The underlying mechanisms of exercise intolerance in sickle cell anemia (SCA) patients are complex and not yet completely understood. While latent heart failure at rest could be unmasked upon exercise, most previous studies assessed cardiac function at rest. We aimed to investigate exercise cardiovascular reserve as a potential contributor of exercise intolerance in adult SCA patients.
In this observational prospective study we compared prospectively 60 SCA patients (median age 31 years, 60% women) to 20 matched controls. All subjects underwent symptom-limited combined exercise echocardiography and oxygen uptake (VO ) measurements. Differences between arterial and venous oxygen content (C(a-v)O ) were calculated. Cardiac reserve was defined as the absolute change in cardiac index (Ci) from baseline to peak exercise.
Compared to controls, SCA patients demonstrated severe exercise intolerance (median peakVO , 34.3 versus 19.7ml/min/kg respectively,p<0.0001). SCA patients displayed heterogeneously increased Ci from rest to peak exercise (median +5.8, range 2.6 to 10.6L/min/m²) which correlated with peakVO (r=0.71,p<0.0001). In contrast, the C(a-v)O exercise reserve was homogenously reduced and did not correlate with peakVO (r=0.18, p=0.16). While hemoglobin level and C(a-v)O were similar in SCA subgroups, SCA patients in the lower VO tertile had chronotropic incompetence and left ventricular diastolic dysfunction (left atrial peak longitudinal strain was reduced and both E/e' ratio and left atrial volume index were increased) and were characterized by a reduced cardiac reserve.
Altered cardiac reserve due to chronotropic incompetence and left ventricular diastolic dysfunction seems to be an important determinant of exercise intolerance in adult SCA patients.

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