FFR-CT for the Selection of a Patient and Vessel for Revascularization: A Case Report

Article Citation:

John R. Lesser, B. Kelly Han, Terrence Longe, Thomas Knickelbine, Marc Newell, Michael Mooney, and Robert S. Schwartz (2018) FFR-CT for the Selection of a Patient and Vessel for Revascularization: A Case Report. Journal of the Minneapolis Heart Institute Foundation: Spring/Summer 2018, Vol. 2, No. 1, pp. 51-53.

Case Report

John R. Lesser, MD

B. Kelly Han, MD

Terrence Longe, MD

Thomas Knickelbine, MD

Marc Newell, MD

Michael Mooney, MD

Robert S. Schwartz, MD

Advanced Imaging and Interventional Section, Minneapolis Heart Institute, Minneapolis, MN; Children’s Hospital and Clinics of Minnesota

Disclosures: None.

Address for correspondence: 
John R. Lesser, MD
920 East 28th Street, Suite 300
Minneapolis, MN 55407
Tel: 612-863-3900

E-mail: John.Lesser@allina.com

ABSTRACT

Stable chest pain has traditionally been assessed using tests that visualize the physiologic response to stress on the myocardium or, more recently, coronary anatomy with non-invasive coronary computed tomography angiography. Either basic approach has advantages and disadvantages relative to diagnostic and therapeutic decision-making. Improved patient outcomes have been achieved with an invasive anatomic assessment using coronary angiography followed by stenosis specific intervention guided by physiologic measurements using invasive fractional flow reserve. Fractional flow reserve computed tomography has been developed to mimic these invasive procedures using noninvasive coronary computed tomography angiography and computer modeling with computational fluid dynamics. We present a case of a man who had stenoses in 2 separate vessels and who received a stent in only the one that was physiologically important on fractional flow reserve computed tomography.

Keywords: coronary CT, fractional flow reserve CT, functional assessment, coronary artery disease, cardiac CT

INTRODUCTION

Exercise stress testing and imaging have most often been used as the initial step in the assessment of chronic chest pain. These tests try to provoke ischemia and visualize the physiologic response of the heart. Coronary computed tomography angiography (CCTA) is a newer test that directly visualizes coronary anatomy. This allows quantification of the extent of coronary plaque and a qualified assessment of the severity of a coronary stenosis. These basic approaches have limitations for both the diagnosis of coronary artery disease and the direction of therapeutic decisions.

Recent trials1,2 have shown improved patient outcomes when decisions about coronary revascularization are guided by the anatomy from invasive coronary angiography and the physiology from the invasive use of fractional flow reserve (FFR) measuring a pressure drop across a stenosis during a vasodilator stress. As a result, a noninvasive test, FFR-CT, was developed that combines detailed information of coronary anatomy and cardiac mass from a CCTA. It then applies the principles of computational fluids dynamics using computer modeling with a simulated vasodilator stress to predict a pressure drop at any point across the coronary tree.3 The clinical use of FFR-CT in patients with chronic chest pain has recently been approved by the Center for Medicare Services. We have used the technology since 2015 and present a case report demonstrating its potential value.

CASE REPORT

A 73-year-old man developed exertional dyspnea and intermittent chest pain with activity and at rest. The character of his pain was atypical and multiple cardiac risk factors were present. A CCTA was performed. The coronary calcium score was 729 and a severe mid–right coronary artery (mid-RCA) stenosis was present. The mid–left anterior descending artery (mid-LAD) had a lesion that was of intermediate severity by visual assessment of the CCTA. He had tolerated only small doses of anti-anginal medication with persistent symptoms. Because the physiologic importance of the LAD lesion was unclear, an FFR-CT was performed. The same digital CT datasets used to interpret the CCTA were sent electronically for analysis. No further radiation or contrast was required.

A highly accurate map of the coronary tree was generated (Figure 1A,B) and specific sites within the coronary arteries (Figure 1, arrows) provided the FFR-CT number. A value <0.75 is severe and >0.8 is insignificant. The FFR-CT just beyond the mid-LAD stenosis was 0.82 (Figure 1B) and the RCA was 0.61 (Figure 1A). He was sent to invasive angiography (Figure 2A,B) and an RCA stent was successfully placed. No stent was placed in the LAD. Following his procedure, both pain and dyspnea resolved.

FIGURE 1
A detailed map of the coronary computed tomography angiography derived coronary anatomy is shown. White arrows point to stenoses in the mid–right coronary artery (mid-RCA) (A) and mid–left anterior descending artery (mid-LAD) (B). The 0.61 (A) distal to mid-RCA lesion represents a severely decreased fractional flow reserve-computed tomography (FFR-CT). The FFR-CT of 0.82 (B) just distal to the mid-LAD lesion is an insignificant pressure drop and strongly suggests that this stenosis will not limit myocardial blood flow.
FIGURE 2
Images from the invasive coronary angiogram are remarkably similar to those from the coronary computed tomography angiography. The arrows point to the lesions that were measured using fractional flow reserve-computed tomography. The mid–right coronary artery (A) received a stent and the mid–left anterior descending artery (B) was left untouched.

DISCUSSION

Stable chest pain is an important problem that can be assessed with tests that either check the physiologic response to myocardial stress or directly visualize coronary anatomy. In our patient, we saw coronary stenoses on CCTA but could not be certain whether a specific lesion might limit myocardial blood flow and contribute to symptoms. The FFR-CT allowed the interventionalist to treat the severe stenosis in the RCA and to avoid treating the LAD stenosis. The insignificant FFR-CT of the mid-LAD meant that the placement of a wire or delivery of adenosine could be avoided. We assume that this information also made it less likely that empiric LAD stent placement based on anatomy alone would be performed.

The FAME 2 trail1 randomized patients with multivessel coronary disease to empiric medical therapy or percutaneous coronary intervention (PCI) based on lesion-specific FFR. FFR-guided therapy was superior to empiric medical therapy or visually driven PCI and has become the standard clinical reference for assessing the importance of a coronary lesion.4 FFR-CT is a noninvasive method for judging the physiologic significance of a stenosis seen using CCTA-derived anatomy.

Studies of this technique have shown a high accuracy relative to invasive FFR in lesions with intermediate severity.5 The multicenter Platform trial randomized patients sent for chest pain to FFR-CT or to a usual planned diagnostic test that included either a noninvasive or an invasive approach. In those initially referred for invasive coronary angiography, the use of FFR-CT eliminated the need for an invasive angiogram in 61% and follow-up showed no difference in cardiac events in either group. The costs in the FFR-CT group were also significantly lower.6 An initial report of the application of FFR-CT in clinical practice described the decreased reliance on invasively measured FFR in those eventually referred to invasive coronary angiography. In addition, excellent results were noted when an insignificant FFR-CT value prompted deferral of invasive coronary angiography.7

Patients with bypass grafts or arteries with stents can’t be analyzed with FFR-CT. However, it is used for patients with stents to assess a different artery without a stent. Coronary calcium does not greatly limit the accuracy of the technique8 and the results are reproducible.9 A clear advantage of FFR-CT is that it is used on a provisional basis after the CCTA has been acquired. There is no additional contrast or radiation.

We present a case of man who had FFR-CT added to CCTA. He was both appropriately sent for invasive angiography and recommended for PCI of only the stenosis with a low FFR-CT value.

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