Exercise performance in thalassemia major: correlation with cardiac iron burden.

Exercise performance is decreased in patients with Thalassemia major (TM), but the relative impact of anemia and iron overload on exercise capacity is unknown. We assessed the cardiopulmonary function of 71, well-transfused TM patients via graded treadmill exercise stress test. All patients underwent MRI of the heart, pancreas, and liver and diagnostic phlebotomy. Patients ranged in age from 13 to 46 years of age. Fifteen patients were excluded from analysis due to submaximal effort. Mean Vo2 max was 83.0% of predicted and was limited by abnormal cardiovascular mechanisms, consisting of a decreased O2 pulse (86.6% of predicted) in men and decreased maximum heart rate (HR) response (85% of predicted) in women. Patients with hemoglobin less than 12 g/dL had lower O2 pulse and Vo2 max, regardless of sex. Cardiac iron was negatively associated with maximum HR response and Vo2 max (r2 = 0.10 and 0.08, respectively, P < 0.05). Vo2 max was correlated with cardiac R2*, hs-CRP, sex and hemoglobin in decreasing strength of association. In thalassemia, exercise performance is limited by impaired stroke-volume reserve in men and blunted HR response in women. Iron toxicity may be mediated through vascular inflammation and direct modulation of HR response to exercise.