Hemodynamic significance of coronary stenosis by vessel attenuation measurement on CT compared with adenosine perfusion MRI

Highlights

• The majority of anatomical coronary stenoses do not cause myocardial ischemia.

• cCTA-derived CCO decrease expresses luminal density gradient across stenosis.

• CCO decrease differentiates between anatomical stenoses with and without associated myocardial ischemia.

• CCO decrease assessment can exclude the majority of stenoses without hemodynamic significance.

Abstract

Purpose

We assessed the association between corrected contrast opacification (CCO) based on coronary computed tomography angiography (cCTA) and inducible ischemia by adenosine perfusion magnetic resonance imaging (APMR).

Methods

Sixty cardiac asymptomatic patients with extra-cardiac arterial disease (mean age 64.4 ± 7.7 years; 78% male) underwent cCTA and APMR. Luminal CT attenuation values (Hounsfield Units) were measured in coronary arteries from proximal to distal, with additional measurements across sites with >50% lumen stenosis. CCO was calculated by dividing coronary CT attenuation by descending aorta CT attenuation. A reversible perfusion defect on APMR was considered as myocardial ischemia.

Results

In total, 169 coronary stenoses were found. Seven patients had 8 perfusion defects on APMR, with 11 stenoses in corresponding vessels. CCO decrease across stenoses with hemodynamic significance was 0.144 ± 0.112 compared to 0.047 ± 0.104 across stenoses without hemodynamic significance (P = 0.003). CCO decrease in lesions with and without anatomical stenosis was similar (0.054 ± 0.116 versus 0.052 ± 0.101; P = 0.89). Using 0.20 as preliminary CCO decrease cut-off, hemodynamic significance would be excluded in 82.9% of anatomical stenoses.

Conclusions

CCO decrease across coronary stenosis is associated with myocardial ischemia on APMR. CCO based on common cCTA data is a novel method to assess hemodynamic significance of anatomical stenosis.

Introduction

Computed tomography (CT) has high diagnostic accuracy for the detection and exclusion of coronary artery disease (CAD), compared with invasive coronary angiography [1], [2]. Coronary stenosis detected on coronary CT angiography (cCTA), however, shows poor correlation with lesion-specific and global myocardial ischemia [1], [2]. In the cath lab, fractional flow reserve (FFR) is used to assess the functional significance of coronary stenosis [3]. This lesion-specific index reflects the effect of stenosis on myocardial perfusion. However, FFR measurement is an invasive procedure with associated costs, and is only performed in symptomatic patients undergoing invasive coronary angiography. Recent imaging techniques can assess the hemodynamic significance of CAD without the risk associated with an invasive procedure. Adenosine perfusion magnetic resonance imaging (APMR) and positron emission tomography are safe and preferable non-invasive alternatives for vessel-specific ischemia detection with similar high diagnostic accuracy [4], [5]. APMR has an excellent sensitivity and specificity of 91 and 94% respectively, as compared with FFR [6].

In view of the increased use of cCTA to assess CAD, it would be extremely valuable if this same non-invasive test could determine the hemodynamic significance of the anatomical stenoses that are readily detected. Recently, an estimate of coronary flow was obtained using common cCTA data. In calculations based on cCTA, reduced flow across an intermediate-grade coronary stenosis points to the presence of hemodynamically significant CAD. Two multicenter studies have demonstrated the preliminary clinical value of this approach, using computational fluid dynamics [7], [8], [9]. This method involves a lengthy and complicated computation, potentially hindering its introduction in clinical practice. A simpler calculation named the corrected contrast opacification (CCO) [10], [11], [12] can also estimate coronary artery flow. So far, clinical studies have compared CT-derived flow measurements with FFR measurements. Due to the nature of FFR evaluation, these studies involved a selected population of symptomatic patients. This is the first study in which CT-derived CCO is compared with non-invasive imaging of functionally significant CAD. The aim of this study, in a high-risk, cardiac asymptomatic population, is to investigate the association between CCO as estimate of coronary flow and ischemia detection by APMR.