Adenosine-Free Pressure Measurement Found Equivalent to FFR

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SAN FRANCISCO, CA—A new type of intracoronary resistance measurement that takes advantage of a naturally occurring period of stasis in the arteries results in a drug-free index of stenosis severity comparable to fractional flow reserve (FFR) measurement, according to new data presented November 11, 2011, at the Transcatheter Cardiovascular Therapeutics scientific symposium.

According to Justin E. Davies, MD, PhD, of Imperial College (London, United Kingdom), recent studies have shown that, at best, FFR is used in about 6% of all PCIs in the United States. The most obvious reason for this minimal usage, he said, is the need to administer adenosine, which minimizes and stabilizes coronary resistance during the test but is uncomfortable for patients as well as time-consuming and expensive.

Dr. Davies explained that his group has identified a period of natural stasis in the waves that travel back and forth within the coronary arteries—called the ‘wave-free period,’ characterized by low resistance.

For the nonrandomized, international, multicenter ADVISE (ADenosine Vasodilation Independent Stenosis Evaluation) study, Dr. Davies and colleagues developed a new pressure-based index, the instantaneous wave-free ratio (iFR), based on this ‘wave-free period’ when intracoronary resistance is naturally constant and minimized. Unlike FFR, iFR calculation does not require the administration of adenosine or any other drug.

ADVISE was designed in 2 parts:

  • A proof-of-concept study that used measurements of pressure and flow to calculate resistance in order to test the stability and magnitude reduction in comparison to hyperemic mean resistance gauged with FFR
  • A validation study comparing iFR against FFR in 131 patients (157 stenoses)

The iFR is calculated as the instantaneous pressure gradient across a stenosis during the wave-free period, when resistance is constant and minimized in the cardiac cycle (Pd/Pa).

iFR Measures Up to FFR

In the proof-of-concept study, the measurement of stability and magnitude of resistance during the wave-free period was statistically similar to that seen under adenosine hyperemia, Dr. Davies reported.

Furthermore, in the validation study, the resting ratio of the distal-to-proximal pressure with iFR and with FFR were similar (r = 0.9; P < 0.001). When the relationship was examined according to both left and right coronary arteries, the differences were minimal.

“One of the things we wanted to determine was whether we could see if there were differences that were happening [between iFR and FFR in diagnostic accuracy],” Dr. Davies said. “We wondered if it was a result of differences in resistance.”

However, in the ROC analysis, the diagnostic efficiency was excellent (receiver operating characteristic area under the curve of 93%). Diagnostic accuracy was 88%, while specificity, sensitivity, and negative and positive predictive values were 91%, 85%, 85%, and 91%, respectively.

“In terms of clinical implications of iFR, we hope that this kind of builds on FFR,” Dr. Davies said. “It’s founded on almost identical physiology and just extends this into the cath lab using modern technology and we hope that this will remove barriers to adoption of physiology assessment in the cath lab.”

In addition, Dr. Davies said the applicability of this technique could spread to a wider range of patients, improve patient experience by eliminating the need for adenosine, and improve work flow for interventional cardiologists since it is quicker and more cost effective than FFR.

Gregg W. Stone, MD, of Columbia University Medical Center (New York, NY) agreed.

"A technology in a guidewire offering a continuous ‘on-line’ adenosine-free measure of hemodynamic lesion severity offers the potential to change how we perform PCI in the cath lab,” he said an e-mail communication with TCTMD. “The ability to easily assess each coronary stenosis and reassess the coronary artery after each intervention should result in better outcomes for patients, facilitating optimal stenting while avoiding unnecessary PCI.

Study Details

The study population was 84% male, with mainly stable single-vessel disease. Hypertension was present in 56% and diabetes in 34%.

Source:

Davies J. Primary results of ADVISE (ADenosine Vasodilation Independent Stenosis Evaluation). Presented at: Transcatheter Cardiovascular Therapeutics 2011; November 11, 2011; San Francisco, CA.

 

Disclosures:

  • The study was funded by the Biomedical Research Council, the Coronary Flow Trust, and the National Institute for Health Research and supported by Volcano Corporation.
  • Dr. Davies reports receiving consulting fees/honoraria from Medtronic and Volcano.

 

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