What is behind the calcium? The relationship between calcium and necrotic core on virtual histology analyses
Scott W. Murray, N. D. Palmer · European Heart Journal · 2008
We read with great interest the investigative paper by Missel et al.1 We would like to thank the authors for furthering our knowledge in this field with their continued production of high-quality research. Our one reservation is with the creation of a necrotic core (NC) to dense calcium (DC) ratio from VH–IVUS data. We are proponents of this excellent tool, but we also have a healthy scepticism regarding its capability to accurately detect what is seen behind calcium in coronary lesions. We do agree that the spectral analysis of the backscatter radio frequency ultrasound signal has 87–92% in vivo accuracy for the characterization of the four basic plaque components. 2 We also do not doubt the ability of IVUS and VH to determine calcified areas. Our main concern involves the commonly seen appearance of NC behind areas of calcification. Only 21 region-of-interests containing NC were actually analysed in the initial accuracy evaluation of the S5/Eagle Eye VH classification tree. 3 Is it possible that some areas appearing as NC are simply a manifestation of the attenuated echo signal behind calcium, which is subsequently classified to this tissue type by the VH algorithm? It is common to see NC coded in areas of echo loss behind stent struts (classified as calcium) if VH is switched on during motorized pullback through a stent. What did the authors do with their more calcified lesions? Were any excluded from the final analysis? If not, what are their thoughts about the contribution of sub-calcific echo dropout to NC percentages and ultimately their important NC/DC ratio? We would be grateful for advice and expert opinion on these observations and whether or not this is a true limitation of the ‘current’ VH algorithm. We feel this is a very significant area in IVUS–VH research that could impact upon the important findings of this study and work continuing in our own department as well as other centres around the world.