November 11, 2011 (San Francisco, California) — A new technology that analyzes pressure inside the vessel without the use of adenosine provides intracoronary pressure measurements similar to fractional flow reserve (FFR), according to the results of a new study. Investigators say the technology should have increased applicability in more patients, especially those who are unable to tolerate adenosine, and can improve work flow in the catheterization lab.

"It's exactly the same as FFR, there's no change, except we've managed to stabilize our resistance using a mathematical algorithm rather than having to give a drug to do the same thing," lead investigator Dr Justin Davies (Imperial College London, UK) told heartwire . "We know now from clinical trials that we do a lot better if we don't make our judgments based on visual estimations of stenosis but actually make an assessment based on the pressure drop across the whole length of the artery."

Data from the Adenosine Vasodilatation Independent Stenosis Evaluation (ADVISE) were presented today here at TCT 2011 during the late-breaking clinical-trials session. Speaking with heartwire , Davies explained that the when coronary resistance is stable, such as when adenosine is used, clinicians are able to measure pressure as a surrogate for coronary flow to assess stenosis. He noted that the Fractional Flow Reserve versus Angiography for Guiding PCI in Patients with Multivessel Coronary Artery Disease (FAME) trial showed that the routine measurement of FFR during angioplasty significantly improved clinical outcomes when compared with traditional angiography-guided treatment.

With the new pressure technology, investigators are able to identify a period of naturally occurring stable resistance within the coronary artery. Instead of giving the patient adenosine, the guidewire-based technology identifies a period of low resistance during the cardiac cycle and uses an algorithm to calculate the pressure within the coronary artery. The instantaneous pressure gradient, which is measured during the wave-free period, is defined as the instantaneous wave-free ratio (iFR) and is taken when resistance is constant and minimized within the cardiac cycle.

In one of their first proof-of-concept experiments, they showed that the stability and magnitude of resistance measured during the resting wave-free period is similar to the mean resistance achieved during adenosine hyperemia. Next, they measured intracoronary pressure in 157 patients using iFR and FFR to determine whether the two measurements were equivalent. Analysis showed that iFR and FFR had a strong positive linear correlation (r=0.90). After adjustment for the variability in FFR, the iFR had a diagnostic accuracy of 95%, positive predictive value of 97%, negative predictive value of 93%, and sensitivity and specificity of 93% and 97%, respectively.

"Studies like FAME have shown that patients generally do better if you use pressure to tell us when to stent and when not to stent," said Davies. "It's hugely important, and it's even more important in the United States because of concerns about appropriateness of stenting. Eventually, what physicians are going to be asked to do is take a physiological type of measurement or an [intravascular ultrasound] IVUS-based measurement to justify why they've put a stent in. Also, iFR, as well as FFR, can be used after the stent has been placed. It can tell us if you performed a successful angioplasty."

Speaking with the media, Davies said that adenosine poses a problem for patients and clinicians. For patients, some are ineligible for adenosine, such as those with asthma, low blood pressure, or atrioventricular (AV) block. For physicians, calling down for adenosine and waiting for infusion lines to be inserted can be time-consuming. For operators using the radial artery, they might be less inclined to insert venous sheaths for FFR. The new iFR measurement simplifies the whole procedure as well as work flow and significantly reduces the time needed to check the pressure/flow of an artery over FFR.