CT FFR

Coronary CTA based comprehensive chest pain diagnostics. A Case Report

Background: Recent European Society of Cardiology guidelines on management of chronic coronary syndromes assign a strong Class I indication for use of coronary computed tomography angiography (CTA) as the first line diagnostics of chest pain in patients with intermediate probability of coronary artery disease (CAD)(1). The main advantage of coronary CTA is a high negative predictive value for exclusion of significant coronary stenosis. However the positive diagnostic performance of the method is poor in case of moderate stenosis; the specificity (per vessel) of coronary CTA for detection of >50% coronary stenosis is 56% (2). The anatomic/angiographic methods of CAD diagnostics are at additional disadvantage with regard of diagnosis of functionally significant stenosis, which is the crucial consideration for decision on medical or additionally interventional treatment. Less than 20% of coronary stenoses diagnosed on coronary CTA as 50-70% is functionally significant, likewise only 40% of the stenoses between 70 and 90% (3). On the other hand, coronary CTA images of the artery and the stenosis allow for reliable and advantegous planning of coronary interventions (4).

Recent advances in computational techniques allow to overcome the shortcomings of coronary CTA as a solely anatomic diagnostics method. Introduction of CTA based fractional flow reserve (CT-FFR) allows to improve the specificty of the noninvasive examination to diagnose functionally significant CAD up to 80%, to the level of other traditional functional tests like SPECT or MRI (2). The CT-FFR analysis relies on the routine set of coronary CTA data, therefore it does not involve any additional patient testing.

Case report: A 46-year-old man developed dyspnea and atypical chest pain with moderate to strenuous physical activity. The cardiac risk factors included family history of CAD, glucose intolerance, hypertension, HDL 38mg%, LDL 134mg%, 28 pack-years of cigarettes smoking. The clinical likelihood of signifcant CAD was moderate.

Therefore, a coronary CTA examination was performed as the first line diagnostics; coronary calcium score was 0, however an intermediate stenosis (50-70%) of proximal left anterior descending artery (LAD) was diagnosed based on visual estimation, left circumflex (LCx) and right coronary arteries (RCA) displayed mild stenoses (<25% each)(Figure 1). Despite already receiving antihypertensive (including antianginal) medications the patient was symptomatic.

Because the functional significance of the LAD stenosis was unclear, a CT-FFR was performed, based on the already acquired coronary CTA dataset, no further radiation or contrast was required. An interactive colour coded three dimensional image of the coronary tree was generated, additionally allowing to mark the specific sites within the arteries and obtain the CT-FFR values (Figure 2). The lower CT-FFR value below the 0.80 threshold, the more reliable diagnosis of a significant CAD (5). In the current case the CT-FFR value at the site which is optimal for evaluation of CT-FFR was 0.75-0.80, however more distal values indicated unambigous ischemia (6).

Following the discussion with the patient, it was decided to perform a percutaneous coronary stenting procedure, appropriate stent planning was performed based on coronary CTA data (Figure 3) and pre-medication with ticagrelol was introduced. The patient was sent to the cathlab directly for the invasive therapeutic procedurę, since no need to cathetherize the RCA was deemed neccessary. The operator proceeded with LAD, performing FFR, obtaining the value of 0.78 (Figure 4 A), and followed by successful coronary stenting (drug eluting stent 3.5mm/25mm)(Figure 4 B, C). After the procedure both pain and dyspnea resolved.

KEY LEARNING POINTS:

• Coronary CTA provides a one-stop-shop for CAD diagnostics; allowing for:

1. fast, single-stage, non-invasive, comprehensive diagnosis of CAD, confirming or excluding the presence of functionally significant stenosis;
2. qualification to further medical or additionally interventional management of CAD, and
3. planning of coronary intervention, patient consenting, operator choice, pre-medication.

• CT-FFR value should be read at the site analogous to potential invasive FFR (2-3 cm below the index stenosis);
• Calcium score zero on noncontrast coronary computed tomography does not exclude significant CAD;

Literature

1. Knuuti J, Wijns W, Saraste A, et al. 2019 ESC Guidelines for the diagnosis and management of chronic coronary syndromes. Eur Heart J. 2020;41(3):407‐477
2. Hecht HS, Narula J, Fearon WF. Fractional Flow Reserve and Coronary Computed Tomographic Angiography: A Review and Critical Analysis. Circ Res. 2016;119(2):300‐316
3. Tamarappoo BK, Gutstein A, Cheng VY, et al. Assessment of the relationship between stenosis severity and distribution of coronary artery stenoses on multislice computed tomographic angiography and myocardial ischemia detected by single photon emission computed tomography. J Nucl Cardiol. 2010;17(5):791‐802.
4. Pregowski J, Kepka C, Kruk M, et al. Comparison of usefulness of percutaneous coronary intervention guided by angiography plus computed tomography versus angiography alone using intravascular ultrasound end points. Am J Cardiol. 2011;108:1728–1734
5. Kruk M, Wardziak Ł, Demkow M, et al. Workstation-Based Calculation of CTA-Based FFR for Intermediate Stenosis. JACC Cardiovasc Imaging. 2016;9(6):690‐699.
6. Solecki M, Kruk M, Demkow M, et al. What is the optimal anatomic location for coronary artery pressure measurement at CT-derived FFR?. J Cardiovasc Comput Tomogr. 2017;11(5):397‐403.

Figure 1. Different views on coronary arteries based on volume rendered images on computed tomography. Panel B optimally shows an intermediate coronary stenosis in proximal LAD (the yellow circle). LAD-left anterior descending artery, LCx-left circumflex, RCA-right coronary artery.

Figure 2. An interactive colour coded image of the coronary tree with displayed CT-FFR values at the specific sites. On the right, the scale shows colour codes for the CT-FFR values. The CT-FFR value at the site which is optimal for evaluation of CT-FFR is between 0.75-0.80, however more distal values shows unambigous ischemia.

Figure 3. Coronary CTA images of the left anterior descending artery with the index stenosis within the proximal segment; quantitative lesion analysis shows the lesion (normal to normal) length of 26 mm and the proximal and distal reference diameters of 3.5 mm and 3.6 mm respectively, allowing to plan the stent size. According to quantitative coronary CTA the diameter stenosis is 47%.

Figure 4. Left anterior descending artery, with FFR probe located distally to the index stenosis (A), followed by successful coronary stenting (B, C).