Hemodynamic Determinants of Activity Measured by Accelerometer in Patients With Stable Heart Failure

Objectives: This study examined the link between accelerometer recordings and cardiac pathophysiology measured with right heart cauterization at rest and with exercise in patients with HFrEF. Background: Patient-worn accelerometers are increasingly being used in patients with heart failure with reduced ejection fraction (HFrEF) to assess activity and serve as surrogate endpoints in heart failure trials. Methods: Physical average daily activity (PADA) and total average daily activity according to accelerometer units were assessed in 63 patients (mean age 58 ± 10 years; mean ejection fraction 26% ± 4%). Patients underwent hemodynamic exercise testing and accelerometry. Patients were divided according to PADA in PADA_Low and PADA_High activity level groups based on median counts per minute of physical activity. Results: Patients in the PADA_Low group were older and more frequently treated with diuretics. At rest, the PADA_Low group was characterized by a lower cardiac index (2.2 ± 0.4 L/min/m² vs 2.4 ± 0.4 L/min/m²; P = 0.01) and stroke volume (70 ± 19 mL vs 81 ± 17 mL; P = 0.02) but not pulmonary capillary wedge pressure (12 ± 5 mm Hg vs 11 ± 5 mm Hg; P = 0.3). The PADA_Low group reached a lower cardiac index (4.8 ± 1.7 L/min/m² vs 6.6 ± 1.7 L/min/m²; P < 0.001) but not in pulmonary capillary wedge pressure (31 ± 12 mm Hg vs 27 ± 8 mm Hg; P = 0.2) at peak exercise. The attenuated increase was associated with an attenuated increase in stroke volume (94 ± 32 mL vs 121 ± 29 mL; P < 0.001) rather than a reduced increase in heart rate (42 ± 23 beats/min vs 52 ± 21 beats/min; P = 0.07). PADA and total average daily accelerometer units were associated with patient-reported functional impairment according to the Kansas City Cardiomyopathy Questionnaire but not with New York Heart Association functional class. Conclusions: Among stable ambulatory patients with HFrEF, lower daily activity is associated with poorer cardiac index reserve and reduced cardiac index during exercise.