What is an appropriate reference standard in the quantitation of plaque surface area by intravascular coronary ultrasound?

We reevaluate the predictive accuracy of intravascular ultrasound (IVUS)-derived per cent plaque area stenosis (PAS) in significant coronary lesions (CLs) with or without proximal and distal reference vessel area adjustment. IVUS is valuable in defining moderate CL severity (30 to 70%) in left main (LM) or non-left main (NLM) coronaries using minimum luminal area (MLA) of ≤5.9 and ≤4 mm(2), respectively. Despite a strong correlation with severe CLs, PAS (≥ 70% for NLM and ≥67% for LM) remains underutilized because of confusion about an appropriate reference standard. We studied 120 patients with symptomatic moderate CLs (74 NLM, 46 LM) who underwent IVUS. In-lesion and adjusted PAS were derived by subtracting MLA from in-lesion and proximal or distal reference's external elastic membrane (EEM) area, respectively, divided by corresponding EEM area multiplied by 100. In-lesion PAS was correlated with MLA cutoffs of ≤5.9 and ≤7.5 mm(2) for LM and ≤4 mm(2) for NLM. Adjusted PAS strongly correlated with in-lesion PAS irrespective of reference segment (proximal reference, r = 0.879, p < 0.001; distal reference, r = 0.833, p < 0.001; mean proximal and distal reference, r = 0.896, p < 0.001). Considering MLA of ≤4 mm(2) (for NLM) and ≤5.9 mm(2) (for LM), in-lesion PAS of ≥70 and ≥67%, respectively, explained the majority of severe CLs but the sensitive LM MLA cutoff of ≤7.5 mm(2) showed higher predictive accuracy. Based on results, both in-lesion PAS and adjusted PAS can be used interchangeably and correlate strongly with MLA.