MIBG imaging. MIBG imaging will be performed in all patients shortly after admission and at 6 and 12 months after the discharge. MIBG will be performed with a The standard protocol for 123I-MIBG cardiac imaging requires that drugs that interfere with 123I-MIBG uptake be withheld. A comprehensive listing of prescription and over-the-counter drugs that interfere with 123I-MIBG biodistribution, and the time for which they should be withheld, has been published . Thyroid uptake of unbound 123I is blocked with 500 mg of potassium perchlorate given orally 30 min before 123I-MIBG injection. Between 148 MBq and 370 MBq of 123I-MIBG are injected intravenously at rest. Both planar and SPECT images are acquired 15 min after injection (early) and 4 h after injection (delayed). A dual head gammacamera (ECAM Siemens, Erlangen - Germany) equipped with a low-energy - high resolution collimator was used. A 20% window is usually centered over the 159-keV photopeak of 123I for imaging. Anterior planar images of the chest are acquired using a 256 x 256 matrix. single photon emission computed tomography (SPECT) images are acquired using a 64 x 64 matrix over 180°, from the right anterior oblique position to the left posterior oblique position. Planar imaging allows for global assessment of cardiac innervation, whereas SPECT allows for regional evaluation. Quantitative evaluations will be performed with a standard protocol previously described.