FFR-CT and iFR Accurately Identify Coronary Stenoses

SAN FRANCISCO, CA — Two new studies presented today at TCT 2013 highlight the benefit of assessing the functional severity of the coronary lesion using new twists on measuring fractional flow reserve (FFR) in patients with suspected coronary artery disease.

In the first trial, known as ADVISE II , researchers measured the instantaneous wave-free ratio (iFR), which is a pressure-derived, adenosine-free measurement of coronary stenosis, and reported that it successfully characterized the hemodynamic severity of more than 90% of stenoses.

In the second study, known as HeartFlowNXT , investigators compared the diagnostic performance of noninvasive FFR derived from computed tomography (FFR-CT) scans vs CT alone and coronary angiography for the identification of patients with ischemia, using an FFR <0.80 as the gold standard. With the FFR-CT, flow-restricting lesions are computed using an algorithm that measures computational fluid dynamics and data from the CT scan.

Presenting the results of HeartFlowNXT during a morning press conference, Dr Bjarne Norgaard (Aarhus University Hospital, Denmark) reported that FFR-CT accurately detected 81% of coronary stenoses in a cohort of 254 stable coronary artery disease patients compared with 64% of stenoses detected with coronary angiography and 53% of stenoses detected with CT alone.

Specificity and positive predictive values (PPV) were also significantly higher among those assessed with FFR-CT than with CT alone or traditional angiography.

"FFR-CT is performed from standard acquired CT data sets without the need for additional imaging, radiation, or medication," said Norgaard. While the cost-effectiveness of the procedure needs to be assessed in future studies, Norgaard noted that FFR-CT performs significantly better diagnostically than other noninvasive modalities, such as single-photon-emission computed tomography (SPECT) and stress echocardiography, for the assessment of coronary stenoses.

"The Best of Both Worlds"

In terms of diagnostic performance, the accuracy, specificity, and PPV of using FFR-CT to detect coronary stenosis were 81%, 79%, and 65%. These values were all significantly greater than those achieved with CT alone and invasive coronary angiography. The sensitivity of FFR-CT was 86% and the negative predictive value was 92%, values that were not statistically different from those achieved with CT and angiography.

Speaking during the morning press conference, Dr Bernard Gersh (Mayo Clinic, Rochester, MN), who was not affiliated with HeartFlowNXT, called the study an "important trial," noting that FFR-CT won't immediately be introduced into clinical practice and requires further testing, but the functional assessment of lesion severity will become much more important in the next two to three years.

Dr James Hermiller (St Vincent's Heart Center, Indianapolis, IN) agreed. "I think this will be incorporated into clinical practice," said Hermiller, "not tomorrow but in the next several years. We need more specificity in our screening studies, and the beauty of this study is that there was much greater specificity but there wasn't much of a price paid on sensitivity. We get the best of both worlds with this."

The ADVISE II trial

In the second study, Dr Javier Escaned (Hospital Clinico San Carlos, Madrid, Spain) presented data on 797 patients who underwent functional testing using iFR, a pressure-derived index that measures coronary stenoses without the use of adenosine. The objective of the trial was to assess the ability of iFR to characterize the severity of coronary stenoses, as determined by the gold-standard FFR, without the use of adenosine.

For patients with an iFR pressure ratio of <0.85 or >0.95, iFR was used to assess the hemodynamic severity of the occlusion and compared with FFR. For patients with an iFR that fell between 0.86 and 0.93, a hybrid approach was adopted where adenosine was used to measure the functional severity of the lesion.

Overall, iFR accurately characterized 91.6% of coronary stenoses with pressure ratios of <0.85 and >0.94. When investigators included lesions that fell within the iFR zone of 0.86 to 0.93, the zone where adenosine is normally used to characterize lesions, the percentage of stenoses properly classified using the hybrid iFR/FFR approach was 94.2%.

"By applying this particular approach, you drastically reduce the need for adenosine," said Escaned. "As a matter of fact, you don't have to give adenosine in 69% of the stenoses you evaluate with the pressure guidewires."

To heartwire , Hermiller said the approach adopted by the ADVISE II investigators has the potential to reduce costs and simplify the functional assessment of coronary lesions. He explained that when the wire is moved across the lesion, iFR is able to identify the pressure gradient by taking an instantaneous snapshot within the pressure tracings. In other words, the iFR provides a signal of the pressure reduction across the lesion relative to the systemic pressure.

If the pressure wire shows there is a large pressure differential across the lesion, those iFR values <0.85, then there is little need to give adenosine because clinicians already know the lesion is physiologically significant, said Hermiller. If the wire shows there is hardly any difference in pressure across the lesion, those iFR values >0.94, then there is also no need to give adenosine because adding it won't help provide any information on the functional significance of the lesion.

"If you're in that middle zone, that's when you give the adenosine," said Hermiller. "To me, this [iFR] is a no-brainer."

Volcano sponsored the ADVISE II study. Escaned reports payment for speaking on behalf of Boston Scientific, St Jude Medical, and Volcano. HeartFlowNXT was funded by HeartFlow. Norgaard reports no conflicts of interest.

Heartwire from Medscape © 2013 

Cite this: FFR-CT and iFR Accurately Identify Coronary Stenoses - Medscape - Oct 30, 2013.