Radioimaging to identify myocardial cell death and probably injury

Annexin V is ubiquitously distributed in myocardial cells and, to a greater extent, endothelial cells and fibroblasts.3 Annexin V is normally found in the sarcolemma, T-tubules, and intercalated discs of myocytes and in the cytoplasm of fibroblasts and endothelial cells. In heart failure annexin V is upregulated, with increased amounts being translocated to the interstitial tissues, which suggests that it has a role in interstitial fibrosis and myocardial remodelling. Annexin V may play significant roles in cell physiology, including such processes as control of membrane permeability to calcium and inhibition of pro-apoptotic signals from protein kinase C and phospholipase A^sub 2^. Also, in some cell lines, annexin V inhibits apoptosis by increasing intracellular calcium concentration.' Circulating concentrations of endogenous annexin V average 1.7 ng/mL in healthy people and increase about ten-fold in acute disease states, such as myocardial infarction.5 Although the localisation of exogenously administered annexin V seems to depend on the occurrence of apoptosis, laboratory work suggests that physiological stresses, such as those induced by ischaemia, may produce transient and reversible phosphatidylserine expression, which may be visualised following administration of radiolabelled annexin. If these processes continue unchecked, they will lead to cell death by apoptosis.6 These observations suggest that the annexin images obtained by [Leo Hofstra] and colleagues may reflect both cells undergoing apoptosis and cells that are severely injured but still capable of surviving.