Late Outcomes of Patients in the Emergency Department With Acute Chest Pain Evaluated With Computed Tomography-Derived Fractional Flow Reserve.

Computed tomography (CTA)-derived fractional flow reserve (FFRCT) guides the need for invasive coronary angiography (ICA). Late outcomes after FFRCT are reported in stable ischemic heart disease but not in acute chest pain in the emergency department (ACP-ED). The objectives are to assess the risk of death, myocardial infarction (MI), revascularization, and ICA after FFRCT. From 2015 to 2018, 389 low-risk patients with ACP-ED (negative biomarkers, no electrocardiographic ischemia) underwent CTA and FFRCT and were entered into a prospective institutional registry; patients were followed up for 41 ± 10 months. CTA stenosis ≥50% was present in 81% of the patients. Positive (FFRCT ≤0.80) and negative FFRCT were observed in 124 (32%) and 265 patients (68%), respectively. ICA was performed in 108 of 124 patients (87%) with positive FFRCT and 89 of 265 patients (34%) with negative FFRCT (p <0.00001). Revascularization was performed in 87 of 124 (70%) patients with positive FFRCT and in 22 of 265 (8%) with negative FFRCT (p <0.00001). Appropriateness of revascularization was established by blinded adjudication of ICA and invasive FFR using practice guidelines; revascularization was appropriate in 81 of 124 (65%) and 6 of 265 (2%) of FFRCT-positive and -negative patients, respectively (p <0.00001). At follow-up, for patients with positive versus negative FFRCT, the rates were 0.8% versus 0% for death (p = 0.32) and 1.6% versus 0.4% for MI (p = 0.24). In conclusion, in low-risk patients with ACP-ED who underwent CTA and FFRCT, the risk of late death (0.2%) and MI (0.7%) are low. Negative FFRCT is associated with excellent long-term prognosis, and positive FFRCT predicts obstructive disease requiring revascularization. FFRCT can safely triage patients with ACP-ED and reduce unnecessary ICA and revascularization.

Assessment of lesion-specific ischemia using fractional flow reserve (FFR) profiles derived from coronary computed tomography angiography (FFRCT) and invasive pressure measurements (FFRINV): Importance of the site of measurement and implications for patient referral for invasive coronary angiography and percutaneous coronary intervention.

BACKGROUND: Fractional flow reserve (FFR)-derived from computed tomography angiography (CTA; FFRCT) and invasive FFR (FFRINV) are used to assess the need for invasive coronary angiography (ICA) and percutaneous coronary intervention (PCI). The optimal location for measuring FFR and the impact of measurement location have not been well defined. METHODS: 930 patients (age 60.7 + 10 years, 59% male) were included in this study. Normal and diseased coronary arteries were classified into stenosis grades 0-4 in the left anterior descending artery (LAD, n = 518), left circumflex (LCX, n = 112) and right coronary artery (RCA, n = 585). FFRCT (n = 1215 arteries) and FFRINV (n = 26 LAD) profiles were developed by plotting FFR values (y-axis) versus site of measurement (x-axis: ostium, proximal, mid, distal segments). The best location to measure FFR was defined relative to the distal end of the stenosis. FFR ≤0.8 was considered positive for ischemia. RESULTS: In normal and stenotic coronary arteries there are significant declines in FFRCT and FFRINV from the ostium to the distal vessel (p < 0.001), due to lesion-specific ischemia and to effects unrelated to the lesion. A reliable location (distal to the stenosis) is 10.5 mm [IQR 7.3-14.8 mm] for FFRCT and within 20-30 mm for FFRINV. Rates of positive FFR (from the distal vessel) reclassified to negative FFR (distal to the stenosis) are 61% (FFRCT) and 33% (FFRINV). CONCLUSION: FFRCT and FFRINV values are influenced by stenosis severity and the site of measurement. FFR measurements from the distal vessel may over-estimate lesion-specific ischemia and result in unnecessary referrals for ICA and PCI.

Computational fluid dynamics applied to cardiac computed tomography for noninvasive quantification of fractional flow reserve: scientific basis.

Coronary computed tomography angiography (CTA) has emerged as a noninvasive method for direct visualization of coronary artery disease, with previous studies demonstrating high diagnostic performance of CTA compared with invasive coronary angiography. However, CTA assessment of coronary stenoses tends toward overestimation, and even among CTA-identified severe stenosis confirmed at the time of invasive coronary angiography, only a minority are found to be ischemia causing. Recent advances in computational fluid dynamics and image-based modeling now permit determination of rest and hyperemic coronary flow and pressure from CTA scans, without the need for additional imaging, modification of acquisition protocols, or administration of medications. These techniques have been used to noninvasively compute fractional flow reserve (FFR), which is the ratio of maximal coronary blood flow through a stenotic artery to the blood flow in the hypothetical case that the artery was normal, using CTA images. In the recently reported prospective multicenter DISCOVER-FLOW (Diagnosis of Ischemia-Causing Stenoses Obtained Via Noninvasive Fractional Flow Reserve) study and the DeFACTO (Determination of Fractional Flow Reserve by Anatomic Computed Tomographic Angiography) trial, FFR derived from CTA was demonstrated as superior to measures of CTA stenosis severity for determination of lesion-specific ischemia. Given the significant interest in this novel method for determining the physiological significance of coronary artery disease, we herein present a review on the scientific principles that underlie this technology.