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Reduced Left Ventricular Contractile Reserve Identified by Low Dose Dobutamine Echocardiography as an Early Marker of Cardiac Involvement in Asymptomatic Patients with Thalassemia Major

Patients with beta thalassemia major present with severe anemia and need continuous transfusion therapy. The consequent iron overload leads to hemochromatosis. Initial cardiac involvement can be present in thalassemic patients without clinical manifestations of heart failure. The purpose of this study was to assess the contractile reserve of the left ventricle in patients with normal baseline two‐dimensional (2‐D) echocardiographic findings using low dose dobutamine echocardiography. The underlying hypothesis was that, at an early stage, structural impairment of the myocardial wall due to myocardial iron deposits and/or secondary fibrotic changes could be so subtle so as not to impair resting systolic function, but is severe enough to blunt or even exhaust the contractile response to inotropic stimulation. Twenty‐four consecutive patients (13 men and 11 women;/ages 18 ± 3.8 years) with beta thalassemia major undergoing evaluation for bone marrow transplantation entered the study. By selection, all were asymptomatic, without clinical signs of cardiac failure, and had normal regional and global systolic function at baseline echocardiographic study. A control group of 16 age and sex matched subjects was also studied. All underwent baseline, 2‐D, and Doppler study, as well as dobutamine stress (up to 5 μg/kg per min) 2‐D echocardiographic study. Patients and controls showed comparable values of indexes of global (ejection fraction: 0.64 ± 0.06 vs 0.65 ± 0.05, P = NS) and regional (systolic thickening of posterior wall: 90 ± 34 vs 91 ±34%, P = NS) function at baseline. Left ventricular diastolic filling was evaluated with Doppler echocardiography. Peak flow velocity in early diastole was increased in thalassemic patients compared to controls (114±16 vs 96±18 cm/sec, P < 0.01), and flow velocity deceleration time was reduced (139±17 vs 157±20 msec, P < 0.01). At peak dobutamine, thalassemic patients showed a blunted contractile response compared to controls for indexes of both global (ejection fraction: 0.62±0.06 vs 0.69±0.05, P < 0.01) and regional (% systolic thickening of posterior wall: 91±36 vs 130±39%, P < 0.01) function. When individual patient analysis was performed, echocardiographic parameters were beyond the 95% confidence limits obtained from normal controls in 5 (21%) of the 24 study patients by one or more Doppler diastolic indexes, in 6 (25%) by indexes of contractile reserve, and in 11 (46%) by one of either diastolic function or contractile reserve indexes. These data demonstrate that the “iron heart” of asymptomatic thalassemic patients is a weak heart. Even if the regional and global systolic functions are similar to normals under resting conditions, the application of an inotropic challenge unmasks the weakness of these hearts, which can be identified at an earlier stage of their natural history through the blunted contractile response following the infusion of low dose dobutamine. The information on contractile reserve is not redundant, but rather incremental and in addition to that provided by Doppler echocardiographic indexes, which may be abnormal in these patients.