Fractional flow reserve derived noninvasively from coronary CT angiography is a safe and accurate method for assessing the significance of coronary artery disease in patients with severe aortic stenosis who are headed for transcatheter aortic valve replacement (TAVR), according to results of the CAST-FFR prospective study.
Indeed, utilization of coronary CT angiography–derived fractional flow reserve (CT-FFR) for this purpose offers the advantage of using a single noninvasive imaging method to replace two invasive procedures: coronary angiography to assess the anatomy of coronary lesions, and conventional FFR using a pressure wire to determine the functional significance of a given coronary stenosis as a cause of ischemia, Michael Michail, MBBS, explained in reporting the results at the virtual annual meeting of the European Association of Percutaneous Cardiovascular Interventions.
“Because up to 50% of patients with severe aortic stenosis undergoing TAVR have coexisting coronary artery disease, it remains common practice to perform prior invasive coronary angiography. However, this is associated with inherent risks, particularly in an elderly cohort with comorbidities. Additionally, coronary angiography provides no information on the functional impact of coronary stenoses, which may be important in guiding revascularization decisions prior to TAVR,” noted Dr. Michail, a cardiologist at Monash University, Melbourne.
Simulating FFR: ‘A one-stop shop cardiac CT’
Dr. Michail presented the results of the prospective CAST-FFR study, the first evaluation of CT-FFR for assessment of coronary arteries in patients with severe symptomatic aortic stenosis. This method uses computational fluid dynamics to transform data obtained noninvasively from a standard coronary CT angiography acquisition into a simulated FFR. And it offers the potential to streamline patient care.
“In current practice we see elderly patients with a long pre-TAVR assessment period, with numerous appointments and invasive procedures. Our vision is a one-stop shop cardiac CT that will provide the cardiologist with a complete assessment of the annular measurements, peripheral vasculature, and the coronary arteries ahead of their procedure,” according to Dr. Michail.
“We believe the ability to perform the requisite coronary assessment using CT-FFR will translate to improved patient care in several ways,” he continued. “Firstly, this will shorten the number of tests and overall diagnostic journey for patients. It will reduce the risk from unnecessary invasive procedures, and this will also reduce discomfort for the patient. Based on emerging evidence on the adverse prognostic impact of functionally significant coronary disease in aortic stenosis, this data has the potential to improve procedural risk stratification. And finally, contingent on further data, this may improve lesion selection for upfront revascularization.”
The CAST-FFR study was a small, single-center, proof-of-concept study in which 42 patients with severe aortic stenosis underwent both coronary CT angiography and conventional FFR with a pressure wire. The CT data was sent to a core laboratory for conversion into CT-FFR by evaluators blinded to the conventional FFR values.
Of the 42 participants, 39 (93%) had usable CT-FFR data on 60 coronary vessels. Dr. Michail and coinvestigators found a strong correlation between the conventional pressure wire FFR and CT-FFR findings, with a receiver operating characteristic area under the curve of 0.83 per vessel. CT-FFR had a diagnostic sensitivity and specificity of 73.9% and 78.4%, respectively, with a positive predictive value of 68%, a negative predictive value of 82.9%, and a diagnostic accuracy of 76.7%.
He cited as study limitations the small size, the fact that patients with previous revascularization or significant left ventricular impairment were excluded, and the study cohort’s relative youth.
“With a mean age of 76.2 years, it’s unclear whether these results can be extrapolated to very elderly patients with more calcified arteries undergoing TAVR. Encouragingly, though, a subgroup analysis based on calcium score showed no effect on accuracy,” according to the cardiologist.
CT-FFR may ‘shorten the diagnostic journey’ for fragile patients
Discussant Daniele Andreini, MD, PhD, praised the investigators’ concept of integrating the functional assessment provided by CT-FFR into a one-stop shop examination by cardiac CT angiography for TAVR planning.
“I would like to underline one of Dr. Michail’s messages: It’s really important to shorten the diagnostic journey for these fragile, older patients with aortic stenosis in order to improve safety, use less contrast, and avoid complications,” said Dr. Andreini, a cardiologist at the University of Milan and director of the cardiovascular CT and radiology unit at Monzino Cardiology Center, also in Milan.
Both Dr. Michail and Dr. Andreini reported having no financial conflicts of interest.