Influence of reconstruction kernels on the accuracy of CT-derived fractional flow reserve.

OBJECTIVES: We evaluated the influence of image reconstruction kernels on the diagnostic accuracy of CT-derived fractional flow reserve (FFRCT) compared to invasive FFR in patients with coronary artery disease. METHODS: Sixty-nine patients, in whom coronary CT angiography was performed and who were further referred for invasive coronary angiography with FFR measurement via pressure wire, were retrospectively included. CT data sets were acquired using a third-generation dual-source CT system and rendered with medium smooth (Bv40) and sharp (Bv49) reconstruction kernels. FFRCT was calculated on-site using prototype software. Coronary stenoses with invasive FFR ≤ 0.80 were classified as significant. Agreement between FFRCT and invasive FFR was determined for both reconstruction kernels. RESULTS: One hundred analyzed vessels in 69 patients were included. Twenty-five vessels were significantly stenosed according to invasive FFR. Using a sharp reconstruction kernel for FFRCT resulted in a significantly higher correlation with invasive FFR (r = 0.74, p < 0.01 vs. r = 0.58, p < 0.01; p = 0.04) and a higher AUC in ROC curve analysis to correctly identify/exclude significant stenosis (AUC = 0.92 vs. AUC = 0.82 for sharp vs. medium smooth kernel, respectively, p = 0.02). A FFRCT value of ≤ 0.8 using a sharp reconstruction kernel showed a sensitivity of 88% and a specificity of 92% for detecting ischemia-causing lesions, resulting in a diagnostic accuracy of 91%. The medium smooth reconstruction kernel performed worse (sensitivity 60%, specificity 89%, accuracy 82%). CONCLUSION: Compared to invasively measured FFR, FFRCT using a sharp image reconstruction kernel shows higher diagnostic accuracy for detecting lesions causing ischemia, potentially altering decision-making in a clinical setting. KEY POINTS: • Image reconstruction parameters influence the diagnostic accuracy of simulated fractional flow reserve derived from coronary computed tomography angiography. • Using a sharp kernel image reconstruction algorithm delivers higher diagnostic accuracy compared to medium smooth kernel image reconstruction (gold standard invasive fractional flow reserve).

After ISCHEMIA: Is coronary CTA the new gatekeeper?

The ISCHEMIA trial investigated two major principles in the therapy of coronary artery disease (CAD), i.e., symptom relief and improvement of prognosis. Specifically, it was designed to answer the question of whether, after ruling out left main stenosis, a routine interventional strategy in addition to optimal medical therapy can improve clinical outcome. Overall, this hypothesis could not be confirmed. Nevertheless, the trial yields interesting new aspects in the field of cardiac imaging. As a noninvasive diagnostic approach for individuals with suspected coronary artery disease, two different concepts are available: stress testing for ischemia (single-photon emission computed tomography, positron emission tomography, cardiac magnetic resonance imaging, stress echocardiography) and anatomic visualization of coronary artery stenosis by coronary computed tomography (CT) angiography (coronary CTA). While there was no randomized comparison between these two approaches in ISCHEMIA, the good outcome achieved by using coronary CTA as a "gatekeeper" to randomization supports the potential of coronary CTA as a diagnostic tool-both as first- and as second-line-when CAD is suspected. However, the trial also raises new questions in the field of cardiac imaging that need to be addressed in future studies.

Commissural misalignment independently predicts leaflet thrombosis after transcatheter aortic valve implantation.

AIMS: Transcatheter aortic valve implantation (TAVI) has become a minimally invasive alternative to surgical aortic valve replacement. Hypo-attenuated leaflet thickening (HALT)-a marker of subclinical leaflet thrombosis commonly detected by cardiac computed tomography (CT) after TAVI-may influence valve durability and function. The purpose of this study was to compare commissural alignment of the native and prosthetic aortic valves in cardiac CT in subjects with and without HALT and thereby identify commissural misalignment as potential predictor for leaflet thrombosis after TAVI. METHODS AND RESULTS: In 170 subjects, 85 with and 85 without HALT in post-TAVI CT, commissural orientation of the prosthesis was determined comparing native and prosthetic aortic valve orientation in cardiac CT by measuring the commissural angle relative to the right coronary ostium in the aortic valve plane. For the prosthetic valve, any deviation ≤ 15° compared to the native valve was classified as "aligned"; 16-30° as "mild", 31-45° as "moderate" and ≥ 45° as "severe" misalignment. Among subjects with HALT, median angular deviation was higher (36°, IQR 31°) than in the control group (29°, IQR 29°, p = 0.042). "Severe" misalignment was more frequent in subjects who developed HALT (n = 31, 37%) compared to the control group (n = 17, 20%, p = 0.013). In logistic regression analysis, more severe deviation (p = 0.015, OR = 1.02 per 1° deviation) and "severe" misalignment (p = 0.018, OR = 2.2) represented independent predictors for the occurrence of HALT after TAVI. CONCLUSION: Subclinical leaflet thrombosis after TAVI is associated with commissural misalignment. Potential clinical advantages of obtaining commissural alignment remain to be systematically assessed.

[Coronary computed tomography and cardiac devices : Diagnostic results or nothing but artifacts?] / Koronare Computertomographie bei Device-Trägern : Sinnvolle Diagnostik oder nur Artefakt?

Coronary computed tomography (CT) angiography has become a major cornerstone in the diagnostic workup of cardiologic patients, particularly for evaluation of the coronary arteries and preprocedural planning of interventions for structural heart disease. Despite the possible problems that intensive electromagnetic radiation (including X­rays) might cause when directly impacting on implanted cardiac devices, cardiac CT is a safe diagnostic test and should not be withheld from patients with devices if properly indicated. Sufficient image quality is paramount for the evaluation; hence, special attention should be paid to a low heart rate (< 60 bpm) and sufficient compliance with breathing instructions. Furthermore, pacemaker or implantable cardioverter-defibrillator (ICD) leads may cause metal artifacts, especially around the lead tip. Their dense material causes beam hardening and streak artifacts which may result in reduced image quality and limited diagnostic assessability. The prevalence of such artifacts depends not only on lead material but also on lead positioning relative to the gantry plane. Metal artifacts are more frequent in patients with unipolar leads and shock coils, which can impair the assessment of coronary arteries, mainly of the right coronary artery (RCA). Artifacts caused by left ventricular (LV) leads of cardiac resynchronization therapy (CRT) systems tend to affect assessment of the left circumflex artery (LCX). By using dual energy CT and postprocessing algorithms, the impact of artifacts can be reduced and diagnostic image quality can be achieved in most cases. Unfortunately, the actual occurrence of such artifacts or the degree of impairment of image quality cannot be reliably predicted.