Relationship of late loss in lumen diameter to coronary restenosis in sirolimus-eluting stents

Background - Observed rates of restenosis after drug-eluting stenting are low ( < 10%). Identification of a reliable and powerful angiographic end point will be useful in future trials. Methods and Results - Late loss ( postprocedural minimum lumen diameter minus 8-month minimum lumen diameter) was measured in the angiographic cohorts of the SIRIUS (n = 703) and E-SIRIUS (n = 308) trials. Two techniques, the standard normal approximation and an optimized power transformation, were used to predict binary angiographic restenosis rates and compare them with observed restenosis rates. The mean in-stent late loss observed in the SIRIUS trial was 0.17 +/- 0.45 mm (sirolimus) versus 1.00 +/- 0.70 mm ( control). If a normal distribution was assumed, late loss accurately estimated in-stent binary angiographic restenosis for the control arm ( predicted 35.4% versus observed 35.4%) but underestimated it in the sirolimus arm ( predicted 0.6% versus observed 3.2%). Power transformation improved the reliability of the estimate in the sirolimus arm ( predicted 3.2% [CI 1.0% to 6.7%]) with similar improvements in the E-SIRIUS trial ( predicted 4.0% [ CI 1.2% to 7.0%] versus observed 3.9%). In the sirolimus-eluting stent arm, in-stent late loss correlated better with target-lesion revascularization than in-segment late loss (c-statistic = 0.915 versus 0.665). Conclusions - Because distributions of late loss with a low mean are right-skewed, the use of a transformation improves the accuracy of predicting low binary restenosis rates. Late loss is monotonically correlated with the probability of restenosis and yields a more efficient estimate of the restenosis process in the era of lower binary restenosis rates.