IS FRACTIONAL FLOW RESERVE-COMPUTED TOMOGRAPHY EFFECTIVE IN THE REAL WORLD?

Background: Coronary Computed Tomography Angiography (CCTA) is a common anatomic modality for detection of cardiac ischemia in the setting of chest pain hospitalizations. However, invasive coronary angiography (ICA) is the gold standard for diagnosing ischemic coronary artery disease. Research showed that CCTA has a high sensitivity but lacks the specificity and accuracy component of Fractional Flow Reserve-Computed Tomography (FFR-CT)1. FFR-CT utilizes data from coronary CT angiography to calculate a virtual fractional flow reserve, providing information about blood flow in coronary arteries without the need for invasive procedures. Past research showed that utilizing FFR-CT as a noninvasive tool in conjunction with CCTA can significantly increase the accuracy of these exams and decrease unnecessary ICA. This study aims to describe a single-center experience and analyze CCTA and FFR-CT in comparison to ICA data. We hypothesize that CCTA with FFR-CT will have a high sensitivity and specificity in comparison to CCTA alone.

Methods: Our retrospective study assessed 237 adult patients who underwent clinically indicated CCTA and FFR-CT at Ascension St. Vincent Heart Center hospital in Indianapolis. Patients with moderate or severe stenosis on CCTA or those exhibiting strong clinical indications were subsequently referred for ICA. The study comprised individuals who had an invasive angiogram within one year from the initial CCTA/FFR-CT. We conducted a comparative analysis to evaluate the sensitivity and specificity of CCTA and FFR-CT using ICA-detected stenosis as the reference standard. CCTA stenosis cutoff was set at >70%, because only CCTA data displaying stenosis >50% were forwarded for FFR-CT analysis at our facility, so patients with CCTA stenosis < 50% were not included in the study. Like prior research studies 2,3,4, a positive assessment of FFR-CT was determined when it fell below 0.7 and 0.75. The stenosis criterion on ICA was set at 70%.

Results: This study aims to compare the sensitivity and specificity of CCTA and FFR-CT data in detecting ischemic coronary artery disease. Consistent with prior research, CCTA exhibited a high sensitivity of 75% but a low specificity of 42%. In contrast, FFR-CT demonstrated sensitivities of 71% at the < 0.7 cutoff and 90% at the < 0.75 cutoff. Specificities were noted at 70% for the < 0.7 cutoff and 56% for the < 0.75 cutoff. The positive predictive value of CCTA was 78% and the negative predictive value was 39%. Comparatively, FFR-CT had positive predictive values of 85% and negative predictive values of 67%.

Conclusions: The integration of FFR-CT with CCTA has increased utilization in the hospital to evaluate suspected coronary artery disease. Our study highlights FFR-CT’s performance in a real-world scenario as part of a routine clinical practice. A recent meta-analysis reported FFR-CT’s sensitivity of 90% and specificity of 71% for the detection of significant coronary artery stenosis using the threshold of < 0.75.1 In our study, FFR-CT remained sensitive (90%) with much lower specificity (56%) using < 0.75 as the cutoff. The elevated false positive rate may stem from potential over-diagnosis of diffuse coronary narrowing via FFR-CT and the absence of invasive iFR and DFR measurements during catheterizations to validate true flow limitations. Despite this, FFR-CT outperformed CCTA alone, indicating its ability to enhance diagnostic accuracy and reduce the necessity for invasive procedures in evaluating suspected coronary artery disease.