Correlation between intracoronary ultrasound and fractional flow reserve in long coronary lesions. A three-dimensional intracoronary ultrasound study.
INTRODUCTION AND OBJECTIVES
Intracoronary ultrasound estimation of the functional significance of intermediate angiographic lesions has mainly been based on measuring the minimal lumen area. These estimates take no account of lesion length and pay insufficient attention to long coronary lesions.


METHODS
We included 61 lesions with visual angiographic stenosis of 40% to 70% that required treatment with a ≥20mm stent, studied with ultrasound and fractional flow reserve. Three-dimensional analysis of the ultrasound study was conducted offline and blinded to fractional reserve values. Angiographic and ultrasound parameters were correlated with fractional reserve.


RESULTS
From the angiography we obtained data on mean reference diameter (2.87 [0.57] mm), length (29.8 [10.01] mm), and severity of stenosis (50.3% [8.7]%). Mean fractional flow reserve was 0.78 (0.09). We found a weak linear correlation (R) between fractional reserve and the ultrasound parameters that did not include lesion length: fractional reserve-minimal luminal area (R=0.4; P=.003). The correlation was stronger when lesion length was included: fractional reserve-volume of plaque (R=-0.65; P<.0005); fractional reserve-length/mean luminal area (R=0.73; P<.0005). The strongest correlation came from the product of mean stenosis by area multiplied by lesion length (R=-0.78; P<.0005).


CONCLUSIONS
In long coronary lesions, the correlation between ultrasound-measured minimal lumen area and functional significance is weak. In these cases, estimates of functional significance should incorporate lesion length or be derived from direct fractional flow reserve measurement.