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Relationship of Magnetic Resonance Imaging Estimation of Myocardial Iron to Left Ventricular Systolic and Diastolic Function in Thalassemia

Department of Cardiology, Children's Hospital Boston, and the Department of Pediatrics, Harvard Medical School, Boston, Massachusetts

^_* Reprint requests and correspondence: Dr. Andrew J. Powell, Department of Cardiology, Children's Hospital Boston, 300 Longwood Avenue, Boston, Massachusetts 02115 (Email: andrew.powell{at}cardio.chboston.org).

Objectives: We sought to evaluate whether echocardiographic diastolic function indices correlate with myocardial iron and systolic function in patients with transfusion-dependent thalassemia (TDT) who are at risk for cardiomyopathy.

Background: In thalassemia syndromes, there is an important clinical need to risk stratify patients for the development of iron-overload cardiomyopathy so that chelation therapy can be adjusted and cardiac morbidity averted. This purpose may be served by measuring the magnetic resonance imaging (MRI)-derived parameter T2*, which varies inversely with tissue iron concentration but has limited availability. As diastolic dysfunction may precede systolic dysfunction, we sought to directly compare more readily available echocardiographic indices of diastolic function to myocardial T2* and ejection fraction (EF).

Methods: We identified 47 paired echocardiography and MRI examinations in 24 patients with TDT. Echocardiographic measurements of transmitral flow velocities (E, A), tissue Doppler velocities (E'), and left ventricular volume and EF were compared with MRI measurements of myocardial T2*, ventricular volume, and EF.

Results: All patients had a restrictive filling pattern (E/A 1.5 and deceleration time <140 ms) and normal relaxation. There was no significant correlation between E/E' or the Tei index versus EF. Although E/A and E' had statistically significant correlations with EF, the relationships were weak with all correlation coefficients <0.52. The parameters E/A, E', E/E', and the Tei index did not significantly correlate with myocardial iron concentration as assessed by MRI T2*. Increased myocardial iron as measured by T2* was strongly associated with lower left ventricular EF, with a T2* <9 ms having a sensitivity of 100% and specificity of 89% for MRI EF <50%.

Conclusions: In patients with TDT, echocardiographic diastolic function parameters correlated poorly with EF and myocardial T2* and were thus not well-suited for risk stratification. Myocardial T2* had a strong relationship with EF and appears to be a promising approach for predicting the development of heart failure and for iron chelator dose adjustment.

Key Words: thalassemia • myocardial T2* • diastolic function • cardiac siderosis

Abbreviations and Acronyms   DT = deceleration time   EF = ejection fraction   IVRT = isovolumic relaxation time   LV = left ventricular   MRI = magnetic resonance imaging   TDT = transfusion-dependent thalassemia

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				D. J. Pennell T2* magnetic resonance: iron and gold. J. Am. Coll. Cardiol. Img., September 1, 2008; 1(5): 579 - 581. [Full Text] [PDF]