Non-invasive FFR superior to CT angiography for diagnosis of lesion-specific ischaemia

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A new non-invasive method to assess coronary artery disease may reduce unnecessary invasive angiography and revascularisation procedures, EuroPCR delegates were told in May. Results of fractional flow reserve combined with computed tomography (FFR-CT) were presented by Bon-Kwon Koo, Seoul National University Hospital, Seoul, South Korea, in a Late-Breaking Trials session. The technology won the EuroPCR Innovation Award.

FFR-CT is a novel non-invasive method that enables physiologic assessment of coronary artery disease from coronary CT angiography, without any additional imaging or medications, Koo said. “Coronary CT angiography provides accurate anatomical information. However, it does not reliably predict functional significance of a lesion. Widespread use of CT angiography may result in excessive unnecessary invasive procedures. FFR is the gold standard for diagnosis of lesions that cause myocardial ischaemia. However, FFR requires invasive procedures.”

 

The new system is a combination of the anatomical information derived from static coronary CT angiography and the functional information derived from FFR – but the latter no longer obtained invasively. From a coronary CT angiography investigation, the computational technology incorporates myocardial mass, aortic pressure, coronary microcirculatory resistance and the viscosity and density of blood. Underpinned by physiologic models and using proprietary algorithms, a 3D patient-specific epicardial model is extracted from coronary CT angiography, and equations are solved to calculate blood flow, from which velocity and pressure is measured. The output is a combined functional and anatomic assessment in the form of a colour-coded map able to show the location of functionally critical points.

 

“There is a good linear relationship between invasive FFR and FFR-CT. While the two techniques have similar sensitivity, the specificity and positive predictive value of FFR-CT are much better,” Koo explained. “In practice, a CCTA file will be uploaded onto a secured website, quality assessed, analysed and a report returned to the physician. The strengths of this technique far outweigh any weaknesses, being a low risk, accurate, non-invasive, lesion-specific, functional assessment of coronary artery disease severity. The better diagnostic performance compared with CCTA alone may improve patient selection for invasive evaluation.”

 

Koo presented results of the DISCOVER-FLOW (Diagnosis of ischaemia-causing stenoses obtained via non-invasive fractional flow reserve) first-in-man study. The objective, he said, is to determine the diagnostic performance of non-invasive FFR as compared to invasively measure FFR.

 

The study was conducted in five centres in South Korea, Latvia and the USA. The inclusion criteria was stenosis in a major epicardial coronary artery ≥2mm, and diagnostic quality CCTAs from ≥64-detector row CT scanners. Obstructive coronary artery disease was defined as ≤50% diameter stenosis and lesion-specific ischaemia was defined as FFR ≤0.80.


From October 2009 to January 2011, 159 vessels (54.7% left anterior descending) in 103 patients were included in the study. Mean age was 62.7 years and 72% of the patients were men.


The results, Koo said, showed that FFR-CT had an excellent correlation with invasively measured FFR. The data also showed that FFR-CT was superior to CCTA for diagnosis of lesion-specific ischaemia, with a three-fold reduction in false positives and a two-fold reduction in true negatives.

 

FFR-CT analysis is an investigational technology and was developed by HeartFlow.

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