Correlations between fractional flow reserve and intravascular ultrasound in patients with an ambiguous left main coronary artery stenosis

Background - Intravascular ultrasound (IVUS) is being used to assess the significance of a left main coronary artery stenosis (LMCS). However, the cutoff values of IVUS parameters at which to predict a fractional flow reserve (FFR) of 0.75 are unknown. Methods and Results - In 55 patients with an angiographically ambiguous LMCS, a pressure guidewire was used to calculate FFR, and IVUS parameters were calculated after automatic pullback. FFR averaged 0.86 +/- 0.13 ( range, 0.55 to 1.0). IVUS minimum lumen diameter (MLD), minimum lumen area (MLA), cross-sectional narrowing (CSN), and area stenosis (AS) were 3.8 +/- 0.61 mm, 7.65 +/- 2.9 mm(2), 59 +/- 13%, and 47 +/- 19%, respectively. Regression analysis demonstrated strong correlations between FFR and MLD ( r = 0.79, P < 0.0001) as well as between FFR and MLA ( r = 0.74, P < 0.0001). There were inverse, moderate correlations between FFR and CSN ( r = 0.69, P < 0.0001), followed by those between FFR and AS ( r = 0.54, P < 0.0001). Compared with FFR as the "gold standard," an MLD of 2.8 mm had the highest sensitivity and specificity (93% and 98%, respectively) for determining the significance of an LMCS, followed by an MLA of 5.9 mm(2) (93% and 95%, respectively). Based on an FFR <0.75 and an FFR >= 0.75, the 38-month survival and event-free survival estimates (EFSEs) were both 100% and 100% versus 90%, respectively ( P = NS). Conclusions - We conclude that ( 1) an IVUS MLD and MLA of 2.8 mm and 5.9 mm2, respectively, strongly predict the physiological significance of an LMCS and ( 2) among patients with an LMCS, an FFR of 0.75 is a strong predictor of survival and EFSE.