Electron-Beam Computed Tomography in the Assessment of Coronary Artery Disease After Heart Transplantation

Assessment of Coronary Artery Disease After Heart Transplantation To the Editor: In their study of electron-beam computed tomography (EBCT) for the assessment of coronary artery disease in heart transplantation, Knollmann et al1 noted a significant discrepancy between the amount of calcification measured by EBCT and that measured by intracoronary ultrasound. In their discussion, they suggest a number of possible explanations for this. However, this discrepancy may be related to the different pathogenesis of intimal and medial calcification.2 Intimal calcification occurs within the perimeter of the internal elastic lamina within the atherosclerotic plaque. It is associated with inflammatory cells, lipids, and vascular smooth muscle cells. In contrast, medial calcification occurs as a separate process in the context of aging (Monckeberg’s sclerosis), end-stage renal disease, neuropathy, diabetes, and a number of rare genetic syndromes. It is associated with elastin and vascular smooth muscle cells. EBCT is unable to distinguish between medial and intimal calcification. Thus, the use of EBCT to measure intimal calcification and, therefore, atherosclerosis relies on the assumption that the amount of medial calcification in the coronary arteries is negligible. However, in the case of transplantation it is possible that the denervated heart is prone to medial calcification similar to the medial calcification that occurs in peripheral arteries in neuropathy.3,4 Using intracoronary ultrasound, the extent of deeper medial calcification may be underestimated because of the acoustic shadow of more superficial intimal calcification.5 If EBCT is to be used routinely to assess coronary artery disease in transplanted hearts, it is vital that studies are conducted to determine the incidence of medial calcification within this patient group. This is because the presence of medial calcification will reduce the utility of EBCT calcium score as a measure of atherosclerosis.