Effect of Plaque Burden and Morphology on Myocardial Blood Flow and Fractional Flow Reserve

Background: Atherosclerotic plaque characteristics may affect downstream myocardial perfusion, as well as coronary lesion severity. Objectives: This study sought to evaluate the association between quantitative plaque burden and plaque morphology obtained using coronary computed tomography angiography (CTA) and quantitative myocardial perfusion obtained using [¹⁵O]H₂O positron emission tomography (PET), as well as fractional flow reserve (FFR) derived invasively. Methods: Two hundred eight patients (63% men; age 58 ± 8.7 years) with suspected coronary artery disease were prospectively included. All patients underwent 256-slice coronary CTA, [¹⁵O]H₂O PET, and invasive FFR measurements. Coronary CTA-derived plaque burden and morphology were assessed using commercially available software and compared with PET perfusion and FFR. Results: Atherosclerotic plaques were present in 179 patients (86%) and 415 of 610 (68%) evaluable coronary arteries. On a per-vessel basis, traditional coronary plaque burden indexes, such as plaque length and volume, minimal lumen area, and stenosis percentage, were significantly associated with impaired hyperemic myocardial blood flow (MBF) and FFR. In addition, morphological features, such as partially calcified plaques, positive remodeling (PR), and low attenuation plaque, displayed a negative impact on hyperemic MBF and FFR. Multivariable analysis revealed that the morphological feature of PR was independently related to impaired hyperemic MBF as well as an unfavorable FFR (p = 0.004 and p = 0.007, respectively), next to stenosis percentage (p = 0.001 and p < 0.001, respectively) and noncalcified plaque volume (p < 0.001 and p = 0.010, respectively). Conclusions: PR and noncalcified plaque volume are associated with detrimental downstream hyperemic myocardial perfusion and FFR, independent of lesion severity.