnosed with CA. The control group was extracted by propensity score matching from patients who underwent CPX for chronic heart failure during the same period. Clinical data including assessment of biological responses during CPX were compared between the patients with CA (CA group, n = 16) and the control group (non-CA group, n = 16). Echocardiography suggested more impaired diastolic function in the CA group than in the non-CA group. There was no significant difference between groups in the fraction of end-tidal carbon dioxide (FETCO2) at rest. However, the difference between the FETCO2 at rest and the FETCO2 at the respiratory compensation point (ΔFETCO2) was significantly smaller in the CA group than in the non-CA group (0.40