Myocardial Oxygen Consumption and Efficiency in Patients With Cardiac Amyloidosis

BACKGROUND: This study evaluated myocardial oxygen consumption (MVO(2)) and myocardial external efficiency (MEE) in patients with cardiac amyloidosis (CA). Furthermore, we compared MEE and MVO(2) in subjects with light chain amyloidosis versus transthyretin (ATTR) amyloidosis. METHODS AND RESULTS: The study population comprised 40 subjects: 25 patients with confirmed CA and 15 control subjects. All subjects underwent an (11)C‐acetate positron emission tomography. Furthermore, the CA patients underwent comprehensive echocardiography and right heart catheterization during a symptom‐limited, semi‐supine exercise test. MEE was calculated from (11)C‐acetate positron emission tomography as the ratio of left ventricular (LV) stroke work and the energy equivalent of MVO(2). Myocardial work efficiency was calculated as echocardiography‐derived work pressure product divided by three‐dimensional LV mass. CA patients had significantly lower LV‐ejection fraction (54±13% versus 63±4%, P<0.05) and LV‐global longitudinal strain (LVGLS) (12±4% versus 19±2%, P<0.0001) and a more restrictive filling pattern (E/e′‐ratio 18 [12–25] versus 8 [7–9], P<0.0001) than controls. MEE was severely reduced (13±5% versus 22±5%, P<0.0001) whereas total MVO(2) was higher (18±6 mL/min versus 13±3 mL/min, P<0.01) in CA patients than controls. MEE decreased with increasing New York Heart Association symptom burden (P<0.0001). We found a good relationship between MEE and peak exercise systolic performance (LVGLS: R (2)=0.60, P<0.0001; myocardial work efficiency: R (2)=0.48, P<0.0001; cardiac index: R (2)=0.52, P<0.0001) and between MEE and myocardial blood flow (R (2)=0.44, P<0.0001). CONCLUSION: Myocardial oxidative metabolism is disturbed in CA patients with increased total MVO(2) and reduced MEE. MEE correlated significantly with echocardiographic derived systolic parameters such as myocardial work efficiency and LVGLS that might be used as surrogate MEE markers.